By Professor Ron Maughan, University of Aberdeen.
For some athletes, alcohol does not feature at all in their diet but for others, it is an important part of the diet. Abstainers do so for a variety of reasons, including taste, social and religious reasons and an unwillingness to experience some of its unwanted effects. Some also avoid alcohol because of the possible effects on exercise performance, but there is much confusion and uncertainty in this area.
Alcohol is a high-energy food, giving 7 calories per gramme, compared with about 4 calories/g for protein and carbohydrate (CHO) and 9 calories/g for fat. Some drinks contain small amounts of carbohydrate, but most of the calories in alcoholic drinks come from alcohol and alcohol is not a good fuel for exercising muscles. The liver converts alcohol to a form that can be used as a fuel or can be converted to fat for storage, but it cannot be used at high rates as can carbohydrate. Beer does supply some carbohydrate, but
only about one third of the total calories are in the form of carbohydrate, so it is certainly not a good source. The standard measure of different alcoholic drinks is roughly inversely proportional to the alcohol content. In the UK, one unit of alcohol contains about 8-10 grammes of ethyl alcohol, whether in the form of beer, wine or spirits. Note that one unit equals one half-pint of beer.
Alcohol and health
Although the picture is by no means clear, it does seem that regular moderate alcohol intake is associated with an increased body fat content and that chronic alcohol abuse is associated with a number of nutritional deficiencies. Men who regularly drink more than 25 pints of beer or its equivalent (50 units) each week are likely to develop some form of alcohol related damage. For women the comparable amount is lower, at 35 glasses of wine or its equivalent (35 units). Approximately 6% of men and 1% of women in the UK drink above that level. Binge drinking, where large amounts of alcohol are consumed on an episodic basis, is common in some groups of athletes, but is far more likely to be damaging than consumption of the same amount spread over the week. Alcohol intake is associated with a number of health risks and possibly some health benefits. A major problem with epidemiological surveys is the difficulty in obtaining reliable estimates of intake. Nonetheless, the available data show a clear relationship between alcohol intake and cirrhosis of the liver. Epidemiological studies show a clear link between alcohol consumption and high blood pressure. Reducing alcohol intake results in a fall in blood pressure. The risk of suffering a stroke is increased by alcohol. There is a clear “J-shaped” relationship between alcohol consumption and coronary heart disease. Lifelong abstainers are at slightly higher risk than light or moderate consumers, but risk increases with higher intakes. The reasons for this are the subject of much debate. Epidemiological evidence suggests a link between alcohol intake and cancers of the mouth, oesophagus and larynx. This effect is small, but smoking multiplies the risk substantially. Most athletes, however, have a healthy lifestyle and high levels of physical activity, low levels of body fat and a good diet are all protective against most of these diseases. The good news is that a recent comprehensive review of the evidence on alcohol and health concluded that: “There can be little doubt that light to moderate consumption of alcoholic beverages (not exceeding 40 grammes of alcohol per day) is associated with benefit to health and social interactions”. 40 grammes of alcohol is about five units.
Alcohol and performance
Alcohol was formerly widely used in endurance sports, being administered during exercise. There are potential benefits and disadvantages of alcohol use in sport:
Psychological effects: - CNS (Central Nervous System) disinhibition
- reduced pain sensitivity
- reduced anxiety & tremor
Physiological effects: - cardiovascular/thermoregulatory
- impaired gluconeogenesis
- negative fluid balance
There are few controlled studies on the effects or after effects of alcohol on sport or exercise performance. There are real ethical difficulties with the conduct of such studies. Reviewing the limited data in the published scientific literature, Mel Williams concluded that: “Social alcohol consumption, in moderation, has no beneficial or detrimental effect upon physical performance.” Anecdote is generally unreliable, especially when self-reports are concerned, but the available evidence suggests that there is little effect on performance of exercise while recovering from acute alcohol intake.
Alcohol after exercise
Alcohol has been reported to decrease the rate of glycogen synthesis after exercise, but this may not be a metabolic effect. Burke and her colleagues at the Australian Institute of Sport investigated effects of adding alcohol to high carbohydrate meals consumed after exercise. When alcohol (100 grammes) was added to the diet, glycogen synthesis was not affected, but when alcohol displaced carbohydrate (so that the meals contained the same amount of energy, i.e. they had less carbohydrate) glycogen synthesis was slowed. Alcohol consumption is often associated with poor food choices and with reduced (non-alcohol) energy intake and the main effect of alcohol on glycogen synthesis is therefore likely to be a reduced CHO intake. This will reduce the rate of glycogen resynthesis and may impair recovery. If you do want to go out after a training session or competition, the message should be to make sure that you have a good carbohydrate meal first.
Alcohol has a diuretic action, stimulating urine formation, and for this reason, it is usually recommended that alcohol (and caffeine!) intake be reduced or avoided when fluid balance might be compromised. This advice is given to air travellers and to athletes competing in warm climates where water losses in sweat are likely to be high. However, as long ago as 1942, it was shown that small amounts of alcohol did not impair rehydration in subjects who were already dehydrated. More recent studies have also confirmed this. Drinking strong alcohol is probably not a good idea, but weak beer (or beer shandy) is an effective way to rehydrate. There is also habituation to the effects of caffeine: the situation with alcohol is less clear, but those who drink regularly are probably better able to cope.
There is no firm evidence, but reports from sports physiotherapists who are used to working with athletes suggest that soft tissue injuries may take longer to repair if athletes consume alcohol after the injury. This may relate to several factors:
- increased muscle blood flow leading to increased muscle swelling
- decreased pain sensitivity encouraging over-use
- failure to observe good practice – RICE (Rest, Ice, Compression, Elevation), to promote recovery
It seems sensible to restrict intake whenever there is a risk of muscle damage. Remember too that alcohol impairs judgement. It is a good thing to socialise and celebrate with teammates, but serious athletes will recognise that excess alcohol is very definitely harmful and will moderate their intake accordingly. Equally, a small amount of alcohol is not harmful and there is no reason not to be sociable from time to time. Cheers!
