BMI changes substantially with age. After about one year of age, BMI-for-age begins to decline and it continues falling during the preschool years until it reaches a minimum around 4 to 6 years of age.

Here you see a section of the BMI-for-age chart for boys enlarged to show the shape of the curve in more detail. After 4 to 6 years of age, BMI-for-age begins a gradual increase through adolescence and most of adulthood. The rebound or increase in BMI that occurs after it reaches its lowest point is referred to as "adiposity" rebound (Whitaker et al., 1998; Rolland-Cachera et al., 1991; Rolland-Cachera et al., 1984). This is a normal pattern of growth that occurs in all children.

Recent research has shown that the age when the "adiposity" rebound occurs may be a critical period in childhood for the development of obesity as an adult (Whitaker et al., 1998). An early "adiposity" rebound, occurring before ages 4 to 6, is associated with obesity in adulthood. In the example shown here, adiposity rebound occurred at around age 3. BMI reached the lowest point at 32 months (2 years 8 months) and then began to increase.

However, studies have yet to determine whether the higher BMI in childhood is truly adipose tissue versus lean body mass or bone. Additional research is needed to further understand the impact of early adiposity rebound on adult obesity. (Note that we put the word adiposity in quotations when using it in this context since we do not know if it is truly adipose tissue.)