A 42-Year-Old Childhood Obesity Theory May Be Wrong

New research challenges a 42-year-old theory about why children’s body mass index (BMI) declines after infancy and then begins climbing steadily from about age 6. This pattern has long been described as the ‘adiposity rebound,’ based on the idea that body fat first decreases and then returns.

However, the new analysis suggests that the later increase in BMI is not caused by a rebound in fat. Instead, it may largely reflect the normal growth of muscle and other lean tissue.

The research, led by Professor Andrew Agbaje, a physician and associate professor of clinical epidemiology and child health at the University of Eastern Finland, Kuopio, Finland, was presented at this year’s European Congress on Obesity in Istanbul, Turkey, and published in The Journal of Nutrition.

Why the Adiposity Rebound Theory Matters

Questioning the existence of the ‘adiposity rebound’ could have important consequences for childhood health care. Since the theory was introduced, some physicians, including pediatricians, have treated the pattern as a meaningful warning sign that might be prevented or modified through diet and lifestyle changes.

If the rise in BMI is actually a normal result of muscle development, however, efforts to stop it may be addressing a problem that does not exist.

The concept dates back to 1984, when French researcher Marie Françoise Rolland-Cachera and her colleagues described ‘adiposity rebound’ in a paper published in The American Journal of Clinical Nutrition.

The researchers reported a connection between the age at which a child’s BMI began rising again and the child’s BMI adiposity at age 16 years. An early rebound (before age 5.5 years) was associated with greater adiposity later in adolescence than a rebound occurring after age 7 years. Some later studies reported similar associations.

BMI tends to follow a recognizable pattern during childhood. It rises quickly during infancy and reaches a high point at about age 1 year. It then gradually declines, reaching its lowest level at around age 4 years, before beginning to rise again.

By age 6 years, a child typically returns to the same BMI recorded at age 2 years. This pattern occurs across the childhood population and became known as the ‘rebound.’

Researchers have often focused on the timing of the decline and subsequent rise. They proposed that children whose BMI begins climbing at a younger age may reach a higher BMI later in life and face a greater risk of BMI-obesity.

The theory was based partly on statistical models suggesting that when BMI reaches its lowest point earlier, it also begins rising earlier, potentially leading to a higher BMI in later childhood or adolescence.

A Statistical Link May Not Reflect Biology

Professor Agbaje argues that the BMI pattern should not be compared with major biological transitions such as puberty.

Puberty occurs in nearly every child who reaches adulthood, but unusually early puberty has been linked to health risks supported by known biological mechanisms. According to Agbaje, no comparable biological explanation supports the idea that an early ‘adiposity rebound’ causes later obesity.