Study Evaluates Impact of Dietary Acid Load on Weight Loss in Vegan and Mediterranean Diets

Dietary acid load (DAL) significantly decreased on a low-fat vegan diet and was linked with weight loss compared with a Mediterranean diet among participants in a randomized cross-over trial (NCT03698955) conducted by the Physicians Committee for Responsible Medicine. The findings, published in Frontiers in Nutrition, showed the alkalizing effect of a vegan diet in promoting weight loss.^1-3

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Effects of Dietary Acid Load

DAL refers to the body’s overall acid-base balance influenced by diet, and a high DAL has been previously linked with chronic low-grade metabolic acidosis, inflammation, and obesity. Foods like meat, fish, eggs, cheese, and some grains produce acid in the body, whereas most fruits and vegetables have an alkalizing effect. Alkaline diets, including vegan diets, are linked to health benefits such as weight loss, insulin sensitivity, and lower blood pressure.¹

Researchers use the Potential Renal Acid Load (PRAL) to estimate the effect of food on the pH balance, based on 5 nutrient values, including protein, phosphorus, potassium, magnesium, and calcium, along with the Net Endogenous Acid Production (NEAP) to further adjust for an individual’s height and weight to estimate DAL. To further assess how dietary patterns affect DAL, the researchers compared Mediterranean and low-fat vegan diets and whether the impact is connected to changes in body weight.^1,2

Mediterranean Diet vs Vegan Diet

A total of 62 individuals who were overweight were included in the trial and were randomly assigned to follow a Mediterranean or a low-fat vegan diet for 16 weeks, separated by a 4-week washout, before switching to the opposite diet. In the Mediterranean diet, individuals followed the PREDIMED protocol, which involves fruits, vegetables, legumes, nuts or seeds, fish or shellfish, and white meat over red meat, with the use of 50 g of extra virgin olive oil daily. For the low-fat vegan group, individuals consumed vegetables, grains, fruits, and legumes. Outcomes were measured at weeks 0, 16, 20, and 36 as individuals were instructed to complete a 3-day food diary.¹

The results demonstrated that PRAL and NEAP significantly decreased on the vegan diet (95% CI −35.4 to −18.7) compared with no change on the Mediterranean diet (95% CI −34.1 to −17.5). Additionally, body weight was reduced by 6.0 kg, or 13.2 pounds, on the vegan diet, compared with no change on the Mediterranean diet.¹

The findings suggest that over the initial 16 weeks of the study, a reduction in DAL measured by PRAl and NEAP was directly linked to reductions in body weight. This association weakened slightly when accounting for changes in calorie intake. In the subsequent 16 weeks, the positive association between a reduced DAL and weight loss became even stronger and remained significant even after adjusting for calorie intake.¹

“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,” Hana Kahleova, MD, PhD, director of clinical research at the Physicians Committee and lead author of the study, said in a news release. “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.”²

REFERENCES

1. Kahleova, H., Maracine, C., Himmelfarb, J., Jayaraman, A., Znayenko-Miller, T., Holubkov, R., & Barnard, N. D. (2025). Dietary acid load on the Mediterranean and a vegan diet: a secondary analysis of a randomized, cross-over trial. Frontiers in Nutrition, 12, Article 1634215. https://doi.org/10.3389/fnut.2025.1634215

2. Vegan diet improves dietary acid load, a key risk factor for diabetes, new study finds. EuerkAlert!. News release. June 26, 2025. Accessed July 1, 2025. https://www.eurekalert.org/news-releases/1088985

3. Low-Fat Vegan Diet Versus a Mediterranean Diet on Body Weight. ClinicalTrials.gov: NCT03698955. Updated September 27, 2024. Accessed July 1, 2025. https://clinicaltrials.gov/study/NCT03698955