Weight loss through diet is achieved by limiting the calories consumed to less than what is needed by the body's metabolism. Keeping a normal weight is important because obesity increases the incidence of diabetes, cardiovascular diseases, and cancer. Reducing calories below a normal level of consumption while maintaining appropriate nutrition, also known as Caloric Restriction (CR) or Caloric Restriction with Optimum Nutrition (CRON), has been shown to extend the lifespan of many species, and there is much interest in finding out whether CR will extend human lifespan.
Measuring Caloric Restriction
In animal experiments, a number of genetically similar animals are selected and divided into a control set and an experimental set. The amount of food eaten by the control animals is weighed, and the weight of the food is used as the basis for calculating the amount of food given to the experimental animals. This procedure cannot be implemented for humans because genetically similar humans are not readily available. However, it is possible to use the Mifflin-St Jeor equations[1,2] to estimate the energy requirements of a "Control Twin" of normal weight for any particular person and compare that with the actual calories consumed by the person. This is the method used by the Caloric Restriction Calculator which is different from the method presented here.
The Weight-Based Percent CR Calculator
Some people find it difficult or tedious to count calories. The following calculator uses the Mifflin-St Jeor equations to estimate the percentage of caloric restriction based on changes in weight and physical activity. This method assumes that the "before" and "after" weights which are being compared were, or have been, stable for several weeks and represent an equilibrium between the calories consumed and the calories spent. Do not use this calculator if you have changed your diet or exercise habits recently, or if your weight has not remained steady for at least three weeks.
These equations require the weight in kilograms, the height in centimeters, and the age in years. BMR represents the Basal Metabolic Rate in Calories. To determine your total daily calorie needs, the BMR has to be multiplied by the appropriate activity factor, as follows:
Estimating caloric restriction based on weight and activity changes has two fundamental problems:
The method is indirect. No actual calories are measured. The energy equations are assumed to give a correct estimate of the BMR for any particular person with any particular weight. This may not always be true.
Changes in calorie consumption affect BMR. It is well known that dieting lowers the Basal Metabolic Rate[3,4]. The equations may overestimate the calories required to maintain the "after" weight, thus underestimating the Percent of Caloric Restriction.
The Effect of Exercise
The energy equations basically state that the number of calories needed to maintain a specific body weight depend on BMR adjusted by an exercise factor, i.e.,
This means that an increase in the level of exercise will require an increase in the total calories to keep the same weight and maintain an equilibrium between the energy consumed and the energy spent. People who have been conditioned to think that weight can be lost by exercising will find it counterintuitive that exercise actually increases the number of calories calculated by the equations and may result in negative percentages of Caloric Restriction.
For example, suppose that a male who is 5 feet 8 inches tall weighed 160 pounds at age 45 being lightly active. A year later, at age 46, this person weighs 150 pounds and is moderately active. The calculator shows that the lower weight and higher exercise level requires 200 more Calories to maintain, resulting in a negative 10.8 percent CR. If the person had continued being lightly active and achieved the weight loss only through diet, instead of by increasing the exercise level, he would require 69 fewer calories than at the higher weight, and the percent CR would be 3.2 percent.
The Effect of Age
Since metabolism slows down over time, fewer calories are needed to maintain a specific weight with advancing age. A lightly-active 5 foot 8 inch male weighing 150 pounds who maintains the same weight from age 45 until age 65, has a relative 6.5 percent CR because 138 fewer calories are required to maintain the same weight at age 65 than at age 45. This is the reason why people generally gain weight as they age. Their eating habits remain the same, but their metabolism slows down. The excess calories get stored as extra weight.
This Weight-Based Percent CR Calculator is not as accurate as the Caloric Restriction Calculator which uses a "Control Twin" as reference. The control twin calculator uses the energy equations only to calculate the caloric requirements of the control twin and then uses that value as a reference for comparison with the actual calories consumed. The only advantage of the Weight-Based Percent CR Calculator is that it is not necessary to count calories.