Early life events, such as mode of delivery at birth, antibiotic use, and diet, all play a big role in what bacteria develop in the intestinal tract, which, in turn, determines how healthy an individual will be. In a recent study published in the journal Science Translational Medicine, researchers from UC Davis and UC San Francisco compared breastfed and bottle-fed infant rhesus monkeys in an attempt to better understand what immune effects occur as a result of the monkeys’ diets.

They found that the breastfed monkeys had more immune cells, called memory T cells and T helper 17 cells, known for fighting certain pathogens. The differences in immune development were still present for months after weaning. Even when weaned to the same diet as bottle-fed monkeys, the improvement in immune development persisted in the breastfed monkeys.

The researchers followed six breastfed and six bottle-fed monkeys from age 5 months to one year and found that at six months, the breastfed monkeys had higher amounts of Prevotella and Ruminococcus bacteria and the bottle-fed monkeys had higher amounts of Clostridia. In addition, the breastfed monkeys had a higher diversity of gut bacteria compared to bottle-fed monkeys, a finding consistent with healthier outcomes. In general, the more diverse your gut bacteria, the healthier you are.

“Our study suggests that the gut microbiota present in early life may leave a durable imprint on the shape and capacity of the immune system, a programming of the system if you will,” noted Amir Ardeshir, PhD.

The results of this study are not surprising when you consider that up to 80 percent of your immune system resides in the gut. During early life, gut bacteria evolve and are thought to prime the immune system, teaching it how to appropriately respond. This study helps to illustrate just how this intricate relationship plays out on immune function.