RP: Your body will need to make some sugar for your brain, so it starts to break down tissue. The first to go is your thymus. In just a few hours they use to think that adults do not have a significant amount of thymus tissue. They looked at people who dieted after being sick.
Even if you die slowly after a traumatic incident, your thymus is gone. It just takes a few hours of intense stress for the thymus to be dissolved, so a long fast will completely devastate your thyroid as it turns into sugar very quickly. The skin is relatively dispensable in the long run so your skin will atrophy very quickly during a fast or even a low calorie diet and then the muscles will provide sugar for your brain as necessary.
Women I use to see who went through a weight loss diet, you could not find a bicep muscle or a calf muscle. They would try to tighten their muscle and they could not feel of find anything, even in their upper arm or lower leg. Muscle was the size of a person’s index finger. So when they started eating a good diet, the first thing that would happen would be pounds of water loss. Their tissue would suddenly come out of the stress condition and get rids of some of the stored water then the muscle would start growing. In the first week they might lose ten or fifteen pounds of water and then for about a month they would start putting on weight as their muscles start growing.
We would have people measure waist and thighs and hips and each week they would grow smaller as they gain weight.