The gut microbiome, diet and mental health connection

It's no secret that when we eat better, we feel better. A wide and varied diet has been shown to improve mood, memory and concentration. But what is the exact relationship between the gut microbiome, diet and mental health? That's what this presentation explores.

1. The gut microbiome, diet and mental health connection Dr Tim Crowe BSc(Hons), MNutrDiet, PhD, AdvAPD

2. What is the gut microbiota? Your gastrointestinal tract is inhabited by over 100 trillion microorganisms including bacteria, viruses and fungi – this is called the gut microbiota Can weigh around 0.5 kg Think of it an ecosystem - just like a rainforest ecosystem of plants, animals and insects living together supporting each other

3. Our gut bacterial fingerprint

4. Changes in the gut microbiota over life Nagpal R et al. Nutr Healthy Aging 2018;4:267-85

5. Can we define a ‘healthy gut’? The Issues Microbiome communities are highly individualised Not established if dysbiosis is a cause or consequence of disease A ‘ healthy microbiome’ for one person can be ‘unhealthy’ in a different context e.g. A microbiome linked to weight gain would be detrimental in an obesogenic environment but beneficial during food deprivation What is likely Bacterial diversity is more important than the presence of specific taxa Low dietary fibre intake does not support a healthy, diverse gut microbiome McBurney M et al. J Nutr 2019;11:1182-95

6. Prebiotics Prebiotics are a type of dietary fibre that serve as food our gut bacteria thrive on Think of prebiotics as like ‘ gut fertiliser ’ that promote the growth of beneficial bacteria P lant foods are the main source of prebiotics Can be used by gut microorganisms to give a health benefit for us

7. Health benefits of prebiotics Less harmful bacteria Less inflammation Improved heart and diabetes health Mental health benefits Improved bone health

8. Top prebiotic foods Onions, leeks, asparagus, garlic and Jerusalem artichokes Legumes (beans, soy, lentils) Barley and oats Bananas and apples Potatoes

9. Grains and your gut Grains contain prebiotic fibres that are important fuels for gut bacteria Can increase growth of beneficial bacteria such as Bifidobacterium and Lactobacillus Improve stool frequency and consistency Anti-inflammatory benefits

10. Reasons to love your legumes Legumes tend to have higher levels of prebiotic fibre than fruits and vegetables Lentils Soybeans Split peas Cannellini beans Kidney beans Navy beans (baked beans) Broad beans Mung beans Chickpeas Lima beans

11. Reasons to love your legumes Lower risk of heart disease Improved blood glucose control Lowers blood cholesterol and blood pressure Positive changes in the diversity of gut microbes Better bowel habits Absorb more calcium

12. Fill up on fruit Two serves of fruit per day has significant prebiotic activity ↑ Bifidobacteria and ↓ harmful pathogenic bacteria

13. ✅ Resistant starch ✅Pectin ✅Polyphenols (anthocyanins)

14. Fermented foods Marco ML et al. Nat Rev Gastroenterol Hepatol 2021;18:196-208

15. Fermented foods – the evidence ✅ Yoghurt - Beneficial for lactose intolerance, constipation, diarrhoeal diseases, body weight, type 2 diabetes and cardiovascular disease ✅ Kefir - Beneficial for lactose malabsorption, Helicobacter pylori eradication and ↑ Lactobacillus and Bifidobacterium ❓ Kimchi, sauerkraut, natto and sourdough ❌ Kombucha Dimidi E et al. Nutrients 2019;11:1806 Marco ML et al. Nat Rev Gastroenterol Hepatol 2021;18:196-208

16. Probiotics: benefits and evidence rating Neunez M et al. Front Med 2020;6:296

17. What does a ‘gut health’ diet look like?

18. How food can improve your mental health

19. One in five Australians aged 16-85 years will experience a mental illness each year The most common conditions are depression, anxiety and substance use disorder

20. What you eat can affect your mood B ut your mood also influences what you choose to eat People in a good mood are more likely to choose nutritious foods and to focus on the long-term benefits of these healthy foods

21. The Gut-Brain-Mood Link

22. Inflammation and its link to gut health

23. What is inflammation? Part of the body's normal response to protect against infection, injury or disease Involves several parts of our immune system from the activation of white blood cells to the release of chemical inflammatory mediators Without inflammation, wounds and infections would never heal so it is something we need, but too much is not good for our health Acute inflammation happens quickly following an injury like a splinter in your finger or an infection Chronic inflammation involves an ongoing body defense response that can end up damaging blood vessels and other body tissues, accelerating development of long-term health problems

24. Causes of chronic inflammation Autoimmune diseases ( e.g rheumatoid arthritis, lupus) Infections Cardiovascular disease Environmental factors (smoking, pollution) Allergies Obesity (especially excess abdominal fat) Ageing Smoking Sedentary lifestyle Poor sleep Poor diet

25. Chronic inflammation and health Chronic inflammation promotes the development of heart disease, type 2 diabetes and even some forms of cancer Unlike acute inflammation which promotes redness, swelling and pain, chronic inflammation can be invisible

26. Gut health and chronic inflammation Disorders that cause changes in the gut microbiota can lead to an imbalance in immune regulation By-products of metabolic processes of bacteria in the gut can play a role in inhibiting inflammation Bander ZA et al. Int J Res Public Health 2020;17:7618

27. Nutrition, inflammation and depression A highly refined and processed food diet (typical Western diet) is associated with higher rates of depression This same type of diet is linked with higher markers of inflammation in the body

28. Nutrition, inflammation and depression Marx W et al. Mol Psychiatry 2021;26:134-150

29. Prebiotic fibre and inflammation Because of the connection between the gut microbiota and inflammation, fibre is one of the best ‘anti-inflammatory foods’ you can eat Can shape the bacterial community into a healthier, more inflammation-protective one P rovides compounds that gut bacteria convert to certain fatty acids and other substances that are anti-inflammatory

30. Food, inflammation and your gut A n ‘anti-inflammatory diet’ is one high in fruits, vegetables, healthy fats, legumes and wholegrains A Mediterranean-style diet would be one example of this especially when you add in fish (for the omega-3s) and olive oil Such a diet is high in antioxidants, anti-inflammatory compounds and prebiotic fibre

31. Review of 20 randomised-controlled trials looked at the effect of diets considered ‘anti-inflammatory’ versus a normal diet on blood measures of inflammation A Mediterranean-style diet shown to bring about significant changes in inflammatory markers Diet and inflammation Mukherjee MS et al. Nutrition Reviews 2022;81:55-74

32. People who follow traditional diets, like the Mediterranean and the Japanese diets, have a one-third lower risk of depression compared to those following a typical Western diet

33. Fruits, vegetables and happiness Mujcic R and Oswald AJ. Am J Public Health 2016;106:1504-1510

34. The SMILES Trial 67 people with moderate to severe depression 12 weeks of diet counselling versus a control group in a social support group, but no diet advice Dietary advice was about having more wholegrains, fruits, vegetables, nuts, legumes, lean meat, chicken and seafood and less highly refined starches, sugar and highly processed foods Significant improvement in depression in the diet group One third of people in the diet group achieved clinical remission from their depression compared to just 8% in the control group

35. Mediterranean diet and depression Systematic review of 5 clinical trials that used the Mediterranean diet versus a control diet to treat symptoms of depression Involved 1,507 adults with major or mild-to-moderate depression Saw a significant reduction in depression symptoms Mechanism Fibre, vitamins, minerals, polyphenol and omega-3 content of the diet Antioxidant and anti-inflammatory effects Direct brain effects on brain plasticity by ↑ BDNF production Gut microbiota changes

36. Review of 8 clinical trials (5 with depression, 1 with anxiety, 2 with schizophrenia) Additive benefit on SSRI use for depression and anxiety Improved tolerability of antipsychotic medication Probiotics and mental health

37. Physical activity is associated with neurochemical changes, including alterations in cortisol levels and increased production of endorphins, endocannabinoids, serotonin, and dopamine Also causes positive changes in microbiome bacterial diversity Exercise also improves blood flow to brain and stimulates brain cell regeneration via BDNF Socialising while exercise gives an additional mood boost

38. If you are struggling with your mental health, reach out for help It can be hard to eat well when you are feeling down. Know that each positive step you take to eating better is a step in the right direction for your mental health Fruits, vegetables, wholegrains, nuts, legumes and fish are the cornerstone of a diet for good mental health

39. www.thinkingnutrition.com.au Thinking Nutrition @CroweTim Thinking Nutrition @doctimcrowe @doctimcrowe www.slideshare.net/timcrowe