Hana Kahleova, MD, PhD, on the Health Benefits of a Low-Fat Vegan Diet

While it is well known that adults with overweight or obesity are at higher risk for a range of major health problems, debate among the medical community as to which dietary intervention is best for these individuals remains.

In a recent study, researchers investigated the impact of a low-fat vegan diet on adults with overweight. The research team conducted a randomized clinical trial that examined body weight, insulin resistance, postprandial metabolism, and intramyocellular and hepatocellular lipid levels to better understand the effect this dietary intervention may have.

Lead study author Hana Kahleova, MD, PhD, is the director of clinical research for the Physicians Committee for Responsible Medicine in Washington DC. Dr Kahleova answered our questions about the study findings and their clinical implications.

Nutrition411: Your study examined various associations of a low-fat vegan diet in adults with overweight. What prompted this study, and why did you decide to focus on this specific diet?

Hana Kahleova: Many previous studies have shown how effective plant-based diets can be for weight loss, so we decided to build on this data by looking into the mechanisms of how this weight loss occurs. In our study, we asked participants to begin eating a low-fat, plant-based diet, which meant they eliminated all animal products; focused their diets on fruits, vegetables, whole grains and legumes; and limited oils and other high-fat foods. We decided to look at metabolism because weight management is more challenging when our metabolism slows down as we age. Our study shows that we can turn this around. Switching to a plant-based diet increased postprandial metabolism by 18.7%. Getting rid of extra calories in the form of heat may be a great tool for long-term weight management.

N411: The results of the study showed that the vegan diet group had decreased body weight, insulin resistance, hepatocellular lipids, and intramyocellular lipid levels. What does this finding mean for how physicians might consider weight loss options for this patient population in the future?

HK: About 160 million US adults currently struggle with overweight and obesity. Over the course of years and decades, burning more calories after every meal can make a significant difference in weight management, and we hope that physicians will consider this when talking with their patients about their health goals.

N411: Based on what is currently known about the impact of a low-fat vegan diet, could you discuss some of the long-term effects of this dietary intervention?

HK: During the study, it was great to see how powerful simple diet changes can be in a relatively short period of time. But eating a plant-based diet not only helps with weight loss and health improvements in the short term, but it also helps reduce long-term risk for other health problems. People who eat a plant-based diet have a lower risk of dying from heart disease compared with non-vegetarians.

Plant-based diets have been proven to improve cholesterol and lower blood pressure. Plant-based diets have also been proven to benefit type 2 diabetes over the long term, including improving insulin function and increasing the ability of β-cells to regulate glucose, which helps improve symptoms associated with type 2 diabetes. Avoiding animal products and high-fat foods and eating high-fiber plant-based foods has also been associated with a reduced risk for developing certain types of cancer.

N411: How does a low-fat vegan diet compare with other dietary interventions that provide health benefits in overweight patients?

HK: A plant-based diet not only helps with weight loss, but all of the other “side effects” are good ones. Cardiovascular risk factors improve, diabetes often improves, and people often report feeling more energized. Unlike other dietary approaches, a plant-based diet does not require calorie counting, carbohydrate counting, or limiting portions. It can be a simple, accessible, and easy-to-follow approach. In our study, we asked participants to focus on fruits, vegetables, grains, and legumes and to eat as much as they wanted until they felt full. These foods are not only accessible, but they’re also very affordable.

N411: How do you hope the results of this research impacts clinical practice?

HK: Poor diet is now the leading risk factor for early death worldwide. Our study shows that simple diet changes can have an enormous impact on improving people’s health. We hope that clinicians will consider these results when talking with their patients about their health.  

Another important aspect of the study that we hope will impact clinical practice is that the plant-based group reduced liver fat by 34%. Fatty liver disease is a common condition and increases the risk of metabolic syndrome, diabetes, and cardiovascular disease. Currently, there is no causal treatment for this condition, and diet continues to be the main recommendation. A reduction in liver fat by 34% in 16 weeks is an important finding and shows that a plant-based diet may be an effective treatment option. 

Reference:

Kahleova H, Petersen KF, Shulman GI, et al. Effect of a low-fat vegan diet on body weight, insulin sensitivity, postprandial metabolism, and intramyocellular and hepatocellular lipid levels in overweight adults. JAMA Netw Open. 2020;3(11):2025454. doi:10.1001/jamanetworkopen.2020.25454