KEY TAKEAWAYS
Alcohol intake impairs metabolic performance via effects on dehydration, reduces digestive absorption, and reduces levels of sex hormones, sleep patterns, and liver function.
Alcohol also increases metabolic rate when consumed regularly at low to moderate levels.
An animal study done in 2017 showed that moderate intake increases metabolism by increasing thermogenesis and energy expenditure, thus increasing calorie intake but reducing weight [1].
This study implies that drinking incurrs weight loss faster, but this is not always the case.
A review in 2015 stated that frequent and moderate drinking is not related to obesity risk, but heavier drinking is, and reduces metabolism [2].
Speed of metabolism differs from person to person, but heavy drinking slows down metabolism and affects weight loss, fitness journey, and the digestive system.
Excessive drinking also inhibits muscle growth and counteracts the results usually obtained from exercising and dieting.
How Does Alcohol Affect Metabolism?
Metabolism is the chemical reaction that changes food to energy.
Metabolic processes differ for each person.
When metabolism is slow, the body burns fewer calories at rest and during activity, requiring the individual to eat less [3].
Individuals with fast metabolism burn many calories while at rest, but this does not necessarily lead to thinness or weight loss [4].
Consuming moderate to large amounts of alcohol decreases physical fitness.
Alcoholic drinks provide empty calories, which means they contain little nutrients but provide the body with a lot of calories [5].
The liver burns alcohol first as a fuel source before any other food is consumed, and since it contains a lot of calories, this causes excess glucose and lipids to end up in the liver as fat [5].
There are different ways alcohol affects metabolism in the human body.
Lowers Physical Performance
Alcohol is considered a sedative because it lowers physical performance.
Studies have shown that high blood alcohol content decreases reaction time [6].
Drinking slows body function, causes clouded thoughts, and degrades hand-eye coordination.
Promotes Fatigue And Dehydration
Attempting to achieve fitness goals during a period of active drinking, typically results in greater fatigue and dehydration than normal.
Combining alcohol consumption with exercise causes dehydration and a worse hangover.
The dehydration leads to tiredness and sluggishness, reducing fitness performance and glycogen storage.
Glycogen is stored in the liver to provide energy, and consuming alcohol while increasing the metabolic rate causes it to get used up and affect workout sessions [7].
Causes Weight Gain
Alcohol consumption is related to metabolic rate in terms of weight loss.
Alcoholic drinks contain little nutritional value but high calories.
These calories are referred to as empty calories.
Sometimes, these drinks are mixed with sugary beverages that increase the calorie intake.
Studies show alcohol impairs muscle growth by reducing protein synthesis [8].
Alcohol is also said to impair calcium metabolism and bone structure [9].
Consuming alcohol after working out hinders fitness because the body switches to burning empty calories instead of fat.
This is because the liver does not store alcohol due to toxins such as acetaldehyde..
Furthermore, excess calories are stored in the body as fat, mostly in the abdominal area, hence the term 'beer gut.'
Alcohol inhibits the weight loss process, and increases the chances of developing chronic illnesses.
Studies have shown that alcohol causes weight gain by increasing appetite [10].
A July 2015 study [10] revealed that women ate more desirable foods when alcohol was in their blood.
Additionally, binge drinkers are more likely to have obesity and related medical conditions like high blood sugar and blood pressure [11].
Binge drinking, in this case, is more than four standard drinks in a session or ten standard drinks per week [12].
Affects Digestion And Nutrition Intake
Intake of alcoholic beverages negatively affects the digestive function.
Alcohol strains the stomach and intestines when consumed excessively, leading to reduced digestive secretions and peristalsis through the digestive tract [13].
Enzymes and digestive acids are required to break food down into micro and macronutrients, which are absorbed by the small intestine and converted into energy.
Drinking impairs the absorption of nutrients, greatly affecting the metabolism.
Reduces Liver Function
Alcohol affects the body organs, specifically the liver, which acts as a filter between alcohol and other toxins and the body.
The liver is important in metabolising carbohydrates, fats, and proteins.
Excess alcohol consumption causes an alcoholic fatty liver [14], affecting the body's rate of metabolism.
It also damages the liver and changes the way the body stores energy from food.
Aside from the liver, alcohol inhibits muscle repair by decreasing the secretion of human growth hormone and lowering testosterone production.
Negative Effect On Sleep Pattern
Contrary to popular opinion, drinking alcohol before bed does not increase sleep quality.
Research shows that alcohol increases the periods of wakefulness during sleep cycles [15] and causes an imbalance in hormones related to energy storage, hunger, and satiety.
This wakefulness makes an individual hungrier the next day, and makes it more difficult to meet fitness goals since it affects the energy storage in the liver and muscles.
Furthermore, studies have shown that sleep deprivation alters glucose metabolism and hormones related to metabolism regulation [16].
In this way, drinking causes sleep quality issues and alters metabolism-related hormones like ghrelin and leptin.
Drinking Alcohol And Sex Hormones
Alcohol intake affects the levels of hormones in the body, including the sex hormone testosterone.
Testosterone is used in different metabolic processes, including fat burning and muscle formation.
Testosterone plays a key role in fat, carbohydrate, and protein metabolism [17], and low testosterone levels cause metabolism to slow down as muscle mass declines.
A study shows that low testosterone increases men's chances of metabolic syndrome [18].
Some symptoms of metabolic syndrome include [18]:
Low testosterone adversely affects quality of sleep, which is related to the body's metabolic rate.
What Determines Rate Of Alcohol Metabolism?
In general, alcohol is a smooth muscle inhibitor that prevents body parts from absorbing the nutrients needed.
Alcohol-related muscle inhibition is not significant with moderate drinking, but excessive alcohol consumption prevents the body from processing nutrients.
Some factors influence how efficiently alcohol is metabolised in the human body.
Age
The enzymes that break down alcohol and the water volume in the body decrease as age increases.
Thus, alcohol metabolism is slower in older than younger people [19].
Gender
Males have more muscle and bone mass and less fat than females.
Due to this, females feel the effects of alcohol intake more, and alcohol stays in the system longer.
Studies show that women have higher alcohol metabolic rates than men due to hormonal differences [20].
Food Intake
Eating food while consuming alcohol affects the alcohol absorption rate in the body by up to three times.
Food in the stomach dilutes the alcohol, slowing its absorption in the small intestine, where most alcohol is absorbed.
Since alcohol has multiple effects on appetite, failure to balance it with food intake makes moderate alcohol consumption a risk factor for obesity [21].
Alcohol influences the body's metabolism, including physical performance, sex hormones, weight gain and loss, sleep patterns, dehydration, and digestive processes.
Due to its toxins, alcohol is not stored in the body but processed first, leaving excess glucose from food intake that causes a person to gain weight disproportionately.
Drinking alcohol moderately limits its adverse effects on metabolism.
