How Moms Pass on Their Microbiome

Your microbes are inherited, mostly from your mom.

Reviewed by Kaja Perina

Key points

• Beneficial gut microbes are essential to good health.
• Mothers harbor a collection of these beneficial microbes in their breast milk.
• These are passed on to the baby, along with prebiotics and immune factors.

“Sometimes the smallest things take up the most room in your heart.” — A.A. Milne

If you have good gut microbes, you can thank your mom for kickstarting that. And your dad too, a little. Microbes are shockingly central to your health, so getting good ones can set you up for life; getting bad ones can plague you forever. Microbes are just too important to leave them to chance, so all animals have figured out some interesting techniques to ensure their proper handoff to their kids.

But why do we have microbes in the first place? Isn’t that just gross? The answer to the last question is “yes”. But the whole world is gross; microbes cover every surface in sight. You can’t take a step, a breath, or a bite without getting intimate with microbes. Most of them are eager to eat you, given the chance. That’s why your cuts and scratches get infected. That’s what food poisoning is. It’s a jungle out there!

Our friendly microbes

Animals evolve slowly; there is simply no way that animals can keep up with the genetic fireworks of a microbe that can reproduce every 20 minutes. So, millions of years ago, the very first animals struck a deal with some friendly microbes: in exchange for sharing our meals, we enlisted them to fight off the nastier microbes of the world. It takes a germ to fight a germ. Animals and microbes have co-evolved ever since.

Animals have developed amazing and sometimes unsavory techniques to ensure that the next generation gets a solid microbiome. For instance, horses eat poop, as do rabbits, geese, mice, pigs, dogs, and more. That gives their babies a big starter dose of gut microbes from other community members, but especially mom, who is close by.

Some insects have special glands that anoint their eggs with microbes as they are laid. That’s because some creatures, like termites, will die if they don’t have specialized microbes. We think termites can eat wood, but that’s actually a job for their gut microbes.

Woodrats in the Mojave have a microbe that allows them to eat poisonous creosote bushes that would kill their country cousins. Their pups must eat droppings to kick-start their unique microbiome, or they won’t survive. The longer the Mojave woodrat exploits that creosote niche, the more its genes can drift away from other woodrats. Thus, microbes could even create new species. This is the magic of co-evolution.

Microbes can convert indigestible fiber—even wood—into short-chain fatty acids (SCFAs) that both heal and nourish the cells lining the gut. That makes them essential for grazing animals like horses, cows, and goats. Herbivores in general depend on microbes to squeeze useful energy out of mere vegetation. They would all die within days of losing their microbiome.

The magic of milk

Mammals like us have bacteria in their milk. These microbes are transported from the mother’s gut to the mammaries by special immune cells. Most of the sugars in milk are meant for those microbes, not the baby. That emphasizes the importance of microbes to our development. Passing on microbes is not a casual affair.

One genus of bacteria, Blautia, may even help people live at high altitudes. Blautia bacteria produce SCFAs, keeping the gut lining healthy. That reduces inflammation and eases the symptoms of high-altitude hypoxia. Passing down a good set of microbes is almost as valuable as passing down a good set of genes.

Most of the microbial action discussed here has been maternal, but the dad at least gets to kiss and hold the baby, and thereby donate a little of his microbiome. But since Mom got there first, it will be a tough introduction. With mom’s microbes dominating, dad’s microbes will have an uphill battle finding a niche. This job requires a mom; dads are an afterthought.

What to do

Here’s how to be a super mom (or dad) for your baby:

Eat plenty of vegetables, especially those with a lot of fiber, like onions, beans, asparagus, and artichokes. For fruit, berries are best, because we eat the seeds, which are full of fiber and polyphenols. Try to eat fresh food, because processed food often contains emulsifiers, food dyes, and preservatives that are not good for your gut microbes.

Eat fermented foods. This includes pickles, yogurt, kombucha, sauerkraut, kefir, and more. Make sure to get the foods that have live cultures. These are full of good bacteria, like Lactobacillus and Bifidobacteria, that will produce SCFAs down your gut, as well as fight off pathogens.

Weirdly, exercise is good for your microbes. Through a variety of pathways, exercise helps to create a diverse and healthy microbiome that you’ll be proud to pass down.

Limit sugary foods. A lot of your cravings are actually caused by gut microbes. But sugar-eating microbes tend to be troublemakers, while fiber-eaters are healthier. You’re going to get cravings, but you should probably try to ignore some of them. Hopefully, berries will satisfy your sweet tooth. Your resolve can weaken in times of duress, so do your best, but don’t stress over it. After all, stress isn’t good for your microbes either.

Talk all of this over with your doctor before you do anything. These recommendations seem innocuous, but microbes are real and they are potent. If your doctor agrees, start all of these actions slowly. Your microbes hate quick changes and there could be bloating and discomfort if you take it too fast.

If for some reason you can’t breastfeed your baby, many formulas now contain probiotics, and you can introduce ferments like yogurt when the baby is ready for solid foods around 6 months.

Having a baby is a lot of work, and most people don’t realize that includes passing on a good set of microbes. Fortunately, our bodies have been crafted by evolution to ensure a good handoff. With the steps above, you can give your baby an extra boost. It’s a phenomenal birthday present.