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Journal of Geriatric Cardiology (2017) 14: 342354
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Review Open Access
A plant-based diet for the prevention and treatment of type 2 diabetes
Michelle McMacken, Sapana Shah
Division of General Internal Medicine, Department of Medicine, New York University School of Medicine, New York, USA
Abstract
The prevalence of type 2 diabetes is rising worldwide, especially in older adults. Diet and lifestyle, particularly plant-based diets, are ef-
fective tools for type 2 diabetes prevention and management. Plant-based diets are eating patterns that emphasize legumes, whole grains,
vegetables, fruits, nuts, and seeds and discourage most or all animal products. Cohort studies strongly support the role of plant-based diets,
and food and nutrient components of plant-based diets, in reducing the risk of type 2 diabetes. Evidence from observational and interven-
tional studies demonstrates the benefits of plant-based diets in treating type 2 diabetes and reducing key diabetes-related macrovascular and
microvascular complications. Optimal macronutrient ratios for preventing and treating type 2 diabetes are controversial; the focus should instead
be on eating patterns and actual foods. However, the evidence does suggest that the type and source of carbohydrate (unrefined versus refined),
fats (monounsaturated and polyunsaturated versus saturated and trans), and protein (plant versus animal) play a major role in the prevention and
management of type 2 diabetes. Multiple potential mechanisms underlie the benefits of a plant-based diet in ameliorating insulin resistance, in-
cluding promotion of a healthy body weight, increases in fiber and phytonutrients, food-microbiome interactions, and decreases in saturated fat,
advanced glycation endproducts, nitrosamines, and heme iron.
J Geriatr Cardiol 2017; 14: 342354. doi:10.11909/j.issn.1671-5411.2017.05.009
Keywords: Diabetes mellitus; Insulin resistance; Vegan; Vegetarian
1 Introduction
Type 2 diabetes is a global epidemic, with approximately
422 million cases worldwide and a rapidly rising prevalence
in middle- and low-income countries.[1] In the United States
in 2011–2012, 12%–14% of adults had type 2 diabetes and
38% had prediabetes.[2] Prediabetes is even more common
among those aged ≥ 65 in the United States, with a preva-
lence of 50%.[3] Diabetes accounts for $176 billion of direct
medical costs in the US, including annual per capita costs of
$7900, a number 2.3 times higher than costs for adults
without diabetes.[4] In 2015, type 2 diabetes was the 7th
leading cause of death in the United States.[5] Diabetes in
older patients is associated with an increased risk of mortal-
ity, reduced functional status, and increased risk of institu-
tionalization.[6] Older patients also have the highest rates of
macro- and micro-vascular complications from diabetes,
including myocardial infarction, major lower extremity
Correspondence to: Michelle McMacken, MD, Department of Medicine,
New York University School of Medicine, Bellevue Hospital Center, 462
First Avenue, New York, NY 10016, USA.
E-mail: michelle.mcmacken@nyumc.org
Telephone: +1-212-562-8783 Fax: +1-212-562-1597
Received: March 1, 2017 Revised: May 18, 2017
Accepted: May 23, 2017 Published online: May 28, 2017
amputations, end stage renal disease, and visual impair-
ment.[3] Moreover, geriatric patients are at increased risk of
medication-related complications, particularly hypoglyce-
mia; the elderly have twice the number of emergency room
visits for hypoglycemia than the general population with
diabetes.[6]
Dietary choices are a key driver of insulin resistance, es-
pecially in an aging, more sedentary population. Increases in
consumption of calorie-dense foods, including fast foods,
meats and other animal fats, highly refined grains, and su-
gar-sweetened beverages, are thought to play a critical role
in the rising rates of type 2 diabetes worldwide.[7] Lifestyle
changes, particularly diet, can be highly effective in pre-
venting, treating, and even reversing type 2 diabetes.[8–11]
Among the 20% of participants in the landmark Diabetes
Prevention Program who were ages 60 and over, lifestyle
changes conferred a 71% reduction in risk of type 2 diabetes,
demonstrating that older adults reaped the greatest benefit
from lifestyle interventions compared to other age groups.[8]
Lifestyle changes address the root causes of type 2 diabetes
and can ameliorate comorbidities while reducing the risk of
polypharmacy, particularly in the elderly. Plant-based di-
ets―i.e., eating patterns that emphasize legumes, whole
grains, vegetables, fruits, nuts, and seeds and discourage
most or all animal products―are especially potent in pre-
McMacken M & Shah S. Plant-based diets for diabetes prevention and treatment. 343
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venting type 2 diabetes and have been associated with much
lower rates of obesity, hypertension, hyperlipidemia, car-
diovascular mortality, and cancer.[12] We will review the
evidence supporting the use of plant-based diets for the
prevention and treatment of type 2 diabetes and its compli-
cations, and explore mechanisms by which plant-based diets
reduce insulin resistance.
2 Plant-based diets for the prevention of type
2 diabetes
Observational studies strongly support the role of plant-
based diets, and components of plant-based diets, in reduc-
ing the risk of type 2 diabetes.
2.1 Plant-based diets in cohort studies
Large cohort studies demonstrate that the prevalence and
incidence of type 2 diabetes are significantly lower among
those following plant-based eating patterns compared with
omnivores and even semi-vegetarians. Those following plant-
based diets tend to have lower body mass indices,[13] which
protects against type 2 diabetes. Nevertheless, differences in
diabetes risk persist despite adjustments for adiposity.
The Adventist Health Study 2 examined disease preva-
lence by different eating patterns in an overall health-con-
scious cohort. Among nearly 61,000 individuals, the preva-
lence of type 2 diabetes decreased in a stepwise fashion with
each reduction in animal products in the diet: from 7.6% in
non-vegetarians, 6.1% in semi-vegetarians, 4.8% in pe-
sco-vegetarians, 3.2% in lacto-ovo vegetarians, to 2.9% in
vegans.[13] The apparent protection of the vegan dietary pat-
tern remained after adjustment for body mass index and
other variables, with vegans having half the rate of type 2
diabetes compared with non-vegetarians (OR: 0.51; 95% CI:
0.40–0.66). Semi-vegetarians experienced intermediate bene-
fit (OR: 0.76; 95% CI: 0.65–0.90). It is worth noting that the
non-vegans in this cohort ate meat and poultry relatively
infrequently (once a week or more for non-vegetarians; less
than once a week for semi-vegetarians), suggesting that
even small increases in red meat and poultry consumption
disproportionately increase the risk of type 2 diabetes.
Prospective studies of the same Adventist cohort demon-
strate similar findings. Among 41,387 individuals followed
for two years, multiple logistic regression analysis control-
ling for body mass index and other variables demonstrated
that vegans had a dramatically lower risk of developing type
2 diabetes compared with non-vegetarians (OR: 0.381; 95%
CI: 0.236–0.617).[14] In another study of 8401 members of
the Adventist Mortality Study and Adventist Health Study,
long-term (17-year) adherence to a diet that included at least
weekly meat intake was associated with a 74% increase
(OR: 1.74; 95% CI: 1.36–2.22) in odds of developing dia-
betes compared with long-term adherence to a vegetarian
diet (zero meat intake); this association was attenuated but
persisted after statistical adjustment for weight and weight
change (OR: 1.38; 95% CI: 1.06–1.68).[15]
In a cohort of 4384 Taiwanese Buddhists, vegetarian
men had approximately half of the rate of diabetes (OR:
0.49, 95% CI: 0.28–0.89), and vegetarian post-menopausal
women had one-quarter the rate of diabetes (OR: 0.25, 95%
CI: 0.15–0.42), compared with their omnivorous counter-
parts, despite statistical adjustment for body mass index and
other factors. Interestingly, the omnivores in this study con-
sumed a predominantly plant-based diet with little meat or
fish, again implying that small amounts of meat contribute
significantly to the development of insulin resistance.[16]
In the largest prospective study of plant-based eating
patterns to date, Satija, et al.,[17] evaluated dietary choices
and type 2 diabetes incidence in the Nurses’ Health Study,
Nurses’ Health Study 2, and the Health Professionals Fol-
low-up Study. Eating patterns were stratified by an overall
plant-based diet index, in which plant foods received posi-
tive scores while animal foods (including animal fats, dairy,
eggs, fish/seafood, poultry, and red meat) received reverse
scores. In the “healthful” version of this plant-based index,
fruit juices, refined grains, and added sugars also received
reverse scores. Analysis of data from 4.1 million person-
years of follow up revealed that those most adherent to the
healthful plant-based dietary index had a 34% lower risk of
developing diabetes compared with those least adherent.
These associations were independent of body mass index
and other diabetes risk factors.
2.2 Food and nutrient components of plant-based diets
A whole-foods, plant-based eating pattern generally in-
cludes legumes, whole grains, fruits, vegetables, and nuts,
and is high in fiber. All of these elements have been found
to be protective against diabetes. Whole grains, including
whole-grain bread, whole-grain cereals, and brown rice,
have been associated with reduced risk of developing dia-
betes;[18,19] a recent systematic review and meta-analysis of
16 cohort studies found a summary relative risk of 0.68 for
three daily servings of whole grains.[20] Specific fruits and
vegetables, including root vegetables, green leafy vegetables,
blueberries, grapes, and apples, have been linked to lower
diabetes rates.[21,22] Legumes have also been shown to ame-
liorate insulin resistance and protect against metabolic syn-
drome,[23–26] and greater nut consumption has been associ-
ated with lower diabetes risk.[7] Cereal fiber appears to be
especially protective against type 2 diabetes.[27–29]
344 McMacken M & Shah S. Plant-based diets for diabetes prevention and treatment.
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Diets based on whole plant foods not only maximize
protective foods, but they also exclude key animal-based
foods that tend to promote insulin resistance, particularly
processed and unprocessed red meat.[7,3038] Risk estimates
from recent meta-analyses on meat consumption and type 2
diabetes range from 1.13 to 1.19 per 100 g of total red meat
per day and from 1.19 to 1.51 per 50 g of processed meat
per day.[39] Animal protein and animal fats have also been
linked in both metabolic as well as large cohort studies to
worsening insulin resistance and increased incidence of type
2 diabetes.[17,39–48] In the EPIC-interact cohort, for example,
van Nielen et al.,[40] observed a 22% higher type 2 diabetes
incidence over 12 years in the highest versus lowest quintile
of animal protein consumption, as well as a 5% higher inci-
dence per 10 g increment of animal protein intake (multi-
variate-adjusted model, including body mass index).
Similarly, during 4.1 million person-years of follow up of
participants in the Nurses’ Health Study, Nurses’ Health
Study II, and Health Professionals Follow-up Study, Malik
et al.,[47] found that individuals in the highest quintile of
animal protein consumption had a 13% increased risk of
type 2 diabetes (95% CI: 6–21) compared with those in the
lowest quintiles (pooled multivariate model including body
mass index). These authors also found that substituting 5%
of energy intake from animal protein with vegetable protein
was associated with a 23% reduced risk of type 2 diabetes
(95% CI: 16–30). In a geriatric population (ages 65 to 100
years) in Greece, a 5% increase in protein intake from meat
and meat products was associated with a 34% greater like-
lihood of type 2 diabetes even after adjustments for age,
gender, obesity, history of hypertension, hyperlipidemia,
and other dietary habits.[49] In contrast, protein intake from
plant sources offered protection against diabetes.
3 Plant-based diets for the treatment of type 2
diabetes
As far back as the 1950s, studies have been published on
treating hyperglycemia with a high-carbohydrate, low-fat
diet,[50–52] documenting the effectiveness of employing a pre-
dominantly vegetarian diet to treat diabetes. Barnard et al.,[53]
performed the first major randomized clinical trial on diabetic
patients treated purely with a plant-based (vegan) diet, com-
paring it to a conventional diet based on the 2003 American
Diabetes Association (ADA) guidelines. A total of 99 indi-
viduals, ages 27–82 years, were randomized to counseling on
a low-fat vegan diet or the ADA diet and followed for 22
weeks. The recommended vegan diet comprised approxi-
mately 10% of energy from fat, 15% from protein, and 75%
from carbohydrates and consisted of vegetables, fruits, grains,
and legumes. Participants in the vegan group were asked to
avoid animal products and added fats and to favor low-gly-
cemic index foods, such as beans and green vegetables. By the
end of the trial, 43% (21 of 49) of the vegan group and 26%
(13 of 50) of the ADA group participants reduced their diabe-
tes medications. Excluding those who changed medications,
hemoglobin A1c fell 1.23 points in the vegan group compared
with 0.38 points in the ADA group (P = 0.01). Body weight
decreased 6.5 kg in the vegan group and 3.1 kg in the ADA
group (P < 0.001). Among those who did not change lipid-
lowering medications, LDL cholesterol fell 21.2% in the vegan
group and 10.7% in the ADA group (P = 0.02). After adjust-
ment for baseline values, even the reduction in urinary albumin
was significantly greater in the vegan group (15.9 mg/24 h)
than in the ADA group (10.9 mg/24 h).
When these individuals were followed for a total of 74
weeks, a sustained and equivalent weight loss was noted in
both groups, but there was a significant absolute reduction
in hemoglobin A1c of −0.40 points in the vegan group ver-
sus +0.01 in the ADA group (using the last available hemo-
globin A1c value prior to any medication changes).[54] In
addition, there was a significant reduction in total choles-
terol (−20.4 mg/dL vs. −6.8 mg/dL) and LDL cholesterol
(−13.5 mg/dL vs. −3.4 mg/dL) in the vegan versus ADA
diet, respectively. Dietary modification is an integral part of
the lifestyle recommendations for persons with diabetes; it
is worth noting that while the vegan diet required greater
changes in macronutrient intake than the ADA-guided diet,
there was no difference in acceptability or adherence to the
diets,[55] a finding that has also been demonstrated in other
trials.[56,57] While this may be surprising given the potential
degree of change required to adopt a vegan diet, the authors
hypothesized that not limiting portion sizes, not counting
calories or carbohydrates, and experiencing of a variety of
new flavors in the vegan diet likely offset any hardship im-
posed by restricting animal products or added oils.[55]
High-carbohydrate, low-fat, predominantly vegetarian
diets are often associated with weight loss, making it diffi-
cult to ascertain what proportion of the improvement in
glycemic control is due to weight loss versus dietary
changes. To evaluate this question, Anderson et al.,[52] per-
formed a study on a metabolic ward enrolling lean men with
type 2 diabetes who were taking insulin, and placing them
on high-carbohydrate, high-fiber (HCF) diet (< 10% calo-
ries from fat, 70% from carbohydrates, and 65 g of fi-
ber/day). Body weights were kept stable by simply having
participants eat more if they lost weight on the HCF diet.
Half of the participants were able to discontinue insulin, and
the remainder were able to significantly reduce their
McMacken M & Shah S. Plant-based diets for diabetes prevention and treatment. 345
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insulin; overall, the average insulin dose decreased from 26
units on the baseline (control) diet to 11 units on the HCF
diet. Fasting and 3 h postprandial plasma glucose values
were lower in most patients on the HCF diets than on the
control diets despite lower insulin doses. These results argue
for the efficacy of low-fat, plant-based diets (which are
naturally high in carbohydrates and fiber) in reversing the
insulin resistance that is at the root of type 2 diabetes—
though it remains unclear what component of a plant-based
diet is most effective: the high carbohydrate and fiber con-
tent, the low fat and low-animal protein content, or both.
A 2014 review and meta-analysis of controlled clinical
trials of vegetarian diets in the treatment of type 2 diabetes
found a significant reduction in hemoglobin A1c of −0.39
points compared to control diets.[58] This effect is approxi-
mately half of that seen with the addition of the first-line
oral hypoglycemic agent, metformin, which in a recent me-
ta-analysis was reported to reduce hemoglobin A1c by 0.9
points.[59] A more recent randomized controlled trial con-
ducted in Korea compared a brown-rice-based vegan diet
with a conventional diabetic diet in patients ages 30−70
years with type 2 diabetes.[60] Participants assigned to the
vegan diet were asked to eat brown rice, favor low-glycemic
index foods (e.g., legumes, legumes-based foods, green
vegetables, and seaweed), and avoid polished/white rice,
processed food made of rice flour or wheat flour, and all
animal food products. Portions, calories, and frequency of
meals were not restricted. Hemoglobin A1c levels decreased
by 0.5 points in the vegan group compared with 0.2 points
in the conventional group, a significant difference that was
even more pronounced when the analysis was restricted to
participants who were highly adherent to their respective
diets (−0.9 vs. −0.3). The inclusion of individuals older than
age of 60 in this trial, and in the majority of vegetarian trials
mentioned in the meta-analysis above, supports recommend-
ing plant-based diets to all age groups with type 2 diabetes,
including older adults.
4 Reduction of diabetes-related complications
The benefits of tight glycemic control with pharmaco-
therapy have been called into question, based on a lack of
evidence for it preventing major clinical endpoints, includ-
ing all-cause mortality, cardiovascular mortality, dialysis,
renal death, blindness, and neuropathy.[61] In contrast, plant-
based diets have demonstrated improvements in glycemic
control while also reducing macro- and micro-vascular risks
of type 2 diabetes.
4.1 Cardiovascular disease and risk factors
Cardiovascular disease is the major cause of premature
mortality in the diabetic population and many trials have
demonstrated the benefits of plant-based diets in preventing
and treating cardiovascular disease. In large cohort studies,
vegetarian diets have been associated with 24%–32% reduc-
tions in ischemic heart disease incidence and mortality relative
to omnivorous diets.[62–64] Intervention trials of plant-based
diets have also documented angiographic and clinical reversal
of coronary artery disease. Ornish, et al.,[56] randomized in-
dividuals with cardiovascular disease to usual care or life-
style treatment that included a low-fat vegetarian diet in
combination with moderate exercise, stress management,
and smoking cessation. After 5 years, LDL levels in the
lifestyle intervention group decreased 20% from baseline
without lipid-lowering medications—levels similar to that
of the usual care group, 60% of whom were on lipid-lo-
wering medications. In the lifestyle group, the average de-
gree of coronary artery stenosis decreased over five years
with a 7.9% relative improvement by year 5, compared to a
27.7% worsening in the usual care group. There was a 60%
reduction in cardiac events in the lifestyle group compared
with the usual care group. Other studies have demonstrated
the significant cardiovascular benefits of using this plant-
based lifestyle approach,[65] and as a result, in 2010 Medi-
care began to reimburse the Ornish lifestyle intervention as
part of an intensive cardiac rehabilitation program.[66]
Esselstyn, et al.,[67] examined the effects of making die-
tary changes alone, without other lifestyle interventions, on
patients with established cardiovascular disease. The au-
thors reported that in 11 patients with severe coronary artery
disease who were compliant with a low-fat plant-based diet,
8 (73%) had documented regression of coronary artery dis-
ease on repeat angiogram after five years on the diet. In a
subsequent review, outcomes were reported on 198 con-
secutive patients with cardiovascular disease who voluntar-
ily came to the Esselstyn program.[68] A total of 89% were
adherent to the diet, consuming a whole-foods, plant-based
diet without any meat (including poultry and fish), dairy,
eggs, or added oils. The cardiovascular event rate was ex-
traordinarily low: 0.6% among the adherent patients versus
62% among the non-adherent group.
A large body of evidence also supports the use of plant-
based diets for the reduction of cardiovascular risk factors.
It is well known that the prevalence and incidence of hyper-
tension are significantly lower in those following plant-
based diets compared with omnivores.[69–72] In the Adventist
Health Study 2 cohort, vegans had approximately half the
odds of having hypertension as omnivores, even after ad-
justment for body mass index.[69] Animal protein has been
346 McMacken M & Shah S. Plant-based diets for diabetes prevention and treatment.
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shown in several prospective studies to increase the risk of
hypertension,[73–75] while plant protein tends to lower blood
pressure, even in elderly patients.[76,77] Interventional trials
of vegetarian diets have been shown to lower blood pressure
when compared to omnivorous control diets.[78]
A literature review of plasma lipids and plant-based diets
found that among different plant-based diets (i.e., lacto-ovo
vegetarian, lactovegetarian, and vegan), populations follow-
ing vegan diets had the lowest cholesterol concentrations.[79]
This review also found that plant-based diets are associated
with up to a 35% reduction in serum LDL cholesterol, whe-
reas interventions allowing small amounts of lean meat
demonstrated less dramatic reductions in total cholesterol
and LDL levels. In the EPIC-Oxford cohort, those following
vegan diets had lower levels of apolipoprotein B, reflecting
lower levels of circulating atherogenic particles.[80]
Chronic inflammation, as measured by serum biomarkers
such as C-reactive protein, has been linked to risk of car-
diovascular events,[81] and is closely tied to dietary choices;
those following Western, or ‘meat-based’ diets, tend to have
higher levels of biomarkers of inflammation, whereas those
following ‘vegetable-and-fruit’ based patterns tend to have
lower levels of these biomarkers.[82] Among intervention
trials of plant-based diets, a recent systematic review and
meta-analysis found that those adopting a fully or mostly
plant-based diet had significant reductions in C-reactive pro-
tein and other obesity-related inflammatory biomarkers com-
pared to those following control, non-plant-based diets.[83]
4.2 Renal disease
Chronic kidney disease rates increase with age, and
among those older than 60 years, renal impairment is more
common in diabetic versus nondiabetic patients (60% vs.
41%).[3] Using NHANES 3 data, Chen, et al.,[84] found that
in individuals with chronic kidney disease, defined as a
glomerular filtration rate < 60 mL/min, every 33% increase
in plant to total protein consumption was associated with a
significant 23% lower mortality risk. To evaluate which
foods may be associated with worsening renal disease in
diabetic patients, Almeida, et al.,[85] obtained a detailed diet
history in diabetic patients with and without micro-albu-
minuria. High intake of protein from animal sources and
low intake of polyunsaturated fatty acids, particularly from
plant oils, was associated with the presence of micro-albu-
minuria.
In a crossover trial testing whether albuminuria can be
improved in diabetic patients with advanced kidney disease
simply by replacing the source of protein, red meat in the
usual diet was replaced by either chicken as the major
source of protein or a low-protein lacto-ovo vegetarian diet.
At the end of four weeks, albuminuria on the vegetarian and
chicken diets (330 mg/day and 387 mg/day, respectively)
was significantly less than after four weeks on the red meat
diet (449 mg/day), strongly suggesting that the protein
source impacts the degree of albuminuria.[86] Similarly,
Azadbakht, et al.,[87] performed a randomized controlled
trial in diabetic adults with macro-albuminuria (300−1000
mg total protein excretion/day), substituting half of the ani-
mal protein for soy protein in the intervention group and
following them for four years. They found that the soy pro-
tein intervention group had a significant improvement in
proteinuria (−150 mg/day vs. +502 mg/day), along with
significant decreases in total cholesterol (−23 mg/dL vs. +10
mg/dL, P = 0.01), LDL cholesterol (−20 mg/dL vs. +6
mg/dL, P = 0.01) and fasting glucose (−18 mg/dL vs. +11
mg/dL, P = 0.03).
A recent review outlined how a Western-style diet, char-
acterized by high intake of red meat, animal fat, highly
processed food and low intake of fruits and vegetables, is
associated with kidney disease.[88] A variety of mechanisms
were proposed for this association, including increased ani-
mal protein leading to decreased renal blood flow and
glomerular filtration rate, an increased acid load from ani-
mal protein that must be excreted by the kidneys, and lower
fruit and vegetable ingestion leading to lower alkali levels
and a net high endogenous acid load, which increases
nephron workload. Taken together, these observational and
interventional studies support the use of a plant-based diet in
treating diabetic nephropathy by both reducing ani-
mal-based foods and increasing plant foods.
4.3 Diabetic neuropathy
Diabetic neuropathy is a microvascular complication of
diabetes that can be debilitating. At least two small studies
have shown that a plant-based diet can ameliorate diabetic
neuropathic pain. One study demonstrated a remarkable
resolution of burning neuropathy in 81% of participants
during a 25-day residential lifestyle program in which plant-
based meals were provided, including a sustained response
in the participants who adhered to the diet after returning
home.[89] A recent randomized controlled pilot study also
demonstrated how a plant-based diet can effectively treat
diabetic neuropathy: among community-dwelling patients
with painful diabetic neuropathy, pain scores were signifi-
cantly improved at 20 weeks on a plant-based diet compared
with a control diet.[90]
5 Current guidelines and macronutrients
In their 2017 “Standards of Medical Care in Diabetes,” the
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ADA states that a variety of eating patterns are acceptable for
the management of type 2 diabetes and pre-diabetes, including
Mediterranean, DASH, and plant-based diets.[91] These guide-
lines recommend carbohydrate intake from legumes, whole
grains, fruits, vegetables, and dairy products, with an empha-
sis on nutrient-dense, high-fiber, low-glycemic load foods.
They also include a recommendation that people with diabetes
follow the guidelines for the general population for intakes of
saturated fat, dietary cholesterol, and trans fat. Plant-based
diets are consistent with these guidelines. The Academy of
Nutrition and Dietetics states that vegetarian and vegan diets
are appropriate for all stages of life, from infancy to adulthood,
and may provide benefits for the prevention and treatment of
diabetes, obesity and ischemic heart disease.[92]
There has been a wealth of research on macronutrient ra-
tios and subtypes in relation to insulin resistance. Current
ADA guidelines state that the optimal mix of macronutrients
in type 2 diabetes has not been established.[91] In general,
sources of foods (e.g., animal vs. plant, refined versus unre-
fined) are equally important as, if not more important than,
specific ratios of carbohydrate, protein, and fats when it
comes to glycemic control and the prevention of type 2 dia-
betes. Moreover, in the most practical terms, people eat foods
and combinations of foods, not individual macronutrients or
macronutrient ratios. However, it is worth highlighting re-
search on macronutrients and food sources that supports the
use of plant-based foods in treating insulin resistance, im-
proving overall health, and reducing mortality.
5.1 Protein
While the 2015 United States Dietary Guidelines empha-
size “lean” sources of protein,[93] the evidence does not sup-
port turning to animal sources for protein, particularly for
individuals with diabetes. Plant sources of protein have the
benefit of being truly low fat in many cases (e.g., most leg-
umes). In addition, they supply fiber and many beneficial
phytonutrients, all of which are lacking in animal foods and
are deficient in the average American diet.[94] In terms of
treating type 2 diabetes, a recent systematic review and
meta-analysis of 13 randomized controlled trials evaluated the
effect of replacing animal protein with plant protein on gly-
cemic control.[45] Among participants, whose average age was
62 years, there was a significant decrease in hemoglobin A1c
(−0.15%), fasting glucose (−0.53 mmol/L) and fasting insulin
(−10 pmol/L) in diets that replaced animal protein with plant
sources of protein at a median level of about 35% of total
protein/day, compared with control diets. Another study car-
ried out among 6107 diabetes patients from 15 European co-
horts demonstrated that replacing 10 g of dietary carbohydrate
with total and animal protein was associated with a mean
5-year weight gain, whereas replacement with plant protein
was not significantly associated with weight change.[95]
Moreover, substitution with plant protein conferred a signifi-
cant 21% decrease in all-cause mortality risk. Similarly, a
recent large cohort study of 131,342 adults found that in par-
ticipants with at least one unhealthy lifestyle factor, substitu-
tion of 3% of energy from plant protein in lieu of animal pro-
tein was associated with a 10% decrease in all-cause mortality
and a 12% decrease in cardiovascular mortality.[96] The mor-
tality benefit of plant protein over animal protein was evident
across the board, for all major types of animal protein sources
(processed meat, red meat, eggs, dairy, poultry, and fish).
These studies point to the importance of specifying the type of
protein recommended for the management of diabetes and for
overall mortality reduction.
5.2 Fats
In relation to insulin resistance, the weight of metabolic
studies and epidemiologic evidence suggests that the type of
fat in the diet (e.g., saturated, polyunsaturated, or monoun-
saturated) is highly relevant. Saturated and trans fats increase
the risk of developing diabetes;[43] moreover, in diabetic pa-
tients, saturated fats are actually associated with increased
mortality when they replace carbohydrates in the diet.[97] A
recent systematic review of randomized controlled feeding
trials evaluated the effects of saturated, monounsaturated, and
polyunsaturated fats, as well as carbohydrates on metrics of
glucose insulin homeostasis.[98] Replacing carbohydrates
(mainly refined starches and simple sugars) and saturated fats
with monounsaturated and polyunsaturated fats lowered he-
moglobin A1c and improved insulin resistance; polyunsatu-
rated fats were also noted to improve insulin secretion. The
authors concluded that in comparison to carbohydrates and
saturated fats, monounsaturated and polyunsaturated fats had
the most favorable effect on glycemia, insulin resistance, and
secretion. In terms of foods, these findings support consump-
tion of vegetable fats (e.g., nuts, avocados, olives) in place of
animal fats and refined grains.
Furthermore, there may be a threshold beyond which total
fat also affects insulin resistance. In an observational study of
1785 European adults aged 50−75 years with type 2 diabetes,
increasing total fat intake from < 25% to ≥ 35% was associ-
ated with a significant increase in LDL cholesterol, triglyc-
erides, hemoglobin A1c, and C-reactive protein (P < 0.05),
whereas increasing carbohydrate intake from < 45 to ≥ 60%
was associated with significantly lower triglycerides, hemo-
globin A1c, and C-reactive protein (P < 0.05).[99] Similarly,
Vessby, et al.,[100] found that the beneficial impact of mono-
unsaturated fats over saturated fats on insulin sensitivity was
absent in individuals with a high total fat intake (> 37% of
348 McMacken M & Shah S. Plant-based diets for diabetes prevention and treatment.
Journal of Geriatric Cardiology | jgc@jgc301.com; http://www.jgc301.com
energy). It is important to note that in key randomized trials of
plant-based diets for type 2 diabetes, recommended total fat
intake has been low (approximately 10% of energy) for inter-
vention groups.[53,55]
5.3 Carbohydrates
It is a common perception that carbohydrate-rich foods
should be avoided in people who have, or are at risk for, type
2 diabetes. As with protein and fat, it is essential to distinguish
between the types and sources of carbohydrates. Meta-analy-
ses of cohort studies demonstrated that carbohydrates from
whole grains and cereal fibers reduce the risk of developing
diabetes while refined,[20,101] low-fiber carbohydrates can in-
crease the risk of diabetes.[29] Metabolic studies also confirm
benefits of carbohydrates in comparison to animal protein.
Sargrad, et al.,[102] compared high-protein versus high-carbo-
hydrate diets, while keeping fat intake constant at 30%, for a
period of eight weeks in patients with type 2 diabetes. The
high-carbohydrate group was instructed to eat more bread,
cereal, pasta, and starchy vegetables while the high-protein
group was instructed to have more fish, chicken, eggs, low fat
milk, cheese, and nuts. Although weight loss was equivalent
in both groups, the high-carbohydrate group had a decrease in
hemoglobin A1c (from 8.2% to 6.9%, P < 0.03) and fasting
plasma glucose (from 8.8 to 7.2 mmol/L, P < 0.02), and an
increase in insulin sensitivity (from 12.8 to 17.2 mmol/kg per
minute, P < 0.03). No significant changes in these parameters
occurred in the high-protein group.
Moreover, low-carbohydrate diets have been found in sev-
eral studies to actually increase the risk of type 2 diabetes.
Among more than 40,000 men in the Health Professionals
Follow-Up Study, the highest quintile of a low-carbohydrate
eating pattern, when based on animal sources, conferred a
37% increased risk of diabetes; interestingly, when the low-
carbohydrate diet was based on vegetable sources, it was
protective, decreasing risk by 22%.[103] Halton, et al.,[104]
found a similar protective effect of plant-based low-carbohy-
drate diets among women in the Nurses’ Health Study, al-
though, in this population, the overall low-carbohydrate score
did not increase risk. In the Nurses’ Health Study II cohort,
among 4502 women with a history of gestational diabetes,
there was a 36% increased risk of diabetes among women
with the highest overall low-carbohydrate diet score, and a
40% increased risk when the low-carbohydrate diet favored
animal products.[105] In the EPIC-Potsdam cohort, Schulze et
al.,[106] noted that a higher carbohydrate intake at the expense
of protein might decrease diabetes risk. In the general and
geriatric populations, low-carbohydrate diets have been asso-
ciated with increased all-cause, cardiovascular, and cancer
mortality.[107–110]
6 Mechanisms of plant-based diets in treating
insulin resistance
Diets based in whole and minimally processed plant foods
reduce insulin resistance and improve glycemic control by a
variety of proposed mechanisms. Plant-based diets are high in
fiber, antioxidants, and magnesium, all of which have been
shown to promote insulin sensitivity.[7,17] Antioxidants such as
polyphenols may inhibit glucose absorption, stimulate insulin
secretion, reduce hepatic glucose output, and enhance glucose
uptake.[111] Fiber, which is found only in plant foods, modu-
lates postprandial glucose response, and is fermented by intes-
tinal bacteria to produce short-chain fatty acids, which also
improve the glucose response, insulin signaling, and insulin
sensitivity.[112–115] Furthermore, fiber reduces the energy den-
sity of foods, promotes satiety, and has been associated with
weight loss, which in turn reduces insulin resistance.[113] Die-
tary fiber has been linked to decreased markers of inflamma-
tion, which may also ameliorate insulin resistance.[17] Finally,
a diet high in plant-based foods and low in meat is likely to
exert beneficial metabolic effects by promoting shifts in the
gut microbial profile, decreasing the production of trime-
thylamine N-oxide, a compound that has been tied to insulin
resistance.[17,39,115]
Plant-based diets also tend to be low in saturated fat, ad-
vanced glycation endproducts, nitrosamines, and heme iron
dietary elements that have been associated with insulin resis-
tance in epidemiologic and metabolic studies. Saturated fat,
which is found primarily in animal-based foods, contributes to
lipotoxicity, a phenomenon in which toxic fat metabolites
(e.g., species of diacylglycerol and ceramide) accumulate in
hepatic and skeletal muscle cells, impairing insulin signaling
and thus decreasing glucose uptake.[116–119] Saturated fat has
been associated with oxidative stress, mitochondrial dysfunc-
tion, and insulin resistance in numerous metabolic and epide-
miologic studies as well.[42–44,98,100,120] In addition, diets high in
saturated fat are associated with a predominantly gram-nega-
tive, lipopolysaccharide-rich gut microbial pattern, which also
leads to insulin resistance and inflammation.[118] A plant-based
diet has been shown to reduce visceral fat and improve mark-
ers of oxidative stress more than a conventional diet in indi-
viduals with type 2 diabetes.[121]
Advanced glycation endproducts are oxidant compounds
that are high in meat (especially when grilled, broiled, roasted,
seared, or fried), and low in plant-based foods such as fruits,
vegetables, legumes, and whole grains.[122] Advanced glyca-
tion endproducts have been implicated in the pathogenesis of
type 2 diabetes,[39] and a diet low in these compounds has
been shown to improve insulin resistance in people with type 2
diabetes.[123] Nitrosamines, which are created when nitrite and
McMacken M & Shah S. Plant-based diets for diabetes prevention and treatment. 349
http://www.jgc301.com; jgc@mail.sciencep.com | Journal of Geriatric Cardiology
nitrate preservatives in processed meat bind to amino com-
pounds in those foods, have been shown to accelerate DNA
damage and generation of reactive oxygen species and pro-
inflammatory cytokines, leading to oxidative stress and insu-
lin resistance.[39] Iron from heme (animal) sources is a pro-oxi-
dant molecule that promotes insulin resistance through vari-
ous likely mechanisms: increased oxidative stress leading to
impaired insulin signaling, direct pancreatic beta cell toxicity,
decreased translocation of glucose transporter type 4 channels
to the cell membrane, and increased hepatic glucose output.[39]
Several meta-analyses have demonstrated a strong link be-
tween serum ferritin or dietary heme iron and the risk of type 2
diabetes.[124–127]
Finally, plant-based diets tend to promote weight loss and
lower adiposity,[13,128–131] factors that are highly protective
against insulin resistance. In contrast, meat consumption (in-
cluding poultry) is highly predictive of obesity and weight
gain over time.[15,132–137] Thus, meat increases type 2 diabetes
risk not only by promoting weight gain, but also by mecha-
nisms independent of body mass index, as aforementioned.
Furthermore, when a hypocaloric high-protein diet is used for
weight loss, the high protein content itself may negate key
metabolic benefits of weight loss. Smith et al.,[138] found that
in obese postmenopausal women, a low-calorie, high-pro-
tein diet prevented the therapeutic effect of weight loss on
skeletal muscle insulin sensitivity—likely due to worsening
oxidative stress, as well as alterations in muscle cell struc-
ture and organization, induced by the high-protein diet.
Refined grains and added sugars have also been implicated
in weight gain and insulin resistance.[29,139,140] A whole-foods,
plant-based dietary approach excludes animal products, re-
fined grains, and added sugars, thus encouraging insulin sen-
sitivity through loss of excess weight and maintenance of a
healthier body weight. However, as noted previously, meta-
bolic and epidemiologic studies confirm that plant-based diets
improve insulin resistance even when there is no weight loss,
and/or with statistical adjustment for body weight.
7 Implementation in clinical practice
Several reviews have presented practical strategies for us-
ing plant-based diets in clinical scenarios, including type 2
diabetes management.[141–143] The key elements of the eating
pattern include avoidance of animal products, highly refined
grains, added sugars, and oils, and consumption of an abun-
dance of legumes, leafy greens, cruciferous vegetables, starchy
vegetables, whole grains, and fruits. In key randomized clini-
cal trials of plant-based diets, low-glycemic index foods have
been encouraged.[53,54]
Some clinicians may assume that their patients will not be
open to adopting a plant-based diet. However, a plant-based
diet has been shown to be similarly acceptable to an ADA diet
among people with diabetes;[55] plant-based diets have also
been found to be highly acceptable in other medical
contexts.[144–146] Common questions about specific macro- and
micronutrients in plant-based diets have been addressed else-
where.[141,143,147,148] Patients who adopt a plant-based diet can
experience decreases in blood sugar and blood pressure rela-
tively quickly after changing their diet, especially if they are
taking medications for these conditions. Close monitoring and
anticipation of hypoglycemia is critical; medications may
require adjustment.[141] Ongoing support, education, and fol-
low-up can help patients achieve and maintain dietary
changes.
8 Conclusions
There is a general consensus that the elements of a
whole-foods plant-based diet—legumes, whole grains, fruits,
vegetables, and nuts, with limited or no intake of refined foods
and animal products—are highly beneficial for preventing and
treating type 2 diabetes. Equally important, plant-based diets
address the bigger picture for patients with diabetes by simul-
taneously treating cardiovascular disease, the leading cause of
death in the United States, and its risk factors such as obesity,
hypertension, hyper-lipidemia, and inflammation. The advan-
tages of a plant-based diet also extend to reduction in risk of
cancer, the second leading cause of death in the United States;
the World Cancer Research Fund and the American Institute
for Cancer Research recommend eating mostly foods of plant
origin, avoiding all processed meats and sugary drinks, and
limiting intake of red meats, energy dense foods, salt, and
alcohol for cancer prevention.[149] Large healthcare organiza-
tions such as Kaiser Permanente are promoting plant-based
diets for all of their patients because it is a cost effective,
low-risk intervention that treats numerous chronic illnesses
simultaneously and is seen as an important tool to address the
rising cost of health care.[147] Plant-based eating patterns also
carry significant environmental benefits. The World Health
Organization and the United Nations have promoted diets
higher in plant foods as not only effective for preventing
chronic diseases and obesity, but also more environmentally
sustainable than diets rich in animal products,[150] a position
also supported in the scientific report of the 2015 United
States Dietary Guidelines Advisory Committee.[151] While
larger interventional studies on plant-based diets carried out
for longer periods of time would add even more weight to the
already mounting evidence, the case for using a plant-based
diet to reduce the burden of diabetes and improve overall
health has never been stronger.
350 McMacken M & Shah S. Plant-based diets for diabetes prevention and treatment.
Journal of Geriatric Cardiology | jgc@jgc301.com; http://www.jgc301.com
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This article is part of a Special Issue “A plant-based diet and cardiovascular disease”.
Guest Editors: Robert J Ostfeld & Kathleen E Allen
