Carbohydrate Loading Effects In Males and Females
The pre-race pasta dinner is an endurance running staple. However, the scientific evidence suggests that loading up on carbohydrate-rich foods like pasta the night before a race, while beneficial for men, may not make a difference either way for women. Briefly, there are three major sources of energy utilized by the human body: carbohydrate (starches and sugars), protein, and fat. Under resting conditions, humans burn a mix of all three. When exercising at high intensity (near or above lactate threshold), both men and women burn primarily carbohydrate. Men and women burn fuel differently, however, during moderate-intensity exercise. Under such conditions, compared to men, women burn a higher percentage of fat (Phillips et al, Tarnopolsky et al, 1990). This suggests that pre-race carbohydrate loading, which is meant to increase muscle glycogen (carbohydrate stored in muscles) may not be as beneficial to women as it is to men.
Research further indicates that women are less physiologically capable than men of increasing muscle glycogen stores through pre-race carbohydrate loading (Tarnopolsky et al, 1995). In the Tarnopolsky study, groups of trained male and female endurance athletes carbohydrate-loaded for several days before an event by increasing carbohydrate intake from 50% of total calories consumed to 75% of total calories consumed. In response to the carbohydrate loading, male athletes increased muscle glycogen stores by an average of 41%, while female athletes experienced no increase in muscle glycogen stores. Male performance at lactate threshold increased by a factor of 45%, while female performance at lactate threshold increased by only 5%. Whether the minute increase in female performance was due to increased carbohydrate intake or to a placebo effect is not clear, due to the low significance of the increase.
In a follow-up study, Tarnopolsky and colleagues explored the possibility that the lack of increased muscle glycogen and performance capacity in carbohydrate-loading female athletes was due to their overall lower energy intake, relative to male athletes (Tarnopolsky et al, 2000). The researchers studied conditioned male and female endurance athletes who carbohydrate-loaded under a variety of conditions. Men increased total muscle glycogen on diets high in carbohydrate (relative to their typical diet), as well as on diets high in carbohydrate and total calories (relative to typical). Women, as observed in previous studies, did not increase muscle glycogen in response to increased percentage of calories from carbohydrate. When percentage of carbohydrate in the diet increased in tandem with a 34% increase in total caloric intake, however, female muscle glycogen increased by about 17%. Still, this effect is small compared to the 23% increase observed in men with increased percentage of carbohydrate alone, and the 38% increase seen in men with increased caloric consumption plus increased carbohydrate consumption. The researchers concluded that while physiological gender differences play a role in carbohydrate loading capacity, total energy intake is also a major factor.
While there’s no evidence that a woman can increase performance by increasing percent of total calories from carbohydrate before an event, there’s the question of whether a woman should consider increasing total caloric intake as well as percent of total calories from carbohydrate. Research suggests that this is not beneficial. A study in which trained female endurance athletes were carbohydrate-loaded, carbohydrate-supplemented during an event, or both, found that increasing the carbohydrate available to a female athlete increased the percent of carbohydrate burned during the event (the women burned more carbohydrate and less fat than they otherwise would have) (Andrews et al). However, women did not experience an increase in performance in response to the increased carbohydrate burning. Note that these findings are specific to endurance athletes participating in endurance (moderate effort, long duration) events, and do not necessarily apply to harder efforts.
Where does this leave us? Men, tank up at the pre-race pasta feed! In fact, tank up on carbohydrates as well as extra calories (approximately 34% increased total caloric intake, with 75% of those calories from carbohydrate) for about 4 days before an event. Women, eat what ever makes you happy.
Andrews et al. Carbohydrate loading and supplementation in endurance-trained women runners. J Appl Physiol. 2003 Aug;95(2):584-90. Epub 2003 Apr 25.
Phillips et al. Gender differences in leucine kinetics and nitrogen balance in endurance athletes. J Appl Physiol. 1993 Nov;75(5):2134-41.
Tarnopolsky et al. Gender differences in substrate for endurance exercise. J Appl Physiol. 1990 Jan;68(1):302-8.
Tarnopolsky et al. Carbohydrate loading and metabolism during exercise in men and women. J Appl Physiol. 1995 Apr;78(4):1360-8.
Tarnopolsky et al. Gender differences in carbohydrate loading are related to energy intake. J Appl Physiol. 2001 Jul;91(1):225-30.