Nutritional requirements of exercise (Macronutrients)

NUTRITIONAL REQUIREMENTS OF

EXERCISE(MACRONUTRIENTS)

RAMYA.H.

2nd Year M.sc.

ENERGY

• The most important component of successfulsport training and performance is to ensureadequate calorie intake to support energyexpenditure and maintain strength, endurance,muscle mass and overall health.

• Energy and nutrient requirements vary withweight, height, age, sex and metabolic rate andwith the type, frequency, intensity, andduration of training and performance.

• Individuals who participate in an overall fitness program (i.e., 30 to 40 min/day, 3 times per week) can generally meet their daily nutritional needs by following a normal diet providing 25 to 35 kcal/ kg/day or roughly 1800 to 2400 calories a day.

• However, the 50 kg athlete engaging in more intense training of 2 to 3 hours per day 5 to 6 times a week or high volume training of 3 to 6 hours in 1 to 2 workout per day (5 to 6 days a week) may expend up to an additional 600 to 1200 calories a day, thus requiring 50 to 80 kcal/kg/day or roughly 2500 to 4000 kcal/day.

• For elite athletes or heavier athletes, daily calorie needs can reach 150 to 200 kcal/kg, or roughly 7,500 to 10,000 calories a day depending on the volume and intensity of different training phases.

MACRONUTRIENTS • Individuals engaging in a general fitness program can typically meet

their macronutrient needs by consuming a normal diet of 45% to 55% of calories from carbohydrates (3 to 5 gram/kg/day), 10% to 15% from protein (0.8 to 1 g/kg/day) and 25% to 35% from fat (0.5 to 1.5 g/kg/day).

• Athletes involved in moderate to high volume training need greater amounts of carbohydrates and protein to meet macronutrient needs. A minimum intake of at least 50%, but ideally 60% to 70%, total calories (5 to 8g/kg/day or 250 to 1200g/day for 50 to 150kg athletes) should be met by carbohydrates. The remaining calories should be obtained from protein (10% to 15%) and fat (20% to 30%).

• These percentages are only guidelines for estimating macronutrient requirements; however, specific recommendations with respect to carbohydrates, proteins and fats should be used when counseling and active individual or athlete.

CARBOHYDRATES• The first source of glucose for the exercising muscle is its

own glycogen store. When this is depleted, glycogenolysisand then glyconeogenesis both in the liver maintain theglucose supply.

• During endurance exercise that exceeds 90 minutes such asMarathon running, muscle glycogen stores becomeprogressively lower. When they drop to critically low levels,intensity exercise cannot be maintained. In practical terms,the athlete is exhausted and must either stop exercising ordrastically reduce the pace, athletes often referred to this as“hitting the wall”.

• Glycogen depletion may also be a gradual process occurringover repeated days of heavy training, in which muscleglycogen breakdown exceeds its replacement.

• For example, a distance runner who averages 10 miles perday but does not take the time to consume enoughcarbohydrates in his or her diet, or the swimmer whocompletes several intervals sets at about his or her maximumoxygen consumption, deplete glycogen stores rapidly.

CARBOHYDRATE INTAKE BEFORE EXERCISE

• Pre exercise meals serves two purposes-

1. Keep the athlete from feeling hungry before and during the exercise bout and

2. It maintains optimum level of blood glucose for the exercising muscle.

• Those who train early in the morning before eating or drinking risk developing low liver glycogen store, and this can impair performance, if the exercise regimen involves endurance training.

• Pre event meal should be high in carbohydrates, nongreasy, and readily digested. Fat should be limitedbecause it delays stomach emptying time and takeslonger to digest. Exercising with a full stomach also maycause indigestion, nausea, and vomiting.

• The pregame meal should be eaten 3 to 4 hours beforean event and should provide 200 to 350g ofcarbohydrates (4gm/kg). Allowing time for partialdigestion and absorption provide a final addition tomuscle glycogen, blood sugar, also relatively completeemptying of the stomach.

• To avoid gastrointestinal distress, carbohydrate contentof the meal should be reduced to closer the meal is tothe exercise. For e.g., 4 hours before the event it issuggested that the athlete consume 4g of Carbohydratesper kg body weight, whereas 1 hour before thecompetition the athlete would consume 1g ofcarbohydrate per kg of body weight.

CARBOHYDRATE INTAKE DURING EXERCISE

• Carbohydrates consumed during endurance exerciselasting longer than 1 hour ensures the availability ofsufficient amounts of energy during the later stages ofexercise, improve performance, and enhance feeling ofpleasure during and following exercise.

• Carbohydrate feeding does not prevent fatigue; rather,it simply delays it.

• Glucose ingestion during exercise has also been shownto spare endogenous proteins and carbohydrates in fedcyclists without glycogen depletion. Thus consuming anexogenous carbohydrate during endurance exercisehelps to maintain blood glucose and improveperformance.

• The form of carbohydrate does not seem to matterphysiologically; some athletes prefer to use a sportsdrink, others prefer to eat a solid or gel and consumewater.

• If a sports drink with carbohydrates is consumedduring exercise, rate of carbohydrate ingestion shouldbe about 26 to 30g every 30 minutes, equivalent to onecup of a 6% to 8% carbohydrate solution taken every15 to 20 minutes. This ensures that one gram ofcarbohydrate will be delivered to the tissues per minuteat the time fatigue sets in.

• but solution with a concentration greater than 10% areoften associated with abdominal cramps, nausea, anddiarrhoea.

CARBOHYDRATE INTAKE AFTER EXERCISE

• On average, 5% of the muscle glycogen used duringexercise is resynthesized each hour following exercise.

• Accordingly, at least 20 hours will be required forcomplete restoration after exhaustive exercise, providedabout 600 grams of carbohydrates are consumed.

• The highest muscle glycogen synthesis rate have beenreported when large amounts of carbohydrates (1 to1.85g/kg/hour) are consumed immediately afterexercise and at 15 to 60 minute intervals thereafter forup to 5 hour after exercise.

• When carbohydrate ingestion is delayed by severalhours, glycogen synthesis may drop by as much as 50%and reduce muscle glycogen resynthesis.

• consumption of carbohydrates with a high GI result inhigher muscle glycogen levels 24 hours after exercisecompared with the same amount of carbohydratesprovided as foods with a low GI.

• Adding about 5 to 9g of protein with every 100g ofcarbohydrate eaten after exercise may further increaseglycogen resynthesis rate, provide amino acids formuscle repair and promote a more anabolic hormonalprofile.

• Many athletes find it difficult to consume foodimmediately after exercise. When body or coretemperature is elevated, appetite is depressed and it isdifficult to consume carbohydrate rich foods.

• They find it easier and simpler to drink theircarbohydrates rather than eat carbohydrate rich foodsuch as fruit pops, bananas, oranges, melon, or appleslices.

PROTEIN

• Protein requirements of athletes, those engaged instrength and power events maybe increased aboutthose of sedentary people for the followingreasons:

• Amino acids are used to repair muscle trauma thatresults from repeated muscle contraction and forthe repairs of injuries to muscle fibres.

• To remodel muscle tissue in response to strengthtraining and increase in muscle bulk due toresistance training.

• Prolonged exercise increases oxidation of aminoacids for fuel. Protein used as an energy substrateincreases during high intensity, long durationendurance activity.

• Protein makes of greater contribution to total energyproduction during endurance exercise when muscleglycogen levels are low. Protein intake equal to 15 to20% of total calories will meet the protein requirementsof most athletes.

• Inadequate protein intake can result in negativenitrogen balance, which can increase proteinmetabolism and lead to muscle wasting, trainingintolerance, and retarded recovery.

• Consuming more protein than 2 grams/kg body weightresults in increased protein oxidation, urea formation,diuresis and can increase risk for the dehydration.

• The type of sport and total calorie intake influenceprotein requirements.

• High protein diet increases the water requirementnecessary to eliminate nitrogen through the urine. Inaddition, an increase in metabolic rate leads toincreased oxygen consumption.

• Athletes participating in events requiring strengthrather than endurance usually experience only a slightincrease in protein need. There is no evidence thateating more protein can increase metabolic efficiencyor lead to enhanced strength or endurance.

• Increase muscle mass can only be achieved by longterm training. Without a training program extra dietaryprotein is converted to storage fat. There is no reasonto promote or use of protein supplements.

FAT

• Fat is the major, if not most important, fuel for light to moderateintensity exercise.

• Although fat is a valuable metabolic fuel for muscle activity duringlonger aerobic exercise and performs many important functions inthe body, no attempt should be made to consume more fat overthe usual amount unless the athlete is eating less than 15% ofcalories from fat.

• In addition, athletes who consume a high fat diet typicallyconsume fewer calories from carbohydrate.

• If an athlete is consuming a high carbohydrate diet, He or she willuse more glycogen as fuel for the exercise. If the diet is high in fat,more fat will be oxidised as a fuel source.

• Fat oxidation rates have been shown to decline after the ingestionof high fat diet, partly because of adaptations at the muscle leveland decreased glycogen stores.

• Maximum rates of fat oxidation are reached at exerciseintensities between 59% and 64% of vo2 max in trainedathletes and at intensities of 47% to 52% vo2 max inthe general population.

• The mode and duration of exercise can also affect fatoxidation, with running increases fat oxidation morethan cycling and endurance training.

• Following a low fat, high carbohydrate diet is alsoimportant for health reasons because a high fat diet isassociated with cardiovascular disease, obesity, diabetes,and some types of cancers.

• Athletes should consume 20% to 30% of their caloriesfrom fat.

• Severe fat restrictions 15% or less of energy intake maylimit performance and is not advised.

REFERENCES

• Krause’s Food and Nutrition Therapy, 12th

edition, L.Kathleen Mahan and Sylvia Escott-Stump

• Dietetics, 6th edition, B.SriLakshmi