Abstract
The prevalence of type 2 diabetes is rising worldwide, especially in older adults. Diet and lifestyle, particularly plant-based diets, are effective 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 interventional 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, including 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.
Generated Summary
This review article examines the role of plant-based diets in the prevention and treatment of type 2 diabetes. It synthesizes evidence from observational studies, clinical trials, and mechanistic insights to underscore the benefits of plant-based eating patterns. The research approach involves a comprehensive overview of existing literature, including cohort studies, randomized clinical trials, and meta-analyses, to assess the impact of plant-based diets on diabetes risk, management, and related complications. The methodology includes analyzing data from various studies to quantify the effects of plant-based diets and their components on insulin resistance, glycemic control, and cardiovascular health. The scope of the review encompasses the examination of different plant-based eating patterns (vegan, vegetarian) and their effects on diverse populations, highlighting the role of specific food components (legumes, whole grains, vegetables, fruits, nuts, and seeds) in reducing the risk of type 2 diabetes and its complications.
Key Findings & Statistics
- In the United States in 2011-2012, 12%-14% of adults had type 2 diabetes, and 38% had prediabetes.
- 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.
- In 2015, type 2 diabetes was the 7th leading cause of death in the United States.
- In the landmark Diabetes Prevention Program, lifestyle changes conferred a 71% reduction in risk of type 2 diabetes among participants ages 60 and over.
- The prevalence of type 2 diabetes is significantly lower among those following plant-based eating patterns compared with omnivores and even semi-vegetarians.
- Vegans had half the rate of type 2 diabetes compared with non-vegetarians (OR: 0.51; 95% CI: 0.40-0.66).
- Semi-vegetarians experienced intermediate benefit (OR: 0.76; 95% CI: 0.65–0.90).
- Vegans had a dramatically lower risk of developing type 2 diabetes compared with non-vegetarians (OR: 0.381; 95% CI: 0.236–0.617).
- 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 diabetes compared with long-term adherence to a vegetarian diet (zero meat intake).
- 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 counterparts.
- Those most adherent to the healthful plant-based dietary index had a 34% lower risk of developing diabetes compared with those least adherent.
- 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.
- In the EPIC-interact cohort, van Nielen et al. observed a 22% higher type 2 diabetes incidence over 12 years in the highest versus lowest quintile of animal protein consumption.
- 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 in Greece, a 5% increase in protein intake from meat and meat products was associated with a 34% greater likelihood of type 2 diabetes.
- In the vegan group, 43% (21 of 49) of the participants reduced their diabetes medications, and in the ADA group, 26% (13 of 50) participants reduced their diabetes medications.
- After adjusting 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).
- The average insulin dose decreased from 26 units on the baseline diet to 11 units on the HCF diet.
- In large cohort studies, vegetarian diets have been associated with 24%-32% reductions in ischemic heart disease incidence and mortality relative to omnivorous diets.
- After 5 years, LDL levels in the lifestyle intervention group decreased 20% from baseline without lipid-lowering medications.
- 60% of whom were on lipid-lowering medications
- In the lifestyle group, the average degree 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.
- Vegetarians had approximately half the odds of having hypertension as omnivores, even after adjustment for body mass index.
- The review also found that plant-based diets are associated with up to a 35% reduction in serum LDL cholesterol
- In the EPIC-Oxford cohort, those following vegan diets had lower levels of apolipoprotein B, reflecting lower levels of circulating atherogenic particles.
- 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.
- 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, the 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).
- A recent review outlined how a Western-style diet, characterized by high intake of red meat, animal fat, highly processed food and low intake of fruits and vegetables, is associated with kidney disease.
- 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.
- In a randomized controlled pilot study, pain scores were significantly improved at 20 weeks on a plant-based diet compared with a control diet.
- In diets that replaced animal protein with plant sources, there was a significant decrease in hemoglobin Alc (-0.15%), fasting glucose (-0.53 mmol/L) and fasting insulin (-10 pmol/L).
- Among participants, whose average age was 62 years
Other Important Findings
- Plant-based diets, particularly those emphasizing whole grains, vegetables, fruits, nuts, and seeds, are effective for the prevention and management of type 2 diabetes.
- Cohort studies and clinical trials support the role of plant-based diets in reducing the risk of type 2 diabetes and its complications.
- Plant-based diets are effective tools for type 2 diabetes prevention and management.
- Optimal macronutrient ratios are controversial; the focus should instead be on eating patterns and actual foods.
- 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.
- Increases in consumption of calorie-dense foods, including fast foods, meats and other animal fats, highly refined grains, and sugar-sweetened beverages, are thought to play a critical role in the rising rates of type 2 diabetes worldwide.
- Lifestyle changes, particularly diet, can be highly effective in preventing, treating, and even reversing type 2 diabetes.
- Eating patterns were stratified by an overall plant-based diet index, in which plant foods received positive scores while animal foods received reverse scores.
- In the “healthful” version of this plant-based index, fruit juices, refined grains, and added sugars also received reverse scores.
- A whole-foods, plant-based eating pattern generally includes legumes, whole grains, fruits, vegetables, and nuts, and is high in fiber.
- Whole grains have been associated with reduced risk of developing diabetes.
- Specific fruits and vegetables, have been linked to lower diabetes rates.
- Legumes have also been shown to ameliorate insulin resistance and protect against metabolic syndrome.
- Cereal fiber appears to be especially protective against type 2 diabetes.
- 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.
- Protein intake from plant sources offered protection against diabetes.
- Barnard et al., performed the first major randomized clinical trial on diabetic patients treated purely with a plant-based (vegan) diet, comparing it to a conventional diet based on the 2003 American Diabetes Association (ADA) guidelines.
- The recommended vegan diet comprised approximately 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-glycemic index foods, such as beans and green vegetables.
- 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.
- High-carbohydrate, low-fat, predominantly vegetarian diets are often associated with weight loss, making it difficult to ascertain what proportion of the improvement in glycemic control is due to weight loss versus dietary changes.
- Plant-based diets have demonstrated improvements in glycemic control while also reducing macro- and micro-vascular risks of type 2 diabetes.
- Plant-based diets have also documented angiographic and clinical reversal of coronary artery disease.
- Plant protein tends to lower blood pressure, even in elderly patients.
- Plant-based diets are associated with up to a 35% reduction in serum LDL cholesterol.
- Chronic inflammation, as measured by serum biomarkers such as C-reactive protein, has been linked to risk of cardiovascular events, and is closely tied to dietary choices.
- Plant-based diets tend to promote weight loss and lower adiposity.
- The review outlined how a Western-style diet, characterized by high intake of red meat, animal fat, highly processed food and low intake of fruits and vegetables, is associated with kidney disease.
- A variety of mechanisms were proposed for this association, including increased animal protein leading to decreased renal blood flow and glomerular filtration rate, an increased acid load from animal 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.
- Diabetic neuropathy is a microvascular complication of diabetes that can be debilitating.
- In key randomized clinical trials of plant-based diets, recommended total fat intake has been low (approximately 10% of energy) for intervention groups.
- The benefits of carbohydrates in comparison to animal protein.
- 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.
- 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%.
- In the EPIC-Potsdam cohort, Schulze et al., 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 associated with increased all-cause, cardiovascular, and cancer mortality.
- Plant sources of protein have the benefit of being truly low fat in many cases (e.g., most legumes).
- 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 glycemic control.
- In the 2017 “Standards of Medical Care in Diabetes,” the 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.
- These guidelines recommend carbohydrate intake from legumes, whole grains, fruits, vegetables, and dairy products, with an emphasis on nutrient-dense, high-fiber, low-glycemic load foods.
- The key elements of the eating pattern include avoidance of animal products, highly refined grains, added sugars, and oils, and consumption of an abundance of legumes, leafy greens, cruciferous vegetables, starchy vegetables, whole grains, and fruits.
- In key randomized clinical trials of plant-based diets, low-glycemic index foods have been encouraged.
Limitations Noted in the Document
- The effects of plant-based diets on outcomes are diverse, and the mechanisms are multifaceted and complex.
- Optimal macronutrient ratios for preventing and treating type 2 diabetes are controversial.
- The review focuses on eating patterns and actual foods rather than specific macronutrient ratios.
- Some clinicians may assume that their patients will not be open to adopting a plant-based diet.
- 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.
- It remains unclear what component of a plant-based diet is most effective: the high carbohydrate and fiber content, the low fat and low-animal protein content, or both.
- High-carbohydrate, low-fat, predominantly vegetarian diets are often associated with weight loss, making it difficult to ascertain what proportion of the improvement in glycemic control is due to weight loss versus dietary changes.
- The study has not addressed specific nutritional deficiencies in any particular diet.
- 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
Conclusion
The evidence strongly supports the use of plant-based diets for the prevention and treatment of type 2 diabetes and its associated complications. Observational studies consistently show that plant-based diets are associated with lower rates of type 2 diabetes, even after adjusting for factors like body mass index. Furthermore, prospective studies demonstrate a reduced risk of developing diabetes in those following plant-based diets. Clinical trials have shown that plant-based diets can improve glycemic control, reduce the need for diabetes medications, and improve cardiovascular risk factors. Plant-based diets have demonstrated improvements in glycemic control while also reducing macro- and micro-vascular risks of type 2 diabetes. The emphasis on whole foods, particularly legumes, whole grains, vegetables, fruits, nuts, and seeds, along with the avoidance of animal products and refined foods, forms the cornerstone of these beneficial eating patterns. Plant-based diets not only improve glycemic control but also reduce cardiovascular risk factors, the leading cause of death in diabetes patients. 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. The 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. In terms of foods, sources (e.g., animal vs. plant, refined versus unrefined) 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 diabetes. The importance lies in the types and sources of carbohydrates, fats, and proteins. Fiber, antioxidants, and magnesium, all of which are high in plant-based diets have been shown to promote insulin sensitivity. Plant-based diets also tend to promote weight loss, lower adiposity and blood pressure. The benefits of these dietary patterns extend beyond glycemic control, encompassing a reduction in cardiovascular risk factors, making plant-based diets a comprehensive approach to managing diabetes and promoting overall health. 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.
IFFS Team Summary
- Thorough review article by Dr. Michelle McMacken
- Reviews the impact of plant diet to reduce diabetes, heart disease, and related processes like hyperlipidemia
- Also references in cardiovascular disease section