INSIDE SPORTS NUTRITION

Small differences in fuel utilization have been observed between exercising men and women, particularly when:

women are in the luteal phase (LP) of the menstrual cycle (MC) and

exercise is at least moderate intensity (~60% of max or higher) and

exercise takes place in the fasted state

High levels of estrogen during the LP promote carbohydrate (glycogen) sparing and storage and fat utilization during moderate intensity exercise; but, women are able to continue to perform at a high intensity by using exogenous carbohydrates (eating carbohydrates pre-exercise and taking in the recommended amount of carbs during exercise). During exercise, men may also oxidize more amino acids and leucine, specifically, compared to women. However, women may also break down more protein for amino acid oxidation during the LP when progesterone is high, IF they are not taking in adequate carbs. Note that most sex-differences in substrate utilization disappear when exercising in the fed state and when taking in adequate carbs during exercise.

Given potential differences in fuel utilization, are women’s post-exercise recovery needs different from men’s? In general, endurance athletes are advised to take in carbs, fluids containing sodium, and a small amount of protein as soon as possible following exercise to restore glycogen and hydration status, and to prevent muscle protein breakdown and increase protein synthesis.

Just as there are sex-differences observed during exercise, some research has also shown that women may have higher post-exercise blood glucose and lower rates of fat utilization post-exercise, compared to men. Other research has shown that men and women restore glycogen at comparable rates when fed multiple transportable carbs (e.g. maltodextrin-fructose) post-exercise in an amount proportional to body mass. This is not surprising given that glucose transporters, enzymes and activity appear to be similar in men and women.

Even if women may have slightly higher blood glucose levels after exercise, both female and male athletes should prioritize post-exercise carb intake ~1.6 g/kg at multiple intervals for glycogen resynthesis, particularly when there is < 8 hours between training sessions or competition.

Estrogen is suggested to have a protective effect on muscle, attenuating exercise-induced muscle damage and inflammation. Thus, when estrogen is low (follicular phase), women should not neglect daily protein intake or during- and post-exercise fueling, though this is generally recommended for all athletes independent of sex or MC phase. Provided adequate carbs are taken in during exercise, and the athlete is consistently meeting daily protein needs (1.2-1.8 g/kg-day), there does not appear to be any rationale for sex-specific protein recommendations post-exercise.

PMID: 33201156, 21923203, 2744928, 18541557, 9390958, 32215726, 18046188, 18302755