Exploring the Gut-Brain Axis Outdoors

10.25.25

Today marks the first day of my fall break, which I plan on mainly spending outdoors. So, why not research some microorganisms in the process?

In this blog post, I wanted to focus on the bacterium Lactobacillus, which is most commonly found in the gut. This form of bacteria actually lives in a variety of environments and turns out to be extremely beneficial to soil fertility, as well as to our cognitive health. Lactobacillus goes beyond improving gut health and digestion; it is also linked to improved mood and reduced stress.

In the study about Lactobacillus acidophilus conducted by the National Library of Medicine, researchers explored the gut-brain axis (GBA), which is the network of communication that connects the gastrointestinal tract to the central nervous system. The experiment tested the cognitive function of mice that were exposed to three different types of probiotics, including Lactobacillus acidophilus. After eight weeks, the mice that were exposed to Lactobacillus acidophilus had the biggest improvements in their cognitive health. Here, we can see how the bacteria correlated to improved cognitive health in animals, but could this translate to human health?

In the study conducted by the Journal of Neurogastroenterology and Motility, scientists reviewed 38 randomized controlled trials: 25 in animals and 15 in humans (2 studies were conducted in both) to see how probiotics such as Lactobacillus affect depression, anxiety, memory, Autism Spectrum Disorder (ASD), and Obsessive-Compulsive Disorder (OCD). It was proven that, along with Bifidobacterium, Lactobacillus was the most beneficial in improving mental health.

The probiotics positively changed the levels of neurotransmitters like GABA, serotonin, and dopamine. For example, when GABA effects are increased, participants feel “calmer” because it makes it harder for neurons to fire. In the results about human studies, the authors state, “Two studies by Messaoudi … found probiotic formulations of B. longum and L. helveticus could improve anxiety and depression in all participants.”

In addition, probiotics like Lactobacillus support the immune system by reducing inflammation, which also benefits the central nervous system because of the connection to the GBA. Lactobacillus limits the production of harmful molecules called pro-inflammatory cytokines, leading to a stronger gut. With all these positive changes in the gut, substances such as short-chain fatty acids are formed, which indirectly improve the central nervous system and endocrine system.

Lactobacillus is found everywhere: in soil, plants, on skin, animal fur, and food. Just by touching or breathing it in, these microbes can begin positively affecting your gut and cognitive health. The “Old Friends Hypothesis,” introduced by Graham Rook in 2003, states that the immune system requires exposure to microbes found in the environment in order to develop correctly. In the article written by Yolanda Smith, she argued that some microbes are believed to have existed throughout history, including during hunter-gatherer times, meaning they have been present during the evolution of the human immune system. In today’s world, the lack of time humans spend outdoors likely accounts for many immunological dysfunctions. This means that stress can hit harder, increasing the risk of anxiety and depression.

Just by being outside, your cognitive health can improve immensely, and your immune system can get stronger! So go reconnect with nature, whether it is by gardening, going on a hike, or simply lying out in the sun!