by Milene Brownlow, PhD
Nutritional psychiatry is a rapidly growing medical field studying the connection between the role food and diet quality plays in how we feel.1 We intuitively understand the body-mind connection and how it affects our day-to-day. We get butterflies in our stomach when nervous, our heart races when we are excited, and our mindset quickly goes south when we have digestive problems. This connection has led researchers to investigate lifestyle modifications that may optimize mental and cognitive health.
More than just fuel for our bodies, nutrients play an active role in brain functions such as mood and cognition. Cumulative evidence shows an association between unhealthy diets and poor mental health, such as increased incidence of depression.2,3 Cardiovascular mortality, linked to metabolic status, is a common cause of death in depressed individuals,4 and glycemic dysregulation has been shown to affect serotonergic neurotransmission, a crucial pathway in the processing of emotional stimuli.5
Alternatively, a healthy diet can promote wellness by reducing inflammation and introducing essential nutrients for biochemical pathways. For instance, adherence to the Mediterranean diet is associated with decreased incidence of depression,6 and an inverse association is reported between intake of fruits and vegetables and depressive mood,7 with increased wellbeing and happiness scores.8
Key nutrients for healthy mood
Mood-boosting foods provide nutrients that offer neuroprotection and support for the synthesis of neurotransmitters and bioactive molecules such as serotonin, dopamine, melatonin, etc.9 Below are examples of mood-boosting nutrients:
- Omega-3s and fatty fish:
Omega-3 polyunsaturated fatty acids (ω3 LC-PUFAs) are essential components of cellular membranes involved in neurotransmission, synaptic plasticity, and inflammation. Low levels of ω3 LC-PUFAs are linked to depression, suicide, and cardiovascular and inflammatory disorders.10 A strong negative correlation is observed between fatty fish consumption and national rates of major depressive disorder (MDD),11 likely mediated by reduction of proinflammatory cytokines observed in depressed individuals.12 Of note, the positive effect of ω3 LC-PUFAs on depressive symptoms appeared to be associated with eicosapentaenoic acid (EPA) rather than docosahexaenoic acid (DHA) levels.10
- Dose: 200–2,200 mg/day of EPA
- Food sources: cold-water fatty fish (salmon, mackerel, tuna, herring, and sardines), nuts, and seeds (flaxseeds, chia seeds, walnuts)
- Probiotics and prebiotics:
The gut can influence the brain via the vagus nerve (major player in the complex network innervating the digestive system) and via the microbiome (a collection of microorganisms and their genetic material).13 Although it is challenging to define what a “normal” microbiome looks like, a healthy adult microbiome is mostly dominated by the Bacteroidetes and Firmicutes phyla.14 When the human microbiome is exposed to detrimental effects of diet, stress, or antibiotics, its physiology changes, resulting in dysbiosis (an imbalance between beneficial and harmful bacteria)15 and inflammation, often linked to mental illnesses, including anxiety and depression.16
We don’t often hear about the fact that intestinal microbes can produce neurotransmitters including serotonin, norepinephrine, and gamma-aminobutyric acid (GABA). This gut-brain connection has led researchers to investigate the use of probiotics (live microorganisms that, when administered in adequate amounts, confer a health benefit on the host)16 in mental health disorders both as standalone therapy and as adjunct to commonly prescribed medications.
Although the connection between gut-brain axis and mental health is gaining clinical and scientific attention, the use of supplemental nutrition for depressive disorders lacks consensus regarding strain, dose (in colony forming units—CFU), and length of intervention. Genus and species suggested to show benefits: Lactobacillus (casei, acidophilus, rhamnosus, bulgaricus, brevis, helveticus, salivarius) and Bifidobacterium (longum, breve, bifidum, lactis, infantis).19
- Food sources of potentially beneficial bacteria: yogurt with active live cultures (be mindful of sugar content), tempeh, miso, sauerkraut, kefir, kimchi, kombucha, buttermilk, and selected cheeses (cheddar, mozzarella, and Gouda).
Another promising approach may be the introduction of prebiotic (substrates selectively utilized by host microorganisms conferring a health benefit)13 foods in our diets to foster growth of beneficial bacteria.
- Prebiotic-rich foods: legumes, oats, bananas, berries, garlic, onions, dandelion greens, asparagus, Jerusalem artichoke and leeks.20 Learn more about the interaction between prebiotics and probiotics from this blog.
Tryptophan, an essential amino acid for humans, acts as a precursor molecule for the synthesis of serotonin and melatonin. Lower tryptophan levels are consistently associated with higher risk of depression and poor mental health status.21,22 More than 90% of serotonin synthesis occurs in the gut,18 highlighting the important relationship between the gut microbiome composition and its impact on mental health.
- Dose: 250–425 mg/day.23 Bear in mind that tryptophan competes with other amino acids when crossing the blood-brain barrier, so blood levels of other amino acids may interfere with its entry in the brain. One suggestion is to consume tryptophan together with a carbohydrate source.20
- Food sources: cashews, walnuts, peanuts, almonds, seeds (sesame, pumpkin, sunflower), soybeans, grains (wheat, rice and corn)
An amino acid abundantly found in green tea, L-theanine is a popular nutrient due to its calming effects. Its anxiolytic and relaxing effects have been associated with boosting levels of key neurotransmitters that regulate emotions, mood, sleep, and cognition (GABA, serotonin, and dopamine) and by enhancing alpha brain waves (relaxation, focus, and creativity).24, 25 Daily intake of 250 mg of L-theanine for 8 weeks improved depressive symptoms, anxiety, sleep, and cognitive performance in MDD patients.26 Moreover, L-theanine has been shown to attenuate blood pressure increase in subjects exposed to high-stress situations.27
- Dose: 100-400 mg/day
- Food sources: green, black, and white teas
A trace element and abundant mineral in the body, magnesium is essential for hundreds of biochemical reactions. Forty eight percent of Americans reported suboptimal magnesium intake in the National Health and Nutrition Examination Survey (NHANES) of 2013-2016.28 Despite the lack of methodological consensus, studies investigating correlation between magnesium levels (blood, serum, plasma, or CSF) have shown that magnesium supplementation may be effective in improving depressive symptoms and promoting a calming effect.29
- Dose: 300 – 420 mg/day28
- Food sources: green leafy vegetables, avocados, legumes, nuts, seeds, and whole grains28
Diets rich in antioxidants, reducing agents capable of quenching free radicals, have been shown to improve mood, and inverse associations were reported between inflammatory and antioxidative markers such as vitamins C and E, lycopene, lutein, and zeaxanthin.30
- Food sources: Vitamins, flavonoids, and polyphenols contained in most fruits (especially in berries such as cranberries and strawberries) and dark chocolate, vegetables, and nuts.
- Vitamins and micronutrients:20
- Zinc: seafood, lean beef and poultry and lower amounts in beans, nuts, and whole grains
- Potassium: sweet potatoes, bananas, mushrooms, oranges, peas, and cucumbers
- Iron: shellfish, lean red meats, organ meats, legumes, pumpkin seeds, broccoli, and dark chocolate
- B vitamins: legumes, citrus fruits, bananas, avocados, leady greens, cruciferous vegetables, asparagus, nuts and seeds, fish, and shellfish
- Vitamin A: sweet potatoes, carrots, spinach, and black-eyed peas
- Vitamin C: citrus fruits, cantaloupe, strawberries, and cruciferous vegetables (broccoli, cauliflower, and Brussels sprouts)
- Selenium: Brazil nuts
- Dark chocolate (polyphenols and phenylethylamine)
- Seasonings, spices, and herbs: saffron, turmeric, oregano, lavender, passionflower, and chamomile
Why is this important?
Even if most of us haven’t consciously made this connection, it is clear that our food choices impact how we feel. Even a small shift in the positive direction toward metabolic health due to beneficial food choices can trigger impactful benefits, moving patients away from the threshold of psychiatric disorders that could have potentially required lifelong pharmacological treatment.
While most nutrients relevant for mental health can be obtained from a nutrient-rich diet, supplements can help fill in nutritional gaps when deficiencies are present, provided treatment is managed by a healthcare practitioner.
Although dietary advice can be confusing, evidence suggests that there is support for nutritional recommendations for emotional and mental health. If you are not already doing so, start by finding small ways to address emotional eating and being mindful with what you put on your fork. Clearly, Hippocrates was on to something when he suggested: “Let food be thy medicine and medicine be thy food.”
- Jacka FN. Nutritional psychiatry: where to next? 2017;17:24-29.
- O’Neil A et al. A randomized controlled trial of dietary intervention for adults with major depression (the “SMILES” trial): study protocol. BMC Psychiatry. 2014;13:114.
- Gómez-Donoso C et al. Ultra-processed food consumption and the incidence of depression in a Mediterranean cohort: the SUN Project. Eur J Nutr. 2020;59(3):1093-1103.
- Penninx BW et al. Depression and cardiac mortality: results from a community-based longitudinal study. Arch Gen Psychiatry. 2001;58:221-227.
- Watson K et al. Insulin resistance, an unmasked culprit in depressive disorders: promises for interventions. 2018;136:327-334.
- Sanchez-Villegas A et al. Association of the Mediterranean dietary pattern with the incidence of depression. Arch Gen Psychiatry. 2009;66(10):1090-1098.
- Liu et al. Fruit and vegetable consumption and the risk of depression: a meta-analysis. 2016;32(3):296-302.
- Mujcic R et al. Evolution of well-being and hHappiness after increases in consumption of fruit and vegetables. Am J Public Health. 2016;106(8):1504-1510.
- Strasser B et al. Mood, food, and cognition: role of tryptophan and serotonin. Curr Opin Clin Nutr Metab Care. 2016;19:55-61.
- Sublette ME et al. Meta-analysis: effects of eicosapentaenoic acid in clinical trials in depression. J Clin Psychiatry. 2011;72(12):1577-1584.
- Hibbeln JR et al. Fish consumption and major depression. 1998;351(9110):1213.
- Liao Y et al. Efficacy of omega-3 PUFAs in depression: a meta-analysis. Transl Psychiatry. 2019;9:190.
- Gibson GR et al. The International Scientific Association for Probiotics and Prebiotics (ISAPP) consensus statement on the definition and scope of prebiotics. Nat Rev Gastroenterol Hepatology. 2017;14(8)491-502.
- Qin J et al. A human gut microbial gene catalog established by metagenomic sequencing. 2010;464(7285):59-65.
- Zhang YJ et al. Impacts of gut bacteria on human health and diseases. Int J Mol Sci. 2015;16:7493-7519.
- Hill C et al. The International Scientific Association for Probiotics and Prebiotics consensus statement on the scope and appropriate use of the term probiotic. Nat Rev Gastroenterol Hepatology. 2014;11:506-514.
- Clapp M et al. Gut microbiota’s effect on mental health: the gut-brain axis. Clin Prac. 2017;7:987.
- Gershon MD et al. The serotonin signaling system: from basic understanding to drug development for functional GI disorders. 2007;132(1):397-414.
- Misra S et al. Psychobiotics: a new approach for treating mental illness? Crit Rev Food Sci Nutr. 2017;59(8):1230-1236.
- Naidoo U. This is Your Brain on Food. Little Brown Spark, New York. 2020.
- Capuron L et al. Vitamin E status and quality of life in the elderly: influence of inflammatory processes. Br J Nutr. 2009; 102:1390-1394.
- Capuron L et al. Chronic low-grade inflammation in elderly persons is associated with altered tryptophan and tyrosine metabolism: role in neuropsychiatric symptoms. Biol Psych. 2011;70:175-182.
- Richard DM et al. L-tryptophan basic metabolic functions, behavioral research and therapeutic indications. Int J Tryptophan Res. 2009;2:45-60.
- Nobre AC et al. L-theanine, a natural constituent in tea, and its effects on mental state. Asia Pac J Clin Nutr. 2008;17(Suppl 1):167-168.
- White DJ et al. Anti-stress, behavioural and magnetoencephalography effects of an L-theanine-based nutrient drink: a randomised, double-blind, placebo-controlled, crossover trial. Nutrients 2016;8(1):53.
- Hidese S et al. Effects of chronic L-theanine administration in patients with major depressive disorder: an open label study. Acta Neuropsychiatr. 2017;29(2):72-29.
- Yoto A et al. Effects of L-theanine or caffeine intake on changes in blood pressure under physical and psychological stresses. J Physiol Anthropology. 2012;31:28.
- https://ods.od.nih.gov/factsheets/Magnesium-HealthProfessional/. Accessed on September 30, 2020.
- You HJ et al. Decreased serum magnesium levels in depression: a systematic review and meta-analysis. Nordic J Psych. 2018;72(7):534-541.
- Huang Q et al. Linking what we eat to our mood: a review of diet, dietary antioxidants, and depression. 2019;8(9):376.
Milene Brownlow, PhD earned her PhD from the University of South Florida, studying the role of diet-induced ketosis and calorie restriction on Alzheimer’s pathology. During her postdoctoral fellowship at the Air Force Research Laboratory she investigated nutritional approaches to optimizing brain health and cognitive performance. Dr. Brownlow has extensive experience in designing, managing and executing studies in behavioral neuroscience and has authored over 15 peer-reviewed publications. In her spare time, she enjoys spending time with her husband and their daughter, exploring the beautiful Pacific Northwest.