Alcohol is the most often used by athletes recreational drug. According to a dictionary, drug is a substance that acts on the nervous system, causing sedation, pain relieve, intoxication, euphoria or sleepiness. Alcohol is not an essential component of the human diet. 1 g of ethanol provides about 7 calories of energy (in theory, the issue will be developed further in the text).
Let's take into account the amount of ethanol and its caloric value only:
- 500 ml beer, 4.5% - contains 22.5 ml of ethanol (~18 g). This makes 126 kcal in 500 ml,
- 500 ml beer, 6% - contains 30 ml of ethanol (23.7 g). This makes: 142.2 kcal in 500 ml,
- 500 ml beer, 10% - contains 50 ml of ethanol (39.5 g). This makes 276.5 kcal in 500 ml,
- Vodka 250 ml (40% ethanol) - provides 100 ml of ethanol (78.9 g), which makes 552.3 kcal.
For example, a 0,33 l bottle of stout supplies:
- 0.2-1.3 g of fat,
- 3 g of protein,
- 23.1 g carbohydrates,
That is, 105 kcal. Additionally it is known that dark beer may comprise approx. 20 ml of ethanol in 0.33 litre: 140 kcal or more. So a 0,33 l bottle of beer gives your appx. 245 kcal. 
A pint of ale beer has around 371 kcal.
Given all of the nutrients:
- A pint of lager, about 500 g. is 245 kcal
- A pint of stout, about 500 g. is 371 kcal
- A glass of whiskey - 125 kcal,
- Semi-dry white wine - a 100 g glass - 81 kcal,
- Sweet white wine, sweet, a 100 g glass - 95 kcal,
- Dry white wine, a 100 g glass - 66 kcal,
- Red wine, a 100 g glass - 68 kcal,
- Vodka, a 50 g glass - 110 kcal 
Alcohol has a multidirectional impact on:
- metabolism, including obtaining energy from fat,
- heart and circulatory system,
- thermoregulatory functions,
- hormonal system,
- liver, kidneys.
Data from New Zealand have shown that many students who train athletics professionally drink more alcohol in comparison to a group of physically inactive. Research from France brought conflicting results: some say athletes consume greater amounts of alcohol, others - lower.
The impact of alcohol on glycogen metabolism
Glycogen is the primary component of the energy stored in your body. Athletes have large resources of stored glucose, estimated at least at 1,600 kcal for a person weighing 70 kg. Burke checked how drinking alcohol affects the restoration of glycogen after intense cycling.
Three types of "diet" were applied:
- control group: high carbohydrate diet, optimal for glycogen stores recovery,
- alcohol and reduced amount of carbohydrates (instead of 210 grams of carbohydrates, 120 g of alcohol were supplied),
- Alcohol + carbohydrates (120 g of alcohol + a large amount of carbohydrates).
Results: 8 hours after the training (glycogen mmol / kg):
- Control group (carbohydrates): 44.6 ± 6;
- alcohol (120 g), and smaller amounts of carbohydrates: 24.4 ± 7
- alcohol (120 g) + carbohydrates: 36.2 ± 8
Results: 24 hours after training (glycogen mmol / kg):
- Control (carbohydrates): 81.7 ± 5
- alcohol (120 g), and smaller amounts of carbohydrates: 68.4 ± 5
- alcohol (120 g) + carbohydrates 85.1 ± 9
Conclusions from the study:
- As you can see, with reduced resources of carbohydrates in the diet and the addition of alcohol, after 8 hours the glycogen in the muscles has halved in comparison to the high-carbs group.
- However, the impact of alcohol in correspondingly large surplus of carbohydrates is not clear. After 8 hours, the difference in muscle glycogen between the groups (high-carbs, high-carbs and alcohol) was insignificant, and after 24 hours none - control group 81.7 ± 5, and a group with alcohol + carbohydrates: 85.1 ± 9
- Scientists emphasise that individual differences between different people are so important that one participant would suffer big disturbance in restoring carbohydrates resources in the muscles after drinking alcohol (even with an adequate supply of carbohydrates), while another will not feel at all the effects of alcohol on slowing down the process of post-workout regeneration.
- People who drink a lot of alcohol may have a problem with providing the right amount of carbohydrates - another source of energy - and ethanol is not very effective. 
The impact of alcohol on dehydration and thermoregulation
Dehydrating effect of ethanol has been well known for at least a few hundred years. Eggleton estimated that for every gramme of ingested ethanol 10 ml of urine is produced.
Alcohol acts to suppress the secretion of the antidiuretic hormone: vasopressin in the pituitary gland. Research shows that a competitor's rehydration with water or a soft drink containing up to 2% of alcohol is comparable, whereas 4% of alcohol in a drink (for example a weak beer) slows down regeneration processes since there is increased excretion of urine (further loss of water). Interestingly, the higher alcohol concentration, the worse it gets. Vodka containing 40% ethanol has 10 ml of alcohol and 15 ml of water in a 25 ml portion. Drinking 25 ml of vodka causes discharge of more than 100 ml of water, so the water balance worsens by 85 ml.
Alcohol worsens thermoregulation, for instance it increases heat loss in winter. It has been found that consumption of 2.5 ml of alcohol per kg of body weight resulted in increased heat loss during 3 h long endurance training. It was also found that alcohol impairs adaptation to high and low temperatures.