Alcohol is consumed by about two-thirds of adult Americans, and the estimated per capita annual consumption of alcohol exceeds 2 gallons for each US citizen over age 14 years. In the US, young adults between 18 and 25 years of age consume more alcohol than any other age group, and the preferred beverages are wine, beer, and spirits in that order. Men and teenage boys consume about 3 times more alcohol than teenage girls and adult women. Among alcohol consumers, most are moderate drinkers, while about 10% are heavy drinkers at risk of addiction and organ damage. Moderate drinking can be defined as no more than 2 drinks per day for men or 1 drink per day for women, where 1 drink is equivalent to 12-15 g of alcohol. Heavy drinking is defined as consuming more than 5 drinks on any given day per week in men or 4 drinks on any given day per week for women. Chronic alcoholics are addicts who typically consume excessive amounts of alcohol on a daily basis. Binge drinkers are chronic alcoholics who escalate their alcohol intake over weeks or months, typically to the exclusion of the essential components of their regular diets. Alcoholic beverages differ in their alcohol content, such that spirits contain about 40g/100ml, wine about 12g/100ml, and beer about 4.5g/100ml. Thus, the amount of alcohol in 12 oz of beer (16 g) is roughly equivalent to the amount found in 5 oz wine or 1.5 oz spirits.
The effects of alcohol on the diet depend upon the amount consumed each day and changes in overall eating behavior. Although alcohol contains 7.1kcal per gram, it is rapidly metabolized to acetaldehyde in the liver at rates up to 50 gh-1, and none is stored as energy equivalents in the body. Furthermore, the metabolism of alcohol influences the metabolism of dietary fat and carbohydrate. There are three metabolic routes for the disposal of alcohol by the body: two in the liver and one in the stomach. Alcohol dehydrogenase (ADH) is present in the cytosol of hepatocytes and metabolizes the relatively low levels of alcohol that would be expected after moderate drinking. The metabolism of alcohol by ADH causes a redox change that promotes lipid synthesis in the liver as well as reduced gluconeogenesis and increased lactate production. Thus, even moderate drinking can cause fatty liver with elevated serum triglyceride levels and, in the absence of dietary carbohydrate, may result in low blood glucose levels that impair concentration and even consciousness. The second liver enzyme, CYP2E1, is part of the cytochrome P450 family, and metabolizes alcohol at levels to be expected after heavy drinking. During metabolism of high levels of alcohol, CYP2E1 utilizes adenosine triphosphate (ATP) energy units and thus 'wastes' stored calories, with resultant potential for weight loss. Another form of this enzyme, gastric CYP2E1, exists in the stomach and, as the first of the three alcohol-metabolizing enzymes to encounter alcohol, accounts for about 30% of all alcohol metabolism in men, but only 10% in women. This gender difference may explain why women's tolerance to alcohol is much less than men's, hence the recognized lower 'safe' level for moderate drinking in women.
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