The amount of calories an individual requires is going to vary from person to person based on factors such as gender, age, height, weight and activity level, as well as personal needs and goals. While several equations exist, two primary formulas help determine caloric needs: the Harris Benedict formula and the Mifflin-St. Jeor equation. These formulas focus on the understanding and management of energy. Calories are a measure of heat energy, which ultimately translates into weight management. When the calories consumed equal the calories expended or used, weight can be easily maintained.
It is important to start with a baseline. This baseline is known as the basal metabolic rate (BMR). BMR is often synonymous with resting metabolic rate (RMR). The differences between BMR and RMR are so minute, they are inconsequential for the purpose of calculating the calories required. BMR represents the minimum amount of energy needed to run the most basic of all life functions of the body in its sedentary state, such as your heart beat and your lungs' ability to breathe.
Harris Benedict Formula
Step 1
Take precise measurements of your weight and height, in order to obtain an accurate BMR.
Step 2
Use a calculator and convert pounds to kilograms by dividing pounds by 2.2, as there are 2.2 lbs/kg, and convert inches into cm by multiplying inches by 2.54, as there are 2.54 cm/inch. Record the results.
Step 3
Calculate your BMR by using the Harris Benedict formula. Note that the formula differs slightly for males and females. Plug the results from Step 2 into the gender-appropirate equation, and using a calculator, determine the BMR. Record the results.
Males
BMR = 66.5 + (13.7 x weight in kg) + (5 x height in cm) - (6.76 x age in years)
Females
BMR = 655 + (9.6 x weight in kg) + (1.8 x height in cm) - (4.7 x age in years)
Mifflin-St. Jeor Equation
Step 1
Take precise measurements of your weight and height. As does the Harris Benedict formula, the Mifflin St. Jeor equation takes into account gender, age, height and weight to determine BMR.
Step 2
Use a calculator and convert pounds to kilograms by dividing pounds by 2.2, as there are 2.2 lbs/kg, and convert inches into cm by multiplying inches by 2.54, as there are 2.54 cm/inch. Record the results.
Step 3
Calculate BMR using the Mifflin-St. Jeor equation. Plug the results from Step 2 into the gender appropirate equations, and using a calculator, determine the BMR. Record the results.
Males
BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) + 5
Females
BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) - 161
Daily Caloric Requirements
Step 1
Use a calulator to determine daily caloric requirements according to gender.
Step 2
Multiply the BMR obtained from either equation by the factor that best represents your level of activity.
Sedentary (Little to no activity) BMR x 1.2
Light activity (Those who exercise 1-3 days per week) BMR x 1.375
Moderately active (Those who exercise 3-5 days per week) BMR x 1.55
Very active (Those who exercise 6-7 days per week) BMR x 1.725
Extremely Active ( Those who exercise 2 time per day) BMR x 1.9
Step 3
Record the results. The results obtained represent the total daily energy expenditure in calories needed to sustain current body weight.
Tips and Warnings
- Of the predictive energy equations, "The Mifflin-St Jeor equation is 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," according to the "Journal of the American Dietetic Association."
References
- "Exercise Science: Understanding and Evaluating Physical Fitness and Health," 2nd Ed; Rosenberg, Cullen; 2008
- "American Journal of Clinical Nutrition"; A new predictive equation for resting energy expenditure in healthy individuals; MD Mifflin, et al.; February 1990
- "Journal of the American Dietetic Association"; Comparison of Predictive Equations for Resting Metabolic Rate in Healthy Nonobese and Obese Adults: A Systematic Review; David Frankenfield, MS, RD, et al.; May 2005
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