Just as sort of a 100,000 foot level comment about nutrition and diet, I think some general reading about so-called Blue Zones starts to give clues and guidance. Blue Zones are areas in the world that have high concentrations of centenarians. You could argue that it was not always the diet that got them there and that is true, but it at least signals that their diet did not take them down and allowed a long life. I am little zonked right now so I will stay out of any detail but many know about the Blue Zone studies already. Just go to youtube and search on key words Blue Zones. Or search on keywords Ikaria, Greece longevity. Or search Sardinia longevity Or Costa Rica longevity . Can't remember the exact name of the town there. Or Loma Linda, California Blue Zone. Just watch some of that stuff on youtube and think along the way. Those are all "do no harm and probably do lots of good" diets. Where "diet" refers to cultural eating habits and not some weight loss regimen or something. Methinks.
It is different for everyone. To know how much food you require, you need to measure your body size, and factor in your sex, age, activity level, then use that information to figure out how many calories you need to survive. You might need a nutritionist or a doctor for this. Then track the calories of whatever you consume. And ensure that you are properly hydrated, and track the calories of your beverages as well.
It may depend on whether you do it all in one sitting or split it up into 25.714 seconds per day. If you do it daily I would round it up to 26 seconds per day.