Gaining

Brilliant thread. Will star it so hopefully people will stop asking 'how do I get fat?' on threads ad nauseam.

I have thought that it might be easier, to eat a prehistoric diet. Your tribe just killed a mammoth and are eating as much of the meat as possible, before it gets to be spoiled.
After 5 days, you might only drink liquids. You might not eat for 24 hrs and your body would think it is starving, so it would cause you to eat more, to have reserves, when you didn't kill another animal.
Another variation on this would be to exercise as you ate and don't on the 6 th and 7th days,when your body would be expecting to need to replace the calories you would normally need for the exercise.

Perhaps you should look at what foods the human digestive system can process easiest. This would give your stomach more natural nutrients, and the money spent on additives, could be spent on more food.