Calorie Restriction (CR) is a diet in which calorie intake is reduced, compared to diets that do not limit consumption, i.e., ad libitum (AL) diets. CR has been effective in extending the lifespan of many species through biochemical mechanisms that are still not well understood. Mice fed calorically restricted diets generally outlive mice fed AL diets by significant margins. It is not known yet whether CR will extend life on humans, but it is known that being slim, with a Body Mass Index around 21, reduces the incidence of diseases such as cancer, heart disease, and diabetes. Many people have already adopted CR diets to stay healthy and hoping to prolong their lives. To practice CR safely, it is necessary to select foods that provide all the nutritional requirements, but which are low in calories.
How do you measure Caloric Restriction?
In animal experiments, scientists divide a set of genetically homogeneous animals into an experimental group and a control group. They measure how much a control group eats, and then use that amount as the basis for determining how much to feed the experimental CR group, e.g., 30% less, etc. Although it is not possible to find genetically homogeneous controls for humans, the predictive energy expenditure equations like Harris-Benedict and Mifflin-St Jeor, in addition to the Body Mass Index (BMI) formula, make it possible to determine the calorie requirements of a person with your physical characteristics, but having a BMI of 22.0 which corresponds to the middle of the normal range. This theoretical person will be your "Control Twin" and will have your same height, age, sex, and exercise habits, but a weight corresponding to a BMI of 22.0. The BMI is the ratio of the weight to the height squared. It is calculated by dividing the weight in kilograms by the height in meters squared (BMI = weight / height2).
The Harris-Benedict and the Mifflin-St Jeor equations provide an estimate of the Basal Energy Expenditure (BEE), also called the Resting Metabolic Rate (RMR), or Basal Metabolic Rate (BMR). Predictive energy equations are routinely used in hospitals and nutrition clinics to determine the calorie requirements of various patients. Of the four most commonly used predictive energy equations, the Mifflin-St Jeor equations give the most reliable results.
The Mifflin-St Jeor equations are:
These equations require the weight in kilograms, the height in centimeters, and the age in years. To determine your total daily calorie needs, the BMR has to be multiplied by the appropriate activity factor, as follows:
NOTE: A 150-pound (68 kg) person walking at 4 miles per hour uses about 300 Cal per hour (5 kcal/min). The activity factor lightly active corresponds to walking 2 hours per day, moderately active corresponds to walking 3 hours per day, very active corresponds to walking 4 hours per day, and extra active corresponds to walking 5 hours per day (20 miles). Sedentary would include those sitting at a desk all day with no other activity or those confined to a wheelchair or mobility scooters who are not able to exercise.
The "Estimated Calories" is the number of calories required to keep your current weight constant for your level of activity, according to the equations. If your BMI is higher than 22.0, your weight will be more than the weight of your control twin, and the predictive energy expenditure equations will calculate a higher caloric requirement for you than for the control. The opposite is true if your BMI is below 22.0. Your percentage of calorie restriction (%CR) is determined only by the number of calories that you actually consume relative to those required by the control.
A successful weight control program requires accurately calculating the caloric content of food. Carbohydrates contain 4 Calories per gram, proteins contain 4 Calories per gram, fats contain 9 Calories per gram, and alcohol contains 7 Calories per gram. Learn how to count calories.
Create a link to this web page from your blog or your web page. Simply copy the following HTML snippet into your blog or web page, and a hyperlink will be created using the following CR Calculator Icon.
Inadequate low calorie diets can result in malnutrition or death.
You should not attempt a low calorie diet without the aid of nutritional tracking software, a good understanding of nutrition, and competent medical supervision.
Calorie Restriction decreases BMR while overeating increases it.
The Calorie Restriction Society and the CRsupportgroup provide forums where members can exchange information about their practice of CR. Below is the case of a practitioner whose weight and eating habits have remained constant for over 20 years. Analysis of the data provides some interesting insights.
A Case Study:
Lightly active female, age 51, 5 feet 7 inches tall, weighs 120 lb, and eats about 1000 Calories per day.
Using the Calorie Restriction Calculator we find that the subject's BMI is 18.8 and her Percent CR is 43.4%. The estimated calories for her level of activity are 1640, but she actually eats only 1000 Calories. This discrepancy of 640 Calories raises concerns about whether the calories consumed were counted correctly, or whether the subject is still losing weight. Verification by electronic mail was used to establish that the subject's weight had been steady for many years and that the calories consumed were correct.
Data from other long-term CR practitioners reflect similar discrepancies between actual caloric requirements and those estimated by energy equations. Experiments have shown that after weight loss the total energy expenditure is lower than predicted by actual changes in body weight and composition even well beyond the period of dynamic weight loss. A calculated caloric deficit does not imply that a person will lose weight. When a person achieves material and energy equilibrium with fewer calories, the calculated caloric deficit reflects an adaptation to lower calorie consumption compared to the subjects from which the equations were derived. The Biosphere-2 experiment showed that the BMR of the biospherians were approximately 6% lower than those of the control subjects after adjustment for age, sex, fat-free mass, and fat mass. Other experiments have shown that the basal metabolic rate can decrease by approximately 12% in three weeks of a 40% calorie restricted diet, but without reaching material equilibrium. A pioneering six-month semistarvation study by Keys showed that severe energy restriction decreased BMR in absolute terms by 39% and also relative to the weight of metabolically active tissue by 16%. Another study published in 2007 showed that after 3 months of a 25% CR diet, the BMR of calorie-restricted individuals was 91 kcalories per day less than the BMR of the control subjects. The authors concluded that BMR adapted or decreased beyond values expected from changes in weight and body composition as a result of energy deficit.
Experiments of 20 days of overeating have also shown that overfeeding causes a variable increase (1-18%) in basal metabolic rate but no change in metabolic rate during light exercise. This suggests that the BMR adapts to the level of food availability over a period of several days or weeks, but it is not easily affected by demands for energy of short duration.
The term "metabolism" can be interpreted as 1) the total energy required by the body, or 2) as the energy required by a specific weight of metabolically-active tissue. The Basal Metabolic Rate (BMR) is the energy that the body burns at rest to maintain normal body functions. The BMR decreases as the amount of metabolically-active tissue is reduced through diet or surgical losses of body mass. This has been verified in numerous studies using calorimeters, gas exchange studies, radioactive tracers, and other techniques. BMR should not be confused with the Specific Metabolic Rate or mass-specific metabolic rate which is the BMR per weight of metabolically active tissue. The Specific Metabolic Rate is fairly constant and is not influenced in the long term by calorie restriction.
One feature of mice experiments is that the mice are started on calorically restricted diets after 9 weeks, shortly after weaning. The mice on 40% calorie restricted (CR) diets grow to be adults which are approximately 51% of the size of mice fed ad libitum. Considering that the CR mice receive 60% of the food and that they have an adult weight of 51% of the weight of AL mice, CR mice eat 18% more than AL mice on a body weight basis.
Masoro also reported that rats started on a 40% CR diet at 6 weeks of age had lower weights. Masoro's data for rats from 10 to 20 months old can be used to calculate that the 40% CR rats had only 53% of the weight of the AL rats. The restricted rats got 57.9% of the food, but received 9% more calories per gram of body weight than the AL rats. Masoro only remarks about the number of calories that the CR rats consume over their lifetime, but his data indicates that the CR rats routinely ate more calories per gram of body weight from the age of 3 months, and also had a substantially longer lifespan.
What does this mean for humans?
The paradox of increased food consumption per unit of body weight for calorically restricted rodents has been interpreted to mean that it is only the reduction in total calories that really matters for longevity. Humans starting calorie restriction after maturity cannot achieve higher consumption-to-weight ratios than the controls. In the Case Study, above, the actual calories divided by the subject's weight gives 1000/120 = 8.3 Calories/pound, whereas the corresponding control requires 1766/140.2 = 12.6 Calories/pound.
Animal experiments on calorie restriction after maturity indicate that adult-onset CR also increases longevity. This has provided encouragement to the growing number of human CRON practitioners. Human CR diets must be phased in gradually over several years, and moderation is recommended since the optimum percentage of calorie restriction for human adults is still not known.
Research has shown that calories burned as exercise do not increase the life-extending effects of calorie restriction, but the activity of the control has to match the activity of the experimental subject to provide a fair comparison regardless of whether the control is a live animal or a theoretical model. It would not be accurate to compare a sedentary experimental subject to an active control or vice versa. Specifying the activity level allows calculation of the energy required by the control to match the activity of the subject. The calculator does not require a person to exercise. A person can be absolutely sedentary if he or she believes that this will lead to a longer life. The main objection reflected in these comments seems to be the use of terminology. "Percent Caloric Deficit" might be more appropriate than the term "Percent Calorie Restriction" when the activity level is higher than sedentary. A study by Holloszy concluded that 1) moderate caloric restriction combined with exercise does not normally increase the early mortality rate in male rats, 2) exercise does not interfere with the extension of maximal life span by food restriction, and 3) the beneficial effects of food restriction and exercise on survival are not additive or synergistic.
The Institute of Medicine decided that the "normal" BMI range is from 18.5 to 24.9. The BMI reference value of 22 used by the calculator is approximately the middle of the normal range. This makes it suitable for the majority of people. Although it would be possible to modify the calculator to use individualized reference points, it is difficult to decide which anthropomorphic criteria should be used to select other reference BMI values. A fat person could just claim to be "big boned" to use a higher reference BMI and produce more favorable results, whereas a thin person could choose a low reference BMI and end up malnourished trying to achieve a reasonable degree of CR.
The most common mistake that people make using the CR calculator is to overestimate their activity level. The caloric requirement increases substantially as you increase the activity factor. If you feel that you are eating too much and you gain weight eating the amount of food suggested for your activity level, you are not really as active as you think. The category of "very active" corresponds to hard exercise or sports 6 to 7 days a week. You would need to be a sportsman on a soccer field for four hours every day to be in this category, and not just playing softball a few times a year at a family picnic.
Some people prefer not to measure or quantify their practice of Calorie Restriction. We can only hope that they do not harm themselves by reducing their calories too much. As explained above, rodent studies measure the food eaten by control animals and use it as the basis for calculating the percentage of calorie restriction of the experimental animals. Only persons who have an identical twin would be able to conduct such an experiment, assuming that the brother or sister would be willing to be the control. The mid-point of the normal BMI, the "default" of 22, used with the energy equations is a reasonable assumption which is appropriate for people who do not have an identical twin. The suggestion to disregard the "arbitrarily predefined BMI limit" of 18.5, which is the lower limit of what is considered normal, is not wise. It requires a lot of diligence to achieve optimum nutrition with the very low calorie diets required to maintain low BMIs. One of the main reasons to practice CR is to increase longevity. Extremely low weight does not guarantee longevity. Centenarians typically are not underweight.
Kelly Flores received a BS in Physics from Colorado School of Mines in 1997 and a PhD in Computer Science from Florida State University in 2002.
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These are frequent alternate spellings for some of the technical terms:
Miflin St Jeor, Mifflin Saint Jeor, Haris-Benedict, calorie deficit, calory, calori, caloria, calorias, restricción calórica, Interaktiven Kalorienrechner, Kalorienbedarfs Rechner, täglichen Energiebedarf, Kalorienrechner, Kalorienverbrauch