If you get cancer you will be thankful for that extra fat. It does tend to increase the chances of reoccuring cancer- but at the same time that fat reserve can add years to your life as you will have difficulty eating enough to keep weight on. That is one of the factors why I am able to stay active as much as I do I dont require the caloric intake. But I still must make sure I dont get imbalances in vitamins and minerals. Whole milk has been a life saver. Skim milk is essentially kool aid, sugar water with a little calcium that is not easily processed by the body. Ice cream is bad for you. I dont eat it. Salads are helpful to help my colon function but I cannot digest them- they pass unchanged. So whole milk, peanut butter, good oily fish, high proteins are important, beans, brocolli, whole potatoes, cooked vegetables, cereals like oatmeal. The key for me- I avoid as much artificial sweeteners, flavorings and ingrediants as possible. When you are in battle for survival the power of superfoods, protien, and exercise cannot be overstated.
Potassium loss, magnesium loss, iron loss, are the big three you lose when your sick and cause so much pain, dizziness, weakness, mental fog, and a host of health issues. These can also be lost to losing weight too fast and if it does you will suffer for it.