Perspective: Plant-Based Eating Pattern for Type 2 Diabetes Prevention and Treatment: Efficacy, Mechanisms, and Practical Considerations

Abstract

A plant-based eating pattern is associated with a reduced risk of developing type 2 diabetes and is highly effective in its treatment. Diets that emphasize whole grains, vegetables, fruits, and legumes and exclude animal products improve blood glucose concentrations, body weight, plasma lipid concentrations, and blood pressure and play an important role in reducing the risk of cardiovascular and microvascular complications. This article reviews scientific evidence on the effects of plant-based diets for the prevention and treatment of type 2 diabetes. The mechanisms by which plant-based diets improve body weight, insulin sensitivity, and β-cell function are described. Practical considerations including education, nutrition adequacy, and adjusting medications will enhance the success of patients who have diabetes.

Full text

PERSPECTIVE
Perspective: Plant-Based Eating Pattern for Type 2
Diabetes Prevention and Treatment: Ecacy,
Mechanisms, and Practical Considerations
Meghan A Jardine,1Hana Kahleova,2Susan M Levin,1Zeeshan Ali,1Caroline B Trapp,1and Neal D Barnard1
1Department of Nutrition, Physicians Committee for Responsible Medicine, Washington, DC, USA; and 2Department of Clinical Research, Physicians
Committee for Responsible Medicine, Washington, DC, USA
ABSTRACT
A plant-based eating pattern is associated with a reduced risk of developing type 2 diabetes and is highly effective in its treatment. Diets that
emphasize whole grains, vegetables, fruits, and legumes and exclude animal products improve blood glucose concentrations, body weight, plasma
lipid concentrations, and blood pressure and play an important role in reducing the risk of cardiovascular and microvascular complications. This
article reviews scientific evidence on the effects of plant-based diets for the prevention and treatment of type 2 diabetes. The mechanisms by which
plant-based diets improve body weight, insulin sensitivity, and β-cell function are described. Practical considerations including education, nutrition
adequacy, and adjusting medications will enhance the success of patients who have diabetes. Adv Nutr 2021;00:1–11.
Keywords: type 2 diabetes, plant-based nutrition, vegan diet, vegetarian diet, insulin resistance, diabetes, diet quality
Introduction
Diabetes is a major worldwide health challenge aecting
individuals, families, communities, and governments. The
International Diabetes Federation estimated that 463 million
people (9.3% of the worldwide population) had diabetes
in 2019. Prevalence is expected to increase to 578 million
(10.4%) by 2030 (1).Globally,diabetescaused15million
deaths and contributed to 12% of health care expenditures
This article was funded by the Physicians Committee for Responsible Medicine, Washington
DC, USA..
Author disclosures: MJ, HK, SL, ZA, and CT are employees of the Physicians Committee for
Responsible Medicine in Washington, DC, a nonprot organization providing education,
research, and medical services related to nutrition. NDB is an Adjunct Professor of Medicine at
the George Washington University School of Medicine. He serves without compensation as the
President of the Physicians Committee for Responsible Medicine and the Barnard Medical
Center in Washington, DC, nonprot organizations providingeducational, research, and
medical services related to nutrition. He writes books and articles and gives lectures related to
nutrition and health and has received royalties and honoraria from these sources.
Perspective articles allow authors to take a position on a topic of current major importance or
controversy in the eld of nutrition. As such, these articles could include statements based on
author opinions or point of view. Opinions expressed in Perspective articles are those of the
author and are not attributable to the funder(s) or the sponsor(s) or the publisher, Editor, or
Editorial Board of Advances in Nutrition. Individuals with dierent positions on the topic of a
Perspective are invited to submit their comments in the form of a Perspectives article or in a
Letter to the Editor.
Address correspondence to MAJ (e-mail: meghan.jardine@sbcglobal.net).
Abbreviations used: AND, Academy of Nutrition and Dietetics; AHS-2, Adventist Health Study-2;
CVD, cardiovascular disease; DASH, Dietary Approaches for Stopping Hypertension; HbA1c,
glycated hemoglobin.
in 2015 (2). In addition to contributing to mortality,
macrovascular and microvascular complications of diabetes
greatly reduce quality of life.
Diabetes prevalence has increased in recent decades in
the context of signicant diet changes, including reduced
consumption of vegetables, fruits, and legumes, coupled with
increased consumption of animal-derived and processed
food products (3). A plant-based eating pattern is associated
with a signicantly lower prevalence of type 2 diabetes,
compared with nonvegetarian diets (4), and there is strong
evidence supporting the use of a plant-based eating pattern
in clinical practice for individuals with type 2 diabetes. The
American Association of Clinical Endocrinologists and the
American College of Endocrinology, as well as the American
College of Lifestyle Medicine, recommend a plant-based
eating pattern as a key component of lifestyle therapy for
patients with type 2 diabetes (5,6). Both the American
and Canadian Diabetes Associations include vegetarian
and vegan eating patterns among those shown to improve
glycemic control, body weight, and cardiovascular risk
factors (6,7). In addition to these organizations that support
a plant-based diet for diabetes, the USDA lists a Healthy
Vegetarian Dietary Pattern as an example of a healthy meal
plan in the 2020–2025 Dietary Guidelines for Americans
(8).
C
The Author(s) 2021. Published by Oxford University Press on behalf of the American Society for Nutrition. This is an Open Access article distributed under the terms of the Creative Commons
Attribution-NonCommercial License (http://creativecommons.org/licenses/by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the
original work is properly cited. For commercial re-use, please contact journals.permissions@oup.com Adv Nutr 2021;00:1–11; doi: https://doi.org/10.1093/advances/nmab063. 1
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The aim of this article is to provide an overview of the
evidence on the prevention and treatment of type 2 diabetes
with a plant-based eating pattern, the mechanistic actions
by which a plant-based eating pattern improves insulin
sensitivity and weight management, and considerations in
recommending a plant-based eating pattern. This article
includes earlier evidence that provides a foundation for
more current research. It also includes recent studies on
the mechanistic actions that demonstrate a plant-based diet
improves clinical outcomes for diabetes.
“Plant-based”isagenerictermthatmayrefertodiets
consisting mainly of grains, vegetables, legumes, fruits, nuts,
seeds,andproductsmadefromthem.Vegetariandiets
exclude meat. Subsets of vegetarian diets are lacto-ovo
vegetarian diets, which include dairy products and eggs,
and vegan diets, which exclude all animal products (9).
Hereafter in this article, the term “plant-based” will refer to
vegetarian (including lacto-ovo vegetarian and vegan) diets,
unless otherwise indicated.
A Plant-Based Eating Pattern Is Associated with
Reduced Risk of Type 2 Diabetes
Observational studies in widely diverse locales have iden-
tied large reductions in diabetes risk among populations
consuming vegan and vegetarian eating patterns, compared
with other dietary patterns.
Many Seventh-day Adventists limit or avoid meat and
other animal products, whereas others do not, providing
a unique opportunity to study the eects of dierent diet
patterns (10). In 1985, Snowdon and Phillips rst reported
a strongly positive association between meat consumption
and diabetes prevalence in 25,698 men and women from
California who were followed for 21 y in the Adventist
Mortality Study (11). Fifty per cent of this cohort reported
following a vegetarian diet. Age-adjusted diabetes prevalence
ratios in participants who consumed meat 6 or more times
per week were 1.9 for men and 1.6 for women, compared
with vegetarians (11). Fraser reported similar ndings from
the Adventist Health Study, in which men and women
meat consumers reported a 97% (OR: 1.97; 95% CI: 1.56,
2.46, P=0.0001) and 93% (OR: 1.93; 95% CI: 1.65, 2.25,
P=0.0001) greater diabetes risk, respectively, compared with
vegetarian participants (10). Vang et al. (12) followed 8401
Adventists, all of whom were free of diabetes at study onset,
for 17 y. After controlling for dierences in body weight,
those who consumed any type of meat (including poultry)
atleastonceaweekhada38%increasedriskofdeveloping
diabetes during the follow-up period, compared with those
who consumed no meat (12).
The Adventist Health Study-2 (AHS-2), which started
in 2002, included 22,434 men and 38,469 women living
throughout the USA and Canada; 65.5% were non-Hispanic
white and 26.9% were black (13). Compared with nonveg-
etarians, the OR for diabetes prevalence was 49% (0.51;
95% CI: 0.40, 0.66) less among vegans and 46% (0.54;
95% CI: 0.49, 0.60) less among lacto-ovo vegetarians, after
adjustments for BMI and other lifestyle variables (13).
Diabetes prevalence among those limiting meat consumption
to sh was 30% (0.70; 95% CI: 0.61, 0.80) less and those
eating meat less than once per week was 24% (0.76; 95% CI:
0.65, 0.90) less compared with the nonvegetarians. The vegan
participants consumed 33% more fruits and vegetables than
the nonvegetarians and avoided animal products that are
high in saturated fat and are associated with insulin resistance
(13).
In a prospective analysis of this same cohort (AHS-2) of
15,200 men and 26,187 women (17% black) who did not
have diabetes at baseline, vegan and lacto-ovo vegetarians
had a 77% and 54% reduction in risk of developing diabetes,
respectively (4). After controlling for BMI and other lifestyle
factors, odds were 62% less for vegans and 38% less for the
lacto-ovo vegetarians. The reduced risk was particularly pro-
nounced among black vegans who, in the adjusted analysis,
hada70%reducedrisk,andblacklacto-ovovegetarians
(52% reduced risk), compared with nonvegetarians (4). The
Adventist studies suggest a strong reduction in diabetes risk
as a result of avoiding animal-derived products that is, in part,
independent of the diet’s benecial eects on body weight.
Othercohortstudieshavereportedsimilarndings.A
Harvard study that included 26,357 men from the Health
Professionals Follow-Up Study (1986–2006), 48,709 women
from the Nurses’ Health Study (1986–2006), and 74,077
women from the Nurses’ Health Study II (1991–2007)
foundthatincreasingmeatbyhalfaservingperdaywas
associated with a 48% (1.48; 95% CI: 1.37, 1.59) increase
in diabetes risk over a 4-y period (14). Decreasing meat
portions by half a serving a day was associated with a
reported 14% (0.86; 95% CI: 0.80, 0.93) reduction in diabetes
risk. In another report that included over 200,000 men and
womenhealthprofessionalsfromthesameHarvardcohorts,
16,162 participants developed diabetes during 4,102,369
person-years of follow-up (15). It was reported that when
participants followed a healthy plant-based diet that focused
on whole grains, fruits, and vegetables, and was low in rened
grains, sugar-sweetened beverages, and red and processed
meats, there was an associated 34% reduction in diabetes risk
(15).
Similarly, the European Prospective Investigation into
Cancer and Nutrition (EPIC) study’s InterAct Project
followed 340,234 adults from 8 European countries for
11.7 y and reported signicant associations between meat
consumption and type 2 diabetes risk (16). For men,
consumption of red and processed meat increased diabetes
risk, whereas for women there was a positive association
between total meat and poultry consumption (16).
In the Rotterdam study, a high intake of plant-derived
products and a low intake of animal products was associated
with lower insulin resistance, prediabetes, and type 2 diabetes
(17). These outcomes remained signicant after adjustment
for body weight (17). The authors proposed that dietary
guidelines should recommend a plant-based diet to reduce
the burden of type 2 diabetes.
In Taiwan, the Tzu Chi Health Study found signicant
reductions in diabetes risk among vegetarian Buddhists.
2 Jardine et al.
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Compared with the omnivore group (N =2900), the
vegetarian group (N =1484) had a 51% lower risk in
men (OR: 0.49; 95% CI: 0.28, 0.89) and a 75% lower risk
in postmenopausal women (OR: 0.25; 95% CI: 0.15, 0.42)
for type 2 diabetes after controlling for BMI and other
lifestyle factors (18). It should be noted that “omnivores”
in this population consume relatively little meat or sh by
Western standards. The vegetarian group consumed more
soy products, total and green leafy vegetables, nuts, and
whole grains, less tea, and a similar amount of dairy products
and fruits, compared with the omnivores (18). Within the
vegetarian group were a small number of vegans (N =69)
among whom no cases of diabetes were found.
A Plant-Based Eating Pattern Is Eective for
Treating Type 2 Diabetes
Plant-based diets, particularly vegan diets, improve glycemic
control, body weight, and cardiovascular risk factors in
individuals with type 2 diabetes. Each of these is central
to diabetes management and is described below. A meta-
analysis of 6 randomized controlled trials (N =255)
demonstrated that vegetarian diets were associated with a
0.4% greater reduction in glycated hemoglobin (HbA1c)
when compared with other prescribed eating patterns for
diabetes (19).
Low-fat, plant-based diets improve glycemic control.
Various formulations have been tested for many years.
In 1979, a 16-d, mainly plant-based, dietary intervention
designed to maintain body weight was tested in a closed
setting.Nineoutof20menwithtype2diabeteswereableto
eliminate insulin, and the other 11 were able to reduce it by
60% after following a high-ber, high-carbohydrate diet (65 g
of ber, 70% calories from carbohydrate, 21% from protein,
9% from fat) (20).
A 22-wk randomized controlled trial compared a low-fat,
vegan diet (N =49) to a conventional portion-controlled diet
(N =50). The vegan diet (∼10% of energy from fat, 15%
protein, and 75% carbohydrate) excluded animal products
and favored low-fat, low-glycemic-index foods. The portion-
controlled diet (15–20% protein, <7% saturated fat, 60–70%
carbohydrate and monounsaturated fats) was individualized,
basedonbodyweightandplasmalipidconcentrations,
following 2003 American Diabetes Association guidelines
(21). Those with a BMI >25 kg/m2were prescribed energy
intake decits of 500–1000 kcal/d. Among participants
who made no medication changes, the vegan group had a
signicantly greater reduction in HbA1c (1.23% compared
with 0.38%, [P=0.01]) (22). The Pearson’s correlation of
weight change with HbA1c change was r=0.51, P<0.0001
within the vegan group, suggesting that factors other than
weight changes inuence glycemic control. The authors
proposed that high-fat diets increase lipid accumulation in
the skeletal muscle, which contributes to insulin resistance
by reducing mitochondrial activity.
Vegan diets have been shown to improve glycemic control
in Asian populations that are already consuming diets that
are generally rich in plant-derived foods. In a Korean
study, 93 volunteers with type 2 diabetes were randomly
assigned to either a vegan diet (N =46) or a conventional
diet recommended by the Korean Diabetes Association
(KDA) 2011 (N =47) for 12 wk (23). The vegan diet
consisted of whole grains, vegetables, fruit, and legumes. The
mean HbA1c concentrations fell in both groups, however,
the reductions were greater for the vegan group (–0.5%
compared with –0.2%; P-interaction =0.17). These results
were greater in the participants who closely followed the
prescribed eating patterns (–0.9% compared with –0.3%)
(23).
Potential Mechanisms by Which Plant-Based
Eating Patterns Aect Insulin Resistance and
Weight Management
Insulin resistance
Insulin resistance and subsequent impairment in β-cell
function are the hallmarks of type 2 diabetes pathophysiology
(24). Plant-based eating patterns are benecial for patients
with diabetes by improving insulin sensitivity and improving
body weight. Insulin resistance is caused by lipid accumu-
lation within muscle and liver cells that typically begins
many years before the diagnosis of type 2 diabetes. This
lipid accumulation is highly responsive to diet changes. High-
fat diets downregulate the genes required for mitochondrial
oxidative phosphorylation in skeletal muscle (25). High-fat
diets also appear to disrupt the normal intestinal barrier
to bacterial endotoxins that, entering the bloodstream, may
disrupt glucose oxidation processes (26). The eects of
changes in fat intake on glycemic control can be observed,
not only after long-term interventions, but after single meals;
high-fat meals can cause postprandial elevations in plasma
glucose that can remain high for a long period of time
(27).
In a case-control study, Go et al. (28)compared24
healthy vegans to 25 healthy omnivores matched for sex, age,
BMI, per cent body fat, energy intake, and physical activity
levels. Individuals who followed a vegan diet had signi-
cantly lower intramyocellular lipid concentration, which was
associated with 32% greater homeostatic model assessment
of β-cell function (28). In a randomized trial in overweight
nondiabetic individuals without limitations on energy or
carbohydrate intake, a low-fat vegan diet reduced hepatocel-
lular lipid concentrations by 34.4% and intramyocellular lipid
concentrations by 10.4%. These changes in hepatocellular
and intramyocellular lipid concentrations correlated with
changes in insulin resistance (both r=0.51; P=0.01) (29).
These ndings suggest that low-fat, plant-based (especially
vegan) diets improve glycemic control because of their ability
to reduce lipid accumulation in muscle and liver, in addition
to their eects on body weight.
Plant-based diets may also improve β-cell function. In
a randomized trial, 75 participants who were overweight
or obese were assigned to a low-fat plant-based diet or no
diet changes for 16 wk. Meal-stimulated insulin secretion
markedly increased in the intervention group compared
Plant-based nutrition for diabetes 3
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with controls (interaction between group and time, G×t[P
<0.001]) (30). This study demonstrates the potential that a
plant-based eating pattern can play a role in reversing β-cell
dysfunction and peripheral insulin resistance in patients with
type 2 diabetes.
Weight management
Weight management plays an important role in improving
insulin sensitivity and glycemic control and reducing cardio-
vascular disease (CVD) risk factors (31). Excess body weight
is associated with risk of CVD and all-cause mortality among
people with type 2 diabetes (32). Individuals following
vegetarian, especially vegan, diets have lower mean BMIs,
compared with nonvegetarians (33). Population studies
have revealed that body weight increases progressively with
increased meat consumption (10,34).
In addition to preventing weight gain, a plant-based eating
pattern is an eective weight management tool (35,36).
In randomized trials, plant-based interventions for patients
withtype2diabeteshaveresultedingreaterweightloss
compared with control diets containing animal products (22,
23,37), with a major portion of weight loss attributable to
a loss of visceral fat, a major advantage for reducing insulin
resistance and inammation (23,37). The BROAD study
demonstrated signicant weight loss using a low-fat (∼7–
15% of calories from fat), plant-based diet in overweight
individuals with ≥1 of the following comorbidities: type 2
diabetes, ischemic heart disease, hypertension, or hyperc-
holesterolemia (38). Sixty-ve adults (aged 35–70 y) were
randomly assigned to the plant-based diet or usual care. The
reductioninBMIat6mowasgreaterintheplant-based
group compared with the usual-care group (4.4 compared
with 0.4, dierence: 3.9) (95% CI: ±1, P<0.0001). At 12 mo,
the reduction in BMI in the plant-based group was 4.2 (±0.8).
The program did not require restrictions on portion sizes, yet
participants reported feeling satised, potentially enhancing
compliance (38).
In a randomized trial of individuals with type 2 diabetes,
a low-fat vegan diet prescribed with no energy-intake limits
was associated with greater weight loss at 22 wk, compared
with a conventional diet that required energy-intake restric-
tions (–6.5 kg compared with –3.1 kg [P<0.001]) (22). At 74
wk, weight loss remained signicant within each diet group
but not signicantly dierent between groups (–4.4 kg in
the vegan group and –3.0 kg in the conventional diet group,
P=0.25) (39).
In a 24-wk trial, researchers tested the eects of plant-
based diets when used in combination with other inter-
ventions, comparing an isocaloric vegetarian diet (animal
products were limited to 1 serving of low-fat yogurt per
day) with a conventional diabetes diet that followed the
guidelines of the Diabetes and Nutrition Study Group of the
European Association for the Study of Diabetes (37). Aerobic
exercise was added to both study groups for the second 12
wk of the study. The macronutrient breakdown was 60% of
kcal from carbohydrate, 15% protein, and 25% fat for the
vegetarian intervention and 50% from carbohydrate, 20%
protein, and <30% fat (≤7% saturated fat, <200 mg/d of
cholesterol) for the conventional group. Both diets restricted
calories by 500 kcal/d, which was individualized based
on indirect calorimetry (37). Meals were provided to the
participants in both groups, supporting adherence to the
prescribed diet interventions. The vegetarian intervention
resulted in more weight loss (–6.2 kg; 95% CI: –6.6, –
5.3 compared with –3.2 kg; 95% CI: –3.7, –2.5; interaction
group ×time P=0.001) and greater improvements in insulin
sensitivity (30%; 95% CI: 24.5, 39 compared with 20%; 95%
CI: 14, 25). Reductions in visceral and subcutaneous fat were
signicantly greater (P=0.007 and P=0.02, respectively) in
the vegetarian group (37).
Weight loss on plant-based diets appears to be attributable
to 2 main diet eects. First, increased ber and carbohydrate
intakeandreducedfatintakeleadtoareductionintheenergy
density of the diet. Second, plant-based diets have been
shown to increase postprandial metabolism (the thermic
eect of food) (36). In a randomized trial, participants with
a diagnosis of overweight or obesity (BMI 28–40) were
assigned to either a low-fat, vegan diet or to make no dietary
changes for 16 wk. The vegan group lost 5.9 kg (95% CI: 5.0,
6.7 kg; P<0.001) and its thermic eect of food (measured by
indirect calorimetry) increased by 14.1% (95% CI: 6.5, 20.4;
P<0.001). These changes were associated with reductions in
hepatocellular and intramyocellular fat and increased insulin
sensitivity (29).
Plant-Based Eating Pattern for Macrovascular
and Microvascular Complications of Diabetes
CVD
The eects of plant-based diets on glycemia, body weight,
plasma lipids, and blood pressure collectively reduce the risk
of CVD, the leading cause of morbidity and mortality in
diabetes patients. CVD encompasses coronary heart disease,
cerebrovascular disease, and peripheral arterial disease (32).
A meta-analysis of 9 randomized controlled trials in patients
with type 2 diabetes (N =664), comparing vegetarian
interventions with control diets, showed signicant improve-
ments in CVD risk factors, including lipids, blood pressure,
glycemic control, body weight, and abdominal adiposity
(40).
In addition to being associated with reduced CVD
risk, a plant-based diet may help reverse atherosclerotic
plaques. Ornish et al. demonstrated signicant regression in
coronary artery stenosis in patients with moderate to severe
coronary artery disease. Participants were randomly assigned
to usual care or a low-fat vegetarian diet combined with
exercise, stress management, and smoking cessation. After
5 y there was a mean reduction in atherosclerotic stenosis
in the vegetarian group, whereas there was a progression of
atherosclerosis in the control group. The control group was
also more likely to have required coronary angioplasty and
bypass surgery than the vegetarian group (41).
4 Jardine et al.
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Microvascular complications
Chronic kidney disease.
Chronic kidney disease is increasingly prevalent, and dia-
betes accounts for 44% of all new cases; 20–40% of patients
with diabetes have chronic kidney disease (42). A Western
dietary pattern, characterized by a high consumption of red
meat, fat, salt, and sugar, is a major contributor to metabolic
disturbances leading to the progression of kidney disease
(43). In the Nurses’ Health Study, women with mild renal
insuciency at baseline had a signicantly greater reduction
in renal function with greater consumption of animal protein
(especiallyfrommeat)overan11-yperiod(44). In contrast,
a 24-y follow-up of 14,868 adults in the Atherosclerosis Risk
and Communities Study found that a higher adherence to a
healthy plant-based diet was associated with a lower risk of
chronic kidney disease (45).
Several studies have reported a reduction of urinary
albumin excretion in patients with diabetic nephropathy
when consuming a plant-based or reduced-red-meat diet
(46–48). One study showed a 54% decrease in urinary
albumin in patients with type 1 diabetes after 8 wk of a plant-
based diet (48).ThestudybyBarnardetal.describedabovein
which patients with type 2 diabetes followed a low-fat vegan
diet, reported a signicant reduction in urinary albumin in
participants following a low-fat vegan diet, with no change
in the control group following a portion-controlled diet
(22).
Neuropathy.
More than 50% of individuals with diabetes suer from
neuropathy (49). Common clinical manifestations include
pain, insensitivity to injury, orthostatic hypotension, cardiac
autonomic neuropathy, gastroparesis, and erectile dysfunc-
tion (50). Diabetic neuropathycan lead to sleep disturbances,
depression, and anxiety (51), and eventually amputations
(52). Current treatment of diabetic neuropathy includes
glycemic control to slow disease progression and medi-
cations for neuropathic pain (42). There is no pharma-
cological treatment that reverses nerve damage caused by
neuropathy, apart from methods for improving glycemic
control.
A 20-wk randomized, controlled trial using a low-fat,
vegan intervention demonstrated improved nerve function,
as measured by electrochemical skin conductance in the foot,
and reduced pain, compared with an untreated control group.
(53). These results are consistent with 2 smaller studies that
used a vegan diet, one combined with exercise in which
painful neuropathy symptoms were eliminated in 17 out of 21
patients (54) and another in which cutaneous reinnervation
and reduced pain were reported in 30 individuals with
impaired glucose tolerance (55).
Diabetic retinopathy.
Theinuenceofaplant-baseddietondiabeticretinopathy
has not been studied. However, a plant-based diet is eective
in controlling risk factors for diabetic retinopathy, including
glycemia (19), blood pressure (56), and lipids (57). Studies
have also demonstrated that diets high in fruits, vegetables,
anddietaryberareassociatedwithareductionindiabetic
retinopathy (58).
Comparing a Plant-Based Diet with Key Aspects
of Other Dietary Approaches for Type 2
Diabetes
Very-low-calorie diets and metabolic surgery
Reversalofinsulinresistanceandβ-cell dysfunction with as-
sociated reductions in pancreatic and hepatic triacylglycerol
stores has been demonstrated in patients with type 2 diabetes
with very-low-calorie diets (600 kcal/d) or bariatric surgery
(59). These interventions are not free from clinical challenges
or risk. Very-low-calorie diets require medical management
by trained practitioners and may only be appropriate in select
patients. Further, the long-term sustainability of such diets is
limited; they are frequently followed by progressive weight
gain (60,61). Adverse eects of metabolic surgery include
mortality (rates 0.1–0.5%), dumping syndrome, nutritional
deciencies, increased risk of depression, and substance
abuse (62). A plant-based diet may provide improvements for
diabetes without intentional caloric reduction and may do so
independently of weight loss.
Mediterranean and Dietary Approaches for Stopping
Hypertension
Mediterranean and Dietary Approaches for Stopping Hyper-
tension (DASH) diets both emphasize the intake of plant-
based foods with controlled portions of animal products.
Mediterranean diets have been tested for the prevention and
treatment of diabetes. Like a plant-based diet, Mediterranean
diets emphasize the consumption of fruits, vegetables, whole
grains, and legumes, and reduce meat, rened grains, and
sugar, while allowing modest amounts of animal products.
The term “Mediterranean diet” may be interpreted dierently
by dierent people. In research studies, the term refers to a
diet that includes abundant plant-based foods, favors olive
oil as the primary source of fat, and includes low to moderate
amounts of meat, dairy products, eggs, and wine (63). A
high score (range 0 to 9) for Mediterranean diet-style intake,
measured by study participants’ consumption of fruits,
vegetables,wholegrains,legumes,nuts,andsh,andtheratio
of MUFAs to SFAs, was associated with a 30% reduced risk of
developing diabetes in over 25,000 women followed for 20
y. The high Mediterranean diet scores were associated with
lower biomarkers of insulin resistance (adiposity, lipoprotein
metabolism, and inammation) (64). A meta-analysis of 9
randomized controlled trials with 1178 patients with type 2
diabetes compared a Mediterranean diet with control diets
resulting in a greater reduction in HbA1c (mean dierence,
–0.30; 95% CI: –0.46, –0.14). There were also improvements
in body weight and cardiovascular risk factors (65).
The outcomes for weight loss using a Mediterranean
diet have been mixed. Although a 2016 systematic review
reported that clinical trials using Mediterranean diets showed
Plant-based nutrition for diabetes 5
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TABLE 1 Dietary sources of key nutrients on a plant-based diet
Nutrient Dietary sources Importance for plant-based nutrition and diabetes
Protein Legumes, whole grains, vegetables, nuts, and seeds Consuming more animal protein may increase the risk of type 2
diabetes compared with consuming less and compared with
replacing the animal sources with vegetable protein sources (66)
(67)
ω-3 fatty acids Seeds (hemp, chia, flax), walnuts, leafy green vegetables,
microalgae, soybeans, wheat germ
A low-fat, plant-based diet will be lower in ω-6 fatty acids, thus
allowing for a more ideal ratio to ω-3 fatty acids, with a lower ratio
being preferable (68)
Iron Legumes; leafy greens such as spinach, Swiss chard, kale,
collards, and beet greens; raisins; blackstrap molasses;
pumpkin seeds
Iron deficiencies do not manifest in those following a plant-based
diet any more than in those following other diet patterns (9).
Insulin resistance may be increased by heme iron found only in
animal products (69)
Zinc Legumes, soybeans, nuts, seeds, whole grains Zinc deficiencies do not manifest in those following a plant-based
diet any more than in those following other dietary patterns (9)
Iodine Sea vegetables, iodized salt, supplements Iodine is important for thyroid health
Calcium Kale, collard greens, bok choy, broccoli, green cabbage,
Brussels sprouts, fortified plant milks and juices,
calcium-set tofu, almonds, sesame seeds
The absorption rate of calcium from greens is sometimes twice as
high as calcium from cow milk, which has an absorption rate of
∼30% (70)
Vitamin D Sunshine exposure and supplements Vitamin D status may improve inflammation and oxidative stress
among diabetes patients (71)
Vitamin B-12 Fortified foods and supplements Anyone over the age of 50 and taking certain medications, including
metformin, could benefit from taking a vitamin B-12 supplement,
regardless of eating pattern (72)
signicant weight loss, all of the included studies used
exercise or calorie restriction, confounding the eects of the
dietary change (73). The well-controlled Lyon Diet Heart
Study (74) and the Prevención con Dieta Mediterránea
(PREDIMED) study (75) led to no clinically signicant
weight loss. In a crossover trial including 62 overweight
adults, a low-fat vegan diet led to signicantly greater weight
loss over a 16-wk intervention period, compared with a
Mediterranean diet (76).
The DASH diet was developed to lower blood pressure
without medications. The eating pattern emphasizes fruit,
vegetables, fat-free/low-fat dairy, whole grains, nuts, and
legumes, and limits saturated fat, cholesterol, red and
processed meats, sweets, added sugars, salt, and sugar-
sweetened beverages. In an umbrella review of systematic
reviews and meta-analyses on cardiometabolic outcomes, the
DASH diet was associated with a signicant reduced risk of
diabetes (RR: 0.82; 95% CI: 0.74, 0.92) as well as signicant
reductions in CVD, coronary heart disease, and stroke, and
reductions in blood pressure and body weight. There were no
signicant changes in HDL cholesterol, triglycerides, fasting
blood glucose, HOMA-IR, or C-reactive protein. This review
included 2 controlled trials evaluating the DASH diet in
individuals with diabetes which resulted in a reduction in
HbA1c (–0.53%; 95% CI: –0.62, –0.43) and fasting insulin (–
0.15 μU/mL; 95% CI: –0.22, –0.08) (77).
The absence of any need for portion control is an advan-
tage of a low-fat vegan diet over Mediterranean and DASH
eating patterns. The DASH diet does not appear to provide
the reduction in inammation and improvement in insulin
sensitivity that has been documented in the vegan diet. Given
that even small amounts of animal products may increase
the risk of diabetes (in the AHS-2, the vegan diet provided
a major advantage in reducing the risk of diabetes compared
with the lacto-ovo vegetarian or the semivegetarian where
meat consumption was limited to ≥1 time a month and <1
time/wk), there are theoretical advantages to avoiding animal
products altogether.
Low-carbohydrate eating pattern
Low-carbohydrate diets cause weight loss in overweight
individuals, although they are no more eective for weight
loss than plant-based diets or other dietary approaches in
1-y comparisons (78,79). The common idea that low-
carbohydrate diets suppress appetite was challenged in a
2021 metabolic-ward study (80). Twenty young overweight
adults were assigned to a low-fat, vegan diet (10% fat, 75%
carbohydrate) or a low-carbohydrate diet (76% fat, 10%
carbohydrate) for 2 wk, then switched to the opposite diet
for an additional 2 wk (80). The vegan diet led to a much
greater drop in calorie intake; energy intake was 689 (±73)
kcal/d lower during the vegan phase, compared with the low-
carbohydrate phase (P<0.0001) (80).
In individuals with diabetes, low-carbohydrate diets may
cause an initial reduction in blood glucose values, but these
benets are often largely gone by 12 mo (81).
There may be some safety concerns with a low-
carbohydrate diet. They often elevate plasma LDL cholesterol
concentrations, with widely varying eects between
individuals (82). Because low-carbohydrate diets restrict or
eliminate fruits, whole grains, legumes, and other healthful
foods, and are often high in saturated fats, they raise concerns
about long-term risk of cancer, Alzheimer’s disease, and
other conditions. Long-term use of low-carbohydrate
diets is associated with increased all-cause mortality
(83).
6 Jardine et al.
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TABLE 2 Guidelines for implementing plant-based nutrition in clinical practice
Consider patient referral
Health care providers are encouraged to refer patients to a registered dietitian nutritionist (RDN) who specializes in plant-based nutrition. RDNs are
trained to do a thorough nutrition assessment as well as education and counseling. Medicare and most insurance plans cover medical nutrition
therapy (MNT)
Patient assessment for plant-based nutrition
rReadiness for change
rAssess current eating pattern
rFamily and social support
rCultural/religious beliefs
rEducation and socioeconomic traits
rLifestyle: sleep, exercise, tobacco, alcohol, and substance use
rEmotional well-being
rUse of glucose monitoring (self-monitoring of blood glucose/continuous glucose monitoring)
rCulinary skills
rFrequency of eating out and/or traveling
rCurrent dietary habits:
rPlant-based eating habits: fiber, servings of fruit, vegetables, whole grains, legumes, nuts, and seeds
rIntake of animal products and refined carbohydrates: chicken, fish, red meat, processed meat, eggs, dairy (including cheese), fried food,
refined sugar, sugar-sweetened beverages, and processed and fast food
Note: this is in addition to a comprehensive medical evaluation described in the ADA Standards of Care that includes medical and family history,
medications, vaccinations, and technology use (137).
Education: principles of plant-based nutrition
rFocus on the 4 food groups (see Tabl e 3)
r2–4 servings of fruit
r3–5 servings of vegetables
r5–8 servings of whole grains
r2 or more servings of legumes
rLimit added oils, fried foods, and other high-fat foods
rLimit nuts and seeds to 1 ounce per day (scant 1
4cup or 2 tablespoons of nut butters)
rAim to consume 40 g of fiber per day. A gradual intake may be necessary to minimize gastrointestinal symptoms
rAvoid all animal products including meats, fish, dairy, and eggs
rSupplement with vitamin B-12: 500–1000 μ2–3 times per week (5)
Methods of intervention
rMeal planning
rGrocery shopping and label reading
rCooking techniques
rSelf-monitoring of blood glucose
rConcerns and treatment of changes in blood glucose with diet intervention (treatment of hypoglycemia)
rHave patient education materials:
rHandouts
rBooks
rCookbooks
rList of appropriate websites
rConsider using telehealth to provide care and education and send motivational messages to patients on a regular basis
rProvide group classes:
rOngoing support groups
rCooking classes
Topics to cover:
Follow-up and ongoing support
rMonitor body weight, self-monitoring of blood glucose, HbA1c, lipids, and blood pressure
rAssess for potential of medication-induced hypoglycemia or hypotension, and adjust medical therapy as needed
rReview diet records
rUse failures as opportunities for problem-solving and skill development
ADA, American Diabetes Association; HbA1c, glycated hemoglobin.
In terms of safety, plant-based diets reduce diabetes risk
without untoward side eects. The same is true for treatment
of diabetes with some precautions for hypoglycemia. In
the study by Barnard et al., 43% of the subjects in the
low-fat vegan group had to reduce or eliminate their diabetes
medications in response to hypoglycemia (22). Low blood
glucose concentrations can be avoided by frequent glucose
monitoring, patient education, and adjusting medications
as needed. Plant-based eating patterns have been found
to have a high diet quality and are nutritionally adequate.
Plant-based nutrition for diabetes 7
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TABLE 3 Plant-based nutrition food groups
Food group Foods Serving size Servings per day
Vegetables: include a
variety of colors from the
rainbow: red, yellow,
orange, green, and
purple
Artichokes, asparagus, beets, bok choy, broccoli,
Brussels sprouts, cabbage (all colors), carrots,
cauliflower, celery, collards, cucumbers, eggplant,
endive, garlic, ginger, green beans, k ale, lettuce,
mustard and turnip greens, okra, onions, parsnips,
peppers, potatoes (all varieties), pumpkin, radishes,
spinach, squash (all varieties), tomatoes, turnip,
watercress
1 cup raw
1
2cup cooked
≥3 to 5 or more servings
or unlimited
Fruits Apples, apricots, bananas, berries, citrus fruit, cherries,
dates, grapes, kiwi fruit, kumquats, mangos,
papayas, peaches, pears, pineapples, plums,
pomegranates, melons, raisins
1medium
1 cup chopped
2 tablespoons dried
2 to 4 or more servings
Whole grains: choose whole
grain versus refined as
much as possible
Amaranth, barley, bread, buckwheat, bulgur, cereal
(hot or cold), corn, millet, oats (rolled, steel cut, or
groats), pasta, popcorn (air-popped), quinoa and
tortillas
1
2cup any cooked grain
3
4cup dry cereal
1 slice bread
1 tortilla
5 to 8 or more servings
Legumes Anasazi beans, adzuki beans, baked beans, black
beans, chickpeas, dahl, hummus, lima beans,
lentils, navy beans, peas, pinto beans, soy milk,
tempeh, and tofu
1
4cup hummus
1
4cup dry legumes
1
2cup cooked beans, lentils,
peas, tofu, tempeh
1cupsoymilk
2ormoreservings
Nuts and seeds Almonds, Brazil nuts, cashews, hazelnuts, macadamia,
peanuts, pinons (pine nuts), pistachios, walnuts,
and seeds: pumpkin, sunflower, hemp, flax, and
chia
Limit to:
1ounce
2 tablespoons nut butter
1servingorless
Herbs and spices Fresh or dried herbs and spices without salt added unlimited
Water and tea Water or herbal teas without sugar added 8 ounces 8 servings
According to the Academy of Nutrition and Dietetics (AND),
“appropriately planned vegetarian, including vegan, diets are
healthful, nutritionally adequate (9).”
Considerations for the Use of a Plant-Based Diet
for Diabetes
Caregivers should help patients who have (or are at risk
of) diabetes to understand the benets of a plant-based
eating pattern and encourage a trial. Patients are typically
willing to try a plant-based diet when its rationale has
been explained, and they can adapt nutrition guidelines
to suit their preferences (84). The fact that a plant-based
diet does not require limits on calories, carbohydrates, or
portions makes it appealing, and most patients nd it to
be no more challenging than other therapeutic diets (85).
Further, the acceptability of a low-fat plant-based diet has
been shown to be comparable to other therapeutic eating
patterns in randomized trials with individuals with diabetes
(85). Adopting a plant-based diet is often highly motivating
due to the improvements with weight loss, glycemic control,
and enhanced quality of life (86).
According to AND, vegan and vegetarian diets are
nutritionally adequate and may provide health benets for
the prevention and treatment of certain diseases, including
type 2 diabetes (9). Plants provide all required vitamins
and minerals except vitamin B-12. Vitamin B-12 is made
neither by plants nor animals but rather by microbes.
Although cereals, plant-based milk, and other plant-based
foods may be fortied with vitamin B-12, a B-12 supplement
will ensure adequacy. AND recommends adults following
a plant-based diet take 500 to 1000 μg several times per
week (9). Metformin use increases the risk of vitamin B-12
deciency, which can contribute to symptoms of neuropathy.
Periodic testing of vitamin B-12 status is suggested by the
American Diabetes Association (ADA) (87). Tab l e 1 is a
resource for dietary sources of key nutrients on a plant-based
diet.
Once patients have a good list of meal possibilities, the
next step is to adopt a fully vegan diet for 3 wk. This
“test drive” is short enough to be readily approachable,
particularly since patients have already drawn up a list of
suitable foods, but it is long enough for health benets to be
noticed. For maximum impact, it is best to ask patients to (1)
avoid all animal products, (2) minimize the use of oils and
oily foods, and (3)favorfoodsthatarehighinber.
Involving the family will shore up support for the
diet changes at home and diminish potential resistance.
Teaching in groups is often particularly eective; groups
bring added experiences, helpful questions, social support,
and, as time goes on, validation for the eectiveness of
the diet change. Additional guidance on how to deal with
social situations and traveling will ensure success. Handouts,
books, videos, and recipes should be readily available in
waiting rooms and examination rooms or made accessible
online. Ta b l e 2 provides guidelines for implementing plant-
based nutrition in clinical practice. Tab l e 3 has a list
8 Jardine et al.
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of plant-based nutrition food groups and recommended
servings.
Adjusting medications in response to a plant-based diet
It is essential to help patients anticipate blood glucose
changes in response to the new eating pattern. Hypoglycemia
is common among individuals treated with insulin or
sulfonylureas as they improve their diets, often necessitating
medication reduction or discontinuation. There is a need for
the development of evidence-based deprescribing guidelines
for patients with type 2 diabetes who need to reduce
medication in response to episodes of hypoglycemia in the
context of a plant-based diet.
Conclusion
Observational studies and randomized controlled trials
support the benets of plant-based nutrition for diabetes. The
consumption of whole grains, legumes, fruits, and vegetables
in conjunction with the elimination of animal products
reduces the risk of developing type 2 diabetes. In individuals
with type 2 diabetes, a low-fat, plant-based diet improves
body weight, glycemic control, plasma lipid concentrations,
and blood pressure, while reducing the risk of CVD and
microvascular complications.
Health care providers should feel condent in counseling
their patients to follow a plant-based eating pattern and
should be prepared to provide education and support to
improve their patients’ diabetes outcomes, general health,
and psychological well-being.
Further research on the eects of a plant-based diet for
thepreventionofnephropathyandretinopathy,aswellas
on their role in improving management of type 1 diabetes,
would be helpful. High-quality studies comparing vegan
and vegetarian eating patterns with DASH and or the
Mediterranean eating patterns would provide more detail
on how various eating patterns aect diabetes outcomes.
Guidelines on reducing reliance on antihyperglycemic med-
ications in response to plant-based lifestyle therapy would
assist health care providers in reducing the risk of hypo-
glycemia and other untoward side eects associated with
overmedication.
Acknowledgments
The authors’ contributions were as follows: MAJ, developed
theoutlineandfocusofthearticleandwasresponsible
for writing the nal manuscript; HK, provided content on
prevention,treatment,andcomplicationsofdiabeteswitha
plant-based diet; SML, worked on the nutrition content as
well as providing editing for each draft; ZA, researched and
wrote content on the mechanisms section of the article; CBT,
wrote section adjusting medications as well as editing to the
nal manuscript; NDB, added content on complications of
diabetes, the mechanisms section as well as providing edits
to the nal manuscript; and all authors: read and approved
the nal manuscript.
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