Fit for Life is a diet and lifestyle, stemming from the principles in Natural Hygiene, promoted by the American writers Harvey Diamond and Marilyn Diamond. As the title of the 1985 book suggests, Fit for Life claims that one can lose excess body weight and maintain good health via long term dietary and lifestyle practices, rather than short term dieting. In the Fit for Life book series many dietary principles are recommended including eating only fruit in the morning, eating predominantly "live...high-water-content" food (as per the raw food diet), and if eating animal protein to avoid combining it with complex carbohydrates (see food combining). Tony Robbins promotes the Fit for Life principles and veganism to increase energy levels in his book Unlimited Power.
The original Fit for Life book was on the New York Times Best Seller list. The books in the series have sold a total of over 12 million copies worldwide.
Despite its popularity, it has received criticism from dietitians and doctors for espousing "pseudoscientific" theories, which include describing the human body as being "cleansed" or "clogged". Few would deny the value of eating more fresh fruit and vegetables, as it may lower the chance of developing heart disease, cancer and diabetes. Fit for Life goes beyond this to argue that these can only be eaten in combination with certain other foods.
In Fit for Life II (1989) the Diamonds warned against eating artificial food additives such as hydrogenated vegetable oil, which at the time was being promoted by the food industry as a healthy alternative to saturated fat. The Diamonds' claims were disregarded by the food industry and criticised by various dietitians. Now nearly twenty years later hydrogenated and partially hydrogenated vegetable oil are regarded by health officials, such as those in New York City, to be so toxic that food containing the additive is classified on a par with food containing rodent droppings