Metabolism is the process by which the body converts calories from food and drink into usable energy. When alcohol is consumed, this system is immediately disrupted. Alcohol is not processed like a typical carbohydrate, fat, or protein. Its presence forces the body to pause the metabolism of other nutrients, creating a bottleneck where detoxification is the immediate priority. This shift significantly alters how the body manages and stores the calories consumed alongside the alcohol.
The Body’s Emergency Response to Alcohol
The body views alcohol as a toxin, triggering an immediate and prioritized response for its removal. This is called metabolic priority, meaning the liver must clear the alcohol before processing fats and sugars. The process begins in the liver, where the enzyme alcohol dehydrogenase (ADH) converts alcohol into a toxic compound called acetaldehyde.
Acetaldehyde is then acted upon by a second enzyme, acetaldehyde dehydrogenase (ALDH), which converts it into acetate. Acetate is a relatively harmless substance that can be used for energy by other tissues or broken down further. These two steps require a diversion of metabolic resources to complete the detoxification. The speed of this clearance dictates how long the metabolism of other nutrients remains on hold.
How Alcohol Disrupts Fat and Carbohydrate Metabolism
The rapid, two-step processing of alcohol significantly impacts the body’s energy regulation. Both the ADH and ALDH reactions require the molecule NAD+ to function, converting it into its reduced form, NADH. This conversion leads to an increase in the NADH/NAD+ ratio within the liver cells.
This high ratio signals a state of high energy, causing the body to conserve energy by switching off normal energy-generating pathways. The high NADH level halts fat oxidation, which is the process of burning stored fat for fuel. The liver also impairs gluconeogenesis, the creation of new glucose from non-carbohydrate sources, because the high NADH state suggests no new energy is needed.
Practical Impact on Calorie Storage and Weight
When fat oxidation is inhibited, the body cannot burn stored fat for energy while clearing the alcohol. Any fat consumed during or immediately after drinking is diverted into storage. Since the body prioritizes alcohol metabolism, all other caloric intake is pushed down the priority list.
Alcohol contains approximately seven calories per gram, often called “empty calories” because they provide minimal nutritional value. The resulting metabolic shift means that calories from both the alcohol and any accompanying meal are predisposed toward fat storage. Regular, heavy alcohol consumption is associated with an accumulation of visceral fat, which is stored deep within the abdomen surrounding the organs.
Why Metabolic Effects Vary Between Individuals
The speed and efficiency of alcohol metabolism, and the extent of its disruptive effect, varies significantly between people. Genetic factors play a major role, specifically variations in the genes that code for the ADH and ALDH enzymes. Some individuals possess enzyme variants that process alcohol faster or break down the toxic intermediate acetaldehyde slower.
Gender is also a factor, as females reach higher blood alcohol concentrations than males after consuming the same amount of alcohol. This difference is partly because women have lower average body weight and less body water, which dilutes the alcohol less effectively. Additionally, females generally have lower levels of alcohol dehydrogenase activity in the stomach, meaning more alcohol is absorbed directly into the bloodstream.