What is the Caloric Balance Equation?

When it comes to maintaining a healthy weight for a lifetime, the bottom line is — calories count! Weight management is all about balance—balancing the number of calories you consume with the number of calories your body uses or “burns off.”

A calorie is defined as a unit of energy supplied by food. A calorie is a calorie regardless of its source. Whether you’re eating carbohydrates, fats, sugars, or proteins, all of them contain calories.

Caloric balance is like a scale. To remain in balance and maintain your body weight, the calories consumed (from foods) must be balanced by the calories used (in normal body functions, daily activities, and exercise).

Body Mass Index Formula

Although the BMI number is calculated using the same body mass index formula for children and adults, the criteria used to interpret the meaning of the BMI number for children and teens are different from those used for adults. For children and teens, BMI age- and sex-specific percentiles are used for two reasons:

The amount of body fat changes with age.

The amount of body fat differs between girls and boys.

The CDC BMI-for-age growth charts take into account these differences and allow translation of a BMI number into a percentile for a child’s sex and age.

Results of the body mass index formula for adults are interpreted through categories that do not take into account sex or age.

Healthy weight ranges cannot be provided for children and teens for the following reasons:

Healthy weight ranges change with each month of age for each sex.

Healthy weight ranges change as height increases.

CDC and the American Academy of Pediatrics (AAP) recommend the use of the Body Mass Index Formula to screen for overweight and obesity in children and teens aged 2 through 19 years. Although BMI is used to screen for overweight and obesity in children and teens, BMI is not a diagnostic tool.

A child who is relatively heavy may have a high BMI for his or her age. To determine whether the child has excess fat, further assessment would be needed. Further assessment might include skinfold thickness measurements. To determine a counseling strategy, assessments of diet, health, and physical activity are needed.

The adult calculator provides only the BMI number and not the BMI age- and sex-specific percentile that is used to interpret BMI and determine the weight category for children and teens. It is not appropriate to use the BMI categories for adults to interpret BMI numbers for children and teens.

The interpretation of BMI-for-age varies by age and sex so if two children are not exactly the same age and of the same sex, the BMI numbers have different meanings. Using the Body Mass Index Formula and calculating BMI-for-age for children of different ages and sexes may yield the same numeric result, but that number will fall at a different percentile for each child for one or both of the following reasons:

The normal BMI-related changes that take place as children age and as growth occurs.

The normal BMI-related differences between sexes.

Source: Centers for Disease Control and Prevention

What is Body mass Index?

Body Mass Index (also known as BMI) is a number calculated from a child’s weight and height. BMI is a reliable indicator of body fatness for most children and teens. BMI is not an exact measurment of body fat, but research has shown that it does correlate to direct measures of body fat. BMI can be considered an alternative for direct measures of body fat. BMI is also an inexpensive and easy-to-perform method of screening for weight categories that may lead to health problems.

For children and teens, BMI is age and sex specific and is often referred to as BMI-for-age.

What is a BMI percentile?

After BMI is calculated for children and teens, the BMI number is plotted on the CDC BMI-for-age growth charts (for either girls or boys) to obtain a percentile ranking. Percentiles are the most commonly used indicator to assess the size and growth patterns of individual children in the United States. The percentile indicates the relative position of the child’s BMI number among children of the same sex and age. The growth charts show the weight status categories used with children and teens (underweight, healthy weight, overweight, and obese).

BMI-for-age weight status categories and the corresponding percentiles are shown below.

Underweight - Less than the 5th percentile

Healthy weight - 5th percentile to less than the 85th percentile

Overweight - 85th to less than the 95th percentile

Obese - Equal to or greater than the 95th percentile

Source: Centers for Disease Control and Prevention