A healthy diet is good for the body … but also for the brain and for mental health

Dr. Anne-Isabelle Dionne
ELNA, Saint-Mathieu-de-Beloeil

A look at some phenomena at play in the relationship between our diet and our moods.

In a previous article, we discussed some clear connections between diet and mental health, and also moods. Various factors are involved in this correlation. Take, for example, the intestinal microbiome. Considered as an “organ” in its own right, it contains nearly 100 trillion bacteria—more than the number of cells that make up our physical bodies.1 These bacteria interact with us symbiotically, forming part of several processes that are essential to human survival: synthesis of vitamins and neurotransmitters, immune system and inflammation regulation, protecting the digestive epithelial barrier that absorbs nutrients, etc. 2

Disruptions in the microbiome, especially a loss of diversity, is associated with a host of cardiometabolic and inflammatory diseases.3 These bacteria that colonize our gut react and support their own growth in response to what they are given to “eat” (i.e., how we feed ourselves on a daily basis). And they interact bidirectionally with the 500 million neurons that line our digestive system. 4

Fibre and several polyphenols (found in nuts, seeds, unprocessed whole grains, legumes, fruits, and vegetables) are prime nutrients for facilitating good selection, diversity, and growth of the healthiest kinds of bacteria.5 Conversely, excessive consumption of some medications (antibiotics, antacids, anti-inflammatories, etc.), chronic stress, diets that are low in fibre and high in processed foods, sugars of all kinds, sweeteners and pesticides can greatly affect microbiome quality.6,7

When the microbiome is disrupted by the stressors mentioned above, it can bring about a loss of integrity of the epithelial barrier that lines the lumen of the digestive tract. This causes a breakdown in the proteins that bind the cells together and ensure healthy permeability between the intestinal contents and the circulatory system.

“Leaky gut syndrome” refers to a phenomenon in which food molecules, bacterial metabolites and/or bacteria themselves enter the blood stream without being adequately filtered and whose presence then triggers activation of the immune system and a continual state of inflammation.

Leaky gut syndrome is connected to several systemic pathologies including inflammatory bowel diseases, diabetes, asthma, as well as psychiatric disorders or neurodiverse conditions like anxiety, depression, and autism.8, 9, 10, 11, 12 The inflammatory molecules produced by foreign molecules exogenous to the bloodstream and neutralized by the immune system affect the entire body: inability to properly regulate blood sugar levels, chronic pain, fatigue, negative or anxious mood, digestive bloating, etc.

A healthy diet, cutting out behaviours and substances that adversely affect the balance of gut microbiota and ingestion of probiotics can prove highly beneficial for restoring diversity and optimal function of the microbiome, with the desired effect on regulating the immune system and inflammatory responses. These also have a positive impact on the metabolism of neurotransmitters and of several vitamins and biochemical molecules essential to the function of the body’s systems.13

Inflammation, oxidative stress, and antioxidant needs
Inflammation is a normal phenomenon that is essential to survival and allows an injured structure to heal after damage of all kinds to structures of the body. It is important in acute and sporadic situations when the damaged is caused accidentally.

Inflammation becomes a problem, however, when it occurs chronically due to regular and persistent damage. For example, daily exposure to toxins (such as cigarettes or mould in the environment), stress and chronic sleep deprivation (involving persistent pro-inflammatory hormonal disturbances) and a diet filled with sugar and processed foods contribute to causing chronic inflammation. Low-grade chronic inflammation is associated with depression, schizophrenia, and bipolar disorder.14, 15, 16

Oxidative stress is an outcome of chronic inflammation. This results in the production of free radicals that attack healthy structures in the body (including neurons!) and cause loss of organ function and accelerated aging. One way to counteract this is to supply the body with a significant quantity of “antioxidants.” Effectively, these are the various phytonutrients, vitamins and minerals found in a healthy, plant-rich, unprocessed, and varied diet. Some studies have shown several antioxidant markers to be reduced in individuals suffering from severe depressive episodes. 17, 18

The hippocampus is a crucial region of the brain involved in the phenomena of learning, creating memories and emotional regulation. Its neurons appear to be able to form and grow under the effect of a substance called BDNF (brain-derived neurotrophic factor).19, 20 When the hippocampus is poorly developed, we can suffer from memory impairment, difficulty learning new tasks and poor emotional regulation, all frequent symptoms in depression and anxiety.

Stress is one of the most potent factors that can negatively impact levels of BDNF.21 However, increasing evidence points to the fact that a highly nutrient-dense diet favourably affects levels of BDNF that can stimulate neurogenesis. Conversely, diets that are high-sugar and high in poor quality fats found in processed foods have an entirely opposite effect.22, 23, 24

Good mental health therefore depends on an optimal intake of essential nutrients. These help to ensure all the body’s biochemical reactions involved in the selection of a diversified microbiome, neurotransmitter synthesis, neurogenesis and attenuating oxidative stress produced by the environment and/or life habits that can cause cellular damage, even to neurons in the brain. Each bite of food should be as nutritious as possible:

  • The food we consume should be as close as possible to what it is we would pick out of a garden or take from a free-range animal in an optimal environment.
  • Eat plenty of plants of all kinds. For example, use the colours of the rainbow in your choice of fruits and vegetables for the week. Prioritize vegetables over fruit to avoid an excess of sugar, something likely to be less well tolerated by individuals who are metabolically vulnerable.
  • Include a substantial amount of fibre each day in the form of nuts, seeds, vegetables and fruit, whole, unprocessed grains, and legumes. 
  • Opt for good quality fats: olive oil, nuts, fatty fish, etc., while being careful not to overheat your oils, as their beneficial properties may be lost.
  • Consume probiotics with the addition of fermented foods (sauerkraut, kimchi, plain yoghurt, kefir, tempeh, etc.).
  • Do not add any refined sugars or concentrated sugars derived from whole foods.

One’s diet should always be calibrated before considering a supplement aimed at sufficient intake of any nutrient. Whole foods provide much more, biochemically speaking, than what a pill can deliver.

Nevertheless, sometimes it is necessary to have recourse to supplements for various reasons (intolerances for certain foods, inability to absorb the recommended nutrients from a particular food, a lifestyle that calls for more than the recommended intake of a certain agent, which is inadequately supplied by diet, etc.).

A personalized approach is key in targeting the risks of deficiencies and levels of nutrient intake. Moreover, a personalized approach lets us assess the quality and diversity of the microbiome that lives in us while looking for strategies to optimize it. Ultimately, psychotherapy and use of antidepressants are not the only options for managing mood disorders. Healthier diet and lifestyle habits can be far more effective for improving mental health!

1 Valdes A M, Walter J, Segal E, Spector T D. Role of the gut microbiota in nutrition and health BMJ 2018; 361 :k2179 doi:10.1136/bmj.k2179

2 Thursby E, Juge N. Introduction to the human gut microbiota. Biochem J. 2017;474(11):1823-1836. Published 2017 May 16. doi:10.1042/BCJ20160510

3 Valdes A M, Walter J, Segal E, Spector T D. Role of the gut microbiota in nutrition and health BMJ 2018; 361 :k2179 doi:10.1136/bmj.k2179

4 Barett KE BS. Ganong’s review of medical physiology: The autonomic nervous system 2010.

August 5, 2021 – Yang Q, Liang Q, Balakrishnan B, Belobrajdic DP, Feng QJ, Zhang W. Role of Dietary Nutrients in the Modulation of Gut Microbiota: A Narrative Review. Nutrients. 2020;12(2):381. Published 2020 Jan 31. doi:10.3390/nu12020381

6 Vich Vila, A., Collij, V., Sanna, S. et al. Impact of commonly used drugs on the composition and metabolic function of the gut microbiota. Nat Commun 11, 362 (2020). https://doi.org/10.1038/s41467-019-14177-z

7 Madison A, Kiecolt-Glaser JK. Stress, depression, diet, and the gut microbiota: human-bacteria interactions at the core of psychoneuroimmunology and nutrition. Curr Opin Behav Sci. 2019;28:105-110. doi:10.1016/j.cobeha.2019.01.011

8 Carabotti M, Scirocco A, Maselli MA, Carola S. The gut-brain axis: interactions between enteric microbiota, central and enteric nervous systems. Ann Gastroent 2015;28:203-9

9 Ait-Belgnaoui A, Durand H, Cartier C, et al. Prevention of gut leakiness by a probiotic treatment leads to attenuated HPA response to an acute psychological stress in rats. Psychoneuroendocrino 2012;37:1885-95

10 Foster JA, McVey Neufeld KA. Gutbrain axis: how the microbiome influences anxiety and depression. Trends Neurosci 2013;36:305-12.

11 Ho JT Chan GC Li JC.. Systemic effects of gut microbiota and its relationship with disease and modulation. BMC Immunol 2015;16

12 Bischoff SC, Barbara G, Buurman W, et al. Intestinal permeability–a new target for disease prevention and therapy. BMC Gastroenterol 2014;14:189.

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14 Berk, M, Williams, LJ, Jacka, FN et al. (2013) So depression is an inflammatory disease, but where does the inflammation come from? BMC Med 11, 200

15 Fernandes, BS, Steiner, J, Molendijk, ML et al. (2016) C-reactive protein concentrations across the mood spectrum in bipolar disorder: a systematic review and meta-analysis. Lancet Psychiatry 3, 1147–1156

16 Fernandes, BS, Steiner, J, Bernstein, HG et al. (2016) C-reactive protein is increased in schizophrenia but is not altered by antipsychotics: meta-analysis and implications. Mol Psychiatry 21, 554–564.

17 Moylan, S, Berk, M, Dean, OM et al. (2014) Oxidative & nitrosative stress in depression: why so much stress?Neurosci Biobehav Rev 45, 46–62.

18 Liu, T, Zhong, S, Liao, X et al. (2015) A meta-analysis of oxidative stress markers in depression. PLoS ONE 10, e0138904.

19 Fernandes, BS, Berk, M, Turck, CW et al. (2014) Decreased peripheral brain-derived neurotrophic factor levels are a biomarker of disease activity in major psychiatric disorders: a comparative meta-analysis. Mol Psychiatry19, 750–751

20 Fernandes, BS, Molendijk, ML, Kohler, CA et al. (2015) Peripheral brain-derived neurotrophic factor (BDNF) as a biomarker in bipolar disorder: a meta-analysis of 52 studies. BMC Med 13, 289.

21 Miao Z, Wang Y, Sun Z. The Relationships Between Stress, Mental Disorders, and Epigenetic Regulation of BDNF. Int J Mol Sci. 2020;21(4):1375. Published 2020 Feb 18. doi:10.3390/ijms21041375

22 Zainuddin, MS & Thuret, S (2012) Nutrition, adult hippocampal neurogenesis and mental health. Br Med Bull103, 89–114.

23 Guimaraes, LR, Jacka, FN, Gama, CS et al. (2008) Serum levels of brain-derived neurotrophic factor in schizophrenia on a hypocaloric diet. Prog Neuropsychopharmacol Biol Psychiatry 32, 1595–1598.

24 Molteni, R, Barnard, RJ, Ying, Z et al. (2002) A high-fat, refined sugar diet reduces hippocampal brain-derived neurotrophic factor, neuronal plasticity, and learning. Neuroscience 112, 803–814.

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