Blood Alcohol Content numbers and effects are estimated based on population data and assume that Jane metabolizes alcohol at a rate that brings her BAC down by 0.015 percent every hour. To describe the physiological effects that occur at higher BACs, we had Jane drinking very quickly—two drinks every 40 minutes. Spacing alcoholic drinks over a longer period would result in lower BACs. Blood alcohol levels are also affected by size (larger people can tolerate more), gender (compared to men, women generally have more fat, which contains less water than muscle, so they don’t dilute alcohol in the blood as much and get drunk faster), tolerance, whether food was eaten before drinking and how much, and variations in levels of alcohol dehydrogenase, the enzyme that breaks down alcohol.
Source: Mark Egli, Ph.D., of the National Institute on Alcohol Abuse and Alcoholism