Nutritional Psychiatry: The Gut-Brain Connection

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There is truth in the saying, “you are what you eat.” We may often feel better when we eat better, and science has shown that it is in fact true-a healthy diet has an impact on physical health. Now, science is showing us that a healthy diet may have an impact on mental health. The impact that food has on mood and other aspects of mental illness is being researched. Nutritional psychiatry¹ is developing into a real opportunity for clinical intervention for patients who suffer from depression and anxiety.

Clinical practice has shown that psychiatric patients experience increased morbidity and mortality associated with a range of medical illnesses. In addition, lifestyle, psychiatric medications, and inadequate health care all contribute to the poor physical health of people with mental illness. Thus, nutritional interventions may be helpful to patients who want to combat the adverse effects of medications.

Although certain recommendations such as eating a healthy diet of fresh fruits, vegetables, whole grains, and lean proteins seems simple, doctors do not routinely discuss diet with their patients. The gap in nutrition education in our medical schools has left many practicing clinicians without a “language” to discuss dietary interventions with patients.

Helping to fill this void, nutritional psychiatry provides useful action-oriented steps to patients, and it is a potentially powerful tool for clinicians.

What’s the connection?

Anatomically speaking, the vagus nerve connects the gut and brain. This gut-brain axis provides us a greater understanding of the connection between diet and disease and is also relevant in psychiatric disease. The human microbiome, which has co-evolved with humans, is a community of different bacteria that inhabit the body and is beneficial to humans. Researchers agree that an individual’s unique microbiome is created within the first 1000 days of life. As clinicians it is useful for us to understand the microbiome.

Nutritional psychiatry

In terms of nutritional psychiatry, we are learning through research that the food we eat impacts how we feel emotionally.^1,2 There are some individuals who seek complementary treatments such as food-mood interventions in addition to allopathic medications to boost their chances of improving mood and anxiety. It’s important to note that such complementary treatments may benefit mild to moderate depression and anxiety; however they are not likely to affect suicidal ideation or a psychiatric emergency. It’s helpful to alert patients to this if you use nutritional psychiatry in your clinical work. Recommendations are not prescriptive but allow the clinician to provide clear guidelines to the patient.

The growing evidence base for nutritional psychiatry in human studies is encouraging. The SMILES (Supporting the Modification of lifestyle in Lowered Emotional States) trial showed that food can improve mood.³ Another study completed a systematic review and meta-analysis of observational studies looking at healthy dietary indices and the risk of depressive outcomes.⁴ The study concluded that following a healthy diet, particularly a traditional Mediterranean diet, or avoiding an inflammation-producing foods appear to confer some protection against depression. A recent report outlined an Antidepressant Food Scale that listed 12 antidepressant nutrients linked to the treatment and prevention of depression (Table).⁵

A good resource for clinicians is the International Society of Nutritional Psychiatry Research (ISNPR) website.⁶

Understanding the microbiome

Diet is thought to be an important factor that can regulate or dysregulate the microbiome. Diseases may occur when the balance between “good” and “bad” bacteria is altered. Examples of these diseases may include: irritable bowel disease, which is caused by dysfunction in the composition and interactions between microbes, the gut lining, and the immune system; as well as asthma, obesity, metabolic syndrome, diabetes, mood and cognitive problems.

Healthy gut bacteria have a number of functions, including the breakdown of complex carbohydrates and the production of vitamins and nutrients as well as of short chain fatty acids. Moreover, they protect against pathogens, help train the immune system, support detoxification, and help modulate the nervous system.

From a mental health perspective, 90% of serotonin receptors are located in the gut. It is therefore not surprising that when someone is prescribed an antidepressant such as sertraline or fluoxetine, the most common adverse effects are gut related. Most commonly patients experience nausea, diarrhea, dry mouth, and sometimes vomiting. These adverse effects tend to remit after the first 1 to 2 weeks if not sooner. Gut dysbiosis can also be caused by prescription antibiotics. Antibiotics negatively impact the good bacteria that protect the gut. A solution to this is to take a probiotic to protect good gut bacteria and/or to include probiotic rich foods in the diet.

Recently, Zinöcker and Lindseth⁷ looked at the western diet, the microbiome-host interaction, and its role in metabolic disease. They report that the gut environment (or microbiome) is changed by what we eat and is affected by the western diet that contains ultra-processed foods. The change that occurs leads to inflammation in the gut, and consequently symptoms of disorders. While we know that processed foods are poor nutritional substitutes for whole foods such as fruits and vegetables-the authors delve further into the impact that these food additives have on inflammation in the body and possibly contribute to diseases.

Many studies have outlined the connection between processed foods and obesity, diabetes and heart disease. This study looked at the additional possibility that food processing affects inflammatory processes in the body (and thereby diseases) via diet-microbiome-host interactions. The food industry has continually increased the number of food additives without testing their impact in the microbiome. The findings from this study suggest that reducing processed foods from our diets would help reduce the likelihood of diseases related to inflammation.

A study at the University of Michigan evaluated withdrawal symptoms that people experience when they stop eating processed foods.⁸ The study looked at data that food addiction (eg, eating highly processed foods) may trigger addictive like symptoms in some people, including withdrawal symptoms. The Highly Processed Food Withdrawal Scale (ProWS) was adapted from self-report measures of drug withdrawal symptoms. The researchers feel that this scale may be a psychometrically sound tool for future research investigating highly processed food withdrawal in humans. The data can inform us of how patients may experience withdrawal-like symptoms when they suddenly stop eating highly processed foods.

Prebiotics and probiotics

Some ways in which we can protect our microbiome balance is to include both prebiotic and probiotic foods in our diets. A prebiotic is a soluble fiber that helps feed the good organisms (probiotics) in our gut. Probiotics already live inside the large intestine. The more prebiotics that the probiotics have to eat, the more efficiently they will work. Examples of prebiotic foods include onions, leeks, asparagus, bananas, Jerusalem artichokes, chicory root, garlic, dandelion greens.

Probiotic foods that supply these bacteria include fermented foods such as sauerkraut, yogurt with active cultures, pickles, kefir, kimchi, kombucha, miso. Have your patients read labels carefully, try to avoid extra sugar/preservatives-pickles and yogurt may have added sugar or food coloring. Select plain yogurt or kefir-adding berries and cinnamon instead of sugar are healthier options.

A recent study suggests that eating a healthy balanced diet such as the Mediterranean diet and avoiding inflammation-producing foods may be protective against depression.⁴ The most compelling evidence was seen with the Mediterranean Diet, which focuses on eating whole grains, seafood and poultry at least twice a week; consuming beans, legumes, fresh fruit, and leafy greens (spinach, kale, arugula, romaine), nuts (almonds, walnuts), cruciferous vegetables (cauliflower, broccoli), healthy fats (olive and canola oil), and less red meat.

Helping our patients understand what they can do

Traditionally, doctors are not well equipped after medical school to discuss nutrition, and most patients do not seek nutritional advice from their doctors. However, given the link between the gut and brain it may be clinically useful for mental health clinicians to have a basic working knowledge of nutrition and tips to share with their patients.

• Eat whole foods and avoid packaged or processed foods

• Think of eating an orange rather than drinking orange juice to avoid added sugars

• Instead of a vegetable juice, consider increasing your daily servings of fruits and vegetables

• Include probiotic-rich foods such as yogurt (avoid fruit-based yogurt, which is high in unwanted sugars)

• Eat foods rich in fiber

• Replace sugary desserts with a serving of fresh fruit and dark chocolate

• Avoid processed and packaged foods that are high in food additives that disrupt the healthy bacteria in the gut

Disclosures:

Dr Naidoo is Director of Nutritional and Lifestyle Psychiatry at the Massachusetts General Hospital (MGH) and Director of Nutritional Psychiatry, MGH Psychiatry Academy, Boston, MA. She is also a Professional Chef, Culinary Instructor, and has studied Nutritional Science.

Dr Naidoo reports no conflicts of interest concerning the subject matter of this article.

References:

1. Sarris J, Logan AC, Akbaraly TN, et al. Nutritional medicine as mainstream in psychiatry. Lancet Psychiatry. 2015;2:271-274.

2. Marx W, Moseley G, Berk M, Jacka F. Nutritional psychiatry: the present state of the evidence. Proc Nutr Soc. 2017;76:427-436.

3. Jacka F, O’Neil A, Opie R, et al. A randomized controlled trial of dietary improvement for adults with major depression. BMC Med. 2017;15:23.

4. Lassale C, Batty GD, Baghdadli A, et al. Healthy dietary indices and risk of depression outcomes; a systematic review and meta-analysis of observational studies. Mol Psychiatry. September 26, 2018; E-pub ahead of print.

5. LaChance LR, Ramsey D. Antidepressant foods: an evidence-based nutrient rofiling system for depression. World J Psychiatry. 2018;8:97-104.

6. International Society for Nutritional Psychiatry Research. http://www.isnpr.org/. Accessed December 7, 2018.

7. Zinöcker MK, Lindseth IA. The Western diet-microbiome-host interaction and its role in metabolic disease. Nutrients. 2018;10:pii:E365.

8. Schulte EM, Smeal JK, Lewis J, Gearhardt AN. Development of the highly processed food withdrawal scale. Appetite. 2018;131:148-154.