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Estimating Percent Calorie Restriction
Based on Weight Change

A Weight-Based Percent CR Calculator

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.

The Mifflin-St Jeor equations are:
Male: BMR = 10×weight + 6.25×height - 5×age + 5
Female: BMR = 10×weight + 6.25×height - 5×age - 161

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:

Weight-Based Percent Calorie Restriction Calculator
Calculates %CR relative to a previous weight using the Mifflin-St Jeor equations
Enter the information requested, then click the "Calculate" button.
  English Units Metric Units
Height   feet      inches     centimeters  
Sex Male       Female      
Weight  pounds    kilograms     
Age  years  
Weight  pounds    kilograms     
Age  years  
Before Basal Metabolic Rate (BMR) 
Before BMR times Activity Factor   (Before Calories) 
After Basal Metabolic Rate (BMR) 
After BMR times Activity Factor   (After Calories) 
 Before Calories minus After Calories 
 Weight-Based Percent CR:   %CR
 A negative %CR value indicates that you are now eating more than before 
See also the Diet Calculator to calculate percent body fat.

Potential Problems
Estimating caloric restriction based on weight and activity changes has two fundamental problems:

  1. 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.

  2. 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.,

Total Calories = BMR Calories + Exercise Calories

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.

Read more about Calorie Restriction
  1. Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals.", Am J Clin Nutr., 1990 Feb;51(2):241-7. PMID: 2305711
  2. Frankenfield D, Roth-Yousey L, Compher C., "Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review", J Am Diet Assoc., 2005 May;105(5):775-89. RESULTS: Four prediction equations were identified as the most commonly used in clinical practice (Harris-Benedict, Mifflin-St Jeor, Owen, and World Health Organization/Food and Agriculture Organization/United Nations University [WHO/FAO/UNU]). Of these equations, the Mifflin-St Jeor equation was the most reliable, predicting RMR within 10% of measured in more nonobese and obese individuals than any other equation, and it also had the narrowest error range. PMID: 15883556
  3. Christian Weyer, Roy L Walford, Inge T Harper, Mike Milner, Taber MacCallum, P Antonio Tataranni and Eric Ravussin, "Energy metabolism after 2 y of energy restriction: the Biosphere 2 experiment", American Journal of Clinical Nutrition, Vol. 72, No. 4, 946-953, October 2000.  Free Full Text
  4. Friedlander AL, et al. "Three weeks of caloric restriction alters protein metabolism in normal-weight, young men" Am J Physiol Endocrinol Metab., 2005 Sep;289(3):E446-55. Epub 2005 May 3. PMID: 15870104

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