Starting a long-distance race with full a full tank of glycogen (a.k.a. stored carbs in your muscles and liver) can help you avoid the dreaded “bonk.” For years, it has been a popular practice to hit up the prerace pasta feed to load up on carbs before the race.
However, guidelines for carb-loading have been developed primarily based on sports science research conducted in male endurance athletes. So, is there evidence to suggest that women (or people who get a period) require a different carb-loading strategy? Here’s what you need to know.
First, a quick refresher on carb-loading
Glycogen depletion has been linked to fatigue and decreased performance during prolonged activity, such as the marathon distance. For this reason, runners have been implementing carb-loading protocols for years to maximize their glycogen stores and improve their performance during competition.
“Carbohydrate-loading involves consuming a higher-than-normal amount of carbohydrates for a few days prior to a race to maximize muscle glycogen stores,” Marie Spano M.S., R.D., C.S.S.D., consulting sports dietitian for the Atlanta Braves, tells Runner’s World.
Those extra carbs from potatoes, bread, rice, pancakes, bagels, or the prerace pasta dinner you eat converts to stored energy in the form of muscle glycogen.
“If runners load up on carbohydrates for a few days prior to a race, they start with more fuel in the tank, which equates to more energy during the later stages of a race. Therefore, if you are competing in an event lasting 90 minutes or longer—a marathon or half marathon, for example—you can benefit from carbohydrate-loading,” Spano says.
Traditional carb-loading protocols involved a glycogen depletion phase where you’d increase your training and decrease your carbohydrate intake prior to increasing carbohydrate intake. But more recently, an Academy of Nutrition and Dietetics position paper on sports nutrition for athletic performance recommended increasing carbohydrate intake up to 10 grams of carbs per km of bodyweight per day, starting around two to three days prior to a running event, without a depletion phase. At the same time, you would taper your amount of running.
“Research suggests when less time is available for carbohydrate loading, in back-to-back events, for example, higher carbohydrate intakes—5 to 10 grams of carbs per km of bodyweight per day—for a shorter period may also benefit performance,’’ Namrita Kumar, Ph.D., R.D.N., tells Runner’s World.
Should people who get a period change their carb-loading strategy according to phases of their menstrual cycle?
While research has shown that there’s no difference in the ability of men and women to load glycogen, women (or any people who get a period) experience hormonal fluctuations throughout the menstrual cycle that can influence glycogen storage and utilization.
When estrogen is higher (the late follicular and mid-luteal phase), the ability to store glycogen may be slightly greater for women, according to a 2021 study published in the European Journal of Sports Science. However, when estrogen is lower (the early- to mid-follicular phase), you may need to emphasize carbohydrate intake (amount and timing) to optimize glycogen storage.
But, when you consume an adequate amount of carbs (more than 5 grams per km of bodyweight per day), there does not appear to be a difference in glycogen storage between the phases of the menstrual cycle. This suggests that any reduced capacity to store glycogen during the mid-follicular phase of the menstrual cycle can be overcome with a higher carb intake that falls within the “carb-loading recommendations.”
“When carbohydrate needs—5 to 10 grams of carbs per kg of bodyweight per day—are being met, then two to three days of increased carb intake should be sufficient to load glycogen, regardless of sex or phase of the menstrual cycle,” Kumar says.
While there’s currently a lack of evidence to suggest that people who get a period should carb load differently than those who don’t, it’s still important to consider that each person’s cycle is different. There is a large variation in menstrual cycle length and hormonal fluctuations that is difficult to account for in sport science research. Therefore, if you get a period, you may benefit from tracking your menstrual cycle and observing changes in appetite, GI symptoms, and cravings, which may ultimately impact your fueling and carbohydrate intake.
The bottom line
Guidelines for carb-loading should be based off a a “grams-per-km” recommendation rather than a percentage of calorie intake, given that many are likely not eating enough. If you are consuming enough carbs, your menstrual cycle shouldn’t get in the way of your body’s ability to load glycogen stores.
“If you don’t want to track food intake or count grams of carbs, then start by just adding an additional serving of carbohydrate—cereal, toast, potatoes, fruit—to each meal in the three days leading up to your event,” Kumar says.
Working with a sports dietitian can help you dial in your prerace carb needs.