Animal vs plant-based processed foods have different effects on body weight: a secondary analysis of a randomized,...

Mediterranean and vegan diets have been extensively studied for health effects. This secondary analysis assessed animal vs plant-based processed foods. We hypothesized that greater intake of minimally processed plant foods and lower intake of animal foods, particularly processed and ultraprocessed, would be associated with lower body weight. In this randomized crossover trial, 62 overweight adults were randomized to a Mediterranean or low-fat vegan diet for 16 weeks, separated by a 4-week washout. Body weight was the primary outcome. Three-day diet records assessed intake of animal- and plant-based foods by NOVA processing category. Compared with the Mediterranean diet, the vegan diet produced greater reductions in minimally processed animal foods (P < .001) and greater increases in minimally processed plant foods (P = .003). Processed animal- and plant-based foods decreased on the vegan diet versus the Mediterranean diet (P <.001 and P = .005, respectively). In the first 16 weeks, changes in processed and ultraprocessed animal foods were nominally associated with weight gain (r = +0.30, P = .02; r = +0.36, P = .004), though neither survived Bonferroni correction. In the second 16 weeks, an increase in minimally processed animal foods was associated with weight gain (r = +0.42, P = .002), the only correlation surviving correction; a nominal inverse association emerged for minimally processed plant foods (r = -0.35, P = .01). In this exploratory analysis, increasing minimally processed plant foods while minimizing animal foods at all processing levels was associated with favorable weight outcomes. Trial registration: ClinicalTrials.gov, NCT03698955.