Fats are the major source of energy provided in breast milk, supplying roughly half of its total calories. Fats provide energy for growth, aid in the maturation of the infant's gut and central nervous system, and provide protection from pathogens, including group B streptococcus bacteria. Nearly 200 fatty acids have been identified in human breast milk. The structural configuration of these fats, which is not always replicated by many infant formulas, enhances their absorption in the infant's gut. All of these fats are encapsulated in fat globules surrounded by a triple layered structure called milk fat globule membrane or MFGM.

Components of the MFGM exert bioactive properties that confer many of the antibacterial in anti-inflammatory properties of breast milk. Unfortunately, most infant formulas do not contain MFGM. However, a recent clinical trial found that the bovine form of MFGM exerts similar beneficial effects on human infants when included in infant formula. The double-blind randomized control trial involved 451 healthy full-term infants who received either regular formula or formula containing MFGM and lactoferrin, an iron-binding protein found in human and cow's milk. At the end of the 18-month long study, the infants who received formula with the MFGM and lactoferrin scored higher on cognitive, language, and motor skills than infants who received ordinary formula. In fact, their scores were similar to those observed in children who were breastfed, suggesting that the addition of MFGM and lactoferrin could narrow the gap in cognitive development commonly observed between formula-fed infants and breastfed infants.

The type of fatty acids present in breast milk are strongly influenced by the mother's diet, especially when it comes to the all-important Omega-3 fatty acids. For example, when lactating women took a dietary supplement containing 400 milligrams of the Marine Omega-3 fatty acid DHA, their breast milk contained 123% more DHA than the breast milk of women who took a placebo. DHA is crucial for proper brain development. The infants whose mothers took the DHA supplement also had lower plasma Omega-6 to Omega-3 ratios. A lower Omega-6 to Omega-3 fatty acid ratio is more desirable in reducing the risk of many chronic diseases.

Smoking cigarettes reduces Omega-3 fatty acid uptake, especially DHA, into breastmilk. Omega-3 fatty acids play key roles in infant brain development. Intake of DHA, in particular, is associated with improved mental and psychomotor development. DHA is the most abundant Omega-3 fatty acid in a newborn's brain. Maternal intake of Omega-3 fatty acids is associated with larger brain volumes in breastfed or mostly breastfed infants.

One study involved 92, one-month-old full-term infants who were breastfed exclusively, or most of the time. MRI studies revealed that the infants of women who consumed higher quantities of Omega-3 fatty acids had greater brain volumes in specific regions of the frontal cortex and corpus callosum, areas of the brain involved in consciousness, communication, memory, attention, and integration of motor, sensory, and cognitive performance between the brain hemispheres.

Breastfeeding also has profound effects on an infant's brain, greatly influencing their intellectual development.

A meta-analysis of 17 studies linking breastfeeding and intelligence found that children and adolescents who were breastfed as infants scored nearly three points higher on intelligence tests than those who were not breastfed, even after taking maternal intelligence into consideration. A large clinical trial that followed up on more than 13,000 infants from around 13 different hospitals found that total and exclusive breastfeeding led to improved performance in intelligence tests at the age of six with breastfed children averaging roughly 7.5 points higher on tests than children who were not breastfed.

Other research has found that by the age of two, babies who were exclusively breastfed for at least three months had 20% to 30% more white matter in their brains, especially in regions associated with language, emotional regulation, and cognition. The beneficial effects of breast milk on infant brain development may be particularly relevant for preterm infants born prior to 37 weeks gestation who have a significantly higher risk for white matter injury during birth. Approximately 1 in 10 infants born in the United States is born prematurely according to CDC data.

Emerging evidence suggests that preterm infants who were fed breast milk have significantly improved microstructural organization of the white matter in their brains compared to preterm infants fed formula. And preterm babies that received breast milk in the neonatal ICU or NICU have higher verbal intelligence, white matter, and total brain volumes, especially in boys.

So, in summary, breastfeeding influences brain development and intelligence even after taking maternal intelligence into consideration. Breastfed babies tend to have higher amounts of white matter in their brains and later in life perform better on intelligence tests than non-breastfed babies.