Although many studies have linked breastfeeding to a protection against obesity, not all studies agree. A recent paper published in The Journal of Pediatrics sought to determine why this might be. They considered one important factor that previous studies had not—the quality of the diet following breastfeeding. When taking this important factor into consideration, they found that breastfeeding is protective against obesity when the follow-up diet follows official recommendations that do not limit fat intake before 2 to 3 years of age.

Breast milk is rich in fat and rightly so. The first few years of life are vital to the development of the nervous system—a system that happens to be rich in fat itself. Babies need fat to fuel the rapid growth of the brain and nerves throughout the body. Many mothers may place infants on low-fat dairy thinking it’s the healthiest choice for their children, but they couldn’t be further from the truth. This diet may actually program the child’s metabolism to make do with much less fat than it needs, which could make the infant more susceptible to obesity later in life, when a high-fat intake overwhelms an unprepared metabolism.

“The beneficial effect of breast milk may be masked by a low-fat diet following breastfeeding, while a diet following official recommendations (no restriction of fats before the age of two to three years) allows its beneficial effect to appear,” noted Sandrine Peneau, PhD, one of the researchers.

This study helps explain why not all studies agree on the protection of breastfeeding against obesity. Now we know, not surprisingly, that diet after breastfeeding also plays an important role.