Protein alone won't shift body fat in menopause

The menopausal transition is a period when women commonly see unwanted shifts in weight and body composition, and higher-protein diets are one of the most popular countermeasures. But protein is not one thing: animal sources such as whey, meat and milk differ from plant sources such as soy, and whether the type of protein matters for fat and lean mass in this life stage has been unclear. This review set out to examine the effect of protein intake on anthropometric and body-composition markers in pre- and postmenopausal women, with a view to informing nutritional strategies for this phase.

The authors searched PubMed, EMBASE and the Cochrane Library following PRISMA guidelines, with the protocol registered on PROSPERO, and assessed risk of bias using the Joanna Briggs Institute tool. Fifteen randomised clinical trials were included, involving 1161 pre- and postmenopausal women in total. Eight trials tested animal-based protein interventions — protocols using whey protein, meat or milk protein — while seven used soy protein isolate. The reviewers examined outcomes on weight, body fat and lean mass, and paid particular attention to whether trials also involved energy restriction or supervised exercise.

Animal-based protein interventions showed the more consistent effects on weight and body-fat reduction, especially when combined with calorie restriction and supervised exercise. Whey, meat and milk protein protocols demonstrated reductions in body fat over 8-16 weeks, with increases in lean mass appearing in longer interventions. Soy protein isolate produced more heterogeneous results — few changes in short-term interventions, and more favourable outcomes when paired with exercise. Crucially, when protein effects were analysed independently of energy restriction and exercise, results for both protein types became less consistent, and the review could not confirm benefits from an isolated increase in protein intake.

This review complicates the popular framing of protein as a standalone body-composition lever. It suggests the type of protein, the dose, the duration of the intervention and — above all — the accompanying strategies of energy restriction and exercise together determine outcomes in women through the climacteric period. It does not show that plant protein fails, but that soy's results are more variable and more dependent on being paired with training. The open question it leaves is whether protein type would matter at all in trials that strictly isolate protein from the co-interventions that usually accompany it.

If you are navigating the menopausal transition, this is a reason to see protein as one component of a package rather than a fix on its own — in these trials, the consistent fat-loss results appeared when protein sat alongside a calorie deficit and exercise. Animal proteins produced steadier results than soy, though soy performed better when combined with training. The review could not confirm that simply eating more protein, in isolation, changes body composition. That distinction — protein as support, not as driver — is the practical heart of the finding.