Page 1
8/7/2019 Vegan Diet and Type 2 Diabetes
http://slidepdf.com/reader/full/vegan-diet-and-type-2-diabetes 1/4
Page 2
8/7/2019 Vegan Diet and Type 2 Diabetes
http://slidepdf.com/reader/full/vegan-diet-and-type-2-diabetes 2/4
Health delivery 1
June 2007 | Volume 52 | Issue 2
evidence-based ranking system for carbohydrates based
on their effect on blood glucose levels in the first two hours
after eating). Typical meals were:
breakfast – porridge (oatmeal) with cinnamon and raisins,
a slice of melon, and perhaps vegetarian sausage
lunch – a bowl of split-pea soup, beans and rice, or
vegetable chilli
dinner – pasta with tomato sauce, vegetable stew, or a
bean burrito, with plenty of vegetables.
The diet did not limit calories, carbohydrates or portions,
and derived approximately 10% of energy from fat, 15%
from protein, and 75% from carbohydrate.
Standard diet
In contrast, the ADA diet limited protein to between 15%
and 20% of overall intake; saturated fat to below 7%;
carbohydrates and monounsaturated fats to between 0%
and 70%; cholesterol not exceeding 200 mg per day; and
Testing the evidence
Based on evidence from these studies, my research team
put plant-based diets to the test. After a series of favourable
preliminary studies, and with the support of the US National
Institutes of Health, we conducted a randomized trial com-
paring a low-fat vegan diet to a comparison diet based on
the guidelines of the American Diabetes Association (ADA).
Working with the George Washington University, USA, and
the University of Toronto, Canada, 99 adults with type 2
diabetes took part in the 22-week study.
Type 2 diabetes is considerably less
common among vegetarians, compared
to people who habitually eat meat.
Vegan diet
The vegan diet had three components: it excluded all
animal products (meat, eggs, dairy products), was low in
fat, and favoured foods with a low glycaemic index (an
The vegan diet excludes all animal products and favours foods with a low glycaemic index.
Page 3
8/7/2019 Vegan Diet and Type 2 Diabetes
http://slidepdf.com/reader/full/vegan-diet-and-type-2-diabetes 3/4
Health delivery4
June 2007 | Volume 52 | Issue 2
A low-fat vegetarian diet is no
more difficult to follow than
other therapeutic diets.
tion in HbA1c alone – without considering the capacity of
the diet to reduce cholesterol and blood pressure.
People on the vegan diet reduced their LDL cholesterol
by 21% – significantly more than the 9% drop that was
seen with the ADA diet. Although most participants were
on blood pressure-lowering medications and had normal
blood pressure levels, those on the vegan diet showed an
average 4% reduction in systolic blood pressure and 5% in
diastolic pressure. Despite the fact that there was no caloriclimit in the vegan group, weight reduction was 5.8 kg,
compared with 4.3 kg in the ADA group.
People on the vegan diet reduced
their HbA1c
and LDL cholesterol
significantly more than people
following the ‘standard’ diet.
Explaining the mechanisms
Recent studies suggest that insensitivity to insulin is related
to the accumulation of fat within muscle cells (intramyocel-
lular lipid), which is apparently due to a genetically based
reduction in mitochondrial activity – conversion of organic
materials into cellular energy, and other metabolic tasks. This
lipid accumulation seems to be influenced by diet. High-fat
diets appear to inhibit the genes required for mitochondrial
action in skeletal muscle, leading to the accumulation of fat
within the muscle cells. Even a few days on a high-fat diet
is sufficient to increase intramyocellular lipid content. Just
as a key cannot open a lock if someone has maliciously
pushed glue into the mechanism, insulin’s ability to bringglucose into a cell, via intracellular signalling, is impaired
by the build-up of intracellular fat.
Researchers at the Catholic University in Rome, Italy, demon-
strated that intramyocellular lipids can rapidly be reduced,
albeit using a method not recommended for routine use.4
In 2002, eight people underwent gastric bypass surgery,
reducing the stomach to a pouch about the size of an egg
and severing the intestine, attaching the lower portion of the
was individualized, based on body weight and plasma
lipid concentrations. Participants in the ADA group with a
BMI above 25 kg/m2 were prescribed reductions in energy
intake of between 500 kcal and 1000 kcal.
For people in both groups, physical activity was kept con-
stant, and medications were not changed, except in cases
of hypoglycaemia.
Contrasting results
Among people whose medications remained constant, thedrop in HbA
1cwas 0.4% in the ADA group and 1.2% in
the vegan group (from 8.0% to .8% during the 22-week
study). This reduction is greater than that seen with typical
oral diabetes medications.
To put this in perspective, the landmark UK Prospective
Diabetes Study demonstrated that a 1% drop in HbA1c for
people with type 2 diabetes lowers the risk of eye or kidney
complications by about 37%. This is the effect of the reduc-
Page 4
8/7/2019 Vegan Diet and Type 2 Diabetes
http://slidepdf.com/reader/full/vegan-diet-and-type-2-diabetes 4/4
Health delivery 1
June 2007 | Volume 52 | Issue 2
small intestine directly to the tiny stomach pouch. Because
fat is absorbed in the upper part of the small intestine, the
procedure results in a massive malabsorption of fat. The
result was not only weight loss (from an average of 137 kgto 104 kg over months), but also an 87% reduction in
intramyocellular lipid – and even though the people re-
mained overweight, their insensitivity to insulin had largely
disappeared.
A low-fat vegan diet approaches the same goal by rear-
ranging the menu, rather than the gastrointestinal anatomy.
Devoid of animal fat and most vegetable oils, the diet
greatly reduces fat intake, presumably leading to a reduc-
tion in intramyocellular lipids. Supporting evidence comes
from a case-control study at Imperial College, London, UK:intramyocellular lipid concentrations were about 30% lower
in a group of vegans, compared with omnivores matched
for age and body weight.5
The lipid-lowering effect of a low-fat vegan diet stems from
the absence of animal fat and cholesterol, and the abun-
dance of soluble fibre. This aspect is particularly important,
given that cardiovascular complications are the primary
cause of death and disability in people with diabetes.
Transient increases in triglyceride levels may occur in peo-
ple who consume refined carbohydrates – foods that have
undergone a process to remove high-fibre content, such
as white rice, white bread, sugary cereals, and pasta and
noodles made from white flour. The diet used in our study
led to the opposite result – a significant drop in average
triglyceride levels. We attribute this to the fact that the
vegan diet was not only low in fat, but also high in fibre
and low-glycaemic-index foods.
The weight change is evidently due to the fact that the re-
duced fat intake and increased fibre intake lower the energydensity of the diet. The reduction in caloric intake is similar
to that achieved with the ADA diet, but is accomplished
without the hunger that caloric limitations typically cause.
In order to reassure healthcare providers who might ques-
tion the acceptability of the diet, we have studied this
aspect with quantitative measures of diet acceptability in
several clinical populations, finding that a low-fat vegetar-
ian or vegan diet is no more difficult to follow than other
Neal Barnard
Neal Barnard is Adjunct Associate Professor of Medicine
at George Washington University School of Medicine,
Washington DC, USA. He is President of the Physicians
Committee for Responsible Medicine (www.pcrm.org).
References1 Kuzuya T. Prevalence of diabetes mellitus in Japan compiled from literature.
Diabetes Res Clin Pract 1994; 24 (Suppl): S15-21.
2 Snowdon DA, Phillips RL. Does a vegetarian diet reduce the occurrence
of diabetes? Am J Publ Health 1985; 75: 507-12.
3 Jenkins DJA, Kendall CWC, Marchie A, et al. Type 2 diabetes and the
vegetarian diet. Am J Clin Nutr 2003; 78 (Suppl): S10-.
4 Greco AV, Mingrone G, Giancaterini A, et al. Insulin resistance in morbid
obesity: reversal with intramyocellular fat depletion. Diabetes 2002;
51: 144-51.
5 Goff LM, Bell JD, So PW, et al. Veganism and its relationship with insulin
resistance and intramyocellular lipid. Eur J Clin Nutr 2005; 59: 291-8.
therapeutic diets. In fact, just as, for many people, giving
up smoking is easier than attempting to moderate cigarette
use, simply avoiding certain foods can be easier than trying
to moderate their intake.
Recommendations
To assist people in beginning a low-fat vegan diet, we
recommend two steps:
Exploration
For 1 to 2 weeks prior to beginning the diet change, a
person can try out recipes, aiming to find several that
are appealing and easy to prepare. People who favour
convenience foods or who dine at restaurants will explore
their options, which are more numerous than they are likelyto imagine a priori.
Test drive
Once a person feels ready, the next step is to begin a
3-week period during which every meal is drawn from those
selected in step one. After 3 weeks, the person is likely to
have lost weight, seen an improvement in blood glucose,
and, most importantly, begun to experience a taste change,
rather like the adjustment that occurs with the switch from
whole milk to non-fat varieties – most people readily adapt
and have little desire to return to previous habits.