Postmenopausal women seeking to lose weight may have an underappreciated tool in their arsenal, according to a new study.

Investigators found that greater reductions in animal protein intake and greater increases in plant protein intake were associated with enhanced weight loss. Women who switched from animal-based to plant-based protein sources lost significant weight, even though their total protein intake remained unchanged.

“Our findings suggest that clinicians should consider not only how much protein postmenopausal women consume but also where that protein comes from,” senior author Hana Kahleova, MD, PhD, director of clinical research at the Physicians Committee for Responsible Medicine, Washington, DC, told Medscape Medical News.

“Women don’t necessarily need to increase total protein intake. Rather, replacing animal protein with plant protein from foods such as beans, lentils, soy foods, and whole grains may help support a healthy body weight while providing additional cardiometabolic benefits.”

The findings were published as a brief report in Menopause.

Protein Type Understudied

Although clinicians often recommend that p ostmenopausal women increase protein intake to preserve muscle mass and counteract naturally occurring weight gain and metabolic changes, there is often little attention given to protein quality and source, Kahleova said.

Previous research has linked diets high in animal protein with greater adiposity and body weight, and those rich in plant protein with lower body weight. Amino acid composition may also influence metabolic outcomes, with lower circulating branched-chain amino acid levels linked to reductions in body fat and restriction of leucine, histidine, and methionine correlated with improvements in body composition.

To investigate whether women could maintain adequate protein intake on a plant-based diet, researchers conducted a secondary analysis of data from a previous 12-week randomized clinical trial of postmenopausal women who reported moderate-to-severe hot flashes and were not using hormonal medications.

Participants were randomly assigned to either a low-fat vegan diet with a daily serving of one-half cup cooked whole soybeans (n = 42; mean age, 53.2 years) or no dietary changes (n = 42; mean age, 55.2 years).

Dietary adherence was assessed at weeks 1 and 12 using 3-day food records. Researchers analyzed changes in animal and plant protein intake as predictors of changes in body weight.

Protein Quality Matters

Neither group had significant changes in total protein intake. However, animal protein consumption decreased in the vegan group by 23.3 g, with no change in the control group (effect size, -24.5 g; P < .001).

Plant protein consumption increased in the vegan group by 22.1 g, again with no change in the control group (effect size, 23.8 g; P < .001).

Changes in animal protein consumption correlated positively with changes in BMI (r = 0.59), whereas changes in plant protein consumption correlated negatively with changes in BMI (r = -0.51; P < .001). These associations remained significant even after adjustment for changes in energy intake.

Each shift of 16.2 g less animal protein and 12.7 g more plant protein per day was associated with 1 kg of weight loss. 

Methionine intake decreased by 0.37 g in the vegan group, with no comparable change in the control group (effect size, -0.41 g; P = .002).

“We found that replacing animal protein with plant protein was associated with greater weight loss, and these associations remained significant even after accounting for differences in calorie intake,” Kahleova said.

Potential explanations behind the beneficial effects include the lower energy density and higher fiber content of plant protein foods, which can promote satiety, as well as differences in amino acid composition. The association between lower methionine intake and greater weight loss is also consistent with previous research suggesting that methionine restriction may enhance fat oxidation and improve metabolic health.

Study limitations include self-reported dietary intake and the fact that participants were volunteers, potentially affecting generalizability. Additionally, the study was not designed to investigate underlying biological mechanisms, so associations with specific nutrients cannot establish causation.

Sustainability Is Key

Commenting for Medscape Medical News, Esther Eisenberg, MD, professor emerita of ob/gyn, Vanderbilt University School of Medicine in Nashville, Tennessee, said the findings “add another potential management tool to the clinician’s armamentarium” for menopause-related changes.

Although she would not make a blanket recommendation that all postmenopausal women adopt this dietary pattern, Eisenberg said “there are few risks to adopting a vegetarian or vegan diet with added soybean protein,” provided patients get adequate vitamin B₁₂, omega-3 fatty acids, iron, calcium, vitamin D, and zinc, which are “likely to be insufficient in a vegan diet.”

She recommends a Mediterranean diet that includes fish, low-fat cheese, eggs, plenty of vegetables, reduced sugar intake, and at least 30 minutes of daily exercise.

Also commenting for Medscape Medical News, Melissa Shoemaker, MD, MPH, a spokesperson for The Obesity Society and assistant professor at UT Southwestern Medical Center in Dallas , said the findings reinforce previous evidence linking plant-based protein to weight loss and reductions in hot flashes or vasomotor symptoms.

However, she cautioned that the study was relatively small and short-term, making long-term outcomes difficult to assess.

“Postmenopausal weight management can be tricky to navigate because we hear a lot about increasing protein, but it’s important to emphasize there are different kinds of protein sources,” Shoemaker said. “Additionally, when we’re thinking about counteracting the accelerated loss of muscle mass during the menopause transition, strength training is just as important as increasing protein intake.”

She emphasized that whole food, plant-based eating does not have to be “an all-or-nothing way of thinking.”

“We don’t have to completely cut out animal proteins but rather try to increase plant-based proteins while gradually reducing animal proteins, refined carbohydrates, and foods high in saturated fats to get health benefits,” she said.

Because obesity is a chronic disease, dietary changes should be sustainable over the long term, Shoemaker added.

The study was funded by the Physicians Committee for Responsible Medicine. Kahleova reported receiving compensation from the Physicians Committee for Responsible Medicine for her work on this study. The other authors’ disclosures are listed on the original paper. Shoemaker and Eisenberg reported having no relevant financial relationships.

Batya Swift Yasgur, MA, LSW is a freelance writer with a counseling practice in Teaneck, New Jersey. She is a regular contributor to numerous medical publications, including Medscape and WebMD, and is the author of several consumer-oriented health books as well as Behind the Burqa: Our Lives in Afghanistan and How We Escaped to Freedom (the memoir of two brave Afghan sisters who told her their story).