Nutritional Differences Between Men and Women (#294)

In article and episode 66, we explored the various phases of menstruation and their impact on metabolism, so if you're looking for a comprehensive understanding, read that first. To summarize, the hormone estrogen serves as a "master regulator" of metabolism. Estrogen, alongside other hormones, fluctuates during the menstrual cycle, influencing how the body utilizes energy.

To keep things simple, I'm including an image from our menstruation article here, since not everyone may be familiar with the follicular and luteal phases—terms that are frequently referenced in this text.

The menstrual phases do not appear to significantly impact strength development. If you want to engage in strength training, just go for it—neither maximum strength (1RM) nor performance at 20, 40, 60, 80% of 1RM is notably affected by the cycle phase.

Recovery time in women is influenced by hormonal fluctuations. A study on eight women found that markers for muscle damage and inflammation were higher during the follicular phase compared to the luteal phase after 90 minutes of running at 70% of VO2max. Additionally, the re-storage of muscle glycogen is faster during the follicular phase.

There are slight differences in the recommendations between genders. Immediately after finishing an activity, males are recommended about 1 g of carbohydrate per kg of body weight, while women should have about 0.75 g/kg of body weight. This recommendation is likely based on the fact that males tend to oxidize more carbohydrates than women at a given intensity, thereby depleting glycogen stores faster.

Studies on the dietary habits of women athletes reveal that women often consume less than they require, especially concerning carbohydrates.

The optimal baseline energy intake, excluding activity energy, should be roughly 40–45 kcal per kg of fat-free mass daily. Many reports on women athletes indicate energy intake as low as 30 kcal/kg of fat-free mass. Such a deficit can noticeably impact performance after just a few days and can lead to relative energy deficiency in sport (REDs) (https://pubmed.ncbi.nlm.nih.gov/31524785/), which is obviously undesirable.

The normal range for body fat in a woman is about 20–30%, but 14–20% is common in some sports where body weight impacts performance. Such cases are often categorized as “very lean.” Below 14% body fat is considered starvation, with increasing problems — including the loss of menstruation.

40–45 kcal/kg of fat-free mass equates to a baseline energy intake of approximately 1,760–1,980 kcal per day for a 55 kg training woman with 20% body fat. Additionally, energy for the sporting activity itself is required. For instance, running at a moderate intensity for an hour adds another 550–600 kcal to energy needs.

It's not feasible to provide an exact recommended energy intake for everyone, regardless of gender. However, for a training woman around 55–60 kg who trains 5–10 hours a week, approximately 2,500–3,000 kcal per day is a reasonable starting point. By aiming for that intake and adjusting up or down based on hunger and recovery, you are likely to achieve a near energy balance.

When it comes to carbohydrate loading, it doesn't seem to be affected by the menstrual cycle. As a woman, adhere to the guidelines of 8-10 g of carbohydrates per kilo of body weight per day for 3 days for optimal supercompensation.

The recommended carbohydrate intake of 1-4 g/kg body weight during the last 1-4 hours before starting is not entirely equivalent between genders. For males, this final loading has shown clear performance benefits, but for women, the data is more uncertain. It's likely that this final loading is important for women during the follicular phase when carbohydrate oxidation rates are higher, but the research isn't as definitive—partly because fewer studies focus on women and do not always consider the phase of the menstrual cycle. However, the recommendation is that women aiming for performance should also follow the plan of approximately 1 g of carbohydrate per kg body weight per hour during the last 1-4 hour period before starting.

Example. If you weigh 60 kg and there is 1 hour left — consume 60 g of carbohydrates; if there are 2 hours left — consume 120 g of carbohydrates during this time; if there are 3 hours left — consume 180 g, and so on.

Carbohydrate intake during activity provides equivalent performance effects regardless of phase and gender — similar improvements have been observed in both the follicular phase and luteal phase.

During the luteal phase, elevated levels of estrogen and growth hormone enhance fat utilization as fuel. This increase in fat oxidation continues at higher intensities—up to relatively high levels. Studies comparing males and women on the same diet and intensity show that women have a lower RER value (indicating they oxidize more fat) up to at least 80% of VO2max compared to males. This implies that at any given exercise intensity up to about 80% of VO2max, women oxidize more fat, conserve muscle glycogen, and might therefore have a higher dietary fat requirement.

An older study from 1984 found that the RER value was significantly lower (by 2–6.25%) in women who cycled to exhaustion at 80% of VO2max. The value was also lower (by 2–5%) when cycling at 90% of VO2max (though not significant, partly because not everyone managed to cycle for that duration, resulting in a smaller study group)— link to the study.

Protein requirements per kilogram of body weight are higher for women compared to males. The minimum level an athlete should maintain to prevent muscle loss is approximately 1.2 g/kg for males and 1.6 g/kg for women. For both genders, consuming more than the minimum level is likely beneficial for optimizing recovery and training adaptations.

Women's protein needs increase, particularly during the luteal phase, due to the heightened turnover/oxidation of protein.

“A study of female cyclists and triathletes (endurance athletes) showed that their mean protein requirement was 1.63 g/kg/day, aligning with male counterpart recommendations [121]. However, an important factor in this study is that women were tested during the mid-follicular phase of the menstrual cycle. With increased protein oxidation during the luteal phase, protein needs may be further elevated. The menstrual cycle phase should be considered when evaluating dietary protein needs for women.” (quote and reference preserved in original)

For optimization, protein intake should be spread across multiple doses throughout the day, with around 20–30 g of complete protein consumed per sitting. This provides repeated signals to the body to repair and build muscle mass (as well as other protein-constructed components: red blood cells, enzymes, hormones, mitochondria, blood vessels, etc.).

Come on, this is the last stretch — I promise. Hang in there 😉

For beta-alanine, there are no gender-specific differences in recommended intake. Taking 4–6 g per day for 4 weeks has been shown to increase carnosine levels in muscle cells by about 64% for both genders. Women might benefit slightly more from beta-alanine since baseline levels of carnosine in muscles tend to be lower in women. Another interesting difference is that women do not seem to experience the harmless tingling sensation (paresthesia) to the same extent — a detail that was unexpected but noted in studies.

Caffeine is a performance enhancer for most people, and the effective range is the same for both genders: approximately 3–9 mg/kg body weight. Many researchers recommend sticking to 3–6 mg/kg for the majority of athletes. Higher doses, up to 9 mg/kg, can increase the risk of side effects such as nausea, anxiety, or excessive hyperactivity — and suddenly you find yourself tempted to sprint at a 4-minute pace when the planned racing pace was a 5-minute pace. ;)

Creatine recommendations do not differ between genders.

When it comes to omega-3, there are some differences in how essential the supplement can be. More specifically, omega-3 may be particularly important for women, partly due to effects related to pregnancy. Some studies have shown that omega-3 can help with depression and anxiety in women—effects that aren't always observed in males. Omega-3 fatty acids are essential and must be obtained through the diet. Women are more susceptible to undereating or relative energy deficiency, making it crucial for them to ensure adequate omega-3 intake. Omega-3 also helps reduce inflammation markers for everyone, but it is particularly significant for women at a higher risk of relative energy deficiency.

Probiotics are beneficial regardless of gender. Different bacterial strains can have varying importance for women and men, and a probiotic with a wide variety of strains may be ideal. For women specifically, one noteworthy detail is that iron absorption has been shown to improve when probiotics are taken at the same time. Probiotics have also been shown to increase the absorption of amino acids for both genders when ingesting plant-based protein, which can be particularly important for active women who require a higher protein intake per kilogram of body weight. However, further studies are necessary to offer clear recommendations.

“A recent study relevant to women demonstrated an improvement in iron levels and absorption when 20 mg of iron (ferrous-fumarate) was combined with Lactobacillus plantarum 299v (LP299V, 10^10 CFU), suggesting this probiotic strain may help enhance iron levels [163].” (quote and reference remain in the original).

Last but not least are vitamins and minerals — here, iron is the most significant gender difference. For athletic males, the ISSN recommends a daily intake (RDI) of 8 mg, while women are advised to have 18 mg per day according to the ISSN. The general figures from the Swedish Food Agency are 9 mg for males and 15 mg for women (not specifically for athletes).

As you can see, the ISSN's recommended iron intake for women is more than twice that for males, even though women generally weigh less and often consume less energy overall. This increases the risk of not meeting the recommended daily intake. Iron deficiency is very common among athletic women.

“Iron deficiencies are extremely common among female athletes, especially those who are vegan/vegetarian and consume fewer calories. The ISSN recommends males consume 8 mg/day, while women should consume 18 mg/day [153].” (quote and reference retained in original)

For other vitamins and minerals, there are small differences in RDI between genders, but if you eat a varied diet, you'll get most of what you need. However, for menstruating women, there is a slightly increased risk of not getting enough folate, riboflavin, and vitamin B12. Folate (or folic acid in supplements) and riboflavin, like B12, are water-soluble B vitamins. Riboflavin deficiency is extremely rare in Sweden according to the Swedish Food Agency, while folate deficiency can lead to anemia and increase the risk of pregnancy-related issues such as miscarriage and neural tube defects in the fetus. B12 deficiency is primarily a risk for vegans/vegetarians because the vitamin is mainly found in animal products — a group that is often already aware and compensates for this.

We also covered this in our article on performance as a vegan/vegetarian.

Men and women have, relative to their body weight, largely similar needs for energy, fat, protein, carbohydrates, vitamins, and minerals. However, there are small but important differences for women between the phases of the menstrual cycle.

Some key points for athletic women:

• Women have a 2% lower VO2max during the luteal phase
• Women have a 7% increased energy requirement during the luteal phase
• Women have impaired recovery during the follicular phase
• Women need to consume more protein than males (at least 1.6 g protein/kg body weight)
• Women are better at using fat as fuel at high intensities. About 5% increased fat burning has been noted all the way up to 80% of VO2max (~90% of max heart rate).

Listen to your body, plan according to your cycle when it helps, but train as usual when you feel like it. And yes — eat properly, especially carbs and protein. Your body does tough jobs for you; give it lunchbox contents that reflect that.