Selectively starving cancer cells through dietary manipulation: methods and clinical implications

95910.2217/FON.13.31 © 2013 Future Medicine Ltd ISSN 1479-6694Future Oncol. (2013) 9(7), 959–976

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Diet modification has been performed for centuries to prevent disease and delay aging [1–4]. The link between obesity and cancer is becoming clearer, and it has been noted that patients who overeat and live a sedentary lifestyle have excessive adipose tissue, which may place them at high risk of malignant transformation [1,2]. These findings have spawned a host of laboratory and clinical investigations to determine if manipulating a patient’s dietary intake or physical activity can alter molecular pathways to prevent the spontaneous development of cancer [3]. There are several host factors related to energy and nutrient balance that have been linked to the progression of tumors and the responsiveness of certain tumors to treatment [4]. This information, combined with the knowledge that obesity and excess adipose tissue negatively affects prognosis in many cancers [5–7], suggests that nutrition is crucial not only in the prevention of cancers, but potentially in improving the prognosis of certain cancers also.

Attention has now turned toward using dietary manipulation as a possible treatment inter vention for cancer. Although many diet regimens have been assessed, caloric restriction (CR), intermittent fasting (IF) and a carbohydrate restriction/ketogenic diet (KD) are the methods that are noted to provide benefit for

tumors in the preclinical setting and are now being implemented in the design of onco logy clinical trials. Table 1 & Figure 1 present a summary of the advantages and disadvantages associated with each regimen from a clinical point of view. These will be discussed later in more detail. Each regimen has been used individually in preclinical studies; however, they all have their own risks and benefits with regard to their applicability to humans. It should be noted that other dietary interventions exist and have been investigated for the prevention of cancerous lesions. These include a Mediterranean diet, a vegan diet and a low fat diet [8–10]. While some of these dietary interventions have shown promising results in the prevention of cancerous lesions, this review aims to focus on the use of dietary intervention as an adjunct to standard cancer therapies.

Understanding the nuances of each diet will allow for better design and greater success in clinical trials as the realms of nutrition and oncology begin to overlap. As more clinical trials using diet modification emerge, the effects of each of these different interventions in humans will be better understood. CR, IF and KD will be delineated in this review, and the logistics and potential benefits of each for oncology trials will be discussed.

Selectively starving cancer cells through dietary manipulation: methods and clinical implications

Brittany A Simone1, Colin E Champ1, Anne L Rosenberg2, Adam C Berger2, Daniel A Monti3, Adam P Dicker1 & Nicole L Simone*1

1Department of Radiation Oncology, Kimmel Cancer Center & Jefferson Medical College of Thomas Jefferson University, Philadelphia, PA, USA 2Department of Surgery, Kimmel Cancer Center & Jefferson Medical College of Thomas Jefferson University, Philadelphia, PA, USA 3Myrna Brind Center of Integrative Medicine, Thomas Jefferson University Hospital, Philadelphia, PA, USA *Author for correspondence: Tel.: +1 215 503 0554 n Fax: +1 215 955 0412 n [email protected]

As the link between obesity and metabolic syndrome and cancer becomes clearer, the need to determine the optimal way to incorporate dietary manipulation in the treatment of cancer patients becomes increasingly important. Metabolic-based therapies, such as caloric restriction, intermittent fasting and a ketogenic diet, have the ability to decrease the incidence of spontaneous tumors and slow the growth of primary tumors, and may have an effect on distant metastases in animal models. Despite the abundance of preclinical data demonstrating the benefit of dietary modification for cancer, to date there are few clinical trials targeting diet as an intervention for cancer patients. We hypothesize that this may be due, in part, to the fact that several different types of diet modification exist with no clear recommendations regarding the optimal method. This article will delineate three commonly used methods of dietary manipulation to assess the potential of each as a regimen for cancer therapy.

Keywords

n caloric restriction n cancer n diet n intermittent fasting n ketosis

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Caloric restrictionTo date, CR has been used in nononcologic clinical trials assessing end points, such as overall health, memory and decreased cardiovascular risks, in healthy human subjects [11–13]. Patients’ baseline caloric intake is assessed prior to the intervention. Based on this reported baseline, a diet that restricts the total number of calories by the desired amount is then recommended [14,15]. In general, protocols in preclinical models tend to restrict by 30–50% of baseline caloric intake, while clinical models of CR utilize a more conservative approach with 20–40% restriction. Since current CR clinical trials are assessing the diet as a means to prevent chronic diseases, some questions have arisen regarding the appropriateness of using this technique in the oncology patient population.

CR in the preclinical realmThe potential for CR to reduce the incidence of spontaneous tumor growth has been demonstrated in a number of in vivo rodent models [16–18]. In most preclinical experiments involving rodent models, primary outcomes consisted of the development of spontaneous tumors induced by carcinogens or disease progression. In 1949, Tannenbaum and Silverstone observed that CR decreased tumor incidence and from their data, they developed a mathematical regression model demonstrating the direct relationship between the

reduction in spontaneous skin and liver tumors and the amount of energy restriction these mice underwent [16]. The optimal reduction in tumor incidence (82%) proportional to the amount of CR was achieved with a 27.5% reduction in calorie intake. This suggests that there is an optimal amount of CR to affect a change in cancer incidence. In vivo, CR is consistently noted to slow primary tumor growth in many types of cancers with a particular effect noted in hormonesensitive cancers, such as breast and prostate cancers [17,19–22]. Dirx et al. compiled a metaana lysis of studies conducted on energy restriction and the development of mammary tumors in mice between 1942 and 1994 [23]. CR protocols ranged from a 23 to 50% reduction in calories with an estimated 55% reduction of mammary tumor development across all studies.

Expanding on the concept of CR, protocols for intermittent or temporary CR combined with fasting were also tested. Two studies using fasting with a 40% CR diet in C3H mice were conducted. One study revealed that mice fed twice per week at a 40% CR had a less than 10% incidence rate of mammary tumors compared with 100% in ad libitum-fed mice [24,25]. There has not been any direct comparison of this type of protocol with any of the other modalities, making it difficult to determine if the effects are additive.

Since CR is noted to slow primary tumor growth in mice, the effect on metastases has now

Table 1. Dietary regimen comparison.

Dietary modifications Advantages Disadvantages

Carbohydrate restriction Does not require patients to calorie restrict Requires patients to cut certain foods

Compliance can be monitored with urine and serum markers

Labor intensive for patients

Does not result in cachexia/muscle wasting Requires days to weeks of compliance for effect

Relies on ketotic state for effect

Caloric restriction Macronutrients not restricted Labor intensive for patients

Associated with long-term weight loss No objective measure for compliance

Amount of restriction needed for effect is low Requires long-term compliance for effects

May induce hormesis without peaks in stress response

Intermittent fasting Macronutrients not restricted at all times Water-only fasts may be challenging for elderly patients

Modification is short lived and requires no calculations

No direct measure for compliance that is fasting specific

Produces effects at the molecular level almost immediately

No sustained weight loss

Does not result in cachexia Timing of fasts may be important

Less labor intensive for physicians Relies on stress response for effects

Review Simone, Champ, Rosenberg et al.

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been investigated. De Lorenzo et al. designed a study to determine the effects of a 40% CR on both spontaneous and experimental metastases in mice using a triplenegative mouse breast cancer line (4T1 cells) in immunocompetent mice [17]. Using this model, they showed that CR alone decreased the number and size of lung nodules in both spontaneous and experimental metastases. In contrast to this breast cancer model, Ershler et al. demonstrated that, while local growth of primary B16 melanomas was slowed in calorically restricted mice, the number of pulmonary

metastases remained unchanged [26]. This discrepancy in findings warrants further investigation and may suggest that only certain subsets of tumors will change their metastatic pattern in response to CR.

CR in the clinical realmAlthough CR has not yet been widely adopted as a treatment intervention for oncology patients, it has actually been used in a cancer biomarkers trial. Ong et al. randomized overweight female patients who were at an increased risk of breast

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Variation in calorie restriction

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Figure 1. The implementation of a ketogenic diet, intermittent fasting and caloric restriction. (A) Caloric restriction is implemented as a reduction of total caloric intake. In general, calories are restricted from baseline by 20–40%. There are different possible combinations of macronutrients that may accompany caloric restriction. Ideally, patients will not have to change what they are eating but the amount. Shown in the figure are two different combinations of macronutrients with restriction to desired levels. (B) Intermittent fasting is a short period of fasting (24–48 h) interspersed between ad libitum feedings. There is no specific recommendation regarding time between fasts, they may be between 3 and 5 days apart. Longer fasts (48 h) are generally carried out once per week and may be coupled with chemotherapy treatments, a low carbohydrate diet requires restriction to at least 20% of calories from carbohydrates; shown here are two possible combinations of carbohydrate restriction. (Ci) Supplementation with fat, is suggested to be optimal for inducing ketosis. (Cii) Supplementation with protein, is another option for a low carbohydrate diet, but the level of protein consumed could affect ketosis.

Selectively starving cancer cells through dietary manipulation: methods & clinical implications Review


cancer [27], as determined by the Tyrer–Cuzick method [28], to a normal diet or an energyrestricted diet, consisting of liquids not exceeding 864 kcal/day. In the energyrestricted arm, patients decreased calories over one menstrual cycle to examine effects on serum markers and gene expression associated with increased breast cancer risk in both breast adipose tissue and abdominal fat during energy restriction [27]. Significant changes were found in the expression of genes related to fat synthesis and glycolysis, including the downregulation in SCD in the breast tissue of women in the energyrestricted group. SCD knockdown reduces proliferation and Akt phosphorylation in cancer cell lines and, therefore, can decrease cell proliferation and preserve energy resources for maintenance functions only [29,30]. This molecular change may be responsible for increased apoptosis in some cancer cell lines, particularly those with p53 mutations [31,32]. This study and molecular correlations suggest that CR targets cell proliferation pathways to reduce spontaneous tumor growth or slow disease progression.

There are several reasons why CR has not yet been used as a treatment intervention for oncology patients, which will be discussed below.

ComplianceIn the setting of cancer treatment and the related significant emotional and biological stress, many clinicians are unsure if patients will be able to successfully adhere to a diet plan set forth for them. In addition, there are no wellestablished objective markers for monitoring compliance. While several serum markers (i.e., fasting insulin, fasting glucose and IGF1) have been noted to change in healthy individuals on a CR diet, there are no specific guidelines as to how much these markers would change to indicate compliance [33]. To rectify this, research is needed to determine serum or urine markers that could establish compliance with a CR diet so that larger clinical trials may begin.

Currently, the best measure for compliance is diet journals that require patients to record their dietary consumption, including food type, amount and other nutritional facts. Although this method is error prone, it has shown success when patients were provided with significant support or electronic diet trackers [34,35]. Internetbased diet logs allow patients to log their intake and receive instant feedback by generating graphs of intake compared with goals. They also allow physicians to monitor patients’ progress remotely [35]. As diet journals are the best method

currently available for measuring compliance, it is important that patients who are on a CR diet receive the behavioral and psychological support that they need to remain on the diet.

Clinical trials with a dietary modification component require a multidisciplinary team with dieticians and behavioral modification specialists for success. Noncancer patients may also find it difficult to add a lifestyle change to their daily routine and oncology patients may have increased difficulty. Compliance is crucial and, therefore, support for oncology patients is vital for intervention success. To ensure success, multidisciplinary teams will need to provide weekly dietary counseling, tools to aid and monitor compliance, and behavioral counseling to navigate psychosocial dietary cues, stressful situations and cultural attitudes towards dieting. In addition, counseling patients on the proper reporting of dietary events is important.

Complexity of treatment/adherenceWhile there are concerns regarding the psychological impact of lifestyle alterations on cancer patients, the implementation of supportive treatment teams and protocols has been successful in reducing added stress caused by dietary modifications. Currently, there are numerous internet support resources to connect people who are on a CR diet [201]. CR may be more readily adopted for some patients as a type of portion control that could be done without quantifying changes in particular macronutrients, such as in a KD. In this sense patients do not necessarily have to change what they are eating or cut out their favorite foods, but they will have to focus on portion control. This element of nutritional freedom combined with the health benefits of CR make it attractive to some patients.

CR is generally regarded as a lifestyle change and not as a diet and, therefore, length of intervention may be limiting for patients. However, data recently published from the DIRECT study, comparing different weight loss strategies (including CR) in overweight patients, revealed that, after 2 years of intervention, 85% of patients remained compliant with their diet [36]. It is unclear how this would translate to cancer patients, although it could be hypothesized that they would increase in motivation

Weight changeWeight loss of up to 15% of body weight has been associated with CR [37,38]. Unlike IF protocols to be discussed later in this review, CR is a constant energy restriction and, therefore,



does not allow for weight cycling or regaining of lost weight. Since weight gain is experienced by 50–90% of breast cancer patients after diagnosis and this is associated with poor outcomes, overweight or obese patients may benefit from a slight weight loss that may be associated with CR. While it is clear that obesity is an important factor in prognosis and recurrence, it should be noted that in most clinical trials involving CR, the study subjects have been a normal weight and healthy. However, in oncologic patients who are of normal weight or underweight, it is crucial to define the amount of calorie reduction and weight loss that will be safe to avoid cachexia or muscle wasting. Heterogeneity in CR techniques may be required as the total amount of calories reduced and potential negative effects must be assessed for each individual patient. Baseline weight and BMI would need to be established for oncologic patients in order to customize a proper CR protocol for these patients. In addition, when using CR as an integrative treatment, it will be important to assess which standard therapies are used, along with the disease site, as some treatment strategies may cause weight loss and some cancer sites are known to interfere with the maintenance of nutritional status.

Should CR be used for a subset of cancer patients?CR may be beneficial for a subset of cancer patients and this has not yet been delineated. It is possible that, in the future, characteristics of the molecular profile of a patient’s tumor might give an indication of which subset might derive the greatest benefit from a dietary modification. It may be determined that responsiveness to CR may in fact depend on tumor biology. Kalaany and Sabatini published a paper suggesting that tumors that have a mutated PTEN (phosphotensin homolog) may have irreversible PI3K activation, leading to resistance to the effects of CR [39]. Therefore, it may be prudent to genetically analyze a patient’s tumor for this mutation, either at the time of biopsy or definitive surgery if applicable. This would allow for the individualization of treatment with dietary modification through tumor biology [39–41].

Implementing CRPatients may respond differently to varying amounts of CR depending on their own individual tumor biology and metabolism [27,39]. Patients may need different amounts of CR to achieve the desired molecular and physiologic response. For example, it might be that patients

with a higher baseline BMI need a 30% reduction to achieve a significant decrease in IGF1; however, those with a lower BMI would only require a 15% reduction to achieve the same effects. Again, it will be vital for future research to define the appropriate amount of CR for subsets of patients based on weight.

Possible side effects/complicationsThere have been concerns regarding the longterm side effects of a CR diet. Some effects will vary depending on the length of time a patient is on a CR diet. It is known, however, that CR can cause muscle wasting, fatigue, electrolyte imbalances, dehydration and changes in mood. These effects are preventable but will need to be monitored by patients and their physicians alike.

A concept that should be taken into account in the design of a CR diet is calorie restriction without malnutrition. In this respect, essential vitamins and minerals need to be maintained. In addition, patients need to be educated about macronutrient balance to ensure adequate protein intake to prevent muscle wasting, iron deficiency anemia and fatigue; fat intake to sustain metabolic processes; and water to avoid dehydration as the body attempts to compensate for lost calories.

Rationale for implementation of CR in a clinical trialPatient adherence to a CR diet may be high since there is no restriction on the type of foods that can be consumed, merely overall quantity. It allows the intervention to be less labor intensive for patients and less restricting in social settings. This will encourage patients to comply with the diet and not necessarily greatly affect psychosocial factors, which will help patients to identify a support system outside of the staff involved in their medical care. Therefore, patients’ overall mood and energy level may not be significantly affected.

CR may induce hormesis without the induction of a full stress response within the body. From a physiologic perspective, hormesis refers to the biological adaptive response that cells undergo after subjection to stress. Low levels of stress can alter gene expression within cells to improve their functional capacity [42]. In particular, CR may induce hormesis in such a way that stress hormones and other harsh signaling molecules are not released into the serum. Increased stress hormones can lead to weight gain and other detrimental effects that are not desirable in the clinical setting. CR provides a lowintensity biological stress that may alter gene expression, causing cells



to switch into a defensive maintenance mode. CR has been noted to decrease lipid peroxidation, increase the efficiency of oxidative damage repair and decrease the generation of mitochondrial free radical formation [42–45]. Ideally, this will occur differentially in cancer cells versus normal tissue owing to the incapability of cancer cells to adapt to this cellular stress. This could decrease normal tissue damage from chemotherapy or radiation therapy (RT) during cancer treatment [46]. This may render cells less susceptible to the effects of oxidative stress and aging [12,47]. CR may create the benefits of hormesis without the negative effects.

Intermittent fastingOverviewAnother method of dietary manipulation that has been used in cancer models is IF consisting of brief periods of fasting in between periods of ad libitum feeding [48,49]. IF may be easier for patients to comply with than a CR diet modification. Typically, patients are expected to fast for a full 24–36 h with 3–5 days of ad libitum eating inbetween. During fasting, patients should ideally consume no calories, but should maintain oral hydration. There are no current guidelines regarding the timing between the fasts and how fasts should be done in relation to cancer treatment. IF does, however, provide an alternative to chronic CR for those concerned about the possibility of longterm CR leading to excessive muscle and fat loss. Despite the fact that IF has shown encouraging results, there are conflicting data with regard to IF’s potential as an adjunct to standard cancer therapy and its effects on tumorigenesis. This is due, in part, to the various protocols that exist within the IF realm, suggesting that there may be an optimal timing for IF with respect to cancer incidence and treatment [48–50].

IF in the preclinical realmThe concept behind IF is relatively simple: by starving tumors of glucose for short periods of time, the growth of these tumors may be stunted. Several studies using different fasting protocols in rodent mammary breast cancer models appear to show a decrease in tumor incidence in fasted mice as opposed to ad libitum-fed mice; however, data are not consistent [22,51]. One of the first studies to be done on mammary tumor incidence in response to IF was in Wistar rats using several different protocols for shortterm fasting [52]. Rats were fasted every other day, every 2 days, every 3 days or every 4 days for 24 h. The greatest impact on mammary tumor incidence was seen in

those mice that fasted every other day [50]. A similar study, using the same dietary protocol, showed a 20% tumor incidence versus a 70% incidence in ad libitum-fed mice [53]. Similarly, Bonorden et al. showed that IF as an intervention lengthened time to detection in a transgenic adenocarcinoma of the mouse prostate (TRAMP) model [51]. By contrast, Buschemeyer et al. attempted a proofofprinciple study using different protocols of IF and were unable to show significantly decreased tumor growth in those mice on the IF diet when compared with ad libitum-fed mice [48]. Their results showed that the group of mice that fasted for 2 days per week and the group of mice that were fed at a 28% CR diet for 7 days per week did show a trend of slowed tumor growth when compared with ad libitum-fed mice, but this did not reach significance.

The preclinical data are also congruent with beneficial effects at the molecular level. Lee et al. have implied that shortterm starvation, or 48h fasting, in a 4T1 mouse model reduces IGF1 levels by 70%, reduces glucose by 60% and increases IGFBP1 11fold [54]. This is the major proposed mechanism behind slowed tumor growth in animal models. An in vitro model designed by the same group using 4T1 cells exposed to cycles of chemotherapy and/or fasting, showed that IF resulted in increased phosphorylation of Akt and S6 kinases, increased caspase3 cleavage and apoptosis [55]. These data suggest that IF has the capability to decrease tumor growth and increase cancer cell apoptosis both in vivo and in vitro.

IF in the clinical realmSimilar to data for CR, clinical data regarding IF for oncology patients are sparse. In contrast to preclinical experiments using dietary intervention, clinical trials tend to focus on treatment of active disease and survival. This is especially true for IF and KD trials in the clinical realm. One small pilot study involving ten patients suggested that if patients fasted for 24 h before and 24 h after receiving chemotherapy, the side effects they experienced from chemotherapy would be decreased [56]. The greatest reduction in side effects was most notably associated with gastrointestinal effects, such as nausea, vomiting and diarrhea, indicating that IF may have had chemoprotective effects. In addition, it was noted that the patients did not experience significant weight loss over the course of the study. While this study was not sufficiently powered to show significance, it does establish feasibility for IF in humans and demonstrates the need for more human studies involving IF.



Currently, a shortterm fasting (24–72 h) study for patients receiving chemotherapy is recruiting patients (NCT00936364 [202]) to assess the feasibility and efficacy of varying lengths of times of fasting in cancer patients. Patients are encouraged to consume plenty of water as well as any zero calorie liquids (i.e., soft drinks, black coffee or tea). There are few other clinical studies involving shortterm fasting that vary with respect to the total fasting time implemented based on timing of chemotherapy. In general, protocols require fasting for 24 h before and/or 24 h after chemotherapy treatment (NCT01304251 [203], NCT01175837 [204] and NCT00757094 [205]). A summary of the existing clinical trials utilizing IF is presented in Table 2.

IF may provide an attractive alternative to CR for some patients in that the modification is short term and less labor intensive. However, IF shares some of the same drawbacks as CR. While IF as a type of dietary modification provides its own unique benefits, it also has its own unique risks.

ComplianceSimilar to CR, there is no direct way to monitor fasting in patients. Some patients will become ketotic while fasting and if this occurs, it would be possible to measure urine ketones. This will not occur in all patients and, furthermore, since some IF diets allow for the consumption of zero calorie liquids, patients might be noted to have a substantial amount of sugar or a sugar alternative

from these liquids. This would, therefore, prevent ketones from being measure and may result in unfavorable results concerning serum IGF1, insulin and glucose levels. Another subjective measure might be the use of fasting glucose; however, these levels will be patient dependent and also dependent on liquid consumption during the fasting period. Baseline fasting glucose levels would need to be established for each patient for comparison, and repeated testing might not be viewed favorably by patients.

In the end, similar to CR, the best way to monitor patients is to directly ask them about their compliance with the fasting. This can be done with food logs for fasting days. Other diet studies have shown that telephone and email reminders to patients about either fasting or logging intake have been helpful in increasing compliance [35]. While this may be labor intensive for treatment teams, ultimately it will result in better compliance and increased patient satisfaction.

Weight changesIn preclinical models, mice that lost weight during periods of fasting typically regained the weight after refeeding [22,57]. Calorie deficits are made up for by this refeeding and, therefore, weight loss is temporary at best. It has been suggested that perhaps this weight cycling is not ideal for cancer patients. In mouse models looking at mammary tumor development, mice who regained the weight that they lost did not experience the full

Table 2. Summary of existing clinical trials using intermittent fasting and caloric restriction in the oncology population.

clinicaltrials.gov identifier

Trial title Concept Status Outcomes

NCT00757094 Safety and Feasibility of Fasting While Receiving Chemotherapy

Observation of patients who choose to carry out fasting for religious reasons while receiving chemotherapy

Completed Patient safety and feasibility of diet intervention

NCT01304251 Effects of Short-Term Fasting on Tolerance to Chemotherapy

Breast cancer patients to fast for 24 h before and after chemotherapy

Not yet recruiting

Feasibility and effects on chemotherapy toxicity

NCT01175837 Short-Term Fasting Before Chemotherapy in Treating Patients with Cancer

Dose escalation of fasting starting at 24 h and increasing up to 48 h before successive chemotherapy cycles in patients with hematologic malignancies

Recruiting Patient safety and efficacy of fasting on reducing chemotherapy toxicity

NCT00936364 Short-Term Fasting: Impact on Toxicity

Comparison of 24-, 48- and 72-h fasting cycles with platinum-based chemotherapy in solid tumor malignancies

Recruiting Patient safety and efficacy of fasting on platinum-based chemotherapy toxicity

NCT01819233 CAREFOR Breast cancer patients to undergo 25% total calorie reduction for a total of 10 weeks to overlap with postlumpectomy radiotherapy

Recruiting Patient safety and compliance to dietary intervention

Details of each trial can be found on www.clinicaltrials.gov and by searching for the relevant trial number.



effect of decreased tumor incidence, suggesting that weight loss may be important [50].

The pilot study done by Raffaghello et al. suggested that patients who were fasting for 24 h before and after chemotherapy also did not experience any significant weight loss [56]. While this is ideal in preventing cachexia and other possible side effects of diet interventions, IF may not be an optimal intervention as weight loss may be essential to the mechanism of retarding cancer growth.

Implementing IFAs demonstrated by the various completed preclinical studies and the currently open clinical trials, the manner in which IF is implemented can vary greatly. The benefits of 24 versus 48 versus 72 h of fasting before receiving chemotherapy remain unknown. This should be clearly delineated before a larger clinical trial is pursued. In addition, it is unknown if fasting both before and after standard cancer treatment is crucial to observe benefit. Pilot trials are attempting to answer these questions before moving to large, randomized trials.

In addition, populations of patients who can tolerate IF will need to be identified since patients who are elderly, or have multiple comorbidities or chronic diseases might not be able to tolerate IF. Elderly patients often have decreased ability to regulate glucose and may become hypoglycemic during a fast [58,59]. The success of IF has been linked to the synchrony of fasting with circadian rhythms [60] and, as people age, sleep–wake cycles become dysregulated, which may prevent significant benefit with IF. Patients with chronic diseases, such as Type I diabetes, adrenal insufficiency or autoimmune disorders, might not be able to fast. Therefore, the need to develop ideal inclusion criteria for clinical trials will need to be established.

Short- & long-term complicationsIF is meant to be a shortterm intervention in that each interval of fasting is relatively short and not a chronic reduction like CR. Acute side effects, such as dehydration, are crucial to monitor since many individuals will only drink water and not replace electrolytes or may not consume the volume of liquid necessary since many individuals drink with meals and may not have the social cues to consume liquids. In a fragile patient population, this could lead to syncopal episodes or even arrhythmias secondary to dehydration.

Women may be at a particularly increased risk for detrimental side effects since IF may induce a stress response that can alter other hormones

and autoregulatory hormones. Women have been noted to be particularly susceptible to increased fatigue, anxiety and may experience irregular periods secondary to hormone dysregulation. One study noted a disproportionate change in brain chemistry when compared with male rats and female rats ceased to ovulate when undergoing IF [61]. While this may be of less concern in women receiving concurrent cancer treatment, fertility issues should be addressed in weighing the risks and benefits of IF as a potential option.

Rationale for the implementation of IF in a clinical trialIF offers patients an intervention that does not require calorie counting or macronutrient intake monitoring. The liberal periods of ad libitum consumption may make this dietary modification most palatable to patients. Unlike CR or ketosis, IF does not require any prior planning with the measurement of baseline calories and the intervention can, therefore, be started immediately. While monitoring compliance is still challenging with IF, intricate measures to calculate calories or examine macronutrient contents can be avoided. Overall, IF may be less labor intensive on both the part of the patient and the treatment team, making it ideal for a clinical trial.

Ketosis or low carbohydrate dietary modification

OverviewA KD has been used in the treatment of seizure disorder for nearly a century [62] and, more recently, for the treatment of obesity, diabetes and hypertension [63]. A KD limits carbohydrates and is low in protein, replacing these macronutrients with fat. A lowcarbohydrate diet generally leads to the production of ketones by the liver. As blood glucose drops and serum ketone concentration increases, cells begin to rely on energy derivation through the Krebs cycle within the mitochondria via respiration, as opposed to glyocolysis within the cytoplasm. The most common ketones produced are bhydroxybutyrate and acetoacetate, which are produced from fatty acid oxidation in the liver. While 50 g/day of carbohydrates is often used as a cutoff for ketone production, a high protein diet can often halt the production of ketones, stressing the necessity of elevated levels of fat intake. Ketones are a source of energy that can be readily used by the brain and body during times of low carbohydrate consumption. These diets have been successfully used in the treatment of obesity and diabetes [57], and may provide benefit in cancers,



with outcomes closely related to metabolic risk factors [58].

KD in the preclinical realmAs first proposed by Nobel Prize Laureate Warburg, a hallmark of tumor cells is mitochondrial deficiency with a reliance on anaerobic glycolysis and glucose for energy production [64]. While the requirement of glucose for ATP production and energy derivation in cancer cells is well known, recent data have revealed its function in moderating reactive oxygen species (ROS) [65]. While the exact mechanism of a KD and its resultant reduction in tumor growth remains unknown, evidence suggests this oxidative mechanism may be partly responsible. Elevated levels of ketones increase mitochondrial respiration for the derivation of energy through the Krebs cycle. However, mitochondrial function has also been shown to be upregulated through metabolic oxidative stress and the generation of ROS [66]. While glucose restriction may selectively starve tumor cells, the production of ketones appears to render cancer cells more vulnerable to oxidative stress and cellular damage from exposure to ROS [67–69]. This increased susceptibility of cytotoxicity and tumor damage from ROS could potentially enhance the effects of RT and chemotherapy, which eradicate cancer cells by inducing oxidative stress and DNA damage. This theory has been supported by recent preclinical data in animal trials, where ketogenic data were found to significantly enhance the antitumor effect of radiation and prolong survival [70].

Further data also have revealed the reliance of cancer cells on the insulin pathway, which is downregulated through carbohydrate deprivation [71]. In this regard, a carbohydraterestricted KD may serve as a method to selectively downregulate cellular pathways in tumor cells, while restricting their energy source and making them more vulnerable to cancer treatment. This pathway, including insulin, IGF1 and its receptor (IGF1R), is associated with cancer initiation and progression [72], angiogenesis and VEGF expression in tumors [21]. The binding of insulin and IGF1 to IGF1R activates the MAPK and PI3K pathway in both normal and malignant cells [73]. A pilot study in advanced cancer patients recently confirmed the safety of a lowcarbohydrate KD in cancer patients and its ability to downregulate the insulin pathway in tumor cells [71]. Diet studies in noncancer patients have shown that carbohydrate restriction significantly lowers serum insulin and glucose levels more than a lowfat calorierestricted diet [63].

KD has also been shown to upregulate the AMPK pathway, which has been shown to be therapeutic towards cancer. AMPK activation, which can be achieved through the drug metformin, also increases insulin sensitivity, and may work through the IGF pathway; however, it also acts by downregulating mTOR [74]. A recent randomized study in noncancer patients has shown that regardless of caloric intake, and even in the presence of overfeeding, AMPK is activated when carbohydrates are restricted and replaced with fat [75]. In fact, this study has suggested that regardless of CR, when high carbohydrates are consumed, AMPK activation is prevented. Similar to CR, glucose reduction alone, like that in a KD, has been shown to result in similar hormetic benefits in rodents and lower organisms [76]. It is hypothesized that these benefits may also be related to AMPK activation [66].

A KD has been shown to decrease tumor progression. Animal glioma tumor models have even demonstrated that tumor growth is inhibited in the presence of ketone bodies [77]. The effect of a KD on decreasing glucose uptake in brain tumor cells was initially shown in two female pediatric patients with highgrade gliomas via a 21.8% decrease in tumor fluorodeoxyglucose uptake on PET scans and clinical improvement [78]. However, it is unlikely that this is the only pathway through which a KD is active against tumor cells.

Ketosis in the clinical realmCurrently, several clinical trials are assessing the safety and efficacy of a KD in combination with traditional cancer treatment, including the KETOPAN trial for pancreatic cancer, the KETOLUNG trial for lung cancer, NCT01092247 [206] and NCT01535911 [207] for highgrade gliomas, NCT01716468 [208] for advanced cancer, and the ERGO trial for recurrent glioblastoma, which has recently finished accruing. While most of these studies are assessing feasibility and efficacy, the KETOPAN and KETOLUNG trials are assessing free radical markers from RT in conjunction with a KD. Table 3 is a summary of the current clinical trials using KD as an intervention in the oncologic population.

ComplianceMonitoring compliance, both for patients and physicians, may be more easily achieved through a KD. While quantifying caloric intake remains challenging, KDs can be monitored merely through initial urine strips and then



daily finger stick blood tests performed at home, which has been successfully achieved in many randomized trials.

Weight changesConcerns of cachexia remain with dietary interventions during cancer treatment. However, a KD is not restricted in overall calories, merely carbohydrates, which may help to avoid weight loss. Also, a KD results in the mobilization of adipose tissue, which is converted to ketones, which are used by the brain for energy derivation. While this diet has been shown to result in fat loss when employed in noncancer patients [63], it has been shown to be effective at muscle sparing [79,80] and may even increase muscle synthesis [81]. Therefore, this diet may benefit patients at risk for cachexia as the main concern of weight loss and cachexia during cancer treatment is muscle wasting. Finally, randomized trials have shown a reduction in several inflammatory markers when a KD was compared with a lowfat diet, which may be further beneficial to patients during treatment [82,83].

Implementing a KDA KD does require significant counseling between physicians, dieticians and patients in an effort to educate the patient on daily macronutrient consumption and methods to limit carbohydrate consumption. The typically large increase in fat consumption often requires higher levels of counseling. Patients must initially

meet biweekly for guidance, and at least weekly thereafter. During RT, which typically occurs on a daily basis, these meetings are more easily accomplished.

Monitoring can take place with the physician or dietician through food journals or through online systems (i.e., [209]) that the physician can remotely check as needed. These systems are easily accessed by patients and give daily macronutrient feedback. If patients do not have computer or internet access, the program can be accessed within the outpatient clinic.

Short- & long-term complicationsKD are generally well tolerated with minimal side effects, including constipation, salt loss, mild acidosis and increased incidence of kidney stones, when employed chronically over 6 years [84].

Rationale for implementation of a KD in a clinical trialDietary manipulation through a KD affords patients several advantages over CR or IF, and may be the easiest to monitor. While calorie restriction via IF may require extended periods of withholding food intake for patients, KDs merely require a restriction of carbohydrate intake and may work independent of caloric consumption or weight changes [85]. An overall reduction of calories by all macronutrients may also be difficult for patients, while minimizing only one of three macronutrients may be more easily achieved. Finally, randomized trials have shown a

Table 3. Summary of existing clinical trials using ketogenic diet in the oncology population.

clinicaltrials.gov identifier

Trial title Concept Status Outcomes

NCT01535911 Pilot Study of a Metabolic Nutritional Therapy for the Management of Primary Brain Tumors

Energy restricted ketogenic diet in glioblastoma patients: 20–25 kcal/kg/day KetoCal® diet for 12 weeks

Recruiting Safety/efficacy with intention to treat

NCT01419843 KETOPAN KetoCal diet starting 2 days before treatment for at least 5 weeks during concurrent chemoradiation for pancreatic neoplasms

Recruiting Safety/efficacy, adverse event monitoring for 8 weeks

NCT01419587 Ketogenic Diet with Chemoradiation for Lung Cancer

Conceptually similar to above study, but for stage III or IV lung cancer patients

Recruiting Safety/efficacy, adverse event monitoring for 8 weeks

NCT01716468 Ketogenic Diet in Advanced Cancer Low carbohydrate diet for patients diagnosed with metastatic disease from a solid tumor malignancy

Recruiting QoL measures, PFS and OS measures to be assessed

NCT00575146 ERGO Mild ketogenic diet used in patients with recurrent glioblastoma

Completed Safety/efficacy with secondary QoL measures

Details of each trial can be found on www.clinicaltrials.gov and by searching for the relevant trial number. OS: Overall survival; PFS: Progression-free survival; QoL:Quality of life.



reduction in several inflammatory markers when a KD was compared with a lowfat diet, which may be further beneficial to patients during treatment [82,83].

Molecular mechanisms of diet modifications

Several metabolic pathways related to growth and proliferation have been noted to be dysregulated in cancer cells (Figure 2). Table 4 summarizes the

distinct effects of each intervention in the serum of laboratory rodents.

The IGF1/Akt/mTOR pathway seems to be the most commonly affected pathway that is universally downregulated with all three interventions. Inhibition of this pathway has been shown to sensitize tumor cells to conventional treatments, such as chemotherapy and RT [86]. In mouse tumor models, CR has significantly decreased IGF1R expression on tumors when compared with

Dietary restriction

Decreased serum IGF-1and growth factors

• Autophagy• Increased stress resistance

• Increased apoptosis• Increased susceptibility to cytotoxic therapies

Normal cell Malignant cell

Carbohydrate restriction

CR/IF/KD

Insulin

IRS1/2

PI3K

mTOR mTORmTOR

Akt

Decreasedserum IGF-1

Decreasedserum glucose

AMPK

• Decreased cellular proliferation and growth• Decreased angiogenesis• Increased autophagy

Decreased serum glucose

Decreased glucoseuptake into cells

Glycolysis

Normal cell Malignant cell

Inability to adapt

Low energy stateBcl-2

Caspase-9 activation

• DNA fragmentation• Apoptosis

Mitochondrial respiration

Krebs cycle

• ATP not derived from glucose• Increased protection to oxidative stress

Proto-oncogenes Other oncogenesRasAkt Akt Ras

Decreased serumglucose and nutrients

Future Oncology © Future Science Group (2013)

Figure 2. Molecular pathways that are altered by decreased nutrient signaling in ketogenic diet, caloric restriction and intermittent fasting. (A) Decrease in the level of environmental nutrients, caused by KD, CR or IF, can be sensed by both normal cells and malignant cells. While nonmalignant cells are able to adapt to this and switch into a maintenance state, cancer cells are unable to undergo this adaptation, resulting in a differential stress response. Normal cells respond by decreasing Akt and Ras signaling in order to shift into autophagy. Malignant cells are affected differently and autophagy in these cells leads to increased apoptosis secondary to mutated DNA damage repair molecules such as p53. (B) Decreased levels of serum IGF-1 and glucose also induce decreased mTOR signaling in cancer cells through either an AMPK- or Akt-mediated pathway. In addition, decreased nutrients in the serum leads to a decrease in serum insulin, thereby decreasing mTOR signaling via IRS1/2 and PI3K. Ultimately, these alterations lead to increased apoptosis in tumor cells. (C) Carbohydrate restriction (and perhaps to an extent IF) leads to increased mitochondrial respiration in normal cells, whereas cancerous cells are unable to adapt to this change in nutrient availability. This leads to increased Bcl-2 and caspase-9 activation in malignant cells causing DNA fragmentation and cell death. CR: Caloric restriction; IF: Intermittent fasting; KD: Ketogenic diet.



ad libitum-fed mice [17]. Serum IGF1 and tissue IGF1R are known to have mitogenic and proliferative effects on tumors, especially in excess [54] and, therefore, reduced activation of the downstream targets of the IGF1R pathway, including Akt and mTOR, may occur. Akt and mTOR are known to potentiate antiapoptotic signals in cancer cells, as well as proangiogenic signals through induced VEGF signaling [87,88]. More specifically, Akt has been implicated in the expression of prosurvival genes by targeting NFkB [89]. mTOR acts to integrate the upstream signals from IGF1, insulin and amino acids into downstream proliferative and prosurvival pathways [90]. Currently, selective mTOR inhibitors, such as everolimus, are being explored as potential chemotherapies for many types of cancers, including gliomas, renal cell carcinoma, urothelial cancers, prostate cancer, and head and neck squamous cell cancers [201]. Dietary modification provides a less expensive, less toxic alternative to these inhibitors; an alternative that broadly affects the IGF1R pathway, as opposed to one constituent.

IF, CR and KD have also been implicated in the upregulation of the AMPK pathway, which has shown to be therapeutic in cancer models. AMPK activation, which can be achieved through the drug metformin, also increases insulin sensitivity, and may exhibit its effects via crosstalk through the IGF pathway. However, AMPK also acts by downregulating mTOR [74]. A recent randomized study in healthy subjects has shown that, regardless of caloric intake, and even in the presence of overfeeding, AMPK is

activated when carbohydrates are restricted and replaced with fat [75]. This may suggest a molecular advantage to KD as opposed to CR or IF. In fact, the same study suggested that regardless of CR, when high carbohydrates are consumed, AMPK activation is prevented.

Altering the oxidative stress response is also noted to be affected by diet modification. CR induces many adaptive mechanisms at the cellular level, one of which is to reduce the formation of ROS, thereby protecting cells against oxidative stress and free radical DNA damage [91–93]. This protective mechanism combats malignant transformation by cells and may be a major contributing factor in the reduction of spontaneous tumor formation. In addition, it has been proposed that a decrease in ROS may alter the tumor microenvironment and generate proapoptotic signals in cancer cells [91,94]. These results have been consistent in rodents and nonhuman primates; however, it remains to be seen whether the same effects will be provoked in humans. A KD is associated with elevated levels of ketones, which can be upregulated through metabolic oxidative stress and can generate ROS [66]. While glucose restriction may selectively starve tumor cells, the production of ketones renders cancer cells more vulnerable to oxidative stress and cellular damage from exposure to ROS [67–69]. Assuming that IF is capable of producing ketone bodies in the later stages of fasting, it may also be able to produce these mitochondrial effects. The increased susceptibility to cytotoxicity and tumor damage from ROS could potentially enhance the effects

Table 4. Effects on serum markers across diet regimens.

Metabolic marker

KD effect IF effect CR effect

GH/IGF-1/insulin

GH ↑ 1.2-fold [109] ↓ 90% [110,111] ↑ 50-fold [112]

IGF-1 ↓ 30% [109] ↓ 40%; ↓ 70% [54,110] ↓ 40% [113]

IGFBP-1 ↓ 30–35% [109] ↑ sevenfold; ↑ 11-fold [54,110]

↑ 20-fold [48]

IGFBP-3 ↓ 15–39% [109] ↓ 50%; ↓ 40% [54,110] ↓ 20% [48]

Insulin ↓ 2.6-fold; ↓ 15–40% [109,114] ↓ 90% [110] ↓ 40% [115]

Insulin sensitivity NC [116] ↑ threefold [117] ↑ 1.2-fold [118]

Adipokines

Leptin ↑ 2.5-fold [109] ↓ 80% [50] ↓ 30% [50]

Adiponectin No data NC [50] NC [50]

Time to effect Days to weeks [109,114] 2–3 days [46,54] Weeks to months [50,119]

↑: Increase in the corresponding marker; ↓: Decrease in the corresponding marker; CR: Caloric restriction; GH: Growth hormone; IF: Intermittent fasting; KD: Ketogenic diet; NC: No change.



of standard cancer therapies, such as chemotherapy or RT. These modalities exert their effects by inducing oxidative stress and DNA damage. This theory has been supported by recent preclinical data in animal trials, where a KD was found to significantly enhance the antitumor effect of radiation and prolong survival [70].

Metabolic pathways also play a critical role in tumors’ response to diet modification and are already known to be an important target for anticancer therapies [95]. In general, tumor cells tend to have dysregulated metabolic signaling and are unable to respond to decreased nutrients in the environment. Normal cells may sense decreased nutrients and adapt to the environment by turning off proliferative signals and turning on maintenance and selfpreservation signals. This is the basic concept behind autophagy and what fuels the phenomenon known as differential stress response. Since cancer cells are unable to adapt appropriately, they are forced into apoptosis. This is particularly relevant to the use of chemotherapeutic agents and other cytotoxic modalities in the treatment of cancer. Several studies have shown that dietary manipulations increase apoptosis preferentially in tumor cells as opposed to normal tissue [49,96]. Targeting metabolism and utilizing diet interventions to affect changes in tumor cell biology offer less toxic and less expensive alternatives to selective molecule inhibitors.

As previously stated, IGF1 levels have been correlated with disease progression and recurrence [97,98]. The liver, as well as visceral fat stores, is primarily responsible for the mobilization of IGF1 within the serum. Animal studies suggest that perhaps intermittent CR or IF may be more effective at reducing IGF1 levels and hepatic fat stores as compared with continuous CR [99]. Due to the relationship between adipose tissue and sex hormones, it is reasonable to propose that by reducing visceral fat stores patients may respond better to hormonal cancer therapies. Randomized studies in noncancer populations have revealed that a carbohydrate restricted diet and KD potently inhibits the insulin pathway, and effectively decreases ectopic fat distribution [83]. Dietary lipids and fat stores have been linked to cancer prevention and, therefore, it is possible that they may also be important in progression and survivorship [100]. The Mediterranean diet is different from a typical Western diet in that fat is derived from sources such as olive oil and fish. Several studies have looked at Mediterranean diets and cancer risk [8,101,102]. Success has been shown in decreasing cancer risk not only with breast cancer, but also with gastrointestinal cancers and skin

cancer [103–105]. This diet has also shown an ability to reduce circulating sex hormones and this may be important in decreasing the incidence and recurrence of breast cancer [106,107]. Currently, the DIANA5 trial is examining the relationship between macronutrient modification and circulating levels of different serum markers and cancer recurrence [107]. These promising prevention studies support the idea that continued research is needed in the field of macronutrient components of diet and hormonesensitive cancers.

While all three diets have demonstrated promising anticancer effects at the preclinical level, they each have something different to offer on the molecular level. All of the interventions seem to have an effect on the IGF1R pathway. Downregulating this pathway in tumors that do not have PI3K activation, will render these cells more susceptible to cytotoxic therapies, such as chemotherapy or RT [86], regardless of which dietary intervention is being used. For tumors that have PI3K activation and are, therefore, resistant to dietary restriction [39], it may be optimal to use a KD or IF for the creation of ketone bodies and increased mitochondrial respiration. Although not confirmed, these modalities may have the potential to affect changes in CRresistant tumors. In addition, it is known that brain tumors, in particular gliomas, rely on glucose as their major source of nutrients and energy. Consequently, it is reasonable to suggest that patients with gliomas and other primary brain tumors may do better with KD or IF (depending on the length of fasting). Lastly, CR offers the advantage of significantly altering gene expression at the level of miRNA. CR is the only modality to date to have a detectable miR signature [108]. This suggests that CR may have the potential to downregulate miRs that regulate the growth and metastasis of certain cancers.

Is one modality better than the rest?Deciding on an optimal dietary intervention is a polarizing topic; scientists and clinicians alike tend to be either proCR, proIF or proKD. These dietary interventions are similar in that they all require patients to be adherent to some type of restriction. This alone makes patient compliance a crucial piece of any of these interventions. Ideally, an intervention should be free of the potential for patient error. Since each modality is user dependent, none are superior to the others in this respect. Dietary preference is also entirely patient dependent. Some patients may prefer to chronically restrict their calorie intake, while others may prefer short fasts with no restriction on nonfasting days. Patients may prefer KD because



therapies such as chemotherapy or ionizing radiation. Therefore, it will be essential for future research to define the appropriate dietary parameters for these interventions in order for adequate comparisons to be made between trials. In addition, subsets of oncology patients will need to be identified to determine who might benefit more significantly from each intervention.

Financial & competing interests disclosureThis article was supported in part by the Kimmel Cancer Center’s National Cancer Institute Cancer Center Support Grant P30 CA56036. The authors have no other relevant affiliations or financial involve-ment with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

No writing assistance was utilized in the production of this manuscript.

it does not require any overall restriction of intake, just modification of macronutrients. The answer to which intervention is ideal for cancer patients lies in the molecular signature of each regimen. As previously noted, the choice of dietary regimen may be cancer subtype dependent. The chosen intervention should be tailored to the individual patients’ tumor biology and personal preferences.

Future perspectiveOwing to an increasing delineation of metabolic properties of cancer, dietary interventions are being explored as possible treatment modalities in oncology trials. A handful of pilot clinical trials have already been opened for accrual using the diet interventions of KD and IF but, to date, none have been established for CR. It is likely that over the next decade large, randomized clinical trials will be pursued using these interventions as an adjunct to widely used cytotoxic

Executive summary

Dietary modification as a treatment intervention in cancer�n Metabolism-based therapies, such as caloric restriction (CR), intermittent fasting (IF) and carbohydrate restriction/ketosis, have

demonstrated efficacy in preclinical models and are becoming of increasing interest because of their anticancer effects.�n Clinical protocols for these modifications have not yet been established for use in oncologic patients.

CR in cancer treatment�n Preclinical data have suggested that CR may delay tumor growth and metastasis in many laboratory rodent models.�n No clinical trials exist using CR as an intervention for cancer patients.�n The subset of patients who may benefit most from CR in combination with standard therapy needs to be defined. �n CR offers the benefits of hormesis combined with the potential to alter cancer cells at the miRNA level to decrease invasiveness and

disease progression.

IF in cancer treatment�n IF has the potential to decrease tumor growth and increase apoptotic signaling in cancer cells in both in vivo and in vitro models.�n Currently, there are three clinical trials using IF either alone or in combination with chemotherapy that are actively recruiting.�n IF offers the benefits of being a short-term intervention as well as being less labor intensive for patients and clinicians.�n This intervention may not be an ideal intervention for all patients depending on their age and range of comorbidities.

Ketogenic diet in cancer treatment�n Preclinical data have shown that a ketogenic diet (KD) may decrease cancer growth and increase the efficacy of radiation therapy.�n A pilot study has shown the safety and feasibility of a KD in patients with advanced cancer.�n A KD offers the benefit in that it may not require a reduction in overall food intake or calories.�n AMPK upregulation may be greater in a ketogenic diet than CR regimens.

Conclusion�n Metabolism-based therapies have the potential to become a powerful adjunct to standard cancer treatment.�n These interventions target molecular pathways, such as IGF-1/Akt/mTOR, as well as AMPK and mitochondrial stress response to exert

their effects.�n Dietary protocols will need to be optimized before larger, randomized clinical trials may begin.�n Each dietary modification has its own unique benefits and, while some are overlapping between therapies, certain interventions may

be better for a particular subset of patients, which has not yet been delineated.

Future perspective�n Future research should be aimed at defining whether or not a certain intervention is better for a particular subset of patients.�n In addition, conditions of these dietary modifications will need to be perfected in order for larger clinical trials to open.�n It is likely that, over the next decade, larger randomized clinical trials will be pursued using these interventions as an adjunct to widely

used cytotoxic therapies such as chemotherapy or ionizing radiation.



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Selectively starving cancer cells through dietary manipulation: methods and clinical implications

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