INSIDE SPORTS NUTRITION

Glycogen depletion has been linked to fatigue during prolonged activity. For this reason, endurance athletes have been implementing carbohydrate loading protocols for years to maximize glycogen stores and improve performance during competition. 

Traditional carb loading protocols involved a glycogen depletion phase prior to increasing carb intake. However currently, carbohydrate loading is commonly accomplished by increasing carbohydrate intake (~8-12 g of carbs/kg of body weight per day) starting ~3 days prior to an event without a depletion phase. At the same time, the athlete would be tapering activity. When less time is available for carb loading (e.g.in back-to-back events), higher intakes (10-12 g carbs/kg-day) for a shorter period may also benefit performance. 

Women experience hormonal fluctuations throughout the menstrual cycle (MC) that can influence glycogen storage and utilization. But what does this mean for female athletes considering carb loading? 

An early study reported women have lower muscle glycogen stores after a carb loading protocol compared to men, but these findings are likely due to a lower overall energy and absolute carb intake in the women (6 g/kg-day compared to 8 g/kg-day in men). A follow up study by the same authors showed no difference in ability to load glycogen when carb intake was matched for men and women (~8g/kg-day). 

When estrogen is higher (e.g. late follicular, & mid-luteal phase-ML), the ability for female athletes to store glycogen storage may be slightly greater. 

When estrogen is lower (early to mid-follicular phase-MF), female athletes may need to emphasize carbohydrate intake (amount and timing) to optimize glycogen storage as evidenced by lower MF glycogen stores reported in several studies (It should be noted that the carb intake (~4-5 g/kg-day) in these studies is much lower than what would currently be considered “carb loading”)

 When females consume a higher relative carb intake (~8g/kg-day), there does not appear to be a difference in glycogen storage between the MF and ML phase, suggesting any reduced capacity to store glycogen during the MF phase can be overcome with a carb intake >8g/kg-day.

TAKEAWAY: Consuming adequate energy & a carb intake of 8-12 g/kg-day as recommended by Thomas et al. (2016) is likely sufficient to “load” glycogen stores for both males & females. In addition, it’s important to take into account the effects of MC phase on individual appetite and regular daily carb intake.

PMID: 34015236; 32661839; 26891166; 17507743