Factors Influencing Energy Metabolism

Nutrients that are consumed, digested, and absorbed must still be delivered to the correct tissues for metabolic purposes. A number of factors may inhibit the normal metabolism of nutrients, including nutrient-nutrient interactions, drug-nutrient interactions, and excess alcohol consumption.¹² Of these, regular alcohol consumption is likely to present the greatest difficulties for athletes.

Alcohol Although alcohol is a nutrient that provides 7 calories per gram, it must also be considered an antinutrient because of the way it inhibits the normal metabolism of vitamins and, therefore, the main energy substrates (carbohydrate, protein, and fat) if consumed in excess. Most important, alcohol should not be mistaken for an essential nutrient, which it is not. It is a toxic substance that humans have a limited capacity to detoxify, and in the process, alcohol leaves other toxic substances in its wake.

A regular high intake of alcohol increases disease risk, including cancers of the liver, mouth, throat, and esophagus (these latter three cancers are even more likely if combined with smoking) as well as cirrhosis of the liver (a condition where increasing portions of the liver become fibrotic and are no longer able to function). In addition, alcohol can be an irritant to all segments of the GI tract and, as a result, can cause the malabsorption of nutrients. To make matters worse, alcohol increases the urinary excretion of calcium and magnesium. Magnesium is a cofactor in enzymes transferring phosphate groups, so it is a needed ingredient in energy metabolism.¹³ Regular alcohol intake lowers the resorption of magnesium (increasing urinary losses) and also increases magnesium excretion in sweat. The result is an increase in muscle cramps, weakness, and cardiac arrhythmias. Athletes can ill afford creating the magnesium deficiency associated with regular alcohol consumption.

Because liver function is impaired, alcohol may also interfere with the normal metabolism and storage of nutrients. Taken together, alcohol increases nutrient requirements so as to repair the damage it creates and to counteract the mal absorption it produces. Chronic alcohol abuse may weaken the heart; alter brain and nerve function; increase blood lipids (particularly triglycerides); result in a fatty, cirrhotic liver that malfunctions; and cause pancreatitis (which can have a major impact on blood glucose control and digestive processes.) Besides the increased risk of athletic injury induced by alcohol consumption, there is also evidence that more than one drink per day can have a clear impact on performance by negatively affecting reaction time, coordination, and energy metabolism.

Alcohol dehydrogenase, a liver enzyme, is made by the liver to dehydrogenate the active form of vitamin A (retinol, an alcohol). However, with alcohol (ethanol) consumption, the limited production of alcohol dehydrogenase is shunted to dehydrogenate ethanol, thereby leaving the potentially toxic form of vitamin A in the alcohol form. The result is an adverse interaction between alcohol and vitamin A that can result in liver toxicity and increased cancer risk.¹⁴

The risk of alcohol-related health effects is real in athletes. Although elite athletes consume alcohol half as often as age-equivalent nonathletes, many athletes (particularly those in team sports) still consume far more alcohol than would support good health, good nutrition, and optimal athletic performance.¹⁵ However, non-elite, adolescent athlete groups are more likely to engage in problem drinking than their nonathlete counterparts.¹⁶ Male athletes appear more likely than female athletes to consume alcohol daily.¹⁷

Nutrients Nutrient intake and availability has a clear impact on energy metabolism. Even a single low nutrient from this list will corrupt the normal metabolic pathways for energy utilization and therefore affect athletic performance. Given the potential hazards of inadequate intake, maldigestion, malabsorption, and altered metabolic processes from drug or alcohol ingestion, it is a credit to the human system that most people are able to supply nutrients to the tissues that need them at the time they're required. However, any chronic insult from poor intake, heavy alcohol abuse, or untreated illness will eventually have a negative impact on performance, a fact that athletes and their coaches should constantly bear in mind.

Physical activity increases the need for fuel and for the metabolic processes that are involved in its utilization. Anything that either limits the provision of adequate calories to support the cellular requirement or alters the cells' capacity to properly metabolize the provided fuel will have a negative impact on performance. Some factors are within athletes' control, including adequate food consumption, careful consumption of drugs and supplements, and avoidance of regular alcohol consumption; other factors are not within athletes' control, including disease states that may alter food intake or food absorption. This book is filled with information on how to best provide the fuels needed for successfully pursuing athletic endeavors. For those conditions that are not within the direct control of the athlete (e.g., celiac and Crohn's disease and other GI tract disorders), an increasing number of medical solutions are available; athletes should not hesitate to seek medical advice that can ameliorate the impact these conditions have on health and performance. Ultimately, if the fuel doesn't make it to a cell that has the capacity to burn it, athletic endeavors cannot be successfully pursued.