Unfortunately I have been in the position of watching friends die who may have been helped by fasting, but were too scared to try it. Too unwilling to go against doctor's advice even when the doctor's themselves admit they have no cures to offer. Indeed modern medicine would far rather invade a body with dangerous chemicals and radiation than allow something as simple and effective in curing the body and regaining strength following illness as fasting can be. I used to see a homeopath for my children who had developed and fully tested a homeopathic antidote for white-tailed spider bites. She was issued with a restraining order to keep her from giving it to a patient in a hospital here even though the treatments of modern medicine available at the hospital had done nothing to stop the spread of the poison. A restraining order for a homeopathic remedy which medical Science has often proved better than conventional remedy and certainly never been proven to be harmful in any way. That is our world. It sounds like your relative has a good strong mind of his own and I hope he gains from your knowledge the next time you visit.
Chris has a great knowledge of fasting books and I'm sure will be able to advise you on the best one to buy for him. I am not so good at retaining the names of my sources, more at retaining the information I need from them.