The official dietary guideline lists two protein numbers. Women: 46 grams a day. Men: 56.
The gap is arithmetic. The guideline assumed a woman weighing 57 kilograms and a man weighing 70. Same formula, different body sizes. Thirteen kilograms of body weight produced the entire difference.
Do Women Need Less Protein Than Men?
The protein-building machinery in women and men is identical. Every comparison of how quickly muscle builds and breaks down in young and middle-aged adults has found the same rates in both sexes: at rest, after a meal, after a workout. No difference in how fast muscle is built. No difference in how fast it breaks down. A 2016 review of all available research confirmed no exceptions across any testing method, eating pattern, or exercise routine.
The question that makes this finding hard to believe: if testosterone builds muscle, and men have far more of it, how can the protein machinery be the same?
The mass difference between men and women was set during one window: puberty. Testosterone drove a growth spurt that packed more muscle onto adolescent males. Once that window closed and muscle mass stabilized, the job of protein synthesis changed. In adults maintaining stable weight, the protein factory is running maintenance — turning over existing muscle, not building new.
Both sexes maintain at the same rate per kilogram. The hormone that built the size difference doesn’t run the upkeep any differently.
The lower serving sizes on products marketed to women, the smaller scoops in “women’s protein” tubs, the assumption that less testosterone means less protein needed — all built on the same confusion. The size of the body changed. The rate at which it repairs itself did not.
The per-kilogram protein recommendation is the same for women and men. The protein-building machinery — synthesis, breakdown, response to meals and exercise — works at identical rates in both sexes through young and middle-aged adulthood. The 46g-versus-56g gap in dietary guidelines came from body weight differences between reference adults, not from differences in how women and men process protein.
— Smith & Mittendorfer 2016 · J Appl Physiol · Comprehensive review of all MPS comparison studies
One caveat that matters: far less research has been done in women than in men. Only 14 study groups in the largest available dataset were exclusively female. The finding is consistent across all of them. The sample is thinner than the confidence deserves.
The per-kilogram recommendation is the same for both sexes. A woman weighing 65 kilograms and a man weighing 85 kilograms both aim for the same grams per kilogram. She eats less total protein because she weighs less, not because her body handles it differently.
The picture holds through young and middle-aged adulthood. After menopause, the machinery shifts in a direction nobody predicts: the baseline rate at which muscle repairs itself actually rises in older women, while the response to each meal blunts more steeply with age. The per-kilogram target stays the same. How the body responds to each individual serving is where the story changes.
Meal by meal, the full protein guide maps what those per-kilogram numbers look like on a plate.