The Barnard Low-Fat Vegan vs. Mediterranean Diet Study

Original Study

Barnard ND, Alwarith J, Rembert E, et al. A Mediterranean Diet and Low-Fat Vegan Diet to Improve Body Weight and Cardiometabolic Risk Factors: A Randomized, Cross-over Trial. Journal of the American Nutrition Association. 2022;41(2):127–139.

Links to This Study

• PubMed record
  The U.S. National Library of Medicine’s record for the study, including the abstract, citation information, and links to other versions.
• DOI — permanent study identifier
  The DOI is the study’s permanent digital identifier and should continue to direct readers to the official article even if the journal’s web address changes.
• Official journal/publisher page
  The study’s page on the journal publisher’s website. Availability of the complete article may depend on the publisher’s current access policy.

What Did the Researchers Study?

Researchers directly compared a low-fat vegan diet with a Mediterranean diet in 62 adults with overweight. Participants were randomly assigned to start with one of the two diets, followed it for 16 weeks, returned to their usual diets for four weeks, and then followed the other diet for another 16 weeks.

Because this was a crossover trial, the same participants experienced both eating patterns. Researchers measured body weight, body composition, cholesterol, blood pressure, and several measures related to insulin sensitivity.

What Were the Two Diets?

The low-fat vegan diet eliminated animal products and emphasized vegetables, fruits, whole grains, and legumes. Added oils, nuts, nut butters, seeds, and certain other high-fat plant foods were limited.

The Mediterranean diet emphasized vegetables, fruits, legumes, whole grains, fish, low-fat dairy products, and extra-virgin olive oil while limiting red and processed meats and foods high in saturated fat.

Neither diet required participants to count calories or deliberately restrict portion sizes.

What Did They Find?

During the low-fat vegan diet, participants lost an average of about 6 kilograms, or roughly 13 pounds. Average body weight did not significantly change during the Mediterranean-diet period.

Total cholesterol and LDL cholesterol decreased more on the vegan diet. Some measures of insulin sensitivity also improved more during the vegan intervention.

What About Blood Pressure?

Blood pressure decreased during both dietary periods. The reduction in systolic blood pressure was larger during the Mediterranean diet than during the vegan diet.

This is an important reminder that two healthful dietary patterns can affect different health measurements differently.

Why Is This Study Especially Interesting?

This was not a comparison between a carefully planned diet and an obviously poor diet. Both the Mediterranean diet and the low-fat vegan diet are widely regarded as health-promoting dietary patterns.

That makes the head-to-head comparison particularly useful. Rather than asking whether healthy eating is better than an unhealthy usual diet, the study asked whether these two substantially different healthy dietary patterns produced different effects in the same participants.

Why Use a Crossover Trial?

In a crossover trial, participants receive both interventions at different times. In this study, each person eventually followed both the Mediterranean and vegan diets.

This allows researchers to compare each participant partly with himself or herself, reducing some of the variability caused by differences among people.

An Important Limitation

The study included only 62 adults and each dietary period lasted 16 weeks, so it cannot tell us what would happen after following either diet for many years.

Participants also knew which diet they were following, which is unavoidable when comparing visibly different eating patterns. As with most dietary trials, long-term adherence outside a research setting may differ from adherence during a study.

Funding and Author Information

Several authors were affiliated with the Physicians Committee for Responsible Medicine (PCRM), an organization that promotes plant-based diets. The published article should be consulted for the complete funding and conflict-of-interest disclosures.

Affiliations and funding do not by themselves determine whether research findings are valid, but they are useful information to consider when evaluating any study.