You’ve probably heard the saying that “you are what you eat”. In many ways, this is true. In fact, research now shows that you even “think what you eat”. In other words, your dietary choices have direct effects on your brain. Wild. Did you decide to read this article, or did the breakfast you ate this morning tell you to read it?
All kidding aside, the research showing this connection has grown so strong that the term “gut-brain axis” has been coined to describe the intricate connection between your digestive tract and cognition (5, 13).
The gut-brain axis is one of the hottest topics in medical research. Why? Because, as famous neurologist David Perlmutter describes it, there aren’t a lot of great ways to treat cognitive and neurological conditions (10). Brain and neurological conditions such as Parkinson’s, depression, autism, anxiety and Alzheimer’s have frustratingly few treatment options. For example, according to the NIH, more than 1 in 10 Americans over age 12 take anti-depressant medication, but these medications have a relatively small effect in all but the most severe cases (12).
So, the idea that diet could have an effect on brain function is pretty attractive. And cool. Think about it – would you ever have guessed that what you ate actually changed the way you thought?
The effects are actually pretty profound. According to the journal Nature, the flora of bacteria in the colon (microbiota) has an impact on motivation, emotions, and higher cognitive functions - even intuitive decision making (1). Your gut and your brain - they talk.
For example, one study compared MRI brain imaging from women who ate food with healthy bacteria (probiotics) versus controls who had no probiotics. The women who had probiotics actually had different brain responses to emotional stimuli than controls (10).
In another example, mice without gut bacteria (germ-free mice) usually demonstrate anxious and anti-social behavior. When gut bacteria are transferred from a healthy mouse to a germ-free one, the normal behavior of the healthy mouse actually transfers with it (9). As it turns out, the gut-brain axis is even linked with specific medical conditions:
- There is a strong connection between migraines and digestive conditions such as Celiac Disease, gastroparesis, Irritable Bowel Disease, and Irritable Bowel Syndrome (2)
- Anxiety and depression are linked to altered gut bacteria (9, 13)
- Obesity is related to gut dysbiosis (unhealthy microbiota), and studies have shown that gut bacteria help mediate satiety and appetite control (14)
How the gut communicates with the brain
You may be wondering how the business going on in your gut can travel all the way to your brain. Although there has been a lot of research on this topic in recent years, the gut-brain axis isn’t fully understood (9). However, scientists have found that there are several mechanisms - neural, endocrine, and immune (6, 9). So, there are actually multiple ways that your gut and brain are communicating with each other.
For example, dietary sugars act on the brain to regulate intake by both neural (vagus) action, and by indirect (endocrine) mechanisms (3). When the vagus nerve (connecting the gut to the brain) is cut, emotions and behaviors are altered (9).
One of the most fascinating of these mechanisms is inflammatory cytokines. A variety of factors can cause inflammation and gut permeability. These include food allergies or sensitivities, medications, exercise, mast cell activation, and stress (2, 8). When these factors induce inflammation, cytokines such as TNF-alpha and IL-1-beta are produced in the gut, enter the bloodstream, and travel to the brain. There, they cross the blood-brain barrier and wreak cognitive havoc (2, 7). This situation has been coined “leaky brain” (2).
Another important factor in the gut-brain axis is the microbiota itself. In fact, animals with no intestinal bacteria have much more permeable blood-brain barriers than controls (7). Also, as described above, germ-free animals are less social and have more anxiety than normal controls (9).
On the other hand, a healthy microbiota has a protective effect, by way of short-chain fatty acids. These molecules are produced by healthy gut bacteria. Two of these – propionate and butyrate – have direct communication with the brain (4). They actually impart positive effects on the brain by decreasing the permeability of the blood-brain barrier (7, 8, 9). In fact, feeding healthy gut bacteria with fermentable fibers known as prebiotics has been shown to decrease depression and anxiety (9).
This fact leads us to an important point - the gut-brain axis can be influenced by diet and lifestyle. Studies have shown that changes to the microbiota caused by bacterial infection, antibiotics, and probiotics have direct effects on anxiety, mood and cognition (6, 9, 10).
How to optimize mental health via the gut
Here are five diet and lifestyle techniques you can use to optimize gut health and minimize "leaky brain":
1. Nurture a healthy microbiome with prebiotics. These fermentable fibers are the food that good gut bacteria need to thrive. Good sources include: sweet potato, orange, asparagus, bananas, Brussels sprouts, avocado, pears, mangoes, apples, pears, sunflower seeds, nuts, blueberries, onions, garlic, artichokes, leeks, white potato, and flax seeds.
2. Consume natural probiotics – foods than contain healthy bacteria. Foods offer a wider variety of strains, and MORE bacteria than most supplements. Good choices include: kombutcha, sauerkraut, kimchi, pickles, kefir, yogurt, and coconut kefir. Make sure you buy refrigerated versions of commercially prepared fermented foods – the shelf stable ones have been pasteurized.
3. Reduce sugar intake – avoid added sugars completely and stick to occasional fresh fruit. Artificial sweeteners have also been shown to have a negative influence on the microbiota, so avoid them as well.
4. Decrease foods most likely to induce gut permeability and inflammation – gluten/wheat, dairy, soy, and food you know you are sensitive to.
5. If you need more help, a functional nutrition practitioner can get you tested for food sensitivities and increased gut permeability, recommend a therapeutic diet, and provide supplement recommendations to aid healing.
The microbiome continues to be an exciting and fascinating area of medical research. It is now clear that gut bacteria effects not only digestive health, but mental health as well. Traditional treatments for cognitive conditions such as depression, anxiety, autism, ADHD, migraines, Parkinson’s, and Alzheimer’s Disease are incredibly limited, and seldom account for the gut-brain connection. Thus, it is critical to address gut health when treating these conditions. In fact, gut health should be optimized for mental health in general.
This can be accomplished through a combination of increasing probiotics and natural prebiotics, reducing sugar intake, avoiding foods that increase gut permeability and inflammation, and possibly working with a practitioner for further testing, therapeutic diet guidance, and supplement recommendations. Please contact me if you’re interested in getting help with your gut health.
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