Does diet impact mental health?

Issue: BCMJ, vol. 60, No. 5, June 2018, Pages 245,269 Council on Health Promotion

Patients often report feeling mentally and physically unwell after eating fat-, salt-, or sugar-laden foods. Though the precise mechanisms underlying these symptoms are unclear, extensive self-reports support the notion that diet impacts mental health. While correlational evidence suggests a bidirectional relationship between diet and mental health, attributing causality is much more challenging.[1] A recent meta-analysis revealed compelling evidence of the relationship between dietary patterns and depression risk, yet concluded that more randomized controlled trials and cohort studies are needed to confirm these findings.[2]

The emerging field of nutritional psychiatry takes a more detailed look at the bidirectional impact of food and nutrition on mental health. This includes a study of gut flora or microbiota and their influence on mood. The “gut-brain axis” is an extensive channel of direct and bidirectional biochemical communications between the GI tract and the central nervous system. Ninety percent of the body’s serotonin, an important neurotransmitter, is produced in the GI tract.[3

If future research determines that probiotic changes to microbiota have significant influence on neuro-transmitter levels, probiotics could become a major player in the management of mental health. Regularly recommending probiotics from dietary sources of live and active cultures or discussing how to choose probiotic supplements may become common in clinical practice. 

Patients also ask about the relationship between nutrients such as omega-3 fatty acids, B vitamins, zinc, and magnesium and mental health. While there are ongoing investigations regarding the impact of these nutrients on mental health, there are no definitive conclusions regarding specific nutrient supplementation for mental health. The benefits of omega-3 fatty acids have largely been reported based on their anti-inflammatory properties. They may also provide a range of neurochemical activities that impact the reuptake of the neurotransmitters dopamine, noradrenaline, and serotonin. Recommending omega-3 fatty acids from dietary sources such as cold-water fish (salmon, tuna, sardines, mackerel), chia or flax seeds, and walnuts is aligned with overall healthy-eating messaging. If patients wish to use a supplement, advise them to use one that has a natural product number (NPN). An NPN ensures that the product has been reviewed by Health Canada.[4]

Focusing on healthy eating patterns rather than individual foods and nutrients is the best dietary advice for both mental and physical health. These patterns, such as the DASH, anticancer, or Mediterranean diets, recommend whole grains; plenty of fruits, vegetables, and legumes; fish; and a sprinkling of nuts, seeds, healthy fats, and nonsalt spices.[5]

To build greater awareness over food choices and the link to emotional well-being, physicians can recommend that patients keep a simple diary of their food, mood, and lifestyle choices, and monitor whether they crave high-sugar or high-fat foods when they are tired, sad, or stressed. Some experts attribute sugar and fat cravings to the addictive nature of humans, as sugar and fat impact dopamine and serotonin levels. Identifying the when, what, and why of cravings may help with successful behavior change. With increased awareness, patients can then switch from negative to healthy behaviors. These changes can also benefit body weight, an independent risk factor for mental ailments, providing even more rationale for using a diary to build awareness around diet and lifestyle choices. 

Emerging alongside nutritional psychiatry is the advent of personalized medicine—a tailored, individualized approach to optimizing patient care. This could prove revolutionary over time. Until then, we can focus on some basics that even our grandmothers would agree on—eat mainly plant-based whole foods, make time for physical activity, eat treats in moderation, and get adequate sleep. These are the current gold standards and safest ways to sustain mental and physical health and well-being.
—Kathleen Cadenhead, MD 
—Mary Hinchliffe, MD
—Tanis Mihalynuk, PhD, RD


This article is the opinion of the Nutrition Committee, a subcommittee of Doctors of BC’s Council on Health Promotion, and is not necessarily the opinion of Doctors of BC. This article has not been peer reviewed by the BCMJ Editorial Board.


1.    Polivy J, Herman CP. Mental health and eating behaviours: A bi-directional relation. Can J Public Health 2005;96 Suppl 3:S43-S46.

2.    Li Y, Lv MR, Wei YJ, et al. Dietary patterns and depression risk: A meta-analysis. Psychiatry Res 2017;253:373-382.

3.    Wallace CJK, Milev R. The effects of probiotics on depressive symptoms in humans: A systematic review. Ann Gen Psychiatry 2017;16:14.

4.    Health Canada. About Natural Health Product Regulation in Canada. Accessed 5 March 2018.

5.    Opie R, O’Neil A, Jacka FN, et al. A modified Mediterranean dietary intervention for adults with major depression: Dietary protocol and feasibility study from the SMILES trial. Nutr Neurosci 2017(April 19):1-15.

Kathleen Cadenhead, MD, Mary Hinchliffe, MD, Tanis Mihalynuk, RD,. Does diet impact mental health?. BCMJ, Vol. 60, No. 5, June, 2018, Page(s) 245,269 - Council on Health Promotion.

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