Vegan Diet Helps Shed Pounds but Doesn't Dint Diabetes

Following a vegan diet for at least 3 months helped people with overweight or type 2 diabetes shed the pounds, but only had a marginal effect on HbA1c levels, on average, new research indicates.

No effect was seen on blood pressure, triglycerides, or the "good" high-density lipoprotein (HDL) cholesterol. HbA1c was reduced by a mean of –0.18 percentage points (P = .002), and there was a small reduction in total cholesterol and low-density lipoprotein (LDL) cholesterol, on average, across all the studies examined in this meta-analysis.

The work, which compared a number of trials looking at vegan diets versus "normal" eating or other kinds of weight loss diets, "indicates with reasonable certainty that adhering to a vegan diet for at least 12 weeks may result in clinically meaningful weight loss...[and] can be used in the management of overweight and type 2 diabetes," said Anne-Ditte Termannsen, PhD, who reported the findings during a press conference at the European Congress on Obesity (ECO) 2022, where the work was also presented as a poster.

A vegan diet most likely led to weight loss because it is "associated with a reduced calorie intake due to a lower content of fat and higher content of dietary fiber," added Termannsen, of the Steno Diabetes Center Copenhagen, Denmark.

Asked to comment, Janet Cade, PhD, who leads the Nutritional Epidemiology Group at the University of Leeds, UK, said the results are likely due to fewer calories in the vegan diet compared with the "control" diets. "Of course, a vegan diet can be healthier in a range of ways, such as higher fruit and vegetables, more fiber and antioxidants, however, the same would be true of a vegetarian diet," she noted.

And she warned that longer-term data are needed on health outcomes associated with vegan diets, noting, "there have been links to poorer bone health and osteoporosis in people consuming a vegan diet."

Gunter Kuhnle, PhD, professor of nutrition and food science, University of Reading, UK, told the UK Science Media Centre: "The authors conducted a systematic review of intervention studies and found that, compared with no dietary interventions, vegan diets showed the strongest association with body weight reduction."

However, "When comparing vegan diets with other dietary interventions — such as the Mediterranean diet — the association was much weaker," he noted.

Vegan, Habitual, or a Range of Weight Loss Diets

Termannsen and colleagues set out to look at the effect of a plant-based diet on cardiometabolic risk factors in people with overweight or type 2 diabetes. They searched the literature for randomized controlled trials with adult participants with overweight (BMI ≥ 25 kg/m²), prediabetes, or type 2 diabetes.

Participants followed a vegan diet that lasted at least 12 weeks; habitual diets without any changes or energy restriction; a Mediterranean diet; a host of different "diabetes" diets; a low-fat diet; or portion-controlled diets.

"The vegan diets were nearly all low-fat vegan diets but vary substantially regarding the protein, fat, carbohydrate content. All but one study was ad libitum fat, and there were no energy restrictions," Termannsen said.

Control diets were more varied. "Some continued their habitual diet, and about half were energy restricted and the others were not," she acknowledged.

Outcomes comprised body weight, BMI, HbA1c, systolic and diastolic blood pressure, total cholesterol, LDL-cholesterol, HDL-cholesterol, and triglycerides, which were assessed across studies.

A total of 11 trials were included in the meta-analysis, and studies were a mean duration of 19 weeks. A total of 796 participants were included.

Compared with control diets, those on vegan diets lost on average –4.1 kg (–9 lb) (P < .001), with a range of –5.9 kg to –2.4 kg.

BMI dropped by –1.38 kg/m² (P < .001). Total cholesterol dropped by –0.30 mmol/L (–11.6 mg/dL; P = .007) and LDL-cholesterol by –0.24 mmol/L (–9.28 mg/dL; P = .005).

Further analyses found even greater reductions in body weight and BMI when vegan diets were compared with continuing a normal diet without dietary changes, on average, at –7.4 kg (–16.3 lb) (P < .001) and –2.78 kg/m² (P < .001) respectively.

When compared with other intervention diets, however, body weight dropped by –2.7 kg (–6 lb; P < .001) and BMI by –0.87 kg/m² (P < .001).

Commenting on limitations of studies compared to the real world, Termannsen said: "Some studies reported high adherence to their diet, usually due to a high level of support, suggesting that providing continued face-to-face contact with participants may partly explain the adherence differences."

"This also questions the long-term feasibility of the diet and the applicability of this as long-term care," she added.

Following a vegan diet requires good planning to ensure adequate nutrition and avoid any deficiencies, she urged. "We need to remember that the menu plans in the studies were created by dietitians."

ECO 2022. Presented May 5, 2022. Poster no. PO4.26.

Termannsen and the authors have reported no relevant financial relationships.

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