What is alcohol?
Alcohol is formed when yeast ferments (breaks down without oxygen) the sugars in different food. For example, wine is made from the sugar in grapes, beer from the sugar in malted barley (a type of grain), cider from the sugar in apples, vodka from the sugar in potatoes, beets or other plants.1
Alcohol is classed as a ‘sedative hypnotic’ drug2, which means it acts to depress the central nervous system at high doses. At lower doses, alcohol can act as a stimulant,3 inducing feelings of euphoria and talkativeness, but drinking too much alcohol at one session can lead to drowsiness, respiratory depression (where breathing becomes slow, shallow or stops entirely), coma or even death.4,5,6
As well as its acute and potentially lethal sedative effect at high doses, alcohol has effects on every organ in the body and these effects depend on the blood alcohol concentration (BAC) over time.7
- Centers for Disease Control and Prevention.(2010). Alcohol and public health:Frequently asked questions. 2010. From http://www.cdc.gov/alcohol/faqs.htm.
- Alcohol. (2008). In C. Kuhn, S. Swartzwelder & W. Wilson (Eds.), Buzzed: The straight facts about the most used and abused drugs from alcohol to ecstasy (3rd ed., pp. 33–61). New York: WW Norton.
- Roehrs, T., & Roth, T. (2001). Sleep, sleepiness, and alcohol use. Alcohol Research & Health, 25(2), 101–109.
- Brust, J. C. M. (2005). Alcoholism. In L. P. Rowland (Ed.), Merritt’s neurology (11th ed.). Philadelphia: Lippincott Williams & Wilkins.
- Vonghia, L., Leggio, L., Ferrulli, A., Bertini, M., Gasbarrini, G., Addolorato, G., et al. (2008). Acute alcohol intoxication. European Journal of Internal Medicine, 19(8), 561–567.
- Lohr, R. H. (2005). Acute alcohol intoxication and alcohol withdrawal. In R. M. Wachter, L. Goldman & H. Hollander (Eds.), Hospital medicine (2nd ed.). Philadelphia: Lippincott Williams & Wilkins.
- Zakhari, S. (2006). Overview: How is alcohol metabolized by the body? Alcohol Research & Health, 29(4), 245–254.
After a drink is swallowed, the alcohol is rapidly absorbed into the blood (20% through the stomach and 80% through the small intestine), with effects felt within 5 to 10 minutes after drinking. It usually peaks in the blood after 30-90 minutes and is carried through all the organs of the body.
Most (90%) of the metabolism, or breaking down, of alcohol from a toxic substance to water and carbon dioxide is performed by the liver6, with the rest excreted through the lungs (allowing alcohol breath tests), through the kidneys (into urine) and in sweat.8
The liver can only break down a certain amount of alcohol per hour, which for an average person is around one standard drink8.
The blood alcohol concentration (BAC) rises, and the feeling of drunkenness occurs, when alcohol is drunk faster than the liver can break it down. However, BAC does not correlate exactly with symptoms of drunkenness and different people have different symptoms even after drinking the same amount of alcohol. The BAC level, and every individual’s reaction to alcohol, is influenced by1,2,7:
- the ability of the liver to metabolise alcohol (which varies due to genetic differences in the liver enzymes that break down alcohol)7
- the presence or absence of food in the stomach (food dilutes the alcohol and dramatically slows its absorption into the bloodstream by preventing it from passing quickly into the small intestine)
- the concentration of alcohol in the beverage (highly concentrated beverages such as spirits are more quickly absorbed)
- how quickly alcohol is consumed
- body type (heavier and more muscular people have more fat and muscle to absorb the alcohol)2
- age, sex, ethnicity (eg, women have a higher BAC after drinking the same amount of alcohol than men due to differences in metabolism and absorption – since men have, on average, more fluid in their body to distribute alcohol around than women do, some ethnic groups have different levels of a liver enzyme responsible for the break down of alcohol)
- how frequently a person drinks alcohol (someone who drinks often can tolerate the sedating effects of alcohol more than someone who does not regularly drink).6
NB - The legal drink driving limits for drivers 20 years and over are a breath alcohol limit of 250 micrograms (mcg) of alcohol per litre of breath and a blood alcohol limit of 50mg of alcohol per 100ml of blood. The alcohol limit for drivers under 20 years is zero.
Energy (kilojoules/Calories) in alcoholic drinks
Alcoholic drinks can add more Calories or kilojoules to our daily diet than we realise.
It’s the alcohol itself that is the main source of energy (kilojoules or Calories), with each gram of alcohol containing 29 kilojoules or 7 Calories. This is more than protein or sugars/carbohydrates (17 kilojoules or 4 Calories per gram) but less than fat (37 kilojoules or 9 Calories per gram).
Other than providing kilojoules, alcoholic drinks have very few nutrients needed for health.
Kilojoule or Calorie information is not usually on alcoholic drink labels. This makes it hard to find out how many kilojoules are in drinks or to compare drinks. Unlike non-alcoholic drinks and packaged foods, alcoholic drinks are not required to be labelled with kilojoules or nutrient content information, unless a nutrient claim is made, such as ‘99% sugar free’.
As a general guide, the higher the percentage of alcohol, the more kilojoules there will be in a drink. Sweeter drinks or drinks that contain sweetened mixers, such as ready-to-drink spirits (RTDs), or cream also have more kilojoules. What we eat and drink alongside also contributes kilojoules.