Nutrition, Alcohol Use and Liver Disease

by National Institute of Health

Many alcoholics are malnourished, either because they ingest too little of essential nutrients (carbohydrates, proteins, and vitamins) or because alcohol and its metabolism prevent the body from properly absorbing, digesting, and using those nutrients. As a result, alcoholics frequently experience deficiencies in proteins and vitamins, particularly vitamin A, which may contribute to liver disease and other serious alcohol-related disorders. Furthermore, alcohol breakdown in the liver, both by the enzyme alcohol dehydrogenase and by an enzyme system called the microsomal ethanol-oxidizing system (MEOS), generates toxic products such as acetaldehyde and highly reactive, and potentially damaging, oxygen-containing molecules. These products can interfere with the normal metabolism of other nutrients, particularly lipids, and contribute to liver cell damage. Nutritional approaches can help prevent or ameliorate alcoholic liver disease. For example, a complete balanced diet can compensate for general malnutrition. Administration of antioxidants (precursors of the endogenous antioxidant glutathione) can help the body eliminate reactive oxygen molecules and other reactive molecules generated from abnormal lipid breakdown. New agents currently are being studied as promising nutritional supplements for alcoholics with liver disease.

A complex interplay exists between a person's alcohol consumption and nutritional status. Many people, including light-to-moderate drinkers who consume one to two glasses or less of an alcoholic beverage per day, consider those beverages a part of their normal diet and acquire a certain number of calories from them. When consumed in excess, however, alcohol can cause diseases by interfering with the nutritional status of the drinker. For example, alcohol can alter the intake, absorption into the body, and utilization of various nutrients. In addition, alcohol exerts some harmful effects through its breakdown (metabolism) and the resulting toxic compounds, particularly in the liver, where most of the alcohol metabolism occurs.

This article explores the relationships between a person's alcohol consumption, nutritional status, and risk of alcoholic liver disease. It first describes the nutritional value of alcoholic beverages and discusses how alcohol consumption can contribute to malnutrition in heavy drinkers, with particular emphasis on the effects of alcohol on the digestion and absorption of various nutrients. The article then summarizes the general influence of a person's nutrition on his or her liver function and explores the most important pathways of alcohol metabolism and their relationships with various nutritional factors. The article concludes by reviewing various current and emerging approaches in the nutritional management of alcoholic liver disease.

The Nutritional Value of Alcoholic Beverages

Alcoholic beverages primarily consist of water, pure alcohol (chemically known as ethanol), and variable amounts of sugars (carbohydrates); their content of other nutrients (proteins, vitamins, or minerals) is usually negligible. (Because they provide almost no nutrients, alcoholic beverages are considered "empty calories.") Therefore, any calories provided by alcoholic beverages are derived from the carbohydrates and alcohol they contain. The carbohydrate content varies greatly among beverage types. For example, whiskey, cognac, and vodka contain no sugars; red and dry white wines contain 2 to 10 grams of sugar per liter; beer and dry sherry contain 30 g/L; and sweetened white and port wines contain as much as 120 g/L. Similarly, the alcohol content varies greatly among beverages, ranging from approximately 40 to 50 g/L in beer and coolers, to approximately 120 g/L in wine and prepacked cocktails, to 400 to 500 g/L in distilled spirits. An average drink - namely, 5 ounces (oz) of wine, 12 oz of beer, or 1.5 oz of distilled beverage - contains 12 to 14 grams of alcohol. Pure alcohol provides approximately 7.1 kilocalories per gram (kcal/g), compared with 4 kcal/g for carbohydrates. Thus, a 12-oz can of beer contains approximately 100 calories.

At least under certain conditions, however, alcohol-derived calories when consumed in substantial amounts can have less biologic value than carbohydrate-derived calories, as shown in a study in which Pirola and Lieber compared the weights of two groups of participants who received balanced diets containing equal numbers of calories. In one of the groups, 50 percent of total calories was derived from carbohydrates, whereas in the other group the calories were derived from alcohol. (The study participants were observed on the metabolic ward of a hospital during the experiments. The quantity of alcohol administered did not exceed the amount routinely consumed by these volunteers.) Although all participants received the same number of calories, those in the alcohol group exhibited a decline in body weight compared with those in the carbohydrate group. Moreover, when the participants received additional calories in the form of alcohol, they did not experience any corresponding weight gain. This suggests that some of the energy contained in alcohol is "lost" or "wasted" - that is, it is not available to the body for producing or maintaining body mass. Under other conditions, however, alcohol-derived calories have the same biologic value as calories derived from other nutrients. The various mechanisms involved and the circumstances in which alcohol calories fully count or do not count are described in detail elsewhere.

Several mechanisms have been implicated in the apparent loss of alcohol-derived energy. For example, some of the energy may be used up (wasted) during the breakdown of alcohol by a pathway known as the microsomal ethanol-oxidizing system. As described later in this article, alcohol may damage the liver cells' mitochondria - small membrane-enclosed cell structures that serve as the cell's power plants - and these damaged mitochondria may waste energy during the breakdown of fats.

About the Author

NIH is the nation's medical research agency - making important medical discoveries that improve health and save lives. The National Institutes of Health (NIH), a part of the U.S. Department of Health and Human Services, is the primary Federal agency for conducting and supporting medical research.