My food consumption yesterday would have been very healthy for most people. Breakfast and lunch were footlong subs at 700 calories each, and for supper we went to a sit-down restaurant. I had soup, a catfish entree, and bread pudding, but the portions were fairly small so the meal was probably less than 900 calories. So overall, I ate lots of vegetables and lean protein and some whole grains, with total calories less than 2300.
This morning I felt a little out of sorts and my gut ached a bit. I was worried that I had eaten something bad. I did not think it was hunger, because when I thought about getting another sub sandwich my body vetoed it with a feeling of disgust. When I got to the airport and got through security, I started looking around for breakfast. I saw a McDonalds and decided I wanted to eat there. I saw the big breakfast and immediately realized that I really wanted 1300 deliciously empty calories for only $5.
When I got the food, I devoured it like a famished hyena, and then immediately started feeling much better. I realized that has not eaten enough calories yesterday to fuel myself. My body had been telling me that 2300 calories just was not enough to do what I asked of it, such as always taking eight flights of stairs up to my hotel room rather than take the elevator like a normal person. The feeling of not wanting to eat a sub was my body telling me not to waste stomach space with low calorie food when I needed fuel.
Until about 100 years ago, good nutrition meant getting enough fat, carbs, and protein to keep one functioning. For those of us who are physically active, sometimes it still is.