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How does nutrition influence mental health?

By Britany Rufenach

If you’ve ever gone too long between meals, you’ve likely experienced the bitter cloud of “hanger” rolling in – your energy drops, your mood sours, and you become unreasonably irritable. But soon after a snack, the clouds part, the sun emerges and you’re back to your regular self. Clearly, food is deeply intertwined with our psychology. 


What can science tell us about the effect of nutrition on our mental health?


A top-down view of a group of people gathered around a table, sharing a healthy meal

Food for thought

 

Let’s start with the basics. Your brain is a complex processing machine that needs energy to keep it running. In fact, the brain uses about 20% of our body energy, coming in the form of calories. Beyond just calories, nutrients like tryptophan, vitamin B6 and B12, and magnesium are needed for the brain to create neurotransmitters like dopamine and serotonin, the molecules that allow our brain to function . That’s (one of the reasons) why it’s important to consume the recommended intake of fruit, vegetables, and whole grains that contain high amounts of these important nutrients. For example, spinach contains vitamin B6, magnesium, tryptophan, and nearly half the recommended daily amount of vitamin C in 100 grams. Omega-3 polyunsaturated fatty acids , found in fish, nuts, and some plant oils, also influence these neurotransmission systems. 


Mental health disorders can make meeting even these basic nutritional requirements difficult. . Depression, for example, is characterized by loss of interest or pleasure, disturbed appetite, poor concentration, and tiredness. These symptoms can make it feel impossible to summon the energy to get up and cook any meal, let alone a healthy one, which leads to a vicious cycle of even lower energy. While mental health can influence our relationship with food, the opposite is also true.


Can an improved diet actually help with mental health?


Several large-scale studies have looked at the effect of diet on mental health and the occurrence of mental disorders. There is, however, a lot of variety in the populations studied, the diets followed, and the rating scales used across different studies, sometimes making consistent conclusions hard to come by. 


The Mediterranean diet is often touted as the gold standard of healthy eating. This diet includes high intake of fruits, vegetables, whole grains, nuts, beans, and olive oil, with limited meat consumption. One study showed that patients diagnosed with clinical depression who followed this diet over 12-weeks had a greater reduction in depressive symptoms compared to patients without diet changes. On the other hand, the so-called “Western” style diet, with high intake of sugars, highly processed foods, and refined carbohydrates (which have been stripped of fibers, vitamins and nutrients) is associated with a higher risk of depression. 


The research suggests that diet can impact mental health, and lead to reduction in symptoms for some disorders. But how does food affect mental function and health?

 

What do specific nutrients actually do in the body and to the brain?

 

Our brain relies on chemicals called neurotransmitters to send signals. The production of important neurotransmitters like serotonin, dopamine, and norepinephrine requires vitamin B12 and folate. Deficiencies in these vital B vitamins are associated with depressed mood. However, instead of vitamin supplements, people should instead focus on a healthy diet to supply the amount of vitamins you need (although vegetarians and vegans may need an extra boost). 


Vitamin D deficiency is also famously associated with low mood, and some mental health disorders, including depression, seasonal affective disorder, and schizophrenia. The “sunshine” vitamin is normally made on the outer layer of our skin when UV light converts a byproduct of cholesterol into Vitamin D3. Without enough Vitamin D, our bodies can’t use calcium properly, leading to many health issues, including fatigue and depressed moods. Severe deficiencies in magnesium and zinc have also been found to  lead to mood changes and cognitive impairment. Both of these vitamins are found in seeds, nuts, and whole grains. 



Vegetables spilling from brown bags, scattered across a marble countertop

 The Microbiota-Gut-Brain Axis

 

We aren’t the only ones affected by the food we consume. The human gut is densely populated by different species of bacteria – collectively called the gut microbiota. The gut microbiota helps increase our energy intake from food, modulates the immune system, and protects us from harmful bacteria. Diet heavily influences the diversity and function of these bacteria, which in turn influence the brain through a system called the microbiota-gut-brain axis.


A healthy gut microbiota is generally characterized by its diversity and resilience to change. Western-style diets have been found to decrease microbial diversity in as little as four days. The Mediterranean diet, on the other hand, increases diversity. The average person has about 160 different species of bacteria in their gut, though thousands of species have been identified in different individuals.


Probiotics, like greek yogurt or kefir, promote the presence of beneficial bacteria, such as lactobacillus and bifidobacterial. These microbes help digest, break down, and absorb nutrients that their human host can’t digest themselves. For example, a chemical group called polyphenols is commonly found in fruits, veggies, cocoa, nuts, red wine, and coffee. But 95% of polyphenols cannot be digested by humans, and are instead broken down primarily by gut microbiota. Once broken down, these chemicals can have beneficial effects by reducing inflammation and oxidation in the brain.  


Highlighting how drastically the gut microbiome can affect mental health, researchers performed a microbiota transplant from patients experiencing clinical depression to rats who had a sterile gut, containing no bacteria of its own. Shortly after the transplant, the rats began experiencing depression-like symptoms. Similarly, direct supplementation of harmful bacterial species into sterile-gut mice quickly provoked anxiety-like symptoms. 


Eating well allows us to take care not only of our own health, but also that of our microscopic friends (who, in turn, help take care of us). 



Diagram of the connection between the brain and gut microbiota, emphasizing how different food groups impact mental health positively or negatively

Image adapted from this source


Conclusion

 

Food is a vital part of our daily and social lives, and there is no harm in occasionally indulging in some comforting junk food as a form of self-care. However, proper nutrition is an important means of empowering mental well-being and one part of building a tool kit to maintain positive mental health. 

 

So remember, an apple a day helps keep the psychiatrist away. 



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