However, at that point, I was running about 1000 calories a day, sometimes less (a big reason I think The Martian is bullshit). I was not starving. My body wasn't starving. You can (and many people should) subsist on far less than the recommended daily allowance of calories.
If I eat a typical 2000 calorie diet, I will not just gain weight, but I will gain weight at a rate of about a pound or two a month.
I've currently gained back about 10 pounds of what I lost, so I'm going to have to turn on the afterburners again, but we really need to change the dialogue of what a standard of consumption and health is.
It's very simple: if your body has a slow metabolism, you have to eat a lot less than most people.