Are the gut bacteria of children different from those of adults?
Yes, the gut bacteria of children differ fundamentally from those of adults, with consequences for allergy and asthma risk. If you want to positively influence a baby's gut microbiota, breastfeeding and a normal vaginal delivery are the factors with the strongest supporting evidence.
From birth, the baby gut is a completely different environment from that of an adult. Bacteria from the mother are the first to arrive, but not all of them take hold equally well: bacteria from the mother's skin and vagina are present only temporarily, while the mother's gut bacteria 'fit' the baby gut better and stay longer. In the first days of life a strong selection process therefore takes place, after which the community gradually becomes more stable.
What a baby is fed makes a big difference to the composition of those gut bacteria. With breastfeeding, the unique sugar molecules in breast milk determine which bacteria thrive, resulting in a relatively simple but well-balanced community. Formula-fed babies, by contrast, harbour a greater variety of species. In adults, dietary pattern also plays a role, but such a direct and pronounced influence on composition is not seen.
Other factors surrounding birth also leave a clear mark: whether a baby is born vaginally or by caesarean section is one of the strongest influencing factors. In addition, the mother's diet during pregnancy, obesity, smoking and antibiotic use all count. These kinds of early circumstances shape the baby gut in a way that has no direct equivalent in adults.
The differences are also visible in disease. Research into children and adults with the same serious liver condition (related to obesity) showed that their gut microbiota are so far apart that a computer model can distinguish between them with 97% accuracy. Even in the presence of the same disease, the childhood microbiota therefore remains clearly distinguishable.
This unique composition in babies has health consequences. Newborns with lower levels of Bifidobacterium and certain protective bacteria in the gut are more likely to have allergies at age 2 and asthma at age 4. In short, the infant gut is not a smaller version of the adult gut, but a distinct, age-specific ecosystem.
Claims are based on five studies (PMID 30001516, 32464473, 27618652, 40396204) using a combination of cohort studies and a machine-learning analysis. Strength of evidence ranges from strong (early colonisation dynamics) to moderate (associations with health outcomes).
Are the gut bacteria of lean people different from those of heavier people?
The gut bacteria of people with excess weight differ measurably from those of lean people, but whether those bacteria are the cause or the consequence of excess weight has not yet been proven. If you want to improve your gut bacteria, a varied diet high in fibre remains the best-supported starting point.
Does my gut microbiome change as I get older, and does it matter?
Your gut microbiome certainly changes as you get older, but whether that is harmful depends strongly on which direction that change goes. What you eat has a major influence on this, so that is a concrete area to pay attention to.
Does eating a varied diet help your gut bacteria?
Fermented products have the strongest evidence base for increasing gut bacterial diversity. Eating broadly varied meals also helps, but above all avoid heavily processed products containing emulsifiers such as CMC.
Can certain fungi or bacteria in your gut influence your cellular ageing?
Certain gut bacteria produce substances that accelerate cellular ageing, while a diverse microbiome rich in fibre-fermenting bacteria is actually protective. You can already take this into account through a high-fibre diet, but direct interventions in humans have barely been studied.
Can you improve your gut bacteria by spending more time in nature?
Whether spending more time in nature improves your gut bacteria is a question the available studies cannot answer; if you want to positively influence your microbiome, diet and body weight have a far better documented effect.
Can you permanently change your gut microbiome through diet?
Diet does indeed change your gut microbiome, but lasting change requires lasting adjustment of your dietary pattern; a temporary diet has only a temporary effect.