Alcohol and Nutrition
Nutrition is a process that serves two purposes: to provide energy and to maintain body structure and function. Food supplies energy and provides the building blocks needed to replace worn or damaged cells and the nutritional components needed for body function. Alcoholics often eat poorly, limiting their supply of essential nutrients and affecting both energy supply and structure maintenance. Furthermore, alcohol interferes with the nutritional process by affecting digestion, storage, utilization, and excretion of nutrients.
Impairment of Nutrient Digestion and Utilization
Once ingested, food must be digested (broken down into small components) so it is available for energy and maintenance of body structure and function. Digestion begins in the mouth and continues in the stomach and intestines, with help from the pancreas. The nutrients from digested food are absorbed from the intestines into the blood and carried to the liver. The liver prepares nutrients either for immediate use or for storage and future use.
Alcohol inhibits the breakdown of nutrients into usable molecules by decreasing secretion of digestive enzymes from the pancreas. Alcohol impairs nutrient absorption by damaging the cells lining the stomach and intestines and disabling transport of some nutrients into the blood. In addition, nutritional deficiencies themselves may lead to further absorption problems. For example, folate deficiency alters the cells lining the small intestine, which in turn impairs absorption of water and nutrients including glucose, sodium, and additional folate.
Even if nutrients are digested and absorbed, alcohol can prevent them from being fully utilized by altering their transport, storage, and excretion. Decreased liver stores of vitamins such as vitamin A, and increased excretion of nutrients such as fat, indicate impaired utilization of nutrients by alcoholics.
Alcohol and Energy Supply
The three basic nutritional components found in food–carbohydrates, proteins, and fats–are used as energy after being converted to simpler products. Some alcoholics ingest as much as 50 percent of their total daily calories from alcohol, often neglecting important foods.
Even when food intake is adequate, alcohol can impair the mechanisms by which the body controls blood glucose levels, resulting in either increased or decreased blood glucose (glucose is the body’s principal sugar). In nondiabetic alcoholics, increased blood sugar, or hyperglycemia–caused by impaired insulin secretion–is usually temporary and without consequence. Decreased blood sugar, or hypoglycemia, can cause serious injury even if this condition is short lived. Hypoglycemia can occur when a fasting or malnourished person consumes alcohol. When there is no food to supply energy, stored sugar is depleted, and the products of alcohol metabolism inhibit the formation of glucose from other compounds such as amino acids. As a result, alcohol causes the brain and other body tissue to be deprived of glucose needed for energy and function.
Although alcohol is an energy source, how the body processes and uses the energy from alcohol is more complex than can be explained by a simple calorie conversion value. For example, alcohol provides an average of 20 percent of the calories in the diet of the upper third of drinking Americans, and we might expect many drinkers who consume such amounts to be obese. Instead, national data indicate that, despite higher caloric intake, drinkers are no more obese than nondrinkers. Also, wh en alcohol is substituted for carbohydrates, calorie for calorie, subjects tend to lose weight, indicating that they derive less energy from alcohol than from food.
The mechanisms accounting for the apparent inefficiency in converting alcohol to energy are complex and incompletely understood, but several mechanisms have been proposed. For example, chronic drinking triggers an inefficient system of alcohol metabolism, the microsomal ethanol-oxidizing system (MEOS). Much of the energy from MEOS-driven alcohol metabolism is lost as heat rather than used to supply the body with energy.
NIAAA
National Institute on Alcohol Abuse and Alcoholism
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