They say that you are what you eat, but did you know that this extends beyond your physical body to reflect on your mood and mental function too?
In fact, the foods that we eat and how they interact with our gut can be a considerable risk factor for developing mental health illnesses such as anxiety and depression. They can also impact on your ability to focus and perform and cause prolonged cognitive symptoms such as fatigue and brain fog.
So how does what you eat feed into how your brain works and responds?
The research linking gut health and brain function, encompassing cognition, mood and mental illness is extensive and continuously growing, as we learn more about the microbiome and the gut-brain connection. What we do know is that they work in symbiosis affecting several different functions and pathways. This includes inflammation and oxidative stress, changes in circulating hormones and neurotransmitters, fibre fermentation and the production of short chain fatty acids, protein metabolism and the function and integrity of the gut microbiota.
You often hear the terms ‘gut-brain axis’ or ‘mind-gut connection’ thrown about but might be wondering what this actually means? The gut-brain axis refers to the pathway that exists between the digestive system and the brain, whereby food that is broken down through digestion, interacts with the gut microbiome and their function. One of their key roles is to produce essential hormones and neurotransmitters which in essence go on to circulate in the blood and send various messages to the brain. It might feel unnatural to connect the brain with the inner workings of the digestive system, but the digestive tract is in fact lined with over 100 nerve cells, sending direct communication up to the brain and vice versa.
In addition, dysregulation of the hypothalamic–pituitary–adrenal (HPA) axis, consisting of a breakdown between the brain (hypothalamus), pituitary and adrenal glands, has shown a strong causation towards anxiety and depressive disorders. One of the key disrupters to the HPA axis is through inflammation leading to an excess production of the ‘stress hormone’ cortisol. One of the biggest triggers for inflammation? You guessed it, diet! Foods that are high in vitamin C, antioxidants, plant polyphenols and omega 3 essential fatty acids can have a positive impact on cortisol, while highly processed grains and foods with a high glycaemic index can lead to higher levels of inflammation. Inflammation can also cause a breakdown of the gut lining which results in a disruption to the plethora of gut-loving bacteria that reside there.
Made in the gut
One of the biggest areas of developing research is in the gut microbiota and the subsequent relationship that these bacteria have on brain function. It is anticipated that our digestive system houses upwards of 1,000 different species of bacteria, often referred to as microbiome or microbiota. These little living organisms play many different roles in digestion, but one critical function is the way they impact on the production of certain brain chemicals critical to mental health.
These include dopamine, acetylcholine and GABA - which are all essential for mood and concentration and are all manufactured through digestion by gut bacteria. An astonishing 90% of serotonin, widely considered as the ‘feel-good’ hormone, is produced in the gut. In fact, serotonin related medication is one of the primary treatment protocols for mental health conditions such as anxiety and depression. In order to make serotonin, the body needs enough tryptophan available, which is an amino acid that can only be obtained through the diet. The bacteria that live in our gut influences the levels of serotonin available through the active metabolism of tryptophan from the diet.
Interestingly, tryptophan can be metabolised to be either neurotoxic or neuroprotective depending on what foods are consumed and the actions of the gut bacteria. Foods that are rich in polyphenols and pre and pro biotics can help the microbiota to steer towards the neuroprotective metabolites. Whereas inflammatory or processed sources of tryptophan can channel in the reverse towards neurotoxicity, causing low mood and depression.
While there has been little evidence to indicate that a particular diet can lead to more beneficial mental health outcomes, anti-inflammatory diets have consistently been shown to reduce the risk and occurrence of depression. Diet is even frequently being used as a treatment tool for clinical anxiety and depression. Foods that are high in plant polyphenols, whole grains and healthy fats also help feed the gut microbiome in the right way. And as we’ve explored a healthy gut leads to a healthy mind.
When it comes to histamine intolerance, high levels of histamine can wreak havoc on the production of other hormones and neurotransmitters including estrogen and epinephrine. Histamine can also cause inflammation and digestive dysfunction which can cause an imbalance in the gut bacteria.