Vegan Diets Can Improve HbA1c, Body Weight in Overweight or Type 2 Diabetes

Anne-Ditte Termannsen, PhD

A systematic review and meta-analysis of randomized controlled trials assessing the effects of vegan diets on cardiometabolic health from the European Congress on Obesity (ECO) provides a comprehensive overview of the impact of adherence to a vegan diet on body weight and glycemic control among patients with overweight weight and those with type 2 diabetes.

Leveraging data from nearly a dozen randomized trials with more than 700 adult participants, results of the study indicate adherence to a vegan diet for at least 12 weeks was associated with greater glycemic control, reductions in body weight, and reduced LDL-C, but had no effect on blood pressure, HDL-C, and triglycerides.

“This rigorous assessment of the best available evidence to date indicates with reasonable certainty that adhering to a vegan diet for at least 12 weeks may result in clinically meaningful weight loss and improve blood sugar levels, and therefore can be used in the management of overweight and type 2 diabetes”, said lead investigator Anne-Ditte Termannsen, PhD, of the Steno Diabetes Center, in a statement. “Vegan diets likely lead to weight loss because they are associated with a reduced calorie intake due to a lower content of fat and higher content of dietary fiber. However, more evidence is needed regarding other cardiometabolic outcomes.”

Interest in dietary science and the role of nutrition is at an all-time in recent years. With this, the popularity of plant-based diets has also grown. Spurred by an interest in further exploring the effects of these diets on cardiometabolic health, Termannsen and colleagues from the University of Copenhagen designed a systematic review and meta-analysis to estimate these effects using data from randomized clinical trials among patients with either overweight, which was defined as a BMI of 25 kg/m2 or greater, or with type 2 diabetes.

Through a systematic literature search of the MEDLINE, Embase, CINAHL, and CENTRAL database, as well as reference lists of relevant articles from inception through February 26, 2021, investigators hoped to identify all randomized controlled trials comparing the effects of vegan diets for at least 12 weeks in adult patients with the aforementioned conditions on outcome measures that included body weight, BMI, HbA1c, systolic and diastolic blood pressure, total cholesterol, LDL-C, HDL-C, and triglycerides. From their initial search, investigators identified 1012 records for potential inclusion and 11 were ultimately deemed eligible for inclusion in quantitative synthesis.

The 11 trials included had a mean duration of 19 weeks and a total population of 796 individuals, with a mean age ranging from 48-61 years. Investigators pointed out these trials considered weight loss of at least 11 pounds to be clinically meaningful.

Upon analysis, results indicated vegan diets were associated with significantly reduced body weight and BMI, with mean differences in reductions of 4.1 kg (95% CI, -5.9 to -2.4; P <.001) and 1.38 kg/m2 (95% CI, -1.96 to -0.80; P <.001), respectively. In contrast, the mean differences observed for HbA1c (-0.18% [95% CI, -0.29 to -0.07]; P=.002), total cholesterol (-0.30 mmol/L [95% CI, -0.52 to -0.08]; P=.007), and LDL-C (-0.24 mmol/L [95% CI, -0.40 to -0.07]; P=.005) with vegan diets compared to control diets were less apparent.

Further analysis revealed reductions in body weight and BMI with vegan diets were greater when compared against coining a normal diet without dietary changes than compared with other intervention diets, with mean differences of -7.4 kg (95% CI, -10.2 to -4.7; P <.001) and -2.78 kg/m2 (95% CI, -3.91 to -1.65; P <.001) compared to -2.7 kg (95% CI, -4.3 to -1.2; P <.001) and -0.87 kg/m2 (95% CI, - 1.34 to -0.40; P <.001), respectively.

In the aforementioned statement, investigators urged caution when interpreting the results of their study. These limitations included the small sample sizes of studies, varied contents of a vegan diet, and none of the studies prescribing a control diet that exactly matched the intervention diet in all other aspects except veganism.

“The results suggest that adhering to vegan diets for at least 12 weeks may be effective in individuals with overweight or type 2 diabetes to induce a meaningful decrease in body weight and improve glycemia. Some of this effect may be contributed to differences in the macronutrient composition and energy intake in the vegan diets versus control diets,” wrote investigators.

This study, “Effects of vegan diets on cardiometabolic health: A systematic review and meta-analysis of randomized controlled trials,” was presented at ECO 2022.