When comparing two individuals with the same alcohol intake, what physical characteristic primarily affects blood alcohol concentration?

Blood alcohol concentration (BAC) is significantly influenced by a person's weight. When two individuals consume the same amount of alcohol, their BAC levels can vary primarily due to their body weight. This is because alcohol distributes itself in body water, and individuals with a higher body weight typically have more body water, which can dilute the alcohol in their system. Consequently, a person with less weight will generally experience a higher concentration of alcohol in their blood compared to a heavier person who has consumed the same quantity of alcohol.

While factors like metabolism, age, and height can also influence how alcohol affects a person, they do not have as direct an impact on the blood alcohol concentration as weight does. Metabolism may affect how quickly alcohol is processed, age can influence overall body composition and liver function, and height might correlate with weight but is not a direct measure of body mass. Therefore, weight is the primary physical characteristic affecting BAC in this context.