For the 16-week trial, scientists randomly assigned participants to a vegan diet or a Mediterranean diet in a 1:1 ratio. All participants were overweight and did not have a history of diabetes.
Half of the participants began with a low-fat vegan diet that saw them eat vegetables, fruits, legumes and whole grains. The other half began the trial with the Mediterranean diet. That means they consumed the same foods as the vegan diet, but they also ate fish, extra virgin olive oil and dairy while restricting their consumption of red meat and saturated fats, or skipping them altogether.
There were no calorie restrictions in either group. Participants did not alter their medication or exercise regimens unless told by their doctors. The crossover design also meant that the participants returned to their baseline diets for four weeks outside the initial 16-week trial period before shifting to the other group for another 16 weeks.
Results showed that participants lost an average of 13 pounds while those who were on the Mediterranean diet had no change in average weight loss. More fat mass was lost on the vegan diet, too — an average of 7.5 pounds.
But there wasn’t only a difference on the scale. Participants had reduced total and LDL cholesterol levels by 0.187 grams per liter and 0.153 grams per liter, respectively. Much like the weight loss results, there were no noticeable shifts in cholesterol on the Mediterranean diet.
Still, the Mediterranean diet won when it came to lowering blood pressure. While both diets led to a decrease in levels, blood pressure dropped 6.0 mm Hg on the Mediterranean diet while it decreased 3.2 mmHg on the vegan diet.
“While many people think of the Mediterranean diet as one of the best ways to lose weight, the diet actually crashed and burned when we put it to the test,” study author Dr. Neal Barnard, president of the Physicians Committee said in a statement. “In a randomized, controlled trial, the Mediterranean diet caused no weight loss at all. The problem seems to be the inclusion of fatty fish, dairy products, and oils. In contrast, a low-fat vegan diet caused significant and consistent weight loss.”
Added Kahleova, “if your goal is to lose weight or get healthy in 2021, choosing a plant-based diet is a great way to achieve your resolution.”