Ethanol, aka "alcohol", is perhaps the most widely consumed drug on Earth. With the exception of its effects on heart disease, few people would claim it is good for you. But, because of its legality, omnipresence, and just the fact that it is so much fun, most think very little of having a few beers or even a few six packs. This includes many bodybuilders.
However, it is far from being a harmless vice, even in non-alcoholics. It affects numerous neurotransmitters, metabolic processes, and hormones -- and many of these effects go beyond the time period of intoxication. These have ramifications, not only for general health, but as you will see, body composition as well.
This is the first of a two parts series -- We will first look at the basic science of ethanol, then we will turn to its effects on body composition in the second installment. We will not be looking at the effects of chronic ethanol consumption, addiction, and withdrawal, as they are not relevant to what I consider as my target audience. Suffice it to say, such a lifestyle is utterly incompatible with getting the most out of one's bodybuilding efforts.
Biochemistry
Ethanol, in addition to being a drug, is also a nutrient (1). However, unlike the other nutrients such as carbs, fat and protein, the body lacks the ability to store ethanol (1) -- It is also the only toxic macronutrient (1). These two characteristics lead to some important consequences -- namely, it must be metabolized, and this metabolism take precedence over all other nutrients (2).
It is metabolized by one of two pathways, depending on blood levels. The primary is to aldehyde, via alcohol dehydrogenase (ADH) (3). However, at high levels, what is known as the microsomal ethanol oxidizing system (MEOS) becomes a significant pathway (4). Both result in conversion to acetate, then acetyl-CoA -- where it can either a) enter the tricarboxylic acid cycle and be oxidized into CO2 and water, or b) be stored a fat (1).
Pharmocokinetics
Ethanol is readily bioavailable with oral administration, however, oral clearance rate and % absorption decrease in the post-prandial state (i.e. with food) (5), due to the presence of ADH activity in the stomach (6). The more food in the stomach, the longer the ethanol stays there to be metabolized before it reaches the bloodstream. The type of food will effect this, with protein and fat have the greater effect. Fat, due to slowing transport into the small intestine, protein, probably through direct binding with the ethanol molecule (7).
The type of drink can also effect blood alcohol levels obtained - particularly in the fed state. For instance, after a meal, a less concentrated drink (such as a beer) will be absorbed more quickly than a more concentrated one (such as a shot) -- and, in rats, this led to an 80% higher peak blood alcohol level and 95% higher overall absorption (8). However, on an empty stomach, the opposite was found, though the magnitude of the difference was not as strong.
It is also interesting to note that when large amounts are taken in, absorption can exceed systemic distribution, thus exceptionally high concentrations can occur in arterial blood, and, therefore, the brain (7). This is why bonging 6 beers right in a row hits you harder than drinking 8 drinks over 2 hours.
Despite popular opinion to the contrary, women do not metabolize ethanol more slowly than men - the opposite is in fact true. Failure to take into account differences in total body water (i.e. LBM) between men and women has accounted for much of this confusion (9). But, when normalized for total body water, women metabolize ethanol 33% faster than men, due to a proportionally larger liver (10).
Due to limitations of ADH, metabolism of ethanol follows zero-order, straight line kinetics - meaning it is broken down at a constant rate (about a drink per hour) rather than having a half-life as most drugs do (11).