Print Friendly, PDF & Email

People have been drinking alcoholic beverages for thousands of years – partly due to their intoxicating effects and partly due to the fact that they once provided a safer means of hydration when clean water was scarce.

For many people around the world today, an alcoholic drink is a regular and enjoyable part of meals and many other social occasions like weddings, parties, etc. There is some evidence that people who drink small quantities of alcohol on a regular basis may have better health outcomes than those who do not drink at all, but these findings have been recently challenged. Heavy drinking has no health benefits and studies consistently report that abstainers have better health outcomes than heavy drinkers.

In terms of nutrition, alcohol is the only substance that is both a food providing energy and a drug affecting brain and nervous system function.

ALCOHOL IS A CONCENTRATED FORM OF ENERGY Pure alcohol provides 29 kilojoules (7 calories) of energy for every gram consumed – second only to fats (37kJ/9 calories per gram) in energy density. Moderate drinkers (1 to 2 standard drinks per day, or 10 to 20 grams of pure alcohol per day) usually consume alcoholic beverages as added energy – on top of their normal food intake. Alcoholic beverages may also stimulate appetite, further increasing energy intakes. For these reasons, some moderate drinkers may inadvertently develop a “beer belly”. Heavy drinkers, on the other hand, usually consume alcoholic beverages instead of food, and consequently are often underweight and malnourished.

ABSORPTION AND METABOLISM When consumed, alcohol is very rapidly absorbed into the blood stream from the stomach and small intestine, as it does not require any digestion, and can consequently bring on the familiar feelings of euphoria within minutes if it is consumed on an empty stomach. Around 2 to 10 percent of the alcohol we drink is lost through urine, sweat, or the breath (this is the basis for the breath test for drunkenness), whereas the other 90 to 98 percent is metabolized in the stomach and liver.

Alcohol metabolism begins in the stomach with an enzyme called alcohol dehydrogenase which converts it to acetaldehyde which in turn is converted to acetate and then acetyl CoA a key energy molecule for most of our body’s cells:

Alcohol metabolism
Women produce less alcohol dehydrogenase than men, which is one of the reasons why they are more affected by alcohol than men of the same body size. Acetaldehyde is a highly reactive and toxic compound that is responsible for many of the damaging effects of excessive alcohol consumption. Excess NADH produced in the first two steps of the metabolism of alcohol inhibits the production of glucose in the liver (via gluconeogenesis) and also inhibits the burning of fatty acids. This is one reason why too much alcohol can cause people with diabetes who take insulin or certain blood glucose lowering drugs to have a hypo.

Most alcohol is metabolised in the liver, and there is a limit to how much it can handle – about 15 grams (or 1½ standard drinks) an hour – so excess amounts can build up in the blood rapidly if you drink more than 1 or 2 Standard drinks (a Standard drink contains 10g of pure alcohol) an hour.

IMMEDIATE EFFECTS Of course, the most immediate affect we associate with drinking alcohol is its effect on the brain and nervous system. Most people think that alcohol is a stimulant because it seems to relieve inhibitions. It is in fact a nervous system depressant. Inhibitions decrease first because inhibitory nerves are more easily sedated than excitatory nerves. Judgement and reasoning are affected first as the alcohol sedates our brain’s frontal lobes first. Next, speech and vision centres are affected – speech becomes slurred and vision becomes blurry. Coordination is affected next, walking becomes staggered. Finally, the conscious brain is subdued, and you pass out, preventing the consumption of more alcohol.

It’s well known that alcohol increases the frequency of urination – indeed, it is the origin of the euphemism for excessive drinking – “getting pissed”. Alcohol depresses the release of anti-diuretic hormone from the pituitary gland. This hormone makes the kidneys re-absorb water, so by reducing its production, more is released into the bladder and thirst increases. Drinking more alcoholic beverages to quench the thirst will of course only make the situation worse. This is why it is important to have a non-alcoholic drink as a spacer between alcoholic drinks – it will help reduce dehydration, one of the more unpleasant symptoms of a hangover.

LONGER-TERM EFFECTS The liver prefers to use fatty acids for fuel, but when alcohol is around, it is forced to use it (alcohol) as a fuel, which can lead to a build-up of fatty acids in the liver and an increase in triglycerides in the blood when consumed in excessive amounts. Frequent excessive drinking may therefore lead to what is known as fatty liver disease (excessive fat accumulation in the liver), which in turn may lead to fibrosis and then cirrhosis if heavy drinking and poor nutrition continue for extended periods of time.

Nutrient deficiencies are virtually inevitable in heavy drinkers, because alcoholic beverages may displace food and alcohol interferes with the body’s use of certain nutrients, making some ineffective even if they are present. For example, small intestinal cells may not be able to absorb certain B group vitamins like thiamin, folate and B12 effectively, liver cells lose their ability to activate vitamin D efficiently, and retinal cells in the eye are not able to utilise vitamin A efficiently. The latter being one of the origins of the old saying for those who are completely inebriated: “blind drunk”.

There may be some social benefits to moderate alcohol consumption but none for heavy drinking: Alcohol is a good servant but a cruel master.

Read more:

Dr Alan Barclay
Alan Barclay, PhD is a consultant dietitian and chef (Cert III). He worked for Diabetes Australia (NSW) from 1998–2014 . He is author/co-author of more than 30 scientific publications, and author/co-author of  The good Carbs Cookbook (Murdoch Books), Reversing Diabetes (Murdoch Books), The Low GI Diet: Managing Type 2 Diabetes (Hachette Australia) and The Ultimate Guide to Sugars and Sweeteners (The Experiment, New York).

Contact: You can follow him on Twitter or check out his website.