Plant-based proteins may help with weight loss in postmenopausal women.A secondary analysis shows that replacing animal protein with plant protein is associated with decreased body weight, independent of changes in energy intake, in postmenopausal women.
Compared with the control group, the vegan group had greater reductions in body weight (–3.6 kg vs –0.24 kg; effect size [ES], −3.4 kg; p<0.001) and in total (–4.7 vs –2.2; ES, –2.4; p=0.003) and moderate-to-severe hot flashes (–4.4 vs –1.5; ES, –2.9; p<0.001) at week 12.
The reduced animal protein consumption in the vegan group (–23.33 g/day; p<0.001) corresponded to an increase in plant protein intake (+22.13 g/day; p<0.001). The control group had no changes. [Menopause 2026;doi:10.1097/GME.0000000000002813]
The change in animal protein consumption correlated positively with changes in BMI (r, 0.59; p<0.001), while the change in plant protein intake yielded a negative association (r, −0.51; p<0.001). “BMI dropped as animal protein was replaced by plant protein,” the researchers said.
The associations remained significant even after adjusting for changes in energy intake (r, 0.53; p<0.001 for animal protein; r, −0.54; p<0.001 for plant protein). Linear regression analyses showed significant graded associations between changes in protein intake and in body weight.
A weight loss of 1 kg 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).
In the energy-adjusted models, each 10 g/day reduction in animal protein consumption was associated with a 0.61 kg decrease in body weight (p<0.001). Conversely, increases in plant protein consumption were inversely associated with changes in body weight, indicating that higher plant protein consumption correlated with greater weight reduction, the researchers noted.
“These associations remained statistically significant after additional adjustment for age, and age was not an independent predictor of weight change (p=0.59). These findings demonstrate consistent dose-response relationships between protein subtype changes and weight outcomes independent of total caloric intake,” they explained.
The effect of methionine
Daily methionine intake decreased in the vegan group by 0.37 g; there was no change in the control group (ES, −0.41 g/day; p=0.002). This reduction correlated with BMI changes (r, 0.62; p<0.001), even after adjusting for changes in energy intake (r, 0.29; p=0.03). A 1-kg weight loss correlated with a decrease in methionine by 0.52 g/day (p=0.007).
“Limiting sulphur-containing amino acids, such as methionine, results in measurable metabolic changes at the biomarker and tissue level,” the researchers said. “[T]hese findings support the concept that reducing sulphur-containing amino acids, such as methionine, can trigger meaningful metabolic responses in humans.”
However, the researchers noted that the changes in methionine intake were observed alongside shifts in protein source. Given the multiple comparisons and the secondary nature of this analysis, these results should thus be deemed exploratory.
Soy is key
Postmenopausal vasomotor symptoms are distressing complications of menopause that are usually worsened by weight gain and metabolic changes associated with declining oestrogen levels. [BJOG 2017;124:1514-1523; Menopause 2023;30:80-87; Menopause 2021;28:1150-1156]
“Managing body weight has been shown to reduce the frequency and severity of vasomotor symptoms. Plant-based diets rich in soy offer dual benefits, supporting weight loss and alleviating vasomotor symptoms,” the researchers said.
This analysis comprised 84 postmenopausal women who had at least two moderate-to-severe hot flashes per day. They were randomized in a 1:1 ratio. They were instructed to either follow a low-fat vegan diet and incorporate a daily serving of half a cup (86 g) of cooked whole soybeans or make no dietary changes at all. Assessments were conducted at weeks 0 and 12.
Takeaways
“[Taken together,] postmenopausal women who replaced animal protein with plant protein in the context of a low-fat vegan diet supplemented with soybeans experienced a significant weight loss along with reductions in vasomotor symptoms,” the investigators said.
Reductions in methionine were also associated with weight loss, independent of energy intake, they added.
However, dietary intake was self-reported, the study was not designed to evaluate underlying biological mechanisms, and the study duration was not long enough to establish long-term sustainability.
“[Nonetheless,] these findings suggest that protein quality may be one of the mechanisms by which plant-based dietary patterns lead to weight loss in postmenopausal women,” the researchers said.