When someone eats only fruit or mostly raw food for a few days the cellular spaces and intestines which are filled with mucous and toxic material stored from many years floods into the blood stream making one ill and even could cause sudden death. Especially if one has not been exercising regularly.
People who have eaten a raw diet for many years will often get weak and lose weight due to the acidic material being released from the deep recesses of their cellular makeup from 15, 20, 30 or more years eating a highly toxic conventional diet.
It's like having 8 layers of over coats consisting toxic residue. When one is removed you feel great but when the next one is being eliminated you feel horrible and need to slow down the elimination with more mucous forming foods. This is why a fruit diet will work for a while as one coat is removed but then a new over coat will be uncovered months later at a deeper level and the person will feel sick.
A gradual and slow change from the ordinary mixed diet to the natural Raw food diet is best to avoid shocking the body. Follow the Food Combining Principles Food Combining Principles.
Changing your diet requires gentleness and taking it easy. If you push too hard and make a radical diet change like eating all fruit for weeks on end you can quite easily become out of balance with weight loss, a puckered face, excess elimination, tooth problems, weakness and depression.
If a normal person eating the normal diet begins eating just fruit they become sick very quickly because the fruit stirs up the stored toxic material in the body and brings it to the surface to be eliminated via the skin and lungs primarily.
Eating all fruit or all raw when first starting to change the diet could be very damaging to the vital organs because highly toxic substances such as pesticides and drugs which are stored in fat cells and the intercellular spaces will be suddenly released flooding the blood stream which can damage tissues and even cause death.
Also the teeth are in danger if one eats only fruit due to the lack of calcium and the acids of the fruits beside the acidic nature of the toxins being release all of which wears away at the tooth enamel. Avoid losing your teeth by eating only fruits for long periods when starting out just to get cleaned out quick or to have a spiritual experience. Its just not worth it in the suffering it causes and the dental bills!
Go slowly and go gradually. For the meat eaters who want to give up meat, potatoes and cooked vegetables, avocados, natural raw cheese and natural raw homemade yogurt are great substitutes. Soy products being a seed have a lot of problems one of which is the causing of goiter or thyroid disease due to binding of iodine causing deficiency besides the toxic chemicals used to process the beans.