Mediterranean diet “crashes and burns” against veganism for weight loss, say PCRN researchers

09 Feb 2021 --- A low-fat vegan diet is more effective in producing weight loss than a Mediterranean diet. This is according to a study from the US-based nonprofit Physicians Committee for Responsible Nutrition (PCRN), which aims to “save and improve human and animal lives through plant-based diets.” 

“Because the Mediterranean diet is often touted for weight loss, it was surprising to see that participants experienced minimal changes – if any at all – when it came to their weight on this diet,” Hana Kahleova, director of clinical research at PCRN, tells NutritionInsight.

PCRN says the findings are “groundbreaking” and is now petitioning the US government to implement agricultural reforms that would promote plant-based diets in the name of public and environmental health. 

The study, now published in the Journal of the American College of Nutrition, pitted a Mediterranean diet against a low-fat vegan diet in 62 overweight participants for 16 weeks. 

Kahleova states the findings showed that the plant-based diet had better weight, body composition, insulin sensitivity and cholesterol levels than a Mediterranean diet. 

“While many people think of the Mediterranean diet as one of the best ways to lose weight, the diet crashed and burned when we put it to the test,” says study author and PCRN president Neal Barnard. 

Following the vegan diet for 16 weeks resulted in an average weight loss of 6 kg.Challenging two diet regimens
The study was conducted in 2019 and enrolled participants with a body mass index (BMI) between 28 and 40 kg per m2. 

Those following the Mediterranean diet consumed over two servings of vegetables and fruits per day, three or more weekly servings of legumes, fish or shellfish, and an equal number of weekly servings of nuts or seeds. 

They were also to select white meats (with visible fat removed) instead of red meats and replace any fats with extra virgin olive oil. 

Those following the low-fat vegan diet consumed 75 percent of their energy from carbohydrates,15 percent from protein and 10 percent from fat. 

Meals consisted of vegetables, grains, legumes and fruits. Participants avoided all animal products and added fats. 

No limit was placed on consumption, and exercise habits were not changed. Each participant filled in a dietary record at baseline and after 16 weeks. 

Mediterranean diet “crashed and burned”
No significant weight loss was found in participants following the Mediterranean diet, whereas those following the plant-based regimen lost an average of 6 kg. 

Kahleova comments that the team at PCRN was not surprised to find the significant weight loss affected by veganism. 

“Based on previous clinical trials and epidemiological studies – which show that people eating plant-based diets tend to have lower body weights – we were not surprised to see the benefits associated with the plant-based diet.”

“Previous studies have also shown that people eating plant-based diets experience fewer cardiometabolic risk factors, compared with those following other dietary patterns. So, we expected to see benefits in cholesterol control and insulin sensitivity on the plant-based diet.”

The Mediterranean diet proved to have no impact on weight loss during the study.The reason for the Mediterranean diet producing such surprisingly insignificant results could be explained by confounding variables in previous studies, says Kahleova. 

“We were aware that previous clinical trials that have shown significant weight loss on the Mediterranean diet included either added exercise or calorie restriction, confounding the effects of the dietary change. Our trial tested each diet without these additional factors.”

Future investigations 
The findings are not without their limitations, notes Kahleova. In particular, a lack of control over participants’ diets resulted from the self-report design. 

“Although self-reported overall adherence to both diets was high, it was not possible to completely eliminate uncertainty regarding participants’ adherence.” 

“However, it is reassuring that changes in weight and health markers paralleled the reported diet changes.”

Moreover, the study’s length did not allow for observations into the long-term metabolic effects of either diet, she remarks. 

Calling for change 
Following publication of the findings, the PCRM yesterday launched a call on the new US administration to begin changing the country’s agricultural and consumer behavior. 

In a petition entitled “Tackling the Climate Crisis at Home and Abroad,” the PCRN is asking the government to address public health issues and associated environmental concerns in a three-step process. 

First, it asks that subsidies are shifted from meat and dairy products to fruits, vegetables, grains and beans meant for human consumption. 

Second, for the Secretary of Agriculture and the Secretary of Health and Human Services is asked to include the climate benefits of a plant-based diet in nutrition policy, including the 2025-2030 Dietary Guidelines for Americans.

Third, the Secretary of Agriculture should propose a plan to include plant-based meals in the National School Lunch Program (NSLP) and monitor the US Department of Agriculture commodity foods' climate impact, including meat and dairy products, used in the NSLP and other federal food programs.

By Louis Gore-Langton