Should Women Fuel Differently Than Men?

What you eat (or don’t eat) before, during and after training can affect your ability to recover, train, and perform.  What’s more, there are considerations based on sex to consider when fueling for trail running. The female physiology can affect everything from the utilization of nutrients during different parts of the menstrual cycle to the risk of nutrient deficiencies.  Though progress and research have been slower than ideal, scientists and nutritionists are gaining a specific perspective on how to feed the female runner.  

Overall Energy Intake 

The biggest challenge female endurance athletes face is underfueling.  Poor energy intake is usually shown to be a result of purposeful energy restriction, injury, illness, loss of appetite from high training volume or from restrictive dietary patterns.   Long-term energy deficiency can lead to a higher risk of decreased bone mass, menstrual irregularities, increased injury risk, hormonal imbalance, and decreased running performance. Eating enough should be the top priority for female runners.  

Active female athletes exercising 6-10 hours per week need at least 2,500 calories or more per day, anything less risks macro and micronutrient deficiencies. Throughout the menstrual cycle, daily energy needs may vary, with some studies showing that athletes need  2.5-11.5% during the second half of their cycles, called the luteal phase. Age also plays a role in dictating energy needs.  For post-menopausal runners, metabolism might decrease due to loss of muscle mass with aging and needs to be taken into consideration when estimating calorie needs. 

Main Takeaway: Eat often and eat enough.  In the second half of your menstrual cycle, you may want to increase energy intake by 100-200 calories per day.  Post-menopausal women should be aware of possible metabolic changes that occur as part of aging.  

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Carbohydrates

Though they’re the powerhouses of energy production for exercise, a diet culture focused on demonizing specific macronutrients has caused some trepidation around carbs. Female runners fueling for performance need 6-10g/kg of carbohydrate per pound of body weight per day.  Ideally, they’ll come from a variety of fruits, vegetables and whole grains. 

Timing your carbohydrate consumption is key for performance.  In menstruating females,  carbohydrates are utilized for energy production more rapidly in the first half of your cycle than in the second half of your cycle. In the first half of your cycle, aim for a pre-workout meal or snack that contains1g/kg carbohydrate, one to four hours before running, to optimize carbohydrate availability.  

During exercise, no matter the cycle phase, aim for 30-60g per hour of carbohydrate for the ideal in-run fueling.  After your run, glycogen replenishment rates will vary depending on the point in the cycle, with lowered glycogen storage during the first half of the cycle.  Take advantage of post running recovery and ensure proper glycogen replenishment by consuming .75g/kg carbohydrate as quickly as possible following more than 90 minutes of exercise.

Main Takeaway: Carbohydrates are essential for energy in female endurance athletes.  Focus on pre-workout carbohydrate fueling is especially important in the first part of a female’s cycle due to decreased glycogen storage rates.  Consume at least 30-60g/hr of carbohydrate during long runs.  Post-run carbohydrate consumption and glycogen replenishment are important during all cycle phases but may occur more rapidly during the first half of the cycle. Cookies and milk anyone?

Fats

Getting enough fatty acids is important for sex hormone production, fat-soluble vitamin absorption, and maintaining a regular menstrual cycle. Research points to getting 20-35% of total calories to come from fat sources for optimal health and performance.  Female runners utilize fats for energy during exercise more than their male counterparts.  Throughout the menstrual cycle fat utilization rates vary, with rates being the highest in the second half of the cycle when estrogen levels are higher.  Female trail runners need extra fats in the second half of their cycles for optimal performance in the singletrack.

Main Takeaway: Female runners rely more on fat utilization during exercise than males.  Increase fatty acid intake during the second half of your cycle to support increased fat utilization of fats during run. A spoonful of peanut butter should do the trick!

Protein

Female trail runners should focus on getting enough protein to maintain lean muscle issue, prevent injury and illness and to optimize neurotransmitter production. Brain health ad cognitive function are important for athletic performance too! We know that exercise increases protein needs, but unfortunately, most of the research has been done on male subjects. A suggested baseline for female athletes is around 1.6 g/kg/day. Ideally, female athletes will space protein intake evenly throughout the day to optimize recovery and promoting lean body mass. Aim for a chunk of your daily protein at each snack and meal, rather than trying to lump it all into one chalky shake!  During mid-cycle and the second half of your menstrual cycle, muscle protein breakdown is higher due to higher estrogen and progesterone, so focus on getting in a slightly higher intake then.  In post-menopausal women, muscle mass decreases with hormonal changes, and getting enough protein becomes even more important.

Main Takeaway:o Female runners should spread out protein consumption evenly throughout the day to optimize muscle maintenance and assist recovery.  Increase protein intake during the mid and second half of the menstrual cycle and after menopause. You probably don’t need a 16oz ribeye, but consider an extra pre-bedtime yogurt parfait.  

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Micronutrients 

For female endurance athletes, specific vitamin and mineral deficiencies matter more than in their male counterparts because of menstrual cycle fluctuations and hormonal changes with aging.  

Iron: Iron plays an important role in making red blood cells and transporting oxygen in the body to the lungs and muscles when running.  Iron deficient anemia is particularly prevalent in female runners due to monthly blood loss during menstruation.  Symptoms include fatigue, high heart rate, feeling cold all of the time, brittle hair and nails and irritability. To up your intake, focus on foods like meat, beans, pumpkin seeds and leafy greens. Tofu and lentils are great too! Female runners should consider regular iron panel readings to check in on iron status work with a nutritionist or GP on supplementation when necessary. 

Vitamin D: Vitamin D is essential for immune support and bone health. Vitamin D deficiency can put female runners at higher risk for stress fractures and osteoporosis.  Daily recommended intake of Vitamin D is 800 IU/day but can be hard to obtain since it is only really found in limited food sources such as fatty fish, fortified dairy and irradiated mushrooms.  Supplementation, if warranted, has been shown to be safe with doses of 2000-4000 IU/day.

Calcium: Due to the high prevalence of underfueling in the female running population, calcium deficiency is a real concern as well.  Similar to Vitamin D, Calcium deficiency can lead to a higher incidence of stress fractures and osteoporosis later in life. High-calcium foods like fortified milks and alternative milks, leafy greens and dairy products are great safeguards.  Runners at risk of deficiency should consider a supplement. 

The best emerging research suggests that sex differences should be considered when coming up with an individualized fueling plan. Normal hormonal fluctuations in menstruating athletes and post-menopausal athletes require a more specific approach, in everything from nutrient intake to timing. Who knows, it might just get you that new PR!