Study challenges report that Mediterranean is best overall diet

February 16, 2021

4 min read


Disclosures:
Barnard reports receiving royalties and honoraria from books, articles and lectures related to nutrition and health. Please see the study for all other authors’ relevant financial disclosures.

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U.S. News & World Report recently named Mediterranean the best overall diet. However, a study has found that a vegan diet improved lipid concentrations, body weight and insulin sensitivity better than the Mediterranean diet.

However, the study also showed that the Mediterranean diet was associated with greater reductions in BP, according to researchers.

“Previous studies have not yet compared the [Mediterranean and vegan] diets head-to-head,” Hana Kahleova, MD, PhD, director of clinical research at the Physicians Committee for Responsible Medicine, a nonprofit organization that promotes plant-based diet and research, told Healio Primary Care. “Our goal was to test the diets in one trial to see which diet is more effective.”

Hana Kahleova

In their randomized crossover trial, Kahleova and colleagues assigned 62 middle-aged adults with a BMI ranging from about 30 kg/m2 to 37 kg/m2 to follow a Mediterranean or vegan diet for 16 weeks. After participants had a variety of parameters measured, they returned to their baseline diets for 4 weeks, then followed the opposite diet for 16 weeks. The same parameters were measured again after a 10-hour fast coinciding with the end of the second 16-week period. Individuals with type 1 diabetes or substance use disorder and those who were pregnant or already on a vegan or Mediterranean diet were excluded.

Kahleova and colleagues wrote that “self-reported overall adherence to both diets was high.” Among the participants, 52 completed the study. The researchers found that the overall net weight changes after 16 weeks were 0 kg with the Mediterranean diet and –6 kg with the vegan diet (treatment effect [TE] = –6 kg; 95% CI, –7.5 to –4.5). The vegan diet was associated with a decrease in insulin resistance, measured by Homeostasis Model Assessment Insulin Reactivity (TE = –0.7; 95% CI, –1.8 to +0.4), and an increase in oral glucose insulin sensitivity (TE = +35.8 mL/min/m2; 95% CI, +13.2 to +58.3); however, the Mediterranean diet was not associated with significant changes in these parameters. Predicted insulin sensitivity did not change significantly in either group.

In addition, among all participants with no medication changes, the researchers reported that total cholesterol dropped 18.7 mg/dL and LDL-cholesterol decreased 15.3 mg/dL with the vegan diet, but there were no significant changes associated with the Mediterranean diet (TE = –15.6 mg/dL; 95% CI, –24.6 to –6.6). Systolic and diastolic BP decreased 9.3 mm/Hg and 7.3mm/Hg (TE = +5.9 mm Hg; 95% CI; +1 to +10.9] with the Mediterranean diet vs. 3.4 mmHg and 4.1 mm Hg with the vegan diet (TE = +1.8 mm/Hg; 95% CI, –4.6 to +8.1).

“We weren’t surprised to see that people saw improvements on the plant‐based diet,” Kahleova said. “Previous epidemiologic studies have shown that people eating plant‐based diets tend to have lower body weights and fewer cardiometabolic risk factors, compared with those following other dietary patterns.

“But because the Mediterranean diet is often touted for weight loss, it was surprising to see that participants in our trial didn’t lose any significant weight at all on this diet,” she continued. “However, previous clinical trials 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, which likely played a role in the results.”

Neal Barnard

Neal Barnard, MD, president of the Physicians Committee for Responsible Medicine and study coauthor, said in a press release that the Mediterranean diet “crashed and burned when we put it to the test” of serving as a weight loss tool.