Alcohol is a popular ‘nutrient’ consumed in large quantities all over the world. In many countries, alcohol consumption is becoming a major problem.
Ethanol (ethyl alcohol) is oxidized in the following steps (Information box 3.4) to acetaldehyde.
1 Acetaldehyde is then converted to acetate mainly in the liver mitochondria.
2 Acetate is released into the blood and oxidized by peripheral tissues to carbon dioxide, fatty acids and water. Alcohol dehydrogenases are found in many tissues and it has been recently suggested that enzymes present in the gastric mucosa may contribute substantially to ethanol metabolism.
Ethanol itself produces 7 kcal s’ (29.3 kJ g-‘), but many alcoholic drinks also contain sugar, which increases their calorific value. For example, one pint of beer provides 250 kcal (1045 kJ). Therefore, the heavy drinker will be unable to lose weight if he or she continues to drink.
Effects of excess alcohol consumption
Excess consumption of alcohol leads to two major problems, both of which can be present in the same patient:
• Alcohol dependence syndrome
• Physical damage to various tissues
Each unit of alcohol, e.g. half a pint of beer, one single spirit, one small glass of wine, contains 8 g of ethanol. All the long-term effects of excess alcohol consumption are due to excess ethanol, irrespective of the type of alcoholic beverage, i.e. beer and spirits are no different in their long-term effects.
Short-term effects, such as hangovers, depend on additional substances, particularly other alcohols such as isoamyl alcohol, which are known as congeners. Brandy and bourbon contain the highest percentage of congeners.
The amount of alcohol that produces damage varies and not everyone who drinks heavily will suffer physical damage. For example, only 20% of people who drink heavily develop cirrhosis of the liver. The effect of alcohol on different organs of the body is not the same; in some patients the liver is affected,in others the brain or muscle. The differences may be genetically determined
In general the effects of a given intake of alcohol seem to be worse in women. The following figures are for men and should be reduced by 50% for women. For liver disease
• 160 g ethanol per day (20 single drinks) carnes a high risk
• 80 g ethanol per day (10 single drinks) carnes a medium risk
• 40 g ethanol per day (five single drinks) carries little risk. Heavy persistent drinkers for many years are at greater risk than heavy sporadic drinkers.
Susceptibility to damage of different organs is variable and the figures in Information box 3.5 are only a guide .
Alcohol consumption in pregnancy
Women are advised not to drink alcohol at all during pregnancy as even small amounts of alcohol consumed can lead to ‘small babies’.
The fetal alcohol syndrome is characterized by mental retardation, dysmorphic features and growth impairment; it occurs in fetuses of alcohol-dependent women.
A summary of the physical effects of alcohol is given. Details of these diseases are discussed in the relevant chapters. The effects of alcohol withdrawal.
Dietary Reference Values for Food Energy and Nutrients for the United Kingdom. 41 DOH 1991. Report of the Panel on Dietary Reference Values of the Committee on Medical.
Aspects of Food Policy. London: HMSO.
Garrow GS (1988) Obesity and Related Disorders. Edinburgh:
Truswell AS (1990) ABC of Nutrition, 2nd edn. London: British Medical Association.
Shilo ME, Young BR (1988) Modern Nutrition in Health and Disease, 7th edn. Philadelphia: Lea & Febiger.