Coffee/alcohol and dehydration

An interesting question which is very hard to find scientific information about on the internetz is this:

How much alcohol does a drink have to contain to give a net loss of fluid (i.e. act dehydrating)?

Unfortunately, there seems to be no simple answer on this question. A couple of sites cite nutrition experts, such as this one, where a lecturer claims that alcoholic beverages containing more than 10% alcohol gives a net loss; however, the percentage seems to be taken out of thin air. Update: This old study from 1941 hints that on an average every 10 g of alcohol makes you pee out 100 ml, which gives a limit on about 9% (100 g fluid and 10 g alcohol = 10/110 = 9.1%). This would indicate that normal strength beer (~5% alcohol) will actually hydrate you, as only about half of the fluid gets lost due to the diuretic effect of alcohol. However, the response varies highly among individuals.

There are also a couple of random people suggesting that the response is highly individual and dependent on a lot of other circumstances. An anonymous comment here (last comment), for example, suggests that low strengh beer hydrates most people whereas a whiskey does not (duh!). This study from 1997 tells us that drinking 4% beer is worse than drinking water for rehydrating, however it is not clear from the abstract if it has a net positive effect. In this study, results indicate that the diuretic action of alcohol lessens when already dehydrated.

Another, related, question is:

Does coffee really act dehydrating?

This question seems simpler to find an answer to, and that answer is simply no. In fact, under normal circumstances and when not exaggerating intake, coffee can be regarded as water from a hydrating point of view (Wikipedia lists a number of sources). So that coffee acts dehydrating seems to be a plain myth.

Exercise and alcohol

Some short notes about alcohol and exercise:

Many sources, as expected, makes it likely that drinking before or after exercise does not have any positive effects on health. However, there are exceptions, for example the study referenced here indicating that a low alcohol consumption (the equivalent of one pint beer) before exercising has a positive effect in that it reduces the level of clotting substances in the blood thereby having a thinning effect which reduces heart strain.

I have not found any studies showing any increased risks with a moderate alcohol (three beers or less) intake before training, however one should be aware that alcohol causes dehydration, and exercise also causes dehydration, so drinking water and keeping the body hydrated is always important, with or without alcoholic intake in conjunction with training. This study shows that after a little higher alcohol intake (1 g/kg body weight, equivalent to about 1,5 liter beer for a 75 kg person), heart rate increases significantly when exercising with a low intensity, whereas there are no significant change at high intensities. No significant change in systolic blood pressure could be seen.

According to this study, alcohol consumption in conjunction with exercise seem to have a negative effect on the hormone response, making the exercise in itself less effective. However, the negative effect started at 0.75 g/kg body weight (roughly 1 liter beer), and lesser consumption (0.5 g/kg) showed no effect. According to the same study, so called Non-endocrine physiological parameters (NEPP), such as heart rate, blood pressure, ventilation, frequency of breathing, tidal volume, oxygen consumption etc., were the same whether or not alcohol was consumed, indicating no immediate health risks associated with a moderate alcohol consumption.

There are a lot of studies showing that moderate alcohol intake benefits health, for example the study referenced here that shows that people drinking moderately and exercising (not simultaneously :)) has a 50% reduced risk of heart disease, whereas people just drinking, or just exercising, only has a 30% reduced risk.

For people trying to loose weight, alcohol intake seem to have a negative impact in the short term, but unexpectedly people drinking moderately actually weighs less than people that avoids drinking, according to this study. Some sources points out that it is not so much the alcohol in itself that causes weight gain, but the loss of self control introduced by alcohol, which causes intake of other, often high calorific, food. While the liver is engaged with getting rid of the alcohol, fat burning pauses, making the high calorific food in combination with alcohol worse from a weight loss perspective. An article with quite a lot of references on this topic could be found here.


Conclusion:
When searching for information on the topic training and alcohol, one gets a lot of interviews with "health people", such as personal trainers. They generally suggest that alcohol and training is an inappropriate combination, though mostly because the training effect decreases. However, it is hard to find scientific evidence saying that low or moderate alcohol consumption is dangerous or even makes exercise less effective.