A new study showed why the gut microbiome in breast milk-fed infants differs significantly from formula-fed babies. Researchers found that a lipid class promotes distinct bacteria in the gut.
The difference in the gut microbiome between breast milk-fed and formula-fed infants was investigated by researchers at Cornell University, a US private research university. They identified two types of gut microbes that use a class of lipid metabolites, which are often found in human breastmilk. If nutritionists would prescribe foods that have the lipid, they could intentionally alter the gut microbiome of patients. The alteration would promote the growth of these microbes in the gut. They published their findings in the Journal of Lipid Research.
The Benefits of Breastfeeding
Clinicians recommend mothers to breastfeed their infants until the age of two years. This is because nothing else can offer the best nutrition than human breastmilk. Aside from excellent nutrients, breastmilk contains antibodies from the mother that can protect infants. For up to two years, breastmilk-fed babies are protected from different kinds of infections. Moreover, breastmilk can influence the infant's health when they reach adulthood.
According to the US Centers for Disease Control and Prevention, breastfeeding is not just a lifestyle change. It is an excellent investment for the family. Studies have shown that breastfeeding can reduce the risk of several chronic illnesses, such as asthma, obesity, type 1 diabetes, and sudden infant death syndrome, among babies. While the investment can decrease the risk of hypertension, type 2 diabetes, and both breast and ovarian cancers among mothers. But breastfeeding can be troublesome for many mothers.
For example, an estimated 60% of mothers in the US stop breastfeeding sooner due to various reasons, including a lack of support and encouragement. Many mothers stop breastfeeding because they need to go back to work, wherein policies of breastfeeding may be nonexistent. Thus, mothers fail to maintain that health investment for two years.
In 2017, 84.1% of infants in the US have been breastfed. However, only 58.3% of them were breastfed for six months. Out of these breastfed infants, 19.2% were supplemented with formula milk before two years of age. That was higher than the 16.9% record in the past year. Despite the efforts from health agencies and other organizations, breastfeeding for two years remains a problem for hundreds of thousands of mothers.
Meanwhile, Statista, a German portal for statistics, showed the results in a survey from October 4 to 26, 2017. A total of 233 women aged 18 years and older responded to the survey. About 30% of them breastfed their baby for five months. Around 22% of them breastfed their baby for up to 10 months. Another 22% breastfed their baby for up to 15 months. But only 9% breastfed their baby for 20 months and 13% breastfed their baby for more than 20 months. About 3% preferred not to say how long they breastfed their baby.
How Breast Milk Shapes the Infant Gut Microbiome
Previous studies suggested that a class of lipid metabolites called sphingolipids could influence the human gut microbiome. This lipid could start their influence as early as during infancy. But the exact interactions of the lipid to the microbiome were not determined. So, a group of researchers at Cornell investigated these interactions. They found that the lipid was used by specific groups of bacteria. The more of this lipid was, the more of those bacteria would be present in the human gut. As such, nutritionists could intentionally change the gut microbiome using the lipid.
"Our lab is very interested in how the diet interacts with the microbiome in order to really understand how you can best modulate it to have positive effects on health. In this study, we were able to see that yes, these dietary lipids that are a big part of [breastfed] infants diets, are interacting quite robustly with the gut microbiome," said Elizabeth Johnson, the senior author of the study and assistant professor of nutritional sciences at Cornell.
In this study, researchers applied an innovative tracking method to learn about the fate of metabolites. They used mice models to track metabolites in the gut and their interactions with the microbiome. The interactions could explain the effects of specific diets, such as low fat, high fat, or keto. Two types of gut microbes were identified by the tracking technique: Bacteroides and Bifidobacterium. Both microbes utilize sphingolipids for their metabolism. The more sphingolipids were available, the more likely the microbes would grow.
These microbes are generally harmless to the human body. But if a situation arises, they can become opportunistic. So, the benefit of the microbes will depend on the context of a person's current health. If they have a compromised immune system, the microbes may be less beneficial to the human body. Regardless, the presence of these microbes can be found in the gut of healthy breastfed infants. Between the two microbes, Bifidobacterium compromises up to 95% of a breastfed infant's microbiome. It is considered a beneficial microbe by default.
In a lab experiment, researchers created a custom synthesized sphingolipid, which they added to the mice's diet. A fluorescent label was used as well to track cells or microbes that absorbed the lipid. Next, they isolated the microbes in the mice's microbiomes. The red microbes were separated from others and were genetically sequenced to unveil their species. Bacteroides and Bifidobacterium would release distinct metabolites after being exposed to the lipid.
The takeaway in the study findings is the potential for exploitation. There are three main sources of sphingolipids: diet, some producing bacteria, and many host tissues. Among these, diet is easiest to change to support the growth of the two microbes. In adults, nutritionists can prescribe diets that can promote either Bacteroides, Bifidobacterium, or both. In infants, mothers can provide that lipid through their breast milk.
Researchers are still continuing their investigation. While they have identified the metabolites produced by the two microbes, they do not if they are beneficial to infant health. If they are, the benefits must be specified: do they protect the babies from infection, or do they lower the risks of some diseases. If the benefits are specified, it will add another reason why infants should be breastfed for two years.