> A high carbohydrate meal consumed prior to caffeine ingestion significantly reduced serum caffeine concentrations and delayed time to peak concentration

https://www.sciencedirect.com/science/article/abs/pii/S14402...

Caffeine is a stimulant, acting on the sympatheitc nervous system. If you're also activating the parasympathetic nervous system, like by eating a meal, the effect won't be as strong.

Another effect of caffeine is as an adenosine re-uptake antagonist. Adenosine levels are usually low in the morning, so the effect is small. Later in the day, it can have a bigger effect on how alert you feel.

I heard that the anxiety from caffeine is worse when you haven’t eaten. No time to check resources for that at the moment

having a full stomach has a moderating effect on most drug uptake.