Low-Carbohydrate Diets and Athletic Performance

Low-carbohydrate diets have been the subject of intense scientific and public interest for many years. As Western society continues to struggle with rising rates of obesity, in both the adult and the youth population, "low-carb diets" in a number of different formulations have become popular weight loss options.

Diet represents a summary of the food consumed by all humans; all foods will be defined as being one of three dietary categories: carbohydrates, the plant-based foods digested by the body to produce glucose and other sugars; proteins, the source of amino acids used to build and restore muscles and tissues; fats, obtained from both animal and plant sources. The traditional balance between these three diet categories to create a healthy diet was accepted by nutritionists as a ratio of 60-65% carbohydrates, 12-15% proteins, and less than 30% fats. It was equally conventional wisdom among sports scientists that dramatic reductions in the amount of carbohydrates ingested by the body would lead to an inability on the part of the body to fuel itself during athletic activity.

There is a measure of historical support for the low-carb diet as an athletic training aid. The ancient Greek Olympians trained by eating a diet restricted to animal meats, and the warriors that played lacrosse in native North America also ate an almost exclusively meat diet in preparation for competition.

Carbohydrates have long been viewed as synonymous with energy. In addition to the requirements of the body that are part of sport, the brain and the central nervous system are built to receive their required energy from carbohydrate sources. A low-carbohydrate diet will be one in which the proportion of carbohydrates is less than 33% of dietary intake. Such diets are distinguished from specific athletic diets in which carbohydrates are reduced slightly, but not eliminated, to achieve an express short-term result (such as increasing proteins for a short period in certain muscle building programs).

Athletes and nonathletes alike have been attracted to the low-carbohydrate diet formulations as a means of achieving a quick weight loss. The overriding physical rule with regard to weight loss diets of any kind remains constant: no matter how a diet is constituted, if the number of calories consumed is exceeded by the energy produced by the body over time, there must be a net loss of weight. Low-carb diets will generally achieve this result, particularly in the short term. Through the elimination of carbohydrate sources, many low-carb diets have as much as 500 fewer calories available for consumption on a weekly basis. The greater weight loss is achieved through the increased diuresis, which is the production of urine, as a low-carb diet will stimulate the release of glycogen stored in the liver and muscles of the body. The utilization of glycogen, converted to glucose, requires water, and wastes in the form of urine are the ultimate consequence. After a period of two to three weeks, the body will essentially stabilize in its new low-carbohydrate state.

The restriction of carbohydrates such as fruits, vegetables, and grains has consequences for athletes and nonathletes as well. These foods are the best sources for a number of the body's noncaloric nutritional needs, including calcium, magnesium, iron, and components of the B-complex vitamins. Low-carb diets will lead to the increased production of uric acid, with long-term consequences for the healthy function of the kidneys. Low-carb diets also are likely to lead to a risk of long-term bone maintenance deficiencies, as calcium is not properly converted into the bone-building cells, which may lead to osteoporosis, the bone thinning and loss disease.

The low-carb diets that are a high fat, low-carb formulation may create other health problems for the consumer. High-fat diets will generally lead to the increased generation of low-density lipoproteins (LDLs), a type of cholesterol that leads to the build-up of plaque in the blood vessels and contributes to the impairment of the entire cardiovascular system.

An athlete must proceed with extreme caution before embarking on a low-carb diet program. It may be that in the short term, in a carefully managed environment, an athlete might achieve a weight loss goal through the modification of the carbohydrate component of the diet. In most situations, weight loss can be achieved through careful attention to overall caloric intake, without sacrificing nutritional needs or risking long-term damage to the body. A well-defined exception to this principle is the technique employed by some endurance athletes, particularly marathon runners, to stimulate increased ability to store carbohydrates. High mileage runners approaching a competition may restrict their carbohydrate intake for a period of days, while maintaining their training levels. The athletes then engage in a practice known as "carbo loading," in which they consume large amounts of carbohydrates, which the body stores in its depleted glycogen reserves, for a desired effect during competition.

SEE ALSO Carbohydrates; Diet; Glycogen depletion; Muscle glycogen recovery.