Plant protein and body weight in postmenopausal women: a secondary analysis from a randomized clinical trial

Haley Brennan; Maya Bach; Richard Holubkov; Neal D Barnard; Hana Kahleova

doi:10.1097/GME.0000000000002813

Plant protein and body weight in postmenopausal women: a secondary analysis from a randomized clinical trial

Menopause. 2026 Jun 9. doi: 10.1097/GME.0000000000002813. Online ahead of print.

Authors

Haley Brennan¹, Maya Bach¹, Richard Holubkov², Neal D Barnard^{1

3}, Hana Kahleova¹

Affiliations

¹ Physicians Committee for Responsible Medicine, Washington, DC.
² School of Medicine, University of Utah, Salt Lake City, UT.
³ Adjunct faculty, George Washington University School of Medicine and Health Sciences, Washington, DC.

PMID: 42262494
DOI: 10.1097/GME.0000000000002813

Abstract

Objective: This secondary analysis evaluated whether changes in plant and animal protein intake were associated with changes in body weight among postmenopausal women participating in a 12-week randomized dietary intervention.

Methods: A secondary analysis of a 12-week randomized clinical trial compared the effects of a vegan diet supplemented with 86 g cooked soybeans (n=42) to a usual diet (n=42) in postmenopausal women. An analysis of 3-day diet records examined animal and plant protein intake as predictors of body weight changes. Effect size was defined as the between-group difference (vegan minus control) for the 12-week change.

Results: Total protein intake did not change in either group. Animal protein decreased in the vegan group by 23.3 g (95% confidence interval [CI]: -31.3 to -15.4), with no change in the control group; effect size: -24.5 g (95% CI: -33.9 to -15.1; P<0.001). Plant protein increased in the vegan group by 22.1 g (95% CI: 17.4 to 26.8), with no change in the control group; effect size: 23.8 g (95% CI: 16.3 to 31.3; P<0.001). Changes in animal protein correlated positively with changes in body mass index (r=0.59; P<0.001), while changes in plant protein correlated negatively with changes in body mass index (r=-0.51; P<0.001), even after adjustment for energy intake changes (r=0.53; P<0.001; and r=-0.54; P<0.001, respectively). A 1-kg of weight loss was associated with a reduction in animal protein intake by 16.2 g/day (P<0.001) and an increase in plant protein intake by 12.7 g/day (P<0.001). Methionine intake decreased in the vegan group by 0.37 g (95% CI: -0.56 to -0.18), with no change in the control group; effect size: -0.41 g (95% CI: -0.66 to -0.15; P=0.002).

Conclusions: Replacing animal protein with plant protein was associated with decreased body weight, independent of changes in energy intake. A dose-response relationship was observed between reducing animal protein intake and increasing plant protein consumption, and weight loss.

Keywords: Amino acids; Diet; Hot flashes; Menopause; Nutrition; Protein; Vegan; Weight.