Fit for Life Diet


Fit for Life is a combination diet that emphasizes eating foods in the correct combination and avoiding the wrong combinations of foods rather than counting calories or controlling portion size. Several aspects of this diet have been disputed by dietitians.


Fit for Life is the creation of Harvey and Marilyn Diamond. The diet first came to the attention of the public in the mid-1980s with the publication of the book Fit for Life, which has sold millions of copies. On the official Fit for Life website, Diamond claims that the diet “spawned juice and salad bars, fruit sellers on the streets of New York, and the juice industry.” He also claims the book “launched a nutritional awakening in the United States and other Western countries.” These are impressive claims for a book written by a man whose “doctoral degree” came from the American College of Life Science, a non-accredited correspondence school founded in 1982 by a high school dropout.

Alternative medicine—
A system of healing that rejects conventional, pharmaceutical-based medicine and replaces it with the use of dietary supplements and therapies such as herbs, vitamins, minerals, massage, and cleansing diets. Alternative medicine includes well-established treatment systems such as homeopathy, traditional Chinese medicine, and Ayurvedic medicine, as well as more recent, fad-driven treatments.
A waxy substance made by the liver and also acquired through diet. High levels in the blood may increase the risk of cardiovascular disease.
Conventional medicine—
Mainstream or Western pharmaceutical-based medicine practiced by medical doctors, doctors of osteopathy, and other licensed healthcare professionals.
Dietary fiber—
Also known as roughage or bulk. Insoluble fiber moves through the digestive system almost undigested and gives bulk to stools. Soluble fiber dissolves in water and helps keep stools soft.
Dietary supplement—
A product, such as a vitamin, mineral, herb, amino acid, or enzyme, that is intended to be consumed in addition to an individual's diet with the expectation that it will improve health.
A protein that changes the rate of a chemical reaction within the body without being depleted in the reaction.
An inorganic substance found in the earth that is necessary in small quantities for the body to maintain health. Examples: zinc, copper, iron.
Naturopathic medicine—
An alternative system of healing that primarily uses homeopathy, herbal medicine, and hydrotherapy and rejects most conventional drugs as toxic.
A nutrient that the body needs in small amounts to remain healthy but that the body cannot manufacture for itself and must acquire through diet.


Fit for Life is a food-combining diet based on the theory that to lose weight one must not eat certain foods together. The philosophy behind the diet comes from Diamond's interest in natural hygiene, an offshoot of naturopathic medicine. In his original book, Diamond claimed that if a person ate foods in the wrong combination, they would “rot” in the stomach. He also categorized foods as “dead foods” that clog” the body and “living foods” that cleanse the body. The newest version of Fit for Life talks less about rotting, dead, and living foods and more about “enzyme deficient foods.” However, the general message about food combining is the same.

According to Diamond, dead foods are meats and starches. Living foods are raw fruits and vegetables. His diet plan requires that these foods not be eaten together. Some of the Fitness for Life rules include:


The goal of the Fit for Life diet is to help people lose weight and keep their body healthy through diet. Diamond states that people do not gain weight because they eat too many calories and exercise too little. Instead, he considers the cause of weight gain to be eating protein-rich foods at the same time as carbohydrate-rich foods. He argues that enzymes that digest proteins interfere with enzymes that digest carbohydrates, and therefore these two foods should not be eaten together. His program makes little mention of the role of different types of fats—saturated, unsaturated, and trans fats—in diet, dietary fiber, the role of water in health, or the need to exercise.



The benefits claimed by Fit for Life are not supported by any scholarly research and are, in fact, refuted by some research. The main claim, supported by testimonials and before and after pictures, is that people who follow Fit for Life will lose weight and keep it off. Along with weight loss will come a general improvement in health. The official Fit for Life Website claims an “86% success rate” and mentions “clinical trials” without providing any details.

Some benefits of the plan are that it encourages people to increase their consumption of fresh fruits and vegetables. Unlike some diets, Fit for Life does not require dieters to buy special foods, keeping food costs moderate. It does, however, encourage dieters to purchase enzyme supplements from Fit for Life Industries.


The Fit for Life website is heavy on the theory behind the Fit for Life diet, but gives few specifics on how the diet can be put into effect in daily life. Sample meal plans and approved food lists are not available until the dieter signs up for the program at a substantial fee. This is very different from programs such as Body for Life or Weight Watchers, which give potential program participants very specific information about diet, menus, and exercise before they pay for the plan.

Fit for Life claims that their rules for eating benefit everyone, from young children to pregnant women to older adults. The diet is intended to be a diet for a lifetime, but it does not take into account changes in life cycle nutrition.


Some registered dietitians feel that the Fit for Life diet can lead to serious vitamin and mineral deficiencies. Banning dairy products makes it extremely difficult for dieters to get the recommended daily allowance of calcium. Calcium is needed to keep bones strong and for many metabolic reactions in the body. Other potential vitamin deficiencies spotted by dietitians who have analyzed this diet include deficiencies in vitamin B and B12.

Research and general acceptance

Many professionals in the nutrition community consider Fit for Life an unhealthy fad diet. The concept behind food combining was tested in a study published in the April 2007 issue of the International Journal of Obesity. In this study, participants were fed a 1,100 calorie a day diet to promote weight loss. One group ate balanced meals containing all the major food groups. The other group ate a similar diet, but tested the food-combining theory by avoiding eating certain food groups at the same time. At the end of six weeks, the blood sugar, cholesterol, insulin, and blood fats were the same for each group. The balanced-meal group had lost an average of 16.5 lb. and the food-combining group had lost 13.6 lb. This strongly suggests that eating a low-calorie diet is much more important than eating foods in certain combinations.

See also Fad diets .



Diamond, Harvey. Fit for Life: A New Beginning: The Ultimate Diet and Health Plan. Updated ed. New York: Kensington, 2011.

Diamond, Harvey, and Marilyn Diamond. Fit for Life. Reprint ed. New York: Grand Central Life and Style, 2010.

Icon Health Publications. Fad Diets: A Bibliography, Medical Dictionary, and Annotated Research Guide to Internet References. San Diego, CA: ICON Health, 2004.

Scales, Mary Josephine. Diets in a Nutshell: A Definitive Guide on Diets from A to Z. Clifton, VA: Apex, 2005.


Callahan, Maureen. “Fit for Life Diet Review.” .,,20410201,00.html (accessed March 29, 2018).

Mann, Denise. “It's the Calories That Count, Not the Food Combinations.” . (accessed March 29, 2018).

Tish Davidson, AM

  This information is not a tool for self-diagnosis or a substitute for professional care.