By Christina Zavaglia, RD
Has your psychiatrist ever asked you what you ate for lunch? Or what types of foods you include in your diet? Probably not. Yet research is growing in the field of nutrition and mental health and there is now a lot of research that suggests that diet is related to mental health and may play a role in the prevention and treatment of mental health disorders such as depression and schizophrenia. A particularly new and hot area of research is on how the health of our gastrointestinal system, or gut, may be related to our mental health. In fact, scientists sometimes refer to our gut as our “second brain.”
Our brain and our gut are closely connected and constantly communicate – this is referred to as the “gut-brain axis.” Many systems, including our immune system, gut microbiome (all the teeny tiny organisms and bacteria in our gut), and central nervous system play an important role in this communication.
Our gut is full of bacteria, in fact there are more bacteria living in your gut, than there are people on the planet (over 100 trillion microorganisms). Our gut microbiome can be thought of as a live organ, just like our liver and heart, that works hard to keep us healthy. The health of our gut is crucial to our overall health and research suggests that changes in our gut bacteria are associated with a variety of diseases.
Our gut bacteria are established very early on in life, when a baby is born, it is thought that the gut is sterile but after about one year old until old age the bacteria remain fairly constant. The way a baby is born (vaginal verse Caesarean section) and the type of feeding method an infant receives (breastfeeding verse formula) plays a large role in the bacteria development along with our interactions with the environment. Ideally, we want to have a robust and diverse range of different species inside us and a healthy balance of good and bad bacteria. However, things like excessive use of cleaning products and obsessing over sanitation as well as antibiotic use, especially in childhood, can disturb the balance of the good and bad bacteria. Environmental factors, chronic stress, and unhealthy diets can also change our gut microbiome. Diseases such as obesity, irritable bowel syndrome, Alzheimer’s disease, anxiety and depression have all been associated with changes in the gut microbiome.
It has been well established that a healthy diet can help reduce our risk for many different types of physical illness – from diabetes to cardiovascular disease and some types of cancer, eating well is an important part of prevention. Newer research is now showing that our diet can also affect mental health. Lots of research has been done to look at diet and depression and with good reason; according to the World Health Organization, depression is a leading cause of disability worldwide and affects more than 300 million people globally. The diet that has been shown to have the most protective effect is a Mediterranean style diet pattern – this diet is not only associated with reduced risk of depression but is also heart healthy and can help promote overall health and wellness. Mediterranean style diets are rich in fruits and vegetables, olive oil, beans, nuts and seeds, and whole grains. They also include fish and seafood a couple of times a week and limits red meat, cheese, butter, and sweets. Regular exercise is also an important component of the diet.
The types of food we eat affect our gut microbiome and the Mediterranean diet can have a beneficial effect on our gut bacteria. Some studies have suggested that increased rates of depression are due to our modern diets that are high in processed foods, sugars, and unhealthy fats and the changes in our gut microbiome that result from this poor-quality eating pattern. It is thought that these foods reduce the diversity of our gut microbiome and can cause an imbalance of our gut bacteria leading to illness.
Aside from the Mediterranean diet, consuming a high-fibre diet has also been shown to have beneficial effects on the types of microbes in our gut by promoting a shift towards more good bacteria and helping keeping the bad bacteria “in check” so we stay healthy. Fibre is found in fruits and vegetables, whole grains, beans and legumes (chickpeas, lentils, kidney beans), and nuts and seeds. Women need 25 grams of fibre each day and men need 38 grams, research has shown that Canadians are only getting about half of what they need. Part of this low intake may be due to our reliance on processed foods and refined carbohydrates like white breads and foods made with white flour, that are often low in fibre. Low fibre diets can lower the diversity of the gut bacteria and make it harder for us to keep out the bad bacteria. To get more fibre into your diet, try having whole fruits more often than juice (apples, pears, and berries are all high in fibre), incorporating beans and lentils in soups and salads more often (eg. 3/4 cup of cooked lentils has 12g of fibre), and choose whole grains over white grains. Aside from the benefits on gut bacteria, high-fibre diets can also help manage blood sugar levels, improve cholesterol, promote bowel regularity, and help with weight management.
Pre-and probiotic foods can also have a positive effect on our gut microbiome. Probiotics are live organisms such as bacteria, that when consumed, can have a positive effect on the host (aka those who eat them), some are also naturally found in our digestive tract. Pre-biotics act as the food for the probiotics to help maintain a healthy balance of gut-bacteria. Prebiotics are naturally found in some foods including bananas, artichokes, asparagus, leeks, onions, tomatoes, as well as whole grains. Prebiotics can also be added to some foods such as snack bars and cereals.
Probiotics are often added to food such as yogurt however not all yogurt sold in Canada is probiotic, which is a common misconception. To find out if a yogurt is probiotic, look for the phrase “contains live active cultures” on the label. Probiotics are also found in fermented foods such as kefir (a fermented milk product) kimchi, and sauerkraut. There are also many probiotic supplements available. The most common probiotics are Lactobacillus and Bifidobacterium, which are often found in dairy products. Some research has shown that probiotic supplementation can have a beneficial effect on mental health. In a systematic review, Pirbaglou et al., 2016, found that anxiety and depressive symptoms were reduced after probiotic supplementation however more research is needed to confirm these findings as well to provide more information on the types and dose of probiotics needed to improve mental health as not all probiotics are the same (eg. different bacteria and species may improve different health conditions).
Research is still in its early stages when it comes to learning about how the health of our gut impacts our mental health as well as other health conditions and illness. However, you can’t go wrong with eating a healthy diet. There is plenty of evidence to suggest that eating a diet that includes lots of fruits and vegetables, whole grains, beans and lentils, as well as fatty fish at least twice a week can have beneficial effects on our physical and mental health. It is also a good idea to limit processed foods and sweets and to consume red meat in moderation. After all, you are what you eat, and what you eat can impact how you feel both mentally and physically.