I’m sitting on the couch between my two daughters. They’re snuggled under soft blankets, sick with a cold, the flu, or maybe RSV—I’m not sure. But it’s been a rough one…

Since my kids are sick, I’ve been thinking about what I want parents to know about the gut microbiome and the immune system.

Maybe you've heard experts say things like "70-90% of the immune system is in the gut."

But what does that really mean?

It means that about 80% of the body's immune cells live in the intestines. This makes the gut the biggest immune organ in the body!

Most people don’t think of the digestive system as part of the immune system, but it plays a huge role!

Here’s why: The mouth is an open doorway into the body. If you think of the digestive system as one long hollow tube running from the mouth to the other end, the inside of the tube is actually still “outside” the body.

One of your intestines' jobs is to keep harmful things — like bad bacteria and toxins — out of the body, The GI tract also notifies the rest of the immune system when it senses foods, infections, or other toxins that it doesn't want to be there.

The gut microbiome affects the way that the immune cells in the GI tract communicate with the rest of the immune system.

When the gut microbiome is healthy, the immune cells in the GI tract function well and communicate appropriately with the entire immune system. When the gut microbiome is not healthy, the GI immune cells can trigger an immune response that is too small, too large or otherwise inappropriate.

What does that actually look like in a child?

• Too small: kids get sick more often or take a long time to get better

• Too large: the immune system starts attacking the wrong things and kids develop inflammatory conditions like eczema, asthma, or allergies

• Inappropriate: the immune system is on "high alert" and starts attacking the wrong things resulting in autoimmune diseases like Type 1 Diabetes

Another way gut health affects the immune system is through the gut lining.

Think about how bacteria can infect a cut if your skin is broken. The same thing happens in the gut. If the gut lining is damaged or inflamed, bad bacteria and toxins can sneak in and directly trigger an immune response.

Here's the thing to remember. Not all bacteria are bad. In fact, some are really important for optimal health! Especially in kids. Good bacteria in the gut improve the function of the immune system both inside the gut and throughout the whole body.

That’s why a healthy gut is key to a strong immune system. A balanced gut microbiome can help prevent illness and also help the body fight infections more effectively when we do get sick.

Here are 4 quick tips to improve your toddler's gut health and support their immune health:

• Increase fiber: good bacteria digest fiber and produce molecules that strengthen the gut barrier

• Eat more plants: Increase both the number of plants your child eats and the number of different plants

• Reduce sugar: sugar weakens the immune system by directly interfering with immune cell function, and also by disrupting the gut microbiome

• Breastfeed: Nurse as much as possible for as long as possible. If nursing isn't an option, choose a formula that contains HMOs like 2'-FL

That’s all for now—it’s time to rewarm some beanbags and read to my little ones!

References:

Wiertsema SP, van Bergenhenegouwen J, Garssen J, Knippels LMJ. The Interplay between the Gut Microbiome and the Immune System in the Context of Infectious Diseases throughout Life and the Role of Nutrition in Optimizing Treatment Strategies. Nutrients. 2021 Mar 9;13(3):886. doi: 10.3390/nu13030886. PMID: 33803407; PMCID: PMC8001875.

Wu HJ, Wu E. The role of gut microbiota in immune homeostasis and autoimmunity. Gut Microbes. 2012 Jan-Feb;3(1):4-14. doi: 10.4161/gmic.19320. Epub 2012 Jan 1. PMID: 22356853; PMCID: PMC3337124.

Arnone D, et al. Sugars and Gastrointestinal Health. Clin Gastroenerol Hepatol. 2022 Sep;20(9):1912-1924.e7. doi: 10..1016/j.cgh.2021.12.011. Epub 2021 Dec 10. PMID: 34902573