There are several different formulas for determining estimated caloric needs. All are based on the principles of energy balance: Energy being used up or expended throughout the day should be equally consumed for weight maintenance. Weight loss occurs when energy intake is lower than estimated energy output, and weight gain occurs when energy intake is greater than estimated energy output. Many different factors effect someone's energy output, such as age, sex, height, weight and energy level. It is important to determine daily caloric intake, to achieve the right energy input balance to suit your lifestyle.
Caloric intake equations are based on determining a person's resting energy expenditure. This is the energy necessary to sustain life and to keep the heart, lungs, brain, liver and kidneys functioning properly. According to the book Nutrition Therapy and Pathophysiology, the average North American's resting energy expenditure accounts for about 60 to 75 percent of total daily energy expenditure. The remaining energy expenditure is through physical activity, about 25 percent, and through the metabolic process of digesting food, about 10 percent.
The Harris-Benedict equation is one of the most popular equations for determining energy needs by nutrition and health professionals. This equation takes into account a persons sex, age, height, weight and level of physical activity. The equation for males is: 66.5 + 13.8 x (Weight in kg) + 5 x (Height in cm); 6.8 x age. The equation for females is: 655.1 + 9.6 x (Weight in kg) + 1.9 x (Height in cm); 4.7 x age. These equations are then multiplied by an energy factor to determining estimated caloric needs. The physical activity factors are 1.2 for sedentary people, 1.3 for moderately active people and 1.4 for active people.
World Health Organization Equation
The World Health Organization (WHO) developed an equation for estimating energy needs in the 1980s. The equation is based on a persons sex, age range and weight. WHO did not feel that height was necessary to include in its equation. The equations are as follows:
Age 3 to 9 years = 22.5 x (Weight in kg) + 499
Age 10 to 17 years = 12.2 x (Weight in kg) + 746
Age 18 to 29 years = 14.7 x (Weight in kg) + 496
Age 30 to 60 years = 8.7 x (Weight in kg) + 829
Age over 60 years = 10.5 x (Weight in kg) + 596
Age 3 to 9 years = 22.7 x (Weight in kg) + 495
Age 10 to 17 years = 17.5 x (Weight in kg) + 651
Age 18 to 29 years = 15.3 x (Weight in kg) + 679
Age 30 to 60 years = 11.6 x (Weight in kg) + 879
Age over 60 years = 13.5 x (Weight in kg) + 487
Again, these equations are multiplied by the same physical activity factors to estimate daily caloric needs.
Mifflin-St. Jeor Equation
According to Nutrition Therapy and Pathophysiology, the Mifflin-St. Jeor equation was developed in 1990 and has been validated by more than 10 studies. The Mifflin-St. Jeor equation is gaining popularity among the nutrition professionals for accurately estimating caloric needs. The equation is as follows: for females = 10 x (Weight in kg) + 6.25 x (Height in cm) - 5 x age - 161; for males= 10 x (Weight in kg) + 6.25 x (Height in cm) - 5 x age + 5. These equations are also multiplied by the same physical activity factors to estimate daily caloric needs.
Which Equation to Choose?
According to the American Dietetic Association, the Mifflin-St. Jeor equation has been found to be the most reliable in predicting actual resting energy expenditure within 10 percent. The equation is recommended by nutrition professionals. For further understanding daily caloric intake needs, a Registered Dietitian should be consulted.