Coaching Management, 14.1, January 2006, http://www.momentummedia.com/articles/cm/cm1401/bbfuelingup.htm
Three recently published nutrition studies have potentially big implications for track and field athletes and their coaches. Each addressed a separate topic, yet taken together these studies make it clear that athletic performance can depend on eating enough, eating right, and eating with the right attitude.
Eating Enough: A University of Missouri study found that the majority of athletes do not properly fuel for performance. The study involved 345 NCAA Division I athletes from a variety of sports. Seventy percent of the female athletes and 73 percent of the men questioned failed to get enough calories to fuel their activity levels. Sixty-two percent of women athletes wanted to lose five pounds or more, which Pamela Hinton, lead researcher and Assistant Professor of Dietetics at Missouri, says is almost always at odds with fueling for athletic performance.
The shortages were most pronounced when it came to carbohydrates and protein—a particularly large problem for athletes, according to Hinton. Eating too little carbohydrate leaves athletes with depleted glycogen stores and a lowered ability to improve lactate threshold, speed, and maximal strength. Athletes are also left more susceptible to the immunosuppressive effects of exhaustive exercise — more prone to get sick. Without enough protein, muscles cannot adapt properly to training, even if athletes are getting enough overall energy.
The good news, says Hinton, is that coaches’ efforts to encourage healthy eating can go a long way. Coaches should not encourage athletes to lose weight during a season or while training, and they should explain to their athletes that the simplest way to improve performance is to eat enough and eat well.
Hinton suggests encouraging athletes to pay attention to how they feel as one way to determine whether they are eating enough. Signs of under-eating include fatigue that doesn’t end with rest, inability to finish workouts, and unexplained drop-off in performance, obsessions about food, and mood changes such as irritability, anxiety, depression, and severe emotional ups and downs.
Stress and Stress Fractures: Cutting out the stress over eating might help cut down on stress fractures in female runners. Or so a group of sports-nutrition researchers hypothesize after studying the diets, eating attitudes, and behaviors of 79 Canadian women with and without stress fractures in their legs.
Researchers at the University of British Columbia had the group of recreational distance runners, whose average age was 29, keep journals of what they ate for three days and answer a questionnaire assessing physical activity, age, height, weight, menstrual cycle history, and perceived stress. Subjects’ diets were analyzed and found to be basically sound and similar to one another, with calcium intakes similar to or slightly higher than those of American or Canadian women as a whole, according to Susan I. Barr, Professor of Nutrition, who worked with lead researcher Nanci S. Guest, a graduate student at UBC. Actual calorie intake did not differ significantly between the two groups, according to Barr.
The only difference between those with stress fractures and those without was how much they focused on limiting calories, which is called cognitive dietary restraint (CDR). “CDR reflects the degree to which one is constantly monitoring and attempting to limit food intake,” Barr explains.
Guest and Barr note that high levels of CDR have been associated with irregularities in the menstrual cycle and increased levels of cortisol, a hormone that is elevated in the “fight or flight” response and can retard muscle and bone growth and recovery from exercise. Will staying relaxed about what they eat help women avoid stress fractures? The authors think it might. “We hypothesize that if women could avoid stressing about what they eat (and what they weigh), it might reduce the cortisol levels that seem to be implicated in the risk for stress fractures,” Barr says.
Going Low Glycemic: A third study looked at how the glycemic index (GI) of recovery meals affects the next day’s workout. Many athletes reach for high-GI foods after workouts, assuming that plenty of quickly digested carbohydrates are the best way to restore glycogen stores. But a study in England last year suggests a low-glycemic recovery diet may help distance runners run longer.
Researchers at Loughborough University had male runners run on treadmills while hooked up to oxygen-mask monitors for 90 minutes at 70 percent of VO2max. Then they fed half the group a low-GI diet for 24 hours while the other half ate a high-GI diet. Both menus provided equal calories and proportions of carbohydrate, fat, and protein. The next day, subjects ran at the same pace until exhaustion. The high-GI group ran for about 97 minutes and the low-GI group for about 109 minutes.
The researchers analyzed the runners’ blood samples taken before and after their workouts and found increased fat oxidation in the low-GI runners. They theorized that the low-GI diet prompted the muscles to use more fat as fuel. They also noted that other research has suggested high-GI diets retard resynthesis in the body of intramuscular triacylglycerol (IMTG), which is believed to be an important energy source during prolonged exercise.
A more comprehensive description of Dr. Pamela Hinton’s study on under-eating in athletes appeared in the September issue of Coaching Management’s sister publication, Training & Conditioning. It can be seen at: www.momentummedia.com/articles/tc/tc1506/empty.htm.
The study “Cognitive Dietary Restraint Is Associated with Stress Fractures in Women Runners” appeared in the International Journal of Sport Nutrition and Exercise Metabolism, in April 2005.
The study “Improved Recovery from Prolonged Exercise Following the Consumption of Low Glycemic Index Carbohydrate Meals” appeared in the International Journal of Sport Nutrition and Exercise Metabolism in August 2005.