Carbohydrates and the Athlete

Athletes are always seeking a competitive edge. Frequently, they look to some new diet, food or vitamin to give them that extra advantage. Most nutrient supplementation programs turn out to be useless, and some may even be harmful.

By contrast, carbohydrate loading can actually help--but only in the right circumstances. To know when to use this measure, one must first understand the principle behind it.

During mild to moderate exercise, free fatty acids derived from stored body fat are the main source of energy for working muscles. But as the intensity and/or duration of the activity increases, the supply of oxygen to the tissues dwindles. The body then relies increasingly upon carbohydrate, which uses less oxygen than fat does as it is converted to energy.

In the body, carbohydrate is stored as glycogen, primarily in muscle tissue and in the liver. We have relatively large quantities of fat, but only small reservoirs of glycogen. This is important to the athlete because muscle fatigue is believed to be directly related to the depletion of muscle glycogen. Theoretically, then, the larger the available carbohydrate pool, the longer the athlete can exercise before she or he “hits the wall” and has to stop.


Demonstrating the Importance

A fair amount of research has been aimed at finding ways to stockpile carbohydrate. Two paths to this goal have emerged. First, physical training itself stimulates glycogen production, increasing stores by as much as 50%. In addition, these reserves can be further augmented by making changes in the diet.

The importance of diet in this respect was first demonstrated in the late 1960s in a study that compared muscle glycogen levels following three different regimens: high-fat and low-carbohydrate; low-fat and high-carbohydrate, and a normal ratio of the two. The researchers found that the high-carbohydrate diet doubled the level of stored carbohydrate--from 1.75 to 3.5 grams per 100 grams of muscle.

The high-fat diet resulted in the lowest concentration of glycogen, just 0.6 grams per 100 grams of muscle. These levels correlated well with the length of time the volunteers could exercise before becoming exhausted--170 minutes on the high-carbohydrate diet, 115 minutes on a normal diet and only 60 minutes following the high-fat regimen. Further studies indicated that the highest stores could be achieved if reserves were first depleted and then built back up again.


This information led to the development of the carbohydrate-loading programs that are in vogue among many athletes today. In general, the procedure has included a period of muscle-glycogen depletion by vigorous exercise coupled with a diet high in protein and fat, and then followed by a rest and replenishment of muscle glycogen with generous amounts of dietary carbohydrates.

Recent studies have suggested that it is unnecessary to use the high-fat diet during depletion to achieve maximal glycogen stores during refeeding. In fact, this may actually impair performance. Thus, the procedure has been altered to include normal carbohydrate intake during depletion.

So far, research has barely touched on the question of whether one carbohydrate is better than another. But one fact is clear: Natural foods containing complex carbohydrates provide essential vitamins and minerals, rather than just calories.

As simple as it seems, carbohydrate loading is not without side effects. It should definitely not be used indiscriminately. Besides the increase in glycogen, there is an upsurge in the water content of the muscles. That can translate into a weight gain of as much as six pounds and can affect performance directly. The added water can also cause muscle stiffness, which can impair ability.

Carbohydrate Loading

Some individuals seem to tolerate the procedure better than others. People with diabetes/hypertriglyceridemia are advised to avoid carbohydrate loading altogether because it alters carbohydrate and fat metabolism in ways that can exacerbate their conditions.

Trainers, coaches and athletes must understand that carbohydrate loading provides endurance, not strength. It is effective only in sports such as long-distance running, cross-country skiing and cycling--competitions in which the exercise continues for more than two hours at a time. A football game may last longer than two hours, but the individual players are involved only a fraction of that time, and the conditioned athlete has more than enough glycogen to see him or her through to the end.

Even for those sports where it is indicated, experts advise that carbohydrate loading be used only occasionally--once or twice a year for big events.


Is Apple Juice the Villain in Children’s Diarrhea?

Question: My grandson, age 2 years, is growing normally and is generally healthy. But he has persistent diarrhea for reasons that are not clear. I think it happens when he drinks a lot of apple juice. Before I suggest to my daughter that she try withholding it, can you tell me if my theory could be right?

Answer: An article in the American Journal of Diseases of Children suggests that apple juice even in reasonable amounts may be related to so-called chronic non-specific diarrhea in children, a common problem without a clear-cut cause.

During a six-month period, the investigators saw five otherwise normal children between the ages of 13 months and 31 months whose parents reported that apple juice seemed to make their diarrhea worse. This represented 15% of those with chronic diarrhea seen in pediatric gastroenterology clinic during that period.

Results of a lactose tolerance test to evaluate whether these children could digest milk sugar were normal. But when given seven to eight ounces of apple juice at room temperature after a 12-hour fast, breath hydrogen began to rise within as little as 30 minutes. In some cases it continued to climb for two hours. This rise indicated that undigested carbohydrate was reaching the bowel, where it was broken down by bacteria. Each of the children also developed diarrhea after drinking the apple juice.

The physicians who saw the children cannot completely explain this observation, but speculate that carbohydrate malabsorption may play a role in the condition. While it does not seem to involve sucrose or fructose found in the juice, it may be related to sorbitol, a sugar alcohol.

How commonly apple juice consumed even in normal amounts might contribute to chronic non-specific diarrhea is unknown. Restricting intake in other patients with this condition had no effect. But in view of your observation, suggesting a brief trial of removing it from your grandchild’s diet seems reasonable. But parents should rely on the child’s pediatrician for the overall monitoring of the condition.

Q: Are cantaloupe and honeydew melons nutritionally equivalent?


A: Not entirely. The clue to the major difference between them is color. The orange hue of cantaloupe indicates that it is an excellent source of beta carotene, which the body converts to Vitamin A. A single cup of the melon more than meets the entire Recommended Dietary Allowance for the nutrient. Honeydew, on the other hand, does not contain appreciable amounts of beta carotene.

Beyond that difference, the two are similar. A cup of either provides about 60 calories and meets the RDA for Vitamin C. They also contain as much potassium as you would get from a cup of orange juice. And both provide small amounts of other vitamins and minerals.

Incidentally, 90% of the weight of both these fruits is water.