“Eating acid-producing foods like meat, eggs, and dairy can increase the dietary acid load, or the amount of acids consumed, causing inflammation linked to weight gain,” says Hana Kahleova, MD, PhD, director of clinical research at the Physicians Committee and lead author of the study. “But replacing animal products with plant-based foods like leafy greens, berries, and legumes can help promote weight loss and create a healthy gut microbiome.”

This new research included 62 overweight adults who were randomized to a Mediterranean or a low-fat vegan diet for 16 weeks, separated by a four-week cleansing period, followed by an additional 16 weeks on the alternate diet.

Participants’ dietary records were used to calculate dietary acid load, which is commonly estimated by two scores: Potential Renal Acid Load (PRAL) and Net Endogenous Acid Production (NEAP). A higher score indicates a higher dietary acid load.

Animal products including meat, fish, eggs, and cheese cause the body to produce more acid, increasing dietary acid load, which is linked to chronic inflammation that disrupts metabolism and can lead to increased body weight. Plant-based diets, which are more alkaline, are associated with weight loss, improved insulin sensitivity, and lower blood pressure.

In the new analysis, both PRAL and NEAP scores decreased significantly on the vegan diet, with no significant change on the Mediterranean diet. The reduction in dietary acid load was associated with weight loss, and this association remained significant even after adjustment for changes in energy intake. Body weight was reduced by 13.2 pounds on the vegan diet, compared with no change on the Mediterranean diet.

The authors say that a vegan diet’s alkalizing effect, which increases the body’s pH level to make it less acidic, may also help promote weight loss. Top alkalizing foods include vegetables, particularly leafy greens, broccoli, beets, asparagus, garlic, carrots, and cabbage; fruits, such as berries, apples, cherries, apricots, or cantaloupe; legumes, for example lentils, chickpeas, peas, beans or soy; and grains, such as quinoa or millet.

Founded in 1985, the Physicians Committee for Responsible Medicine is a nonprofit organization that promotes preventive medicine, conducts clinical research, and encourages higher standards for ethics and effectiveness in education and research.