Key points
- Alcohol is made by fermentation, with fruits and cereals being used in its production.
- It is a source of energy contributing 29 kJ (7 kcal) per gram. Some alcoholic drinks contain traces of vitamins and minerals but not usually in significant amounts.
- Alcohol intake is measured in units of alcohol, with each unit in the UK containing approximately 8 grams or 10 ml of alcohol.
- The Department of Health recommends that men should not consume more than 3-4 units of alcohol/day and women not more than 2-3 units. Regularly drinking more than this can adversely affect health. There is particular concern about binge drinking.
Alcohol (ethanol) is a compound made of carbon, hydrogen and oxygen. It is produced when sugars are fermented by yeasts, producing alcohol and gas (carbon dioxide).
Fruits such as grapes and apples are commonly used to make alcoholic drinks such as wines and ciders, and cereals such as barley and rye form the basis for beers and spirits (whisky or vodka). The alcohol content of drinks varies widely. Other substances provide the flavour associated with the individual drink, e.g. beer draws some of its flavour from barley and hops, gin is traditionally flavoured with juniper berries.
Nutritive Value
Alcohol is a source of energy. It provides 29 kJ (7kcal) per gram of alcohol, compared with 17kJ (4kcal) from protein, 16kJ (3.75kcal) from carbohydrate and 37kJ (9kcal) from fat.
Modest alcohol intakes may be beneficial, although excess is extremely harmful (see below). The UK Department of Health advises that there are no significant health risks at levels of consumption of between 3 and 4 units a day or less for men, and between 2 and 3 units a day or less for women. Consistently drinking more than this per day is not advised as this is linked with a progressive increase of risk to health. For good health, binge drinking should also be avoided. There is particular concern about this behaviour pattern in young people.
Many alcoholic drinks also contain sugars. A few have traces of vitamins and minerals but do not usually make a significant contribution to dietary intake of these. Some alcoholic drinks contain a range of phytochemicals, e.g. red wine contains polyphenols.
Alcohol content of drinks
Since 1989, labels of alcoholic drinks have been required to show the strength. This is expressed as the percentage of alcohol by volume (abv). A 10% abv equates to 7.9 g of alcohol per 100 ml. Beers and cider may range in abv from 4-6%; wines from 9-13%; fortified wines from 18-25% and liqueurs 20-40%.
What happens to alcohol in the body?
Once swallowed, some of the alcohol is quickly absorbed from the stomach and distributed through the body, including the brain, in the blood. If alcohol is consumed with food, it is absorbed more slowly. As blood alcohol levels increase, a person’s judgement is progressively impaired and there is a loss of co-ordination.
Once absorbed, alcohol is metabolised in the liver to provide energy. The rate at which this happens depends on the person’s age, gender, body weight and liver size. On average, 1 unit of alcohol is metabolised ever hour. Generally, symptoms of intoxication appear when blood levels reach about 100mg of alcohol per 100ml blood (~50 g of pure alcohol or ~6 units).
It is very dangerous to attempt to drive after consuming alcohol. In the UK, a person will be prosecuted if found driving with a blood alcohol level of 80mg/100ml and over.
Alcohol in the UK Diet
In 2000 it was estimated by Customs and Excise that each person aged 15 or over consumed, on average, 10.2 litres of alcohol per week (equivalent to 19.3 units of alcohol) per week. Some people drank more than this and some less, with men generally drinking more than women. 60% of all alcohol consumed was in the form of beer and about 25% was wine.
The recent adult National Diet and Nutrition Survey (NDNS) found that, among men and women who drank alcoholic beverages, alcohol contributed on average, 8.1% and 5.7% of their total energy intake. Data from the NDNS suggests that, on average, men were consuming 21.1 units/week and women were consuming 9.0 units/week. The NDNS also highlighted that a number of men and women were drinking more than the recommended guidelines for safe drinking. Among those people who consumed alcohol, 38% of men and 24% of women had more than the maximum, with younger age groups consuming more units/week than older age groups.
Alcohol and health
Excess alcohol intake has been linked to an increased risk of breast cancer in women and to cancers of the mouth and liver in men and women. The risks increase if alcohol consumption is associated with cigarette smoking.
Some studies have suggested that drinking a moderate amount of alcohol regularly can help protect against coronary heart disease (CHD) in those people most at risk, e.g. men over 40 years of age and women who have been through the menopause.
Groups of people requiring special advice about alcohol
Pregnant women
Pregnant women or women trying to become pregnant who wish to drink are advised to drink no more than 1 or 2 units once or twice a week. Alcohol may reduce the ability to conceive, while drinking excessively is associated with a greater risk of miscarriage. Some doctors advise women to avoid alcohol altogether during pregnancy. Fetal alcohol syndrome can occur in babies and children as a result of very heavy alcohol consumption by the mother during pregnancy. The newborn baby may show growth retardation and facial deformities.
Breastfeeding women
Alcohol can pass to the baby in small amounts through breast milk. Therefore women who are breastfeeding should avoid drinking alcohol just before a feed, if they choose not to exclude alcohol while breastfeeding.
People with diabetes
Diabetes UK advises that people with diabetes, like the rest of the population, should not consume excess amounts of alcohol. The carbohydrate content of alcoholic drinks should not be counted as part of the daily allowance. People with diabetes are advised never to drink on an empty stomach.
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