When a person consumes alcohol, the substance ethanol is quickly absorbed into the bloodstream, primarily through the small intestine and stomach. Ethanol is a small, water-soluble molecule that circulates rapidly throughout the body. Blood Alcohol Concentration (BAC) is the standard measurement used to determine the level of intoxication. Many people believe that muscle or fat tissue “soaks up” alcohol, but the reality is that distribution is tied directly to the body’s water content.
How Alcohol Distributes in the Body
Alcohol does not require active absorption by tissues; instead, it simply diffuses into areas of the body containing water. Since alcohol is highly soluble in water, it travels through the bloodstream and disperses throughout the body proportional to the water content of various tissues and organs. This distribution is governed by the Total Body Water (TBW), which includes both the water inside cells and the fluid surrounding them.
The body acts as a collection of water compartments where alcohol seeks to achieve an equal concentration. Tissues highly perfused with blood and possessing a large percentage of water, such as the brain and the liver, receive a substantial share of the distributed alcohol. The final BAC is a function of the total amount of alcohol consumed divided by the total volume of water available for dilution within the body.
Why Muscle Tissue Holds More Alcohol Than Fat
The difference in how muscle and fat tissue interact with alcohol lies in their respective water content. Muscle tissue, which is considered lean mass, is composed of approximately 70% to 75% water. In contrast, adipose tissue, or body fat, contains a much smaller amount of water, typically only about 10% to 20%.
Because alcohol is water-soluble, a given volume of muscle tissue offers far more space for alcohol distribution than the same volume of fat tissue. Consequently, muscle tissue holds a much higher concentration of alcohol compared to an equivalent volume of fat. This difference means that individuals with a greater muscle mass have a larger overall volume of water in their bodies.
If two people of the same weight consume the same amount of alcohol, the person with a higher percentage of muscle mass will have a lower peak BAC. The alcohol is diluted across a greater total volume of water, resulting in a lower concentration in the bloodstream and subsequently in the brain. This dilution effect explains why a muscular person may show fewer effects of intoxication than a person with the same weight but higher body fat.
The Body’s Process for Eliminating Alcohol
Once alcohol is distributed throughout the body’s water, the process of elimination begins. The liver is the primary organ responsible for removing alcohol, metabolizing about 90% of the ingested amount. This process involves a two-step enzymatic reaction starting with the enzyme alcohol dehydrogenase (ADH).
ADH converts ethanol into acetaldehyde, a highly toxic byproduct. A second enzyme, aldehyde dehydrogenase (ALDH), rapidly breaks down acetaldehyde into acetate, which the body can harmlessly excrete.
The rate at which the liver metabolizes alcohol is relatively constant for most people, averaging a decrease in BAC of about 0.015 grams per 100 milliliters per hour. This rate cannot be sped up by external factors like drinking coffee or sleeping. The remaining 2% to 10% of alcohol is excreted directly through the breath, urine, and sweat.