According to the food rules,
A character can go without food for a number of days
equal to 3 + his or her Constitution modifier (minimum
1). At the end of each day beyond that limit, a character
automatically suffers one level of exhaustion.
A normal day of eating resets the count of days
without food to zero.
According to this, a character with a Constitution modifier of 0 can eat normally every 4th day*, and get no penalties from hunger despite only eating twice a week. This seems a tad ridiculous, and I'm wondering if there are other rules that I'm missing that make it a bad idea to eat less often like this, or if eating every 4th day is a totally fine thing to do, by the rules.
* They can get away with four days, because they'll only get the exhaustion penalty if they don't eat by the end of the fourth. This is even assuming the 'minimum 1' doesn't apply to the con mod portion.
Best Answer
Seems legit. Real people having a hard time finding meals can eat like that, and hard-luck adventurers are the kind of people who might see a lot of time between meals.
For someone who can afford to eat though, going hungry is foolish. Having a full belly when you have the opportunity to get one is just a matter of being prepared for the worst when you're venturing into the unknown. You never know when your mule with all the food is going to get eaten by a dragon or your pack might get dropped down a chasm, and then your carefully-timed starvation diet becomes actual starvation, with who knows how long before your next meal.
Mechanically, it would not be unreasonable for the DM to rule that being hungry can cause Disadvantage under the right (or wrong, I suppose) circumstances. If you haven't eaten for three days and you're sneaking through the orcs' kitchen, even revolting cooking smells are potentially distracting and might make the difference between failure and what would have been success—which is nicely modelled by Disadvantage. Similarly, exhausting activity such as climbing or swimming might be harder when your body is being systematically denied fuel.
So yes, you only need to eat every four days to avoid starvation. But as we well know from real-life experience living, going hungry sucks and is worth avoiding if you can, especially if you have any doubt about where your next meal is coming from.