Whether someone has eaten changes how the same drink registers, and the mechanism sits almost entirely in the stomach. What matters is not digestion of the alcohol but the speed at which the stomach passes it onward.
Where absorption actually happens
Only a small share of alcohol crosses into the bloodstream through the stomach wall itself. The great majority is absorbed further along, in the small intestine.
The small intestine has an enormous absorptive surface, so once alcohol arrives there it enters the blood quickly and with very little delay.
That makes the transfer between the two organs the rate-limiting step. How fast the stomach empties largely determines how fast blood alcohol rises.
Why food slows the transfer
The stomach regulates its own emptying through the pyloric valve, holding contents back until they are broken down enough to pass through it.
A meal, particularly one containing fat and protein, extends that holding period considerably. Alcohol taken alongside it is retained rather than delivered straight through.
The same quantity therefore reaches the intestine spread across a longer interval, which lowers the peak concentration even though the total absorbed is broadly similar.
What the liver is doing meanwhile
The liver metabolizes alcohol at a roughly steady rate that does not increase to meet a larger load. It processes what it can and the remainder keeps circulating.
Slower delivery gives that fixed capacity more chance to keep pace, which is why an identical drink can produce a noticeably lower peak when it arrives gradually.
None of this changes the eventual total. The body still has to clear everything consumed, and it does so on its own schedule rather than a convenient one.
Why carbonation moves in the other direction
Carbonated mixers are associated with faster absorption, and the leading explanation involves pressure inside the stomach encouraging quicker passage through the valve.
Warm drinks, and drinks within a particular concentration range, are also absorbed more readily, which is why equal alcohol content can behave differently across formats.
These are modest effects compared with the presence of food, but they explain why two drinks of equal strength do not always register as equal.
Why individual variation stays large
Body composition matters because alcohol distributes into body water rather than fat, so people of different builds reach different concentrations from an identical amount.
Enzyme activity varies as well, and it varies between individuals and populations for reasons that are largely inherited rather than acquired through habit.
Because that spread is wide, none of this supports estimating one's own state from a rule of thumb. A medical question about alcohol needs a clinician, not a general description of a pathway.