Animal vs. Plant-Based Processed Foods Have Different Effects on Body Weight: A Secondary Analysis of a Randomized, Cross-Over Trial

Mediterranean and vegan diets have been extensively studied for their health effects. This secondary analysis assessed the role of animal vs. plant-based processed foods. We hypothesized that increased intake of minimally processed plant foods and reduced intake of animal foods, particularly processed and ultra-processed categories, would be associated with lower body weight. In this randomized cross-over trial, 62 overweight adults were randomized to a Mediterranean or a low-fat vegan diet for 16-weeks, separated by a 4-week washout. Body weight was the primary outcome. Three-day diet records were used to assess intake of animal and plant-based foods by degree of processing using the NOVA system, ranging from minimally processed foods to ultra-processed products. Compared with the Mediterranean intervention, participants experienced greater reductions from baseline in minimally processed animal foods during the vegan intervention (p<0.001) and greater increases in minimally processed plant foods (p=0.003). Processed animal and plant-based foods decreased on the vegan diet, compared with the Mediterranean diet (p<0.001; and p=0.005, respectively). In the first 16 weeks, across both diets, changes in processed and ultra-processed animal foods were nominally associated with increases in body weight (r=+0.30, p=0.02; and r=+0.36, p=0.004, respectively), though neither survived Bonferroni correction for multiple comparisons. In the second 16 weeks, an increase in minimally processed animal foods was associated with weight gain (r=+0.42, p=0.002), the only correlation to survive correction, while a nominal, non-surviving inverse association was observed for minimally processed plant-based foods (r=-0.35, p=0.01). These findings suggest that in the context of the Mediterranean and a vegan diet, increasing the consumption of minimally processed plant-based foods, while minimizing the consumption of minimally processed, processed, and ultra-processed animal foods, were associated with favorable weight-related outcomes within this exploratory secondary analysis in overweight adults.