Imagine a remote island, recently formed by volcanic activity, in the middle of the ocean. At first, it is lifeless, but a growing variety of plants take hold, providing food for pioneering animal species, until eventually there is a diverse and flourishing ecosystem.
This is a useful way to think about how our gut ecosystems develop. 鈥淵our microbiome goes on a journey,鈥� says at the University of Aberdeen, UK. 鈥淲hen you鈥檙e born, some bugs get in and then, when you start eating solid foods, other bugs replace them. There鈥檚 a dynamic process where your microbiome changes until you get to mid-to-late childhood. Then, through adult life, you鈥檝e got a reasonably stable microbial community.鈥�
Does a C-section affect a baby鈥檚 microbiome?
The first individuals that colonise an island can have long-lasting influences on its ecosystem, an idea known as the founder effect. Until recently, the thinking went that if the founder bacteria in a baby鈥檚 gut were unusual 鈥� because the baby was born by Caesarean section, for instance 鈥� this might disrupt their bacterial ecosystems. This idea has led some parents to take radical steps to get their children鈥檚 microbiomes back on the right track. But the science behind these ideas is far from settled.
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One of the first to document the differences between the gut bacteria of babies born by C-sections and those born vaginally was at Rutgers University in New Jersey. Her research team found that when babies born by C-section were a day old, their faeces had and more of the bacteria that usually colonise the skin. 鈥淏abies are like sponges and they get whatever they鈥檙e exposed to,鈥� she says.
Previous studies have found that C-section babies go on to have slightly higher rates of certain health conditions, including obesity, allergies and asthma. As disturbed gut bacteria have been claimed to contribute to these conditions, the concern is that C-sections could be causing lasting harm to children鈥檚 health.
To counter this, Dom铆nguez-Bello鈥檚 group helped pioneer the practice of 鈥渧aginal seeding鈥�, where a baby鈥檚 face and mouth are wiped with a piece of gauze that was previously placed in their mother鈥檚 vagina. Crucially, this is only done after tests to check there are no harmful microrganisms in the mother鈥檚 vagina.
Some researchers are even giving C-section babies small oral doses of their mothers鈥� faecal bacteria (again, they are screened for harmful microbes). But the trials done so far have had small numbers of participants, so this isn鈥檛 yet considered of proven medical benefit.
The microbiome and obesity
Besides, even the basic premises behind the idea are up for debate. The health conditions of interest, such as obesity and allergies, haven鈥檛 been shown to be caused by altered gut bacteria 鈥� only to correlate with them. It could be something else, such as diet or lifestyle, causing both the medical condition and the microbiome differences. In fact, a co-authored by Walker concluded that, so far, no reliable microbial signatures of obesity have been found (see 鈥淒oes the gut microbiome influence body weight?鈥�).
Most importantly, it is questionable if a child鈥檚 mode of birth has a lasting effect on their microbiome. A 2018 study found that, in vaginally born babies, bacteria from the mother鈥檚 vagina are found in the baby鈥檚 gut for only a few days, while the mother鈥檚 gut bacteria continued colonising the baby鈥檚 gut for months after the birth.
Does breastfeeding affect a child鈥檚 microbiome?
A much bigger influence comes from whether or not babies are breastfed, as breast milk contains some sugar-like compounds 鈥� absent in most types of baby formula 鈥� that promote the growth of Bifidobacterium bacteria. This is thought to be beneficial for several reasons, including . Then, as babies are weaned onto solid foods in their first year, their microbiome starts becoming more like that of an adult.
As children grow, the biggest influence on their gut bacteria is the people they live with (see 鈥淗ow your microbiome is shaped by your friends, family, lovers and pets鈥�). 鈥淲hen people go to the toilet, there will be bugs floating around the house that are derived from stools,鈥� says Walker. One study of a family with six children found that, by a few years of age, the children shared about the same number of gut bacteria with their father as with their mother.
Much is still unclear about how our gut ecosystems bloom into their full complexity and individually unique make-up 鈥� even differing between identical twins. 鈥淎 lot of it seems to be quite random and what you鈥檙e exposed to,鈥� says Walker. 鈥淐ertainly, in adults, there鈥檚 no way to tell if someone was breastfed or was born by C-section. The big question is how much that window where it was different really matters. There鈥檚 lots to be learned.鈥�
Speak to your doctor before seeking new treatments for medical conditions
This article is part of a special series on the microbiome, in which we explore:
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