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 Those extra carbs from 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
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“Carbohydrate-loading involves consuming a higher-than-normal amount of carbohydrates for a few days prior to a race to maximize muscle glycogen stores,” Best Energy Gels for Runners., Symptoms of Magnesium Deficiency Runner’s World.
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“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 4.5 to 5.5 grams of carbs per pound 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 5.5 grams of carbs per pound of bodyweight per day—for a shorter period may also benefit performance,’’ Namrita Kumar, Ph.D., R.D.N., tells Runner’s World.
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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 3.5 grams per pound 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—3.5 to 5.5 grams of carbs per pound 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-pound” recommendation rather than a percentage of calorie intake, given that many are likely not eating enough. If you are consuming enough carbs (3.5 to 5.5 grams per pound of bodyweight), 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.
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Kelly Pritchett is an Associate Professor in Nutrition and Exercise Science at Central Washington University. As a board-certified specialist in sports dietetics, she has consulted with both elite and collegiate athletes as well as with active individuals. While in college, she competed on the swimming and diving team at the University of Alabama. Pritchett serves on the leadership committee of the Academy's Sports, Cardiovascular and Wellness Nutrition dietetic practice group as the Education Coordinator, and served as a National Media Spokesperson for the Academy of Nutrition and Dietetics. Pritchett is an active member of the American College of Sports Medicine. She has authored research articles for scientific journals and presented at regional and national conferences. Her current research interests include post exercise nutrition for recovery, vitamin D and the athlete, and energy availability in spinal cord injured athletes. In her spare time, she enjoys running and spending time with her three active boys."
