Of 3115 people screened by telephone, 244 overweight adults met participation criteria and were assigned to the vegan (n = 122) or control (n = 122) groups. The analysis included 223 (91.0%) completers.

Self-reported energy intake was reduced in both groups, more in the vegan group (effect size: −367.6 kcal/day [95% CI −536.8 to −198.5]; p < 0.001). The macronutrient content did not change significantly in the control group, while the vegan group participants increased their intake of carbohydrate (effect size: +22.5% of daily energy [95% +20.1 to +24.9]; p < 0.001) and fiber (effect size: +11.5 g/day [95% +8.1 to +14.8]; p < 0.001), and reduced consumption of fat (effect size: −18.0 % of daily energy [95% −20.1 to −15.8]; p < 0.001), protein (effect size: −4.7 % of daily energy [95% −6.1 to −3.4]; p < 0.001), and cholesterol (effect size: −215 mg/day [95% −261 to −169]; p < 0.001).

Body weight decreased in the vegan group (effect size: −5.9 kg [95% CI −6.7 to −5.0]; p < 0.001). The majority of the weight reduction was due to the reduction in fat mass (effect size: −4.1 kg [95% CI −4.7 to −3.5] kg; p < 0.001), and visceral fat (−209 cm3 [95% CI −304 to −114]; p < 0.001).

All three scores increased in the vegan group, compared with no change in the control group; the effect sizes were: PDI + 10.6 (95% CI +8.6 to +12.6; p < 0.001); hPDI +10.9 (95% CI +8.4 to +13.4; p < 0.001); and uPDI +5.4 (95% CI +3.4 to +7.4; p < 0.001). The change in all three scores significantly correlated with change in body weight, with PDI (r = −0.40; p < 0.001) and hPDI (r = −0.37; p < 0.001) having stronger correlations than uPDI (r = −0.21; p = 0.002).

The scores for fruits, vegetables, whole grains, and legumes increased significantly in the vegan group (Table 1), and changes were negatively associated with changes in body weight (Table 2). The consumption of all animal products decreased in the vegan group. Changes were positively associated with changes in body weight. The change in vegetable oil intake correlated positively with weight changes (r = +0.27; p < 0.001). A multiple linear regression model (r2 = 0.26; p < 0.001) showed that the following food components were independently associated with weight loss: whole grains (p = 0.006) and legumes (p = 0.007) showed a negative association, while meat (p < 0.001), vegetable oils (p = 0.006), and sweets (p = 0.01) showed a positive association. The R-squared is about 0.26 for this model.