There are quite a few reasons why groups like the American Academy of Pediatrics recommend mothers breastfeed for at least 12 months, introducing solids after six months. Breastfeeding has been shown to have many advantages for mother and child. It decreases respiratory illnesses, ear infections, gastrointestinal disease, allergies, eczema and asthma in babies.

Breastfed infants have a lower rate of SIDS, or sudden infant death syndrome. And adolescents and adults who were breastfed are less likely to be obese than their formula-fed peers.

Now there is a new benefit of early exclusive breastfeeding: It appears to help the infant's digestive system transition to solid foods by influencing the make up, stability, and diversity of bacterial population in the gastrointestinal tract.

For parents and babies, this easier transition can translate into less colic, stomach aches, and food intolerance, and other health benefits that last into adult life.

Researchers from the University of North Carolina investigated the types and numbers of bacteria in the guts of breastfed infants from 2 weeks to 14 months of age and compared them to the bacteria in the guts of those who were formula fed or breast milk plus formula fed.

They found that a baby's diet during the first few months of life has a huge influence on the composition, diversity, and stability of the gut microbiome.

The gut microbiomes, or communities of bacteria, were very different between the exclusively breastfed infants and those given formula. The breastfed infants had a higher proportion of bifidobacterium, a type of bacteria known to be beneficial for digestion. Those with breast and formula in their diets had a higher proportion of other types of bacteria.

Exclusively breastfed babies had differing amounts of about 20 bacterial enzymes when compared to babies who received solid food. This seems to indicate that some new bacterial species had entered the scene to help process the new food types. In babies fed both formula and breast milk — and then introduced to solid foods — the samples revealed about 230 enzymes, indicating a much more dramatic shift in microbial composition.

“We found that babies who are fed only breast milk have microbial communities that seem more ready for the introduction of solid foods,” Andrea Azcarate-Peril, the study's senior author said in a statement.

“The transition to solids is much more dramatic for the microbiomes of babies that are not exclusively breastfed. We think the microbiomes of non-exclusively breastfed babies could contribute to more stomachaches and colic.”

Interestingly, the microbiomes of babies who attended daycare also showed lower proportions of bifidobacterium than those who stayed at home, but the type of feeding remained the most important factor for determining the infant's response to solid food.

Previous research has suggested that breast milk contains special sugars that electively nourish the types of gut bacteria that infants need. This provides one explanation for the differences that the researchers found.

The benefits of breastfeeding are numerous and this study supports the importance of exclusive breastfeeding for the first six months of life to provide babies with an optimum start on gastrointestinal health as they transition to a more diverse diet including solid foods.

The study is published in Frontiers in Cellular and Infection Microbiology.