common during birth to 6 months and less common in children aged 2 to 5 years. More research is needed to determine whether there is an increased prevalence of “crossing” percentiles in different populations or during different age intervals and whether there are associations between crossing percentiles and health-related outcomes.
The problem is how to proceed despite this lack of certainty. The committee concluded that because the CDC BMI charts are based on large national samples of the U.S. population of children and youth, they are the best available tools for assessing growth in clinical and public health settings. Although there are many unknowns about how to apply this information to individual children, and clinicians face difficulties in making generalizations regarding normal growth trajectories, experience suggests that children who demonstrate rapid changes—that is, frequently crossing up or down percentiles—may require special health-care attention. Health-and medical-care professionals should be consulted regarding growth-related questions for individual children as they can assess a child’s own growth trajectory in context (see Chapter 6).
Obesity prevention involves maintaining energy balance at a healthy weight while protecting overall health, growth and development, and nutritional status. Energy balance refers to the state in which energy intake is equivalent to energy expenditure, resulting in no net weight gain or weight loss. In adults, who have stopped growing, this relationship between energy intake and output must be equal and reach a zero net energy balance to prevent body storage of extra calories5 from food as fat and result in weight gain, which represents a positive energy balance. Strictly speaking, growing children, even those at a healthy body weight, must be in a slightly positive energy balance to satisfy the additional energy needs of tissue deposition for normal growth. However, for the purpose of simplicity in this report, the committee uses the term “energy balance” in children to indicate an equality between energy intake and energy expenditure that supports normal growth without promoting excess weight gain.
In children, energy expenditure constitutes the calories used for basal metabolism, processing of food, maintenance and repair of the body, and daily physical activity—in addition to the calories required for normal growth and development. Inappropriate weight gain (excess fat storage) results when energy expenditure is consistently exceeded by energy intake over time.