In general, one of the most profound changes in health that I witness on a weekly basis, happens when a patient consumes a diet that is uniquely best for him/her. Again, one size does not fit all. Recently in the news, the vegan diet was purported to be the cure-all for heart disease. Prior to that, it was the meat and protein loaded Zone diet and Atkins diet that reduced the risk of coronary heart disease.
Diet and nutrition is uniquely individual for each person. Some people flourish on raw food diets while others become ill. Some thrive on a vegan diet while others crash and burn. An entire parade of fads and diets have come and gone, and some have hung around for a select and small group of people that have responded well to them.
Even the book "Eat Right For Your Type" (whose original title was "One Man's Food Is Another Man's Poison), written by Dr. Peter D'Adamo N.D., is only helpful for some people. It is a diet plan based on a person's blood type, and for many, this type of diet just does not apply.
No diet is the magic-bullet-fairytale-unicorn-of-ultimate-cures, for every disease. There is however, a diet that is uniquely beneficial for each person as a unique individual living on this planet, being 1 out of approximately 7 billion.
Most people do really well by eating numerous servings of fresh vegetables and fresh fruits, along with eliminating refined sugar from their diet. I have an in-law who has had cancer exacerbate and remit at least half a dozen times, with chemotherapy being the treatment of choice that has so far been successful. I have no doubt that if this relative increased his dietary intake of vegetables and fruits while concurrently eliminating refined sugar from his diet, he would decrease the quality of his life. With a positive diet change, he would likely have more energy and mobility, along with a stronger immune system, but what he would not have, is the daily joy he receives by eating out at restaurants and savoring his favorite desserts and vegetable-less entrees.
Joys come in many forms, and only each person for himself can determine what quality of life means to him.
One size does not fit all.