From Belly to Brain: The Gut-Brain Axis

A mom holds her toddler intent on supporting her child's happiness


Happiness is a fundamental human emotion. And for most parents, seeing their babies smile, laugh, and engage with the world around them is a source of great joy and satisfaction. Accepting this premise, led us to ask: is there a link between food and mood? If parents want their children to experience joy, is there a way to amplify or even ensure happiness? 

Welcome to part 1 of 4 in our Science of Happiness series, where we’ll learn: 

  • How the brain and gut are connected (known as the gut-brain axis),
  • What microbes in your gut can be related to behavior and mood, and
  • How food and nutrition can play a part in all.

Our gut health report gives you deep insights into your baby's gut health. See a sample
Our gut health report gives you deep insights into your baby's gut health. See a sample

The Science of Happiness: It takes guts

Have you heard about the importance of your gut microbiome? Not only does it play a vital role in your digestion and immune system, it also influences many aspects of your overall health. In fact, your brain and gut are connected and communicate with each other! This back and forth communication between your brain and gut may mean that the bacteria in our guts play a bigger role in our lives than we think. 

How does the gut talk to the brain? Understanding the connection

Did you know that the gut has its very own nervous system? There is a network of nerves called the enteric nervous system (ENS) that runs through your intestines. This system helps control digestion and keep everything running smoothly.

The ENS is connected to the brain via the vagus nerve, which carries messages both from the brain to the gut and from the gut to the brain. This two-way communication pathway is known as the gut-brain axis [1].

Gut microbes play an essential role in this communication by sending signals from the gut to the brain via the vagus nerve. Scientists are just beginning to unravel how this communication, known as the microbiota-gut-brain axis, can impact mood, behavior, and cognitive function [2].

The gut microbiome as a regulator of the gut-brain axis

As it turns out, the trillions of microbes that live in your gut are key players when it comes to the mind-gut connection. While the science is still emerging, scientists think there are different ways gut microbes can communicate with the brain:

  • Through the production of messenger molecules that can travel through the blood to the brain
  • By releasing molecules that stimulate gut lining cells, which can in turn release hormones and neurotransmitters, like serotonin
  • By stimulating the vagus nerve through the production of short-chain fatty acids (SCFAs) and other compounds. This pathway would allow gut microbes to influence the brain’s release of hormones and neurotransmitters that can impact mood and behavior [2], [3], [4].

Can gut microbes affect your little one’s behavior and mood?

Research on the relationship between the gut microbiome and mental health is in its early stages. Studies have shown that alterations in gut microbiome composition are associated with changes in behavior and mood in both animals and humans.

For example, studies in mice have shown that changing the gut microbiome composition can lead to changes in anxiety-like behavior and stress response [5], [6]. Similarly, studies in humans have found that certain probiotics can help reduce symptoms of anxiety and depression in some people [7], [8].

Research in babies and toddlers is emerging as only a few studies have explored how the gut microbiome contributes to shaping brain functions in early life. Some of the findings are:

  • Microbial gut diversity at 1 year of age predicts cognitive performance at 2 years of age [9]. 
  • The composition and diversity of the microbiome in a baby’s gut is linked to sleep patterns, which are associated with behavior later in life [10].
  • At 12 months of age, a gut microbiome dominated by Bacteroides is associated with higher cognitive and language scores at age 2, especially in boys [11].
  • Differences in gut microbiome composition, diversity, and the abundance of specific bacterial species seems to be associated with different behaviors in toddlers [12].

Can diet influence mental health?

Gut microbes are like a personal chef, and the ingredients you feed them influences the kind of meals they cook up—for better or for worse.

The gut microbiome thrives on a diet that is high in fiber, as fiber provides the nutrients microbes need to produce SCFAs [13]. SCFAs have been shown to have anti-inflammatory effects, which could be beneficial for mental health, and they also play a role in the production of serotonin [14].

When fiber is lacking in the diet, gut microbes resort to other nutrients and produce less favorable compounds that could potentially impact mental health. For example, studies in mice have found that a diet that is high in fat and sugar leads to changes in the gut microbiome that are associated with increased anxiety [15].

Make sure to keep your little one’s tummy happy by providing plenty of fiber-rich foods, such as:

  • Fruits
  • Vegetables
  • Whole grains
  • Legumes
  • Nuts

This will ensure gut microbes have all they need to send positive messages to your baby’s brain.

Curious about your baby’s gut? We now know healthier guts = healthier babies. Tiny Health’s revolutionary mess-free Baby Gut Health Test takes less than 5 minutes, and you’ll get a personalized report with actionable results so you can start taking steps towards optimal health. 

Ready to learn more? Explore our next post to learn how gut microbes affect infant cognitive development, and what to feed your baby to support their growing brain. 

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[3] K. Gao, C.-L. Mu, A. Farzi, and W.-Y. Zhu, “Tryptophan Metabolism: A Link Between the Gut Microbiota and Brain,” Adv. Nutr. Bethesda Md, vol. 11, no. 3, pp. 709–723, May 2020, doi: 10.1093/advances/nmz127.

[4] B. Bonaz, T. Bazin, and S. Pellissier, “The Vagus Nerve at the Interface of the Microbiota-Gut-Brain Axis,” Front. Neurosci., vol. 12, p. 49, 2018, doi: 10.3389/fnins.2018.00049.

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[7] A. Kazemi, A. A. Noorbala, K. Azam, M. H. Eskandari, and K. Djafarian, “Effect of probiotic and prebiotic vs placebo on psychological outcomes in patients with major depressive disorder: A randomized clinical trial,” Clin. Nutr. Edinb. Scotl., vol. 38, no. 2, pp. 522–528, Apr. 2019, doi: 10.1016/j.clnu.2018.04.010.

[8] R. F. Slykerman et al., “Effect of Lactobacillus rhamnosus HN001 in Pregnancy on Postpartum Symptoms of Depression and Anxiety: A Randomised Double-blind Placebo-controlled Trial,” EBioMedicine, vol. 24, pp. 159–165, Oct. 2017, doi: 10.1016/j.ebiom.2017.09.013.

[9] A. L. Carlson et al., “Infant gut microbiome composition is associated with non-social fear behavior in a pilot study,” Nat. Commun., vol. 12, no. 1, Art. no. 1, Jun. 2021, doi: 10.1038/s41467-021-23281-y.

[10] S. F. Schoch et al., “From Alpha Diversity to Zzz: Interactions among sleep, the brain, and gut microbiota in the first year of life,” Prog. Neurobiol., vol. 209, p. 102208, Feb. 2022, doi: 10.1016/j.pneurobio.2021.102208.

[11] S. K. Tamana et al., “Bacteroides-dominant gut microbiome of late infancy is associated with enhanced neurodevelopment,” Gut Microbes, vol. 13, no. 1, Art. no. 1, Jan. 2021, doi: 10.1080/19490976.2021.1930875.

[12] L. M. Christian, J. D. Galley, E. M. Hade, S. Schoppe-Sullivan, C. Kamp Dush, and M. T. Bailey, “Gut microbiome composition is associated with temperament during early childhood,” Brain. Behav. Immun., vol. 45, pp. 118–127, Mar. 2015, doi: 10.1016/j.bbi.2014.10.018.

[13] F. De Filippis et al., “High-level adherence to a Mediterranean diet beneficially impacts the gut microbiota and associated metabolome,” Gut, vol. 65, no. 11, pp. 1812–1821, Nov. 2016, doi: 10.1136/gutjnl-2015-309957.

[14] B. Dalile, L. Van Oudenhove, B. Vervliet, and K. Verbeke, “The role of short-chain fatty acids in microbiota-gut-brain communication,” Nat. Rev. Gastroenterol. Hepatol., vol. 16, no. 8, pp. 461–478, Aug. 2019, doi: 10.1038/s41575-019-0157-3.

[15] A. J. Bruce-Keller et al., “Obese-type gut microbiota induce neurobehavioral changes in the absence of obesity,” Biol. Psychiatry, vol. 77, no. 7, pp. 607–615, Apr. 2015, doi: 10.1016/j.biopsych.2014.07.012.