Plant-based diet, whether ‘healthy’ or ‘unhealthy’, linked to weight loss

Switching to a plant-based diet leads to weight loss in overweight individuals. That’s according to a new study carried out by the Physicians Committee for Responsible Medicine, published in the European Journal of Clinical Nutrition. And the advantages don’t end there, with findings also showing a plant-based diet lowers cholesterol and fat consumption, and boosts fibre intake.

Many will not be surprised by the initial results of this study, as a plant-based diet typically incorporates nuts, beans and pulses as replacements for meat products. Many will also have seen the Netflix documentary, You Are What You Eat, in which twins were put on separate diets, one following a vegan diet and the other following an omnivorous diet. The results were conclusive, with the leader of the study, director of nutrition studies at the Stanford Prevention Research Center, Christopher D. Gardner, noting “the twins on the vegan diet had a 10% to 15% drop in cholesterol, a 25% drop in insulin, and a 3% drop in body weight in just eight weeks”.

However, perhaps more surprising, was the fact the positive results of the study by the Physicians Committee for Responsible Medicine, were achieved across all participants, regardless of whether the plant-based items consumed were considered to be ‘healthy’ or ‘unhealthy’ on the plant-based diet index.

What is the plant-based diet index?​The PDI is a scoring system, which rates plant-based foods, giving the consumer an understanding of its health benefits. Ingredients and products deemed to be healthful, such as fruits, vegetables, whole grains and nuts are listed on the healthy plant-based diet index (hPDI). Similarly, ingredients and products, deemed to be unhealthful, such as refined grains, sugar and processed foods​ are listed on the unhealthy plant-based diet index (uPDI).

“Our research regularly shows that overweight people can lose a significant amount of weight on a plant-based diet, and the weight loss often comes with other health improvements including improved insulin sensitivity and lowered cholesterol. Our research also shows that a plant-based diet can help maintain weight loss. And compared to costly popular weight-loss drugs, a plant-based diet comes with only good side effects and can help save money.” says study co-author Hana Kahleova, MD, PhD, director of clinical research at the Physicians Committee for Responsible Medicine. She continues “We are currently working on a couple research studies, which will continue to look at the nutrient benefits of a plant-based diet.”

The rising problem of obesity​

According to the World Health Organization (WHO), worldwide obesity has nearly tripled since 1975. In 2016, more than 1.9 billion adults (18 years and over), were overweight. Of these, over 650 million were classified as obese. Those figures amount to 39% of the global adult population being classified as overweight and 13% classified as obese.

This increase is attributed to an increased intake of energy-dense foods that are high in fat and sugars combined with a decrease in physical activity due to the increasingly sedentary nature of many forms of work, changing modes of transportation, and increasing urbanisation.

“A shift in diets is central to tackling obesity and climate change”, according to Eric Lambin, a member of the European Commission’s Group of Chief Scientific Advisors.

How was the study conducted?​The study analysed 244 overweight adults (223 of participants completed the study). According to the WHO, overweight and obese are defined as abnormal or excessive fat accumulation that presents a risk to health. A body mass index (BMI) over 25 is considered overweight, and over 30 is obese.

Each individual involved in the study was randomly assigned to a group, with half entering a vegan group, following a low-fat vegan diet, and the other half entering a control group, making no changes to their diet. Calorie intake was not limited for either group and neither group was given diet quality instructions. The study was conducted over a period of 16 weeks, during which, each participant completed a three-day dietary record (two weekdays and one weekend day). These were then analysed by a registered dietitian to calculate the PDI, hPDI, and uPDI. Following that, ANOVA (Analysis of variance) was used by a statistician, who did not have access to details on dietary interventions. Pearson correlation was then used to evaluate the magnitude and significance of the association between the changes in body weight and changes in all three indices and their individual food components.

Results​In the analysis, all three scores increased for participants following a vegan diet, which was significantly associated with an average weight loss of about 13 pounds, due primarily to the reduction in fat mass and visceral fat. Increased consumption of whole grains and legumes and reduced consumption of meat, vegetable oil, and sweets in the vegan group was associated with weight loss. By contrast, there was no change in scores in the control group.

When asked what impact these results could have, Dr Kahleova concluded, “This analysis and our other research—which shows a plant-based diet is beneficial for weight loss, type 2 diabetes, and heart disease—provides the government the evidence they need to advise people to avoid animal products and choose a plant-based diet as the best diet for overall good health.”

Source: Does diet quality matter? A secondary analysis of a randomized clinical trial
Published online: 28 November 2023
DOI: https://www.nature.com/articles/s41430-023-01371-y​
Authors: Hana Kahleova, Haley Brennan, Tatiana Znayenko-Miller, Richard Holubkov, Neal D. Barnard