Low-fat vegan diet improves blood sugar and liver fat without calorie counting, trial finds

A small 16-week trial found that adults with type 2 diabetes improved glucose control and reduced body, liver and visceral fat after switching to a low-fat vegan diet while eating until satisfied.

A small clinical trial has found that a low-fat vegan diet may help people with type 2 diabetes improve blood sugar control, reduce liver fat and lower skin markers linked with ageing, even when participants were told simply to eat until satisfied rather than cut calories.

The research, published in BMJ Open Diabetes Research & Care and led by Hana Kahleova at the Physicians Committee for Responsible Medicine with collaborators at Yale School of Medicine, followed 25 adults for 16 weeks. Most participants completed the study. They were asked to follow a diet built around vegetables, grains, legumes and fruit, while avoiding animal products and added fats. The plan did not require calorie counting, and participants were told to keep their exercise routines unchanged.

Despite the absence of formal calorie restriction, the group reported eating fewer calories and losing weight. On average, they shed around 6 kilograms, with notable reductions in body fat, visceral fat and liver fat. Their intake of fibre rose sharply, while saturated fat consumption fell. Some lean mass was also lost, a reminder, the researchers said, that longer studies will need to examine how best to preserve muscle during weight loss.

The metabolic changes were just as striking. Average fasting glucose and HbA1c both fell, with HbA1c dropping from 7.6% to 6.6%, below the usual target of 7% for many adults with diabetes. Fasting insulin and LDL, or “bad”, cholesterol also declined. Beta-cell function appeared to improve, suggesting the pancreas may have become better able to respond to rising glucose levels. At the same time, HDL cholesterol fell, and triglycerides were broadly unchanged.

The trial also measured advanced glycation end products, or AGEs, compounds formed when sugars bind to proteins or fats and which have been linked to tissue damage and ageing. Skin AGE scores fell over the course of the study, adding to evidence that the diet may influence more than just weight and glucose. According to the authors, the results suggest that changing the composition of the diet, rather than simply shrinking portion sizes, may help ease several of the metabolic burdens associated with type 2 diabetes.

The findings build on earlier research. A 99-person randomised trial published in Diabetes Care found that a low-fat vegan diet improved HbA1c and body weight more than a diet based on American Diabetes Association guidance. Another long-term comparison, tracked over 74 weeks and indexed in PubMed, reported that both a vegan diet and a conventional diabetes diet led to weight loss and better blood lipid levels, but the vegan plan produced larger gains in glycaemic control and lipids. A separate analysis of adherence found that the vegan diet was broadly as acceptable as the conventional approach, despite producing larger shifts in macronutrient intake.

Taken together, the evidence suggests that a low-fat plant-based diet could offer a practical option for some people with type 2 diabetes, particularly those looking for a less restrictive alternative to calorie counting. The latest trial was small and short, so it does not settle the question on its own, but it adds to a growing body of research indicating that what people eat may matter as much as how much they eat.