The CRON-diet (Calorie Restriction with Optimal Nutrition)[1] is a nutrient-rich, very low calorie diet[2] developed by Roy Walford, Lisa Walford, and Brian M. Delaney.[3][4][5] The CRON-diet involves calorie restriction in the hope that the practice will improve health and retard aging, while still attempting to supply in the recommended daily amounts of various nutrients. Other names include CR-diet, Longevity diet, and Anti-Aging Plan. Several people including the Walfords, Delaney and others founded the CR Society International to promote the CRON-diet.
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The CRON-diet was developed from data Walford compiled during his participation in Biosphere 2,[6] and from Walford's decades of animal testing.[7]
Proponents of the CRON-diet believe that everyone has what they call a "set-point:" a weight, specific to an individual, at which each naturally stays when they eat their usual daily diet. Proponents believe that the "set-point" is determined through heredity and childhood eating habits. Proponents recommend that adherents remain 10% to 25% under their "set-point", suggesting that this is necessary for the diet to be maximally effective.[8]
A guideline that proponents use to determine an individual's "set-point" is to measure that person's body fat content. Proponents state that this should be between 10-15% for a female person and between 6-10% for a male person.[9] Proponents suggest the use of skinfold test tools (they specifically recommend the "Fat-O-Meter"), certain digital scales, densiometry, and/or bioelectrical impedance analysis to determine the body fat content. Proponents then use the current weight and body fat content to determine the goal weight (below the "set point"), and plan and follow a preliminary diet until the goal weight is reached.
Next, the proponent determines the amount of caloric restriction they wish to implement in their regular eating pattern. Proponents recommend a goal of restricting intake by 20%.[9] The actual daily amount eaten depends on the adherent's basal metabolic rate (BMR), although Walford has stated that he doubts the verifiability of BMR calculation tools. A common daily intake is 1800 calories per day.[10]
The Walfords propose three meals in their book, but variation is possible. Adherents can vary the number of meals they eat per day in order to fit their schedules: typically, this is achieved by combining calorie-dense and calorie- lean foods in different ways.[11] Proponents also use "supplements"; they use this word to refer to vitamin pills as well as certain high-nutrition foods (which are necessarily calorie-lean).[12] The Walfords describe these foods as "nutrient super-chargers"; examples include kombu, brewers yeast, wheat bran, wheat germ, shiitake mushrooms, non-fat dry milk, soybeans, and tofu. These "nutrient super-chargers" are used frequently to boost meals' nutritional density.[11]
The Walfords propose that adherents eat three meals per day. They suggest that adherents cook eight meals on a specific day of the week, and then freeze these meals to use during the entire week. They refer to this process as the "Quantity-Cook-and Freeze Option", and the meals themselves as "One-a-day MegaMeals". They suggest that adherents use two "Free-Choice Recipes" for the other two courses per day.
Adherents may compose their own meals. The Walfords caution that such meals must be planned exactly and contain all the required RDA nutrients. There are computer tools available to plan meals, including the official Dr. Walfords Interactive Diet Planner and the unofficial CRON-o-Meter.
Books on the CRON-diet include:
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