Dietary Acid Load Across Vegans, Lacto-Ovo-Vegetarians, Fish-Eaters, and Meat-Eaters, and Its Association with Body Mass Index: A Secondary Analysis from an Italian Survey (The INVITA Study).

Diet represents a key determinant of the body's acid-base balance because foods are metabolized into non-volatile acids or bases. An increase in dietary acid load can elicit low-grade metabolic acidosis, which has been associated with systemic inflammation and the risk of adverse cardiometabolic conditions, including obesity. Potential renal acid load (PRAL) and Net Endogenous Acid Production (NEAP) represent the major markers of dietary acid load. The aim of this secondary analysis was to compare the acid load of four different diets and investigate its association with Body Mass Index (BMI) in a sample of the general population. In an online survey, the INVITA study, four dietary patterns (meat-eaters, fish-eaters, lacto-ovo-vegetarians, and vegans) were compared for their corresponding PRAL and NEAP values, and the associations of both parameters with BMI were evaluated. Multiple linear regression models were progressively adjusted for dietary pattern, energy intake, age, sex, physical activity, smoking status, and education level. The stepwise decrease in animal food consumption across the four dietary patterns was associated with a progressive reduction in dietary acid load, with vegan participants showing the lowest values. While PRAL did not prove consistently associated with BMI in this cohort, NEAP remained significantly associated with BMI even after full adjustment for lifestyle confounders (β = 0.032, p = 0.00013). However, because NEAP includes an anthropometric component based on body surface area, this association should be interpreted cautiously, as it may partly reflect mathematical coupling rather than a purely diet-derived effect. PRAL should be considered the more diet-specific marker, while NEAP represents a composite index combining dietary acid load and anthropometric scaling. Because PRAL and NEAP do not account for protein origin, future studies should assess whether diet-specific reference ranges could improve their comparisons for dietary patterns including mostly or exclusively plant protein.