Objective: The aim was to identify changes in food, nutrient intake, and diet quality on a low-fat vegan diet and associations with changes in body weight and body composition.
Methods: Overweight adults (n=244) were randomly assigned to follow a low-fat vegan diet (n=122) or make no diet changes (n=122) . Main outcome measures were changes in food intake, macro- and micronutrient intake, and dietary quality as measured by AHEI-2010, analyzed from 3-day diet records, and associations with changes in body weight and body composition. A repeated measure analysis of variance (ANOVA) model, Spearman correlations, and linear regression were used for statistical analysis.
Results: The intervention group’s AHEI-20increased by 6.0 points on average in contrast to no significant change in the control group (treatment effect +7.2 [95% CI +3.7 to +10.7]; p<0.001) . Increase in AHEI-20correlated with reduction in body weight (r=0.14; p=0.04) , fat mass (r=-0.14; p=0.03) , and HOMA-IR (r=-0.17; p=0.02) , after adjustment for changes in energy intake. Fruit, vegetable, legume, meat alternative, and whole grain intake significantly increased in the intervention group. Intake of meat, fish and poultry; dairy products; eggs; nuts and seeds; and added fats decreased. Decreased weight was most strongly associated with increased intake of legumes (r=‑0.38; p<.0001) and decreased intake of total meat, fish, and poultry (r=+0.43;p<.0001) . Reduced fat intake was associated with reduced body weight (r=+0.15; p=0.02) and, after adjustment for changes in BMI and energy intake, with reduced fat mass (r=+0.14; p=0.04) .
Conclusions: Diet quality as measured by AHEI-20improved on the low-fat vegan diet, which was associated with improvements in weight and metabolic outcomes. Increased legume intake was the strongest single food group predictor of weight loss.