What is alcohol and its impact on the body

Now we are going to have a look at alcohol and its impact on the body. To begin with, the function and structure of alcohol have been a topic of much debate and discussion. As a central nervous system depressant, alcohol can have varying effects on the brain and body depending on the amount consumed. While moderate alcohol intake may provide a sense of relaxation, excessive drinking can lead to impaired motor function and potential harm to the liver and other organs. It is important to keep in mind that alcohol should be consumed in moderation and with a balanced diet, as it contains empty calories and can contribute to weight gain. Despite its controversies, alcohol remains a prevalent aspect of many cultures, serving various purposes such as recreation, medicine, and even poison. In clients’ diets, it remains a significant factor to consider.

As a Nutrition Coach, the goal of this chapter is to equip you with the knowledge to:

Alcohol and its impact on the body

Ethanol, also known as ethyl alcohol, is the most widely consumed alcoholic beverage in the world. On average, each person (above the age of 15) consumes approximately 1.6 gallons (6.1 L) of ethanol per year globally, with the United States ranking 49th in the world for per capita consumption at 2.35 gallons (8.9 L). Although other forms of alcohol, such as methyl and isopropyl alcohol, are used in industrial and medical settings, only ethanol is safe to consume in moderate amounts. It is important to note that excessive consumption of ethanol can lead to negative effects on the body. Despite its lack of essentiality for health and performance, it is crucial for sports nutrition professionals to understand the effects of ethanol and how it may alter physiological function. Ethanol is produced through fermentation of glucose, and its structure is similar to glucose, with both consisting of carbon, hydrogen, and oxygen. However, while glucose has 6 carbons and 5 hydroxyl groups, ethanol has only 2 carbons and 1 hydroxyl group.

Chemical Structure of Ethanol
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Nutrition Coach.

Ethanol is not essential for biological function

Unlike carbohydrates and fats, the metabolism of ethanol is not controlled by hormones and there is no storage or circulating pool of ethanol in the body. As it is not essential for biological function, ethanol is considered a homeostatic threat, or a form of toxin, and its removal and elimination from the body takes priority over the utilization of other energy-providing macronutrients.

Unlike carbohydrates, fat, and protein, ethanol is not a necessary nutrient in the diet and has no beneficial effects.


  • Alcohol Dehydrogenase (ADH)
    The primary enzyme involved in the metabolism of ethanol is alcohol dehydrogenase (ADH).
  • First-Pass Metabolism
    The initial metabolism of ethanol occurs in the stomach, through the action of ADH, which converts ethanol into acetaldehyde.
  • Rate of Absorption
    The speed at which ethanol enters the bloodstream from the stomach depends on several factors, including the amount consumed, the rate of digestion, the presence of food in the stomach, and the individual’s tolerance to alcohol. Generally, alcohol enters the bloodstream relatively quickly, within 5-10 minutes after consumption.
  • Blood Alcohol Content (BAC)
    The concentration of ethanol in the blood is relative to the amount of water in the body. Ethanol is water-soluble, meaning that it dissolves in water, and its concentration in the blood is influenced by the balance between water and ethanol. A higher concentration of ethanol in the blood indicates a lower concentration of water relative to ethanol.

Ethanol does provide energy through its metabolism, releasing 7.1 calories per gram, but it’s not considered a macronutrient since it’s not essential for biological function and is primarily known for its psychoactive effects rather than its nutritional properties.

Alcohol Absorption

To analyze what alcohol is and its impact on the body, we, of course, must start with alcohol absorption. Alcohol absorption refers to the process by which alcohol (ethanol) enters the bloodstream from the digestive system. This process occurs in the small intestine and is influenced by several factors, including the rate at which alcohol is consumed, the presence of food in the stomach, and the individual’s overall health. Alcohol is rapidly absorbed and rapidly distributed throughout the body. The concentration of alcohol in the blood, known as blood alcohol concentration (BAC), peaks approximately 30-90 minutes after consumption and can remain elevated for several hours, depending on the person’s metabolism and the amount of alcohol consumed.



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In other words, ethanol is absorbed into the bloodstream via the stomach and small intestine by diffusion. The rate of absorption, leading to the blood alcohol content (BAC), depends on various factors such as sex, body mass, type of drink consumed, empty stomach, and drinking speed. The small amount of ethanol metabolized in the gastric mucosa through alcohol dehydrogenase (ADH) is referred to as first-pass metabolism.

Alcoholic Beverages and Food

Alcoholic Beverages and Food

The absence of food in the stomach allows for quicker absorption of ethanol into the bloodstream. This can lead to a rapid increase in blood alcohol content (BAC) and potentially more severe effects from alcohol consumption.

The idea that alcohol should not be consumed on an empty stomach has some validity, as the lack of food in the stomach affects how quickly the ethanol from alcohol is absorbed into the bloodstream. Regardless of the type of food, be it high in fat, protein or carbohydrates, the presence of food in the stomach slows down the absorption of alcohol into the bloodstream.

Food can slow down the absorption of alcohol into the bloodstream, but it can also increase the rate at which alcohol is broken down and converted into energy, through first-pass metabolism and in the liver, due to increased blood flow to the liver, higher activity of ADH, and greater rates of NADH, the reduced form of NAD+. Concequently, the presence of food in the stomach plays a key role in how alcohol impacts on the body.

The coenzyme NAD+ and its reduced form NADH are important in various metabolic processes including glycolysis, gluconeogenesis, fatty-acid oxidation, amino-acid oxidation and the Krebs cycle. NADH supplies most of the electrons needed for ATP production through oxidative phosphorylation in the mitochondria.

Alcoholic beverages with higher concentration of ethanol (such as spirits) tend to result in a higher rise in blood alcohol content (BAC) than drinks with lower percent of ethanol. But whether the alcohol is absorbed more quickly or not depends on whether the person is hungry or not. Ethanol from strong alcoholic drinks may be absorbed more quickly on an empty stomach than weak alcoholic drinks like beer.

Alcohol and its impact on the body: the impact of food on alcohol absorption and the rise in blood alcohol content (BAC) is that it slows down the rate of alcohol absorption and increases the speed at which the body metabolizes the alcohol. The combination of the type of drink and whether the person has eaten or not affects how quickly the body absorbs the ethanol.

When food is present, dilute alcohol drinks such as beer are absorbed faster than concentrated drinks like spirits. Also, alcohol consumed in carbonated drinks is absorbed faster than in non-carbonated drinks.

Sex and Body Composition

The rate of ethanol absorption and metabolism in the liver is similar in both males and females, however, a given amount of alcohol will generally result in a higher BAC in women due to physiological differences. The difference in BAC is because ethanol from the bloodstream enters water-containing tissues, so BAC is lower in individuals with more total body water and those with more lean muscle mass. When the total body water is taken into consideration, there is no difference in BAC between males and females.

Additionally, differences in ADH activity in the stomach result in greater first-pass metabolism in males, leading to less ethanol entering the bloodstream, compared to females. This highlights the need for caution when individuals with varying body sizes, body composition, and sex drink together, as the rate of alcohol absorption and metabolism will differ among them.

Fitness coach: it's important to take into account the differences in body size, body composition, and enzyme activity between females and males when consuming alcohol as it affects the rate of ethanol absorption and metabolism differently. This is significant because standard BAC estimations that only consider number of drinks and body weight may not be accurate for everyone.

BAC Calculator

BAC Calculator
It’s important to keep in mind that the effects of alcohol consumption may vary between individuals, and factors such as sex, body size, and body composition can play a role. Blood alcohol content calculators should be used for estimation purposes only and may not accurately reflect the effects of alcohol on a particular individual.
Use this calculator for estimation purposes only!
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Nutrition Coach.

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