Plant-based diets: How do they keep diabetes, heart disease at bay?

Nov 02, 2024

Eating more fruits, vegetables, and plant-based foods is a long-standing nutritional recommendation for better health.

In fact, current guidelines, like the 2020–2025 Dietary Guidelines for Americans, support vegetarian diets as a dietary option to promote health and prevent disease.

However, some nutrition and health professionals hesitate to advocate for vegetarian or vegan diets. This may be due to outdated resources or misconceptions.

Researchers recently reviewed the literature on these diets and their effects on cardiometabolic health.

They aimed to inform practitioners about the effectiveness of vegetarian and vegan diets in clinical care and bridge the gap between research and practice.

Two review studies published in October 2024 highlight that vegetarian and vegan diets can be beneficial for individuals with type 2 diabetes and may lower heart disease risk across the general adult population.

The study on type 2 diabetes appears in Advances in Nutrition, while the heart disease findings are published in the American Journal of Preventive Cardiology.

This research contributes to an initiative to update the Academy of Nutrition and Dietetics (AND) Evidence Analysis Library, supporting evidence-based nutrition practice.

Both studies were funded by the AND, the AND Foundation, and the AND Vegetarian Nutrition Dietetics Practice Group.

“We now have such an abundance of studies that have examined vegetarian dietary patterns that we’re doing reviews of reviews to systematically examine the research and contribute to evidence-based clinical practice,” Matthew Landry, PhD, RDN, an author on both studies, said in a press release.

Landry is an assistant professor of population health and disease prevention at UC Irvine Joe C. Wen School of Population and Public Health.His previous research was part of a prominent twin diet study.

In a systematic review and meta-analysis, researchers examined seven randomized controlled trials on vegetarian and vegan diets for treating adults with type 2 diabetes.

These studies, which lasted an average of 26 weeks, involved 770 predominantly middle-aged participants aged 44 to 61.

Vegetarian diets generally exclude meat, poultry, and seafood, while vegan diets further eliminate other animal products like eggs and dairy. In this review, “vegetarian” encompassed all types.

Results suggest with moderate certainty that vegetarian diets support blood sugar control, reducing hemoglobin A1c by 0.40% and lowering body mass index by 0.96.

These diets may also allow for a reduction in diabetes medication and may improve insulin sensitivity by about 10% compared to non-vegetarian diets, though the evidence was weaker for these effects.

Vegetarian diets did not appear to significantly affect fasting blood sugar, fasting insulin, or low-density lipoprotein (LDL) cholesterol levels.

These results are largely supported by previous scientific reviews specific to people with type 2 diabetes.

However, other reviews suggest vegan and vegetarian diets can help lower LDL cholesterol, particularly for people with cardiometabolic risk factors.

In the second study, researchers conducted an umbrella review of 21 systematic reviews to analyze how vegetarian, vegan, and non-vegetarian diets might impact cardiovascular health outcomes and risk factors.

Only reviews published since 2018 were included to ensure more up-to-date information.

The focus was on presumably healthy adults aged 18 and older in the general population, with most of the included research being observational.

Compared to nonvegetarian diets, vegetarian dietary patterns appeared to reduce the incidence of cardiovascular disease by 15% and decrease the risk of death from cardiovascular disease by 8%.

Vegan diets, in particular, were associated with improved cardiometabolic risk factors, with lower:

People on a vegan diet showed lower C-reactive protein levels, an inflammation marker often elevated in cardiovascular disease.

The study authors noted that vegetarian diets “likely” reduce cardiovascular disease incidence with moderate certainty. However, evidence for other outcomes was generally low certainty due to varied observational studies.

They call for more randomized control trials to explore the protective effects of vegan and vegetarian diets on cardiovascular health.

Still, the study supports earlier research linking these diets to reduced cardiovascular disease risks.

Type 2 diabetes and cardiovascular disease are significant health concerns, with each being a leading cause of death worldwide.

Medical News Today spoke with Avantika Waring, MD, a board-certified physician in endocrinology, diabetes, and metabolism and chief medical officer at 9amHealth, who was not involved in the study, about how vegan and vegetarian diets can help prevent and manage these chronic diseases.

She explained that while these diets “are generally defined by what they exclude, [like animal products, meat, and fish], the health benefits may be in large part due to what they include.”

Compared to omnivorous diets, vegan and vegetarian diets are typically higher in:

Waring suggested replacing animal fats with plant-based unsaturated fats can reduce cardiovascular disease risk by decreasing blood vessel inflammation and preventing blockages.

Additionally, unsaturated fats and fiber may enhance blood vessel function and lower blood pressure.

Waring said they may also help lower triglycerides, reducing insulin resistance and improving blood sugar and metabolic health.

Thomas M. Holland, MD, MS, a physician-scientist and assistant professor at the RUSH Institute for Healthy Aging, RUSH University, College of Health Sciences, who was not involved in the study, agreed.

Holland noted that vegan and vegetarian diets often lower overall fat intake and increase fiber, which slows sugar absorption and reduces insulin spikes, improving insulin sensitivity.

Another key factor, he said, is reduced inflammation — likely from increased antioxidants and polyphenols from fruits, vegetables, and whole grains — which decreases atherosclerosis and lowers cardiovascular disease risk.

MNT also spoke with Sheri Gaw, RDN, CDCES, a registered dietitian, certified diabetes care and education specialist, and owner of The Plant Strong Dietitian, who was also not involved in the study.

Gaw highlighted that, more broadly, weight management is a key way vegetarian diets offer cardiometabolic benefits.

She said that research suggests people eating a predominantly plant-based diet weigh up to 30 pounds less, on average, than the general population.

She also pointed out that studies indicate weight loss significantly contributes to reduced hemoglobin A1C levels, reflecting improved blood sugar control.

Vegan, vegetarian, and plant-based diets are on the rise.

The International Food Information Council (IFIC) 2024 annual health survey indicates that about 8% of Americans now identify as following one of these diets.

Many others report following largely plant-based diets, like flexitarian, DASH, or Mediterranean diets.

Another IFIC survey suggests plant-based eating has more than doubled from about 4% to 11% in the U.S. in recent years, especially among younger generations.

So, it is beneficial to recognize the potential role of these diets in preventing and managing chronic diseases.

We need more large-scale studies to find out if vegetarian and vegan diets are best for cardiometabolic health, or if diets with mostly plants and some lean animal products might have comparable impacts.

Still, Waring, Holland, and Gaw unanimously agreed that current evidence supports recommending healthy, high-quality vegetarian and vegan diets for diabetes management and heart disease prevention.

“However,” said Gaw, “vegetarian diets that are rich in refined carbohydrates from desserts and sweetened beverages, highly processed foods, trans fats, and saturated fat like palm and coconut oil, can put a person at higher risk for diabetes, cardiovascular disease, stroke, inflammation, obesity, and vitamin and mineral deficiencies.”

Waring also emphasized that a diet’s benefits are achievable only if it is sustainable, suggesting vegetarian or vegan diets only for those interested in sticking with them long-term.

Still, she said:

“Rather than just encouraging people to follow a specific diet, I recommend encouraging them to incorporate the elements of that diet that are specifically associated with improved health — fresh fruits and vegetables, complex carbohydrates and whole grains, and plant-based fats.”

While research supports adopting healthy vegetarian diet patterns, many myths persist, ranging from concerns about protein deficiency to the perception that vegetarian diets are bland or unsatisfying.

One prevalent notion, even among some health professionals, is that you must combine plant-based proteins at every meal to obtain the necessary amino acids. This is based on outdated research.

We now know that simply consuming a variety of plant-based proteins throughout the day can ensure you receive all the essential amino acids.

“It’s true that you have to be a bit more intentional to incorporate adequate protein in your diet without animal products, but there are many healthy sources of protein that are tasty, filling, and plant-based, like nuts, grains like quinoa, lentils and beans,” said Waring.

Holland stated that other common misconceptions about vegetarian and vegan diets include beliefs that they are nutritionally inadequate, expensive, or difficult to follow.

These diets can indeed lead to certain nutrient deficiencies if not practiced mindfully.

This is particularly true of vegan diets and the lack of vitamin B12, found mainly in animal foods. However, adequate levels can easily be maintained through fortified foods or supplements.

“Stigma can also arise from cultural preferences for meat or a perceived lack of variety in plant-based meals,” Holland added.

He suggested that barriers can be addressed by “educating individuals about nutrient-dense plant-based food options, emphasizing affordability, and highlighting the health benefits.”

Finally, he offered practical tips like meal planning, exploring diverse plant-based cuisines, and gradually incorporating plant-based days to ease the transition to these diets.

If you’re thinking about switching to a vegetarian or vegan diet, consult with a registered dietitian for guidance on meeting your nutritional needs.