Weight loss with vegan diet driven by insulin sensitivity increase, liver fat reduction
An increase in insulin sensitivity from a plant-based vegan diet led to a decrease in liver fat and a mean weight loss of 6.4 kg in a cohort of adults with overweight and obesity, according to findings published in JAMA Network Open.
“The study not only showed that a plant-based diet helps people lose weight, but it showed exactly how it happens and the health benefits that can result,” Hana Kahleova, MD, PhD, MBA, director of clinical research at the Physicians Committee for Responsible Medicine in Washington, D.C., told Healio. “After 16 weeks on a plant-based diet, participants increased their after-meal calorie burn by 18.7%, lowered their body weight, saw significant drops in visceral and liver fat by 34.4%, improved insulin sensitivity and lowered their cardiometabolic risk factors.”
Kahleova and colleagues conducted a single-center, open-label, parallel randomized clinical trial between 2017 and February 2019 in Washington D.C. Researchers enrolled 244 adults aged 25 to 75 years with a BMI between 28 kg/m2 and 40 kg/m2. Participants were randomly assigned to an intervention group featuring a low-fat vegan diet (n = 122; mean age, 53 years) or a control group that made no diet changes (n = 122; mean age, 57 years). The diet for the intervention group included vegetables, grains, legumes, and fruits without any added fat or animal products, and a daily supplement of 500 g of vitamin B12. The intervention cohort attended weekly classes where they received detailed instructions, printed materials and food samples and participated in cooking demonstrations. Individuals in both groups were limited to one alcoholic beverage per day for women and two for men. All participants were asked to maintain their normal exercise habits.
Measurements were performed on participants at baseline and 16 weeks. Researchers measured body weight, body composition, visceral fat and postprandial energy expenditure. Insulin resistance was measured through the homeostasis model assessment index, and insulin sensitivity was recorded through a predicted insulin sensitivity index. A subset of 44 participants also had hepatocellular and intramyocellular lipids quantified through proton magnetic resonance spectroscopy.
Plant-based diet reduces body weight
At 16 weeks’ of follow-up, the intervention group had a mean body weight decrease of 6.4 kg, whereas the control group had a mean decrease of 0.5 kg. The intervention cohort had a reduction in fasting plasma insulin concentration of 21.6 pmol/L, whereas no significant change was observed for controls. A decrease in insulin resistance (mean decrease = –1.3; 95% CI, –2.2 to –0.3; P < .001) and an increase in insulin sensitivity (mean increase = 0.9; 95% CI, 0.5-1.2; P < .001) were also observed for the intervention group, with no change observed in the control cohort.
Postprandial energy expenditure increased by 18.7% in the intervention group (95% CI, 4.4-22.3) with no significant change seen in controls. Results were similar after adjusting for age and ethnicity. In both groups, an increase in energy expenditure was correlated with a decrease in fat mass and an increase in insulin sensitivity.
Decrease in hepatocellular, intramyocellular lipids
In the lipid subgroup, hepatocellular lipids were generally in the normal range at baseline. At follow-up, intervention participants had a mean decrease of 34.4% in hepatocellular lipid content, with no change in controls. The decrease significantly correlated with a change in body weight. The intervention group also had a mean decrease in intramyocellular lipids of 10.4%. Decreases in intramyocellular lipids were correlated with a decrease in fat mass and insulin resistance.
“Fatty liver disease is a common condition and increases the risk of metabolic syndrome, diabetes and cardiovascular disease,” Kahleova said. “Yet, there is no causal treatment for this condition and diet continues to be the main recommendation. A reduction in liver fat by 34.4% in 16 weeks is an impressive finding and makes the plant-based diet one of the most effective treatment options.”
Kahleova said the findings show a plant-based diet can be an effective weight-loss treatment for adults with overweight or obesity, with changes taking place within a few months.
“It is fascinating how impressive results we can get in a relatively short period of time,” Kahleova said. “It takes years and decades to store all the fat in the liver, but substantial improvements are possible in a few months. And the same is true about our metabolism.”
Kahleova said future research should focus specifically on the effectiveness of a plant-based diet in a cohort of individuals with diabetes.
For more information:
Hana Kahleova, MD, PhD, MBA, can be reached at email@example.com.