Empowering Female Athletes. Part 2

Digging into the rest of the International Society of Sports Nutrition Female Athlete Position Stand. Here’s what you need to know.

In the last blog, I discussed the first part of the International Society of Sport Nutrition (ISSN) Position Stand for the Female Athlete. In case you missed it, we covered menstrual cycle tracking, the importance of adequate energy availability, and carbohydrate needs. This week, we dig into protein, supplementation, and the other key points from the Female Athlete Position Stand.

And in full disclosure, the lion’s share of this discussion revolves around protein, specifically the call for higher protein intakes, which can be a pretty polarizing discussion in sports nutrition circles. So here goes!

The Protein Perspective

First let’s level-set the basics: The current RDA for protein intake for women is 0.8 grams of protein per kilogram of body weight, or 0.36 grams per pound. At this point, this is fairly common knowledge. What’s less known is how the RDA arrived there. They derived this recommendation using nitrogen balance studies. Your body commonly gets nitrogen, which is essential for human life, from amino acids that make up protein. The concept of nitrogen balance is that the difference between nitrogen intake and loss mirrors the gain or loss of total body protein. If you take in more nitrogen (protein) than you lose, you are considered to be anabolic or in positive nitrogen balance. If you lose more nitrogen than you take in, you’re considered catabolic or in negative nitrogen balance.

As such, nitrogen balance studies are adequate for preventing malnutrition/deficiency, but not for establishing an upper limit, nor are they adequate for quantifying optimal intakes for adaptations needed by athletes. That 0.8 g/kg recommendation also assumes that someone has adequate energy availability (i.e., they’re eating enough to meet their training and basic life needs). Frequently, athletes (especially females) are not in positive energy balance because of the high caloric requirements for training and competition, and due to purposeful calorie restriction. During those times, higher protein intakes preserve lean mass and exercise capacity.

If the body is lacking sufficient levels of amino acids, both pre- and post-exercise, the result is a negative protein balance, leading to detrimental side-effects such as muscle wasting and delayed exercise recovery. It is essential that athletes consume sufficient amounts of protein while also appropriately timing their protein consumption (more on that in a bit) in order to experience a positive nitrogen balance, muscle protein synthesis, and cessation of catabolism.  

There’s also an enduring misconception that resistance training athletes need to pay more attention to protein than endurance athletes. That’s not the case. Both resistance and endurance athletes require high protein intake (hitting the upper recommendations of 1.6 to 2.0 g/kg). Endurance athletes need that protein to replace exercise-induced oxidative amino acid losses and to provide amino acids as precursors for the repair and/or remodeling of body proteins, both within skeletal muscle and throughout the body. (Don’t forget that endurance exercise is highly catabolic, skeletal muscle contraction breaks down tissue, as does eccentric loading and impact of sports like running).

In light of all of this, daily protein intake should fall within the mid- to upper ranges of current sport nutrition guidelines (1.4–2.2 grams per kilogram of body weight per day) for women at all stages of menstrual function (pre-, peri-, post-menopausal, and hormonal contraceptive users) with protein doses evenly distributed, at every meal (~every 3 to 4 hours), across the day. Eumenorrheic athletes in the luteal phase and peri/post-menopausal athletes, regardless of sport, should aim for the upper end of the range.

What About the Window?

For years, athletes have been told to consume protein as soon as possible after training to take advantage of the “anabolic window,” which is thought to be the optimal time to enhance muscle gains and recovery through nutrition. Recently, some have been asserting that the anabolic window post-exercise has been disproven. But the window isn’t closed on that conversation…or the concept of the anabolic window.

The assertion that the anabolic window isn’t relevant arose from a meta-analyses on resistance trained individuals (which has several methodological issues, as do most meta-analyses- read more here) and other studies reporting that total protein intake across the day should count first, then the timing is an additional means of maximizing adaptations. Let’s dig a little deeper.

There are two primary goals of post-exercise nutrition, one being glycogen recovery, and the other, which is sometimes overlooked, is the reduction of muscle protein breakdown. Muscle protein breakdown is only slightly elevated post-exercise, but rapidly goes up soon after;  with some studies indicating ~50% increase still apparent three hours post-exercise. Once protein has been consumed, anabolism is increased for about three hours (with a peak at about 45 to 90 minutes), negating that three-hour peak muscle protein breakdown (as soon as you eat, it stops the breakdown). After those three hours post-food, muscle protein synthesis drops even though blood amino acid levels remain elevated. Although resistance training increases sensitivity to MPS for up to 24 hours, the agreement is there are likely advantages in consuming protein in close proximity to finishing exercise. With endurance exercise, there is total body protein oxidation, thus consuming a leucine-rich fast release protein (e.g. whey isolate) as close to the end of exercise as possible enhances overall metabolic recovery. Note here however, there is still very limited research on women, and we need to consider important sex differences.

Women return to baseline much faster, and more importantly, have different protein needs depending on their hormonal status. Protein oxidation during exercise appears to be greater during the mid-luteal phase. Females also require more lysine during the luteal phase than the follicular phase with a lower ability to uptake and utilize amino acids for protein synthesis. Women who use oral contraceptives (OC) have a different blood amino acid profile than naturally cycling women (the major influencer on protein metabolism and muscle adaptations is the generation of the progestin contained in the OC). Peri and post-menopausal women are increasingly resistant to muscle protein anabolism due to a lack of response to exercise and amino acid uptake (due to the change in the ratio of estrogen:progesterone and sensitivity of receptor sites). So, the picture is more complex for female athletes.

After intensive searches of the literature, we found that pre-menopausal, eumenorrheic, and oral contraceptive using female athletes should aim to consume a source of high-quality protein as close to beginning and/or after completion of exercise as possible to reduce exercise-induced amino acid oxidative losses and initiate muscle protein remodeling and repair at a dose of 0.32–0.38 grams per kilogram of body weight. Eumenorrheic women should aim for the upper end of the range ingestion during the luteal phase due to the catabolic actions of progesterone and greater need for amino acids.  With peri and postmenopausal athletes, the dose is more specific, and we’re looking for high essential amino acid (EAA)-containing (~10 g) intact protein sources or supplements to overcome anabolic resistance.

Insights on Supplements

The final section of the position stand takes a hard look at supplements. There is not much research done on women across the most popular sports supplements. We know that caffeine, iron, creatine, and beta-alanine have good evidence for use in women, with iron and creatine coming out on top for being highly efficacious in women. You can read the synopsis for each one in the paper.

One to keep an eye on especially is creatine, which is the subject of a great deal of research attention right now. A study just came out from Dr Abbie Smith-Ryan’s lab as part of Amanda Gordon’s PhD project, looking at creatine supplementation in the high hormone/luteal phase of the menstrual cycle. They found that sprint performance and recovery are reduced in this phase, but creatine loading during the luteal phase can help off-set this decrement. Exciting stuff, well worth checking out!

Overall, the goal of this Position Stand was to collate the existing research that was conducted with sound methodologies and create guidelines specific for women. We know that as more science emerges, these will change and be updated. Right now, we implore all scientists to take a hard look at what studies they are doing and to think carefully about improving the science done in women (for women, and hopefully more by female scientists!).