Alcohol and nutrition; an overview
Alcohol and Nutrition
Alcohol has profound effects on nutritional status (Lieber 1982; 1988a). In chronic drinkers, ethanol depresses the appetite, displaces other foods from the diet, and decreases the value of food by interfering with digestion and absorption. When nutrients are absorbed, alcohol prevents them from being fully utilized by the body by altering their transport, metabolism, and storage. As a result, patients hospitalized for medical complications associated with alcoholism may be severely malnourished with signs of protein deficiency. Such medical complications--particularly liver disease--were long attributed exclusively to nutritional deficits.
This concept has been challenged over the past 30 years by dramatic research findings regarding the role of alcohol in the disease process. One such finding is the discovery that moderate doses of alcohol, added to a normal diet with plenty of vitamins and protein, can lead to liver damage within a few days (Lieber et al. 1963; 1965; Lieber and Rubin 1968). At the same time, statistics show that the incidence of malnutrition among alcoholics has been decreasing while the number of deaths attributable to alcoholic liver disease continued to rise. Studies show that moderate drinkers--even persons admitted to hospitals for alcoholism rehabilitation--are no more malnourished than are nonalcoholic controls with similar socioeconomic and health histories (Bebb et al. 1971; Neville et al. 1968).
While the effects of alcohol-nutrition interactions can be seen at the organism level--in the consumer of alcohol as well as in the laboratory animal--the key to understanding them is to observe them at the subcellular level. This overview will introduce some of the biochemical bases of these alcohol-nutrition interactions, which will be described further in the series of articles in this issue. Although the molecular mechanisms involved in these interactions may be complex, they all fit into the simple conceptual scheme summarized in Figure 1.
While severe malnutrition may be relatively rare, the effects of subtle nutritional disturbances become more significant as alcohol intake increases. Alcohol supplies extra calories in the diets of light drinkers, but replaces other energy sources in the diets of moderate and heavy drinkers. While the estimated average contribution of alcohol to the diet of Americans is only 4.5 percent of total energy (Scheig 1970), heavy drinkers may derive more than one-half of their total daily energy (measured in calories) from ethanol. This energy represents "empty" calories (Figure 1), because it is not associated with substantial amounts of vitamins, minerals, or protein.
Thus, as alcohol consumption increases, the percentage of energy derived from protein, fat, and carbohydrate decreases and the nutritional quality of the diet declines (Hillers and Massey 1985; Sherlock 1984). Concurrently, intake of vitamins A and C and thiamin may fall below the recommended daily allowances for those substances (Gruchow et al. 1985), and the consumption of calcium, iron, and fiber declines as well (Hillers and Massey 1985). In addition, ethanol may enhance nitrogen loss in the urine of rats (Klatskin 1961) and man (McDonald and Margen 1976; Bunout et al. 1987), thereby possibly increasing protein requirements....