7 ways drinking alcohol can affect your fitness goals

We all know that drinking lowers our inhibitions and leads to poor food choices like late-night pizza and greasy breakfast. And while some swear by the method of sweating off a hangover, you may not even be able to get out of bed, let alone hit the gym, the day after a big night out. But does that mean that the only way to reach your fitness goals is to cut out alcohol altogether? We had two fitness and nutrition experts weigh in on what's really happening when you mix drinking and working out.

First off, it must be said that measuring the direct effect of alcohol on athletic performance is difficult for many reasons, including that alcohol affects every body differently. Body size, body composition and genetics play a role, as does how often you drink and how much. 

"Everyone's excess is different," says Jorie Janzen, a registered dietitian and the director of sport dietetics at the Canadian Sports Centre in Manitoba. Statistics Canada defines heavy drinking as five or more drinks in one sitting but according to Daniel Moore, associate professor of muscle physiology at the University of Toronto's Faculty of Kinesiology and Physical Education, you know you've over-consumed if you start to feel a little fuzzy or start to stumble. It's at this stage that aspects of your fitness might start to be impacted. How exactly? Read on to find out.

Metabolism

According to Moore, our body uses the three classical macronutrients — carbohydrates, fat, and protein — for energy, but we can also use ethanol (the type of alcohol found in alcoholic beverages) as an energy source. We process ethanol in the liver and because it's toxic to humans in high amounts, Moore says the liver prioritizes breaking down ethanol into byproducts that can be used or flushed out of the body.

"When that's happening it actually starts to turn off or to slow down the metabolism of other energy sources," says Moore — especially fat. He says that when we're resting or lightly exercising, more than 50 per cent of the energy we use comes from burning fat (as opposed to protein or carbohydrates, which aren't as energy-dense as fat). Therefore, when we drink alcohol, we get in the way of the liver converting fat into energy and that fat gets stored in our cells instead. 

Moore says this effect is minor with moderate consumption of alcohol — about one or two units of alcohol or approximately one beer, one glass of wine, or an ounce of spirits. 

"If you have more than two drinks in an hour, your blood alcohol content could creep up above 0.05, which is generally the legal limit to drive and that's when you start to see change in metabolism happening.

Compounding that is the fact that alcohol is an energy-dense nutrient. Each gram of alcohol contains seven calories, versus nine calories per gram of fat and four calories per gram of protein or carbohydrates. So a standard drink contains approximately 14 grams, or 100 calories of alcohol, as well as additional calories from carbohydrates.

Performance

When it comes to performance, Moore says moderate drinking isn't likely to affect how you fair in the gym or on the field the next day, but once you move beyond moderate consumption to three or four drinks your performance might be affected in a few different ways. According to one study, a hangover can reduce your aerobic performance by 11.4 per cent, but even just one drink may have an effect. 

Added to that, when your liver is busy breaking down alcohol, it's less efficient at producing glucose to help fuel your workout. This is especially dangerous for diabetics, for whom mixing alcohol and exercise can cause hypoglycemia or low blood sugar.

Dehydration

One reason performance suffers is that alcohol is a diuretic, meaning that it makes you have to pee more by affecting how your kidneys reabsorb fluids, says Moore. If you drink and don't replenish those fluids before going to bed, you're likely to wake up dehydrated. This is important because hydration helps your body circulate blood and oxygen to your muscles and keep your blood pressure regulated so your heart doesn't have to work as hard.

Janzen points out that the timing of your drinking can compound this. If you work out and then go out to a bar after, like in the case of recreational beer leagues, you should drink some water first, or else risk being doubly dehydrated.

And while you may think that people who swear by sweating off a hangover are onto something, they're more likely just making their dehydration worse. About 90-98 per cent of the alcohol you ingest is metabolized by your liver and working out will not impact that process at all says Moore. The other 2 to 10 per cent is expelled via your breath, urine and sweat. Since exercise increases your breathing rate, there's some evidence to show that exercise can reduce blood alcohol content, but Moore is quick to point out that if you're feeling hungover, your body has likely already processed the alcohol. Where exercise might make a difference, he says, is in the release of endorphins, which could make you feel better without being related to alcohol metabolism at all. 

Sleep

A glass of wine might make you drowsy but drinking too much alcohol actually causes your body to spend less time in deep sleep, and more in REM or light sleep, says Moore. "If you go to bed feeling a little bit spinny in the head, then that's a sign that you've over-consumed that alcohol and you oftentimes wake up the next day just not feeling as rested." 

He adds that people who are tired make poor food choices and that a persistent lack of sleep can increase chronic inflammation, which impacts weight gain. 

What's more, "when you don't have that good quality sleep, you are impacting hormones in the body," says Janzen. For example, the production of growth hormone and testosterone, which are released in deep sleep and are necessary for muscle growth is disrupted by a lack of quality sleep.

Muscle growth

"When we exercise, and especially if we lift weights, it produces small amounts of damage, but it's a stress to your muscle that causes it to break down any old or damaged proteins and rebuild new ones in their place," explains Moore. "This process of protein breakdown and protein synthesis basically allows our muscles to recover. And then if you do that chronically, that's how our muscles grow." 

According to Moore, this process of healing can take up to 48 hours after a heavy bout of exercise. Drinking more than a moderate amount during this period can sabotage the muscle's ability to recover and adapt to the exercise. 

Injury and recovery

Some research indicates that athletes who drink are more likely to get injured. Still other studies, including a number by Matthew Barnes at Massey University in New Zealand have shown that even moderate drinking could impact your strength losses and recovery following a weight training session and that heavy drinking increases the recovery time for soft tissue injuries — meaning injuries to your muscles, tendons or ligaments such as sprains or strains. 

Heart health

One of the most unsettling facts about alcohol and fitness doesn't necessarily have to do with exercising at all, but it does have to do with your heart's ability to maintain a regular beat. Even though conventional wisdom has it that drinking a glass of wine per day is good for your heart, a large review study from 2016 which looked at data from close to 900,000 people found that drinking moderately on a regular basis increases your risk of developing arrhythmia or irregular heartbeat.

The final verdict

Ultimately, binging on the weekend may not short circuit a whole week of regular exercise and healthy food choices, but it could certainly slow your progress with both weight and fitness goals.

"In sport we have something that's called periodization and we periodize training, periodize nutrition and, along with those areas, you probably want to periodize when you're going to have the festive moments when you're going to include alcohol," says Janzen.

Moore says, "If you're trying to lose weight, it's definitely a marathon, not a sprint. It has to be done slowly." He says the most effective way to do that is through a lifestyle change that makes room for the occasional glass or two of wine and beer, and an attitude that fights being discouraged and derailing everything if you mess up now and again. 

Eva Voinigescu is a freelance journalist and producer. She writes about health and science, careers, and culture.