This is the first in a three-part series What You Need to Know About Alcohol. This part explains how we process alcohol, its effect on our body and some tips for avoiding and managing the dreaded hangover. Part 2 takes an objective look at the studies to identify whether alcohol is healthy or harmful, and in Part 3 I’ll share public health recommendations for alcohol consumption, as well as a few of my own.

So what exactly is alcohol?

Alcohol is made by fermenting and distilling carbohydrates or starches such as fruits (wine, cider) or grains (beer, spirits). It’s a unique substance as it is both a source of energy/calories, but is also a legal psychoactive substance, and is actually one of the most commonly consumed “recreational drugs” in the world.

Technically, alcohol is a macronutrient. But unlike the other macronutrients (protein, carbs and fat), alcohol has zero nutritional value. Yep, your body doesn’t need it.

But it gets worse: alcohol is very calorie-dense; it has 7 calories (29 kJ) per gram. That’s almost as much as fat, at 9 calories (37 kJ) per gram, and much higher than carbs and protein, at 4 calories (17 kJ) per gram.

And even worse: our bodies actually deal with alcohol as a poison, so when we consume alcohol, our liver cells are forced to process it first, delaying other important metabolic processes. This means that our liver is not available to process other nutrients including the fatty acids in our system, which can lead to significant build-ups of fatty acids in our liver. If you regularly consume alcohol, you can permanently alter how your liver metabolises fats, and over time contribute to the development of fatty liver (discussed in more detail in Part 2 of this series). Increases in liver fat levels have been seen after single night of heavy alcohol consumption.

How is alcohol processed in the body?

When we consume alcohol, 2-8% of it is excreted through sweat, urine, and saliva. This is how blood-alcohol content is measured in breathalyser and urine tests.

But the great majority of the alcohol we consume enters our bloodstream via our digestive system. About 20% is rapidly absorbed via our stomach, with the remaining 80% travelling through the gastrointestinal tract, and entering bloodstream via our small intestine.

Whilst in the stomach, alcohol acts as an irritant. It causes increased secretion of hydrochloric acid, and if you consume it in amounts high enough to cause intoxication it can actually halt digestion of food and impair nutrient absorption. In the short term this can cause nausea and indigestion, but if this happens regularly, you risk causing damage to the lining of your stomach.

Bottom line: whether absorbed via our stomach or small intestine, the alcohol we consume ends up in our bloodstream. And it happens fast. Alcohol molecules are tiny, dissolve in both water and fat. Unlike other macronutrients (carbs, protein and fat), digestive enzymes are not necessary for alcohol absorbtion.

Our bodies can’t store alcohol. Once consumed, it has to be metabolised (or processed). Because our body views alcohol as a toxin, the liver shoulders the lion’s share of the work in alcohol metabolism. Our liver contains a special set of enzymes to metabolise alcohol, converting it to acetaldehyde. Acetaldehyde is then rapidly processed by an enzyme called aldehyde dehydrogenase 2 (ALDH2), converting it to acetate (or acetic acid), which is then broken down into water and carbon dioxide. Acetaldehyde is only present in the body a very short period of time, but it is highly toxic and a known carcinogen. Studies show that it can chemically damage DNA and the DNA cells.

Whenever we have alcohol in our system, the liver’s other important functions are pushed down the list of priorities, including fat metabolism which over time can lead to fatty liver or even cirrhosis.

When we consume alcohol in amounts that are higher than our liver enzymes can process, the excess alcohol just keeps circulating around our body in our bloodstream until our poor liver is eventually able to process it all. Alcohol enters all tissues of the body except bone and fat.

So some other parts of our body, like our brain and pancreas, will also be “forced” to metabolise alcohol. And unfortunately, the acetylaldehyde that is produced, is just as damaging in these organs as it is in our liver.

Alcohol acts as both a sedative and a depressant in the body. It starts to affect our brains within five minutes of consumption. When it reaches the brain, it slows down the body's systems, so our co-ordination, reaction time and cognitive ability are all impaired. Our frontal lobe, responsible for our executive function, judgment and reasoning, is particularly susceptible to alcohol exposure (which goes a long way towards explaining why our commitment to healthy eating often goes out the window when we drink, not to mention increased likelihood of other questionable decisions). With increasing alcohol consumption our speech and vision is impacted, followed by muscle control and in severe cases breathing and heart rate are impacted.

Check out this interactive body map to see how alcohol impacts different organs in the body: https://www.collegedrinkingprevention.gov/specialfeatures/interactivebody.aspx

How long does alcohol stay in our system?

We absorb alcohol into our system at a much faster rate than we can metabolise and eliminate it.

Our blood alcohol concentration peaks between 30 and 45 minutes after consumption of one standard drink**.

There is nothing you can do to speed up your body’s rate of alcohol clearance. Coffee won’t do it. Drinking water won’t do it. Trying to “sweat it out” won’t do it.

Alcohol has a “steady state” metabolism.* On average, we metabolise 10-12g of alcohol each hour. That’s roughly equivalent to one “standard drink”; 350mL beer, 150mL wine or 40mL spirits. But it’s important to realise that we all process alcohol at different rates, and it could take up to three hours for some people to process the alcohol in one alcoholic drink.

What factors influence how alcohol impacts us?

There are many factors that can affect how alcohol affects us. Here are just a few:

1. Age

As we age, our efficiency at metabolising alcohol declines. This means that alcohol will stay in our system longer.

2. Sex

Unfortunately, there is no gender equity when it comes to alcohol.

Women tend to have higher body fat and lower body water percentage, so the alcohol they consume will be less diluted. Women also produce less of the alcohol metabolising enzyme alcohol dehydrogenase (ADH). These factors mean that our blood alcohol levels can climb faster than men, and that we will metabolise alcohol more slowly than men, so alcohol will stay in our system longer.

But it’s not just our size and body composition that influences our response to alcohol. Even when we adjust for height and weight, studies show that alcohol has a much greater impact on women. So we are much more susceptible to adverse health impacts of regular alcohol consumption including liver damage, heart disease and brain atrophy. And women who drink are at increased risk of breast cancer (more on that in Part 2).

3. Body size and composition

People with larger frames will generally metabolise alcohol faster than those with a small frame, as will people with lower body fat percentages. This is because body fat contains less water, which means that alcohol will be less diluted in those with higher body fat percentages.

4. Liver health

If your liver is damaged or impaired, you will of course experience impaired alcohol metabolism, which means your blood alcohol levels will stay elevated for longer.

5. Genetic makeup and Ethnic heritage

We all have different amounts of the liver enzymes which break down alcohol, according to our genetic make-up. So some of us will naturally process alcohol faster than others.

If you are of East Asian heritage, there’s about a 50% chance that you might produce insufficient enzymes necessary to effectively metabolise alcohol, and in particular the ALDH2 that processes the DNA damaging acetaldehyde. So alcohol will cause facial flushing, dizziness, headache, nausea, and rapid heartbeat.

6. Food

We all know we shouldn’t drink on an empty stomach. But I’m going to give you a few science-backed reasons why it really is a bad idea:

Eating before consuming alcoholic drinks can significantly slow the rate of alcohol absorption (and therefore inebriation). Most of the alcohol we consume is absorbed into the bloodstream via our digestive tract. If you consume an alcoholic drink on an empty stomach, the alcohol in that drink will be fully absorbed with about 30 minutes. But if you have already consumed a meal, it can take up to 90 minutes.

In addition to slowing alcohol absorption, eating before you consume alcohol will also cause you to metabolise alcohol faster than if you had consumed it on an empty stomach. This is believed to be due to the fact that your meal has already stimulated your liver and liver enzymes.

It’s an especially bad idea to hit the booze after an all-day fast. Here’s why: our enzymes - including the liver enzymes like ADH that metabolise alcohol - are proteins. Our bodies just aren’t built to store safety reserves of proteins and amino acids. So if you go without food for an extended period, your body will basically grab the amino acids it needs for its protein synthesis from wherever it can get them, and that includes alcohol metabolising liver enzymes like ADH. So fasting all day will deplete your body of the enzymes it needs to metabolise and eliminate alcohol from your system.

So if you are going to imbibe, make sure you eat first, m’kay?

7. Time between drinks

We’ve all heard the advice to space out your alcoholic drinks or to alternate one alcoholic drink with one (or more) non-alcoholic drinks, especially during the party season. This is because our body metabolises alcohol in a steady, linear manner. You can’t speed up the rate of alcohol clearance from your body, so if you consume too many alcoholic drinks too close together you will be consuming alcohol at a faster rate than your body’ can eliminate it - your blood alcohol level will increase, as will your feelings of inebriation.

8. Fizzy alcohol

It’s not just you imagination. Fizzy alcoholic drinks like prosecco, champagne and cava will “go to your head” faster and there’s a super simple scientific explanation: the bubbles in these drinks increase pressure in your stomach which forces the alcohol into your bloodstream faster.

9. Medications

We need to be really cautious about consuming alcohol when we are on medications. Our liver doesn’t just metabolise alcohol. It also has to metabolise any medications we take. So it’s super important to check with your doctor or pharmacist whether your medication interacts with alcohol. Some medication like antibiotics, antidepressants, allergy meds and diabetes meds can interact with alcohol to the extent that you really should not drink alcohol while you are taking them. But even if the warnings aren’t so stringent, it is important to remember that when you load your liver up with the task of metabolising the alcohol you consume, it is likely to be less efficient at metabolising your medication.

10. Illness

While researching this series I discovered that alcohol intolerance can be a sign of Hodgkin lymphoma. So experts recommend you see your doctor if you experience a sudden change in your alcohol tolerance so they can rule out anything sinister like liver damage or lymphoma.

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What about Hangovers?

Hangovers kick in 8 to 12 hours after your last drink when our body has metabolised most of the alcohol we have consumed and our blood alcohol approaches zero. A hangover can last up to 24 hours.

The severity of a hangover depend on how much alcohol was consumed and the individual’s efficiency at metabolising alcohol. The kind of alcohol consumed can also have an impact. Alcoholic beverages which contain congeners are known to contribute to hangover severity. Congeners are produced during the fermentation process, and give drinks like gin and whiskey their characteristic taste and aroma.

While there are a large selection of supplements and cure-alls on the market, no foods or supplements have been shown to prevent hangovers.

The only way to prevent a hangover is to abstain from alcohol or drink in moderation.

You may potentially be able to lessen your hangover misery by making sure you are well hydrated. This is because dehydration causes its own hangover-like symptoms. And it’s a good idea to try to get enough sleep. And eat a healthy meal when you wake up as alcohol can cause your blood sugar to drop which can make you feel shaky and headachy. A hangover plus dehydration, hypoglycaemia and sleep deprivation is a great recipe for hell-on-Earth, no?

Experts recommend against taking pain relievers like panadol before you go to bed after a big night. Your liver already has its work cut out for it metabolising the booze and paracetamol or other medications will only add to its burden.

Whatever you do, do not go for a "hair of the dog”. It’s a myth that consuming more alcohol will get rid of a hangover. All it will do is prolong your hangover symptoms.

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* Many drugs and medications have what is known as a “half life” metabolism. For example, if a drug has a half life of 24 hours and you take 10mg, after 24 hours there will be 5mg left in your system, and after another 24 hours the amount will decrease to 2.5mg and so on.

** I’ll mention this here and cover it in more detail in Part 3 of this series: A “standard drink” is generally MUCH smaller than the amounts actually poured! So you may think you’ve had a glass or two of wine and you may actually be consuming a lot more alcohol than you realise!