ELI5: Do you lose brain power when digesting food? Like having just ate a large meal, does blood being diverted to digestion perceivably effect cognitive ability at all?

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Yes, you do. Digestion takes a lot of energy and that’s why you feel sleepy after eating a big meal. And when you’re sleepy, your brain struggles with tasks more. Affect* not effect.


Oxygen and Blood Pressure. Contrary to popular belief, your stomach isn’t constantly full of acid. When you start thinking about food, your “tummy rumbling” is your stomach starting the process of ‘filling up the tub’. This on-demand process has an impact. Once food enters this violent, inhospitable hell hole, more acids are produced in concert with mechanical digestion. Once broken down to a suitable size, the paste is pushed to your intestines which starts to crush and squeeze like a python around its prey. This too requires oxygen and blood pressure. This process takes hours. If you’ve gorged yourself, think of it like stuffing a front loader washer. It’s gonna take longer than a standard wash. The energy squeezed out of your food from your intestines ends up in your blood stream which then creates a job for your liver.


I live near a toby Carvery and you’d be amazed at how frequently an ambulance is called at lunchtimes. According to the manager, it seems elderly people will eat much more than they would usually and the effort to digest it results in some passing out.


If you feel this causes you a problem, but you don’t want to try some heavy-handed fasting solution, you might at least try a proteinaceous meal rather than sugary, in those times of the day when you ought to not shut down. On top of the usual problems with sugar, it can also inhibit the production of orexin, which is a chemical that promotes wakefulness. In this way, a sugary meal can even produce drowsiness comparable to Suvorexant medicine. Suvorexant is an orexin antagonist medicine to induce sleep. Evidently it works pretty well: it’s on the same drug schedule as Ambien…