Dec 11, 2021
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By Toby Amidor, MS, RD, CDN, FAND
Today’s Dietitian
Vol. 23, No. 9, P. 36

(Source: https://www.todaysdietitian.com/newarchives/ND21p36.shtml)

Evidence suggests certain dietary patterns containing specific nutrients can reduce symptoms of some of the most common mental health disorders.

RDs play an important role in treating clients and patients with mental health issues. In 2016, mental illness of any type affected 44.7 million adults aged 18 and older.1 What has made matters worse is the COVID-19 pandemic, which has upended the lives of Americans and profoundly has affected the state of their mental health.

According to the American Psychological Association’s 2020 survey, “The potential long-term consequences of the persistent stress and trauma created by the pandemic are particularly serious for our country’s youngest individuals, known as Generation Z (Gen Z).” The survey revealed that Gen Z teens (aged 13 to 17) and Gen Z adults (aged 18 to 23) are experiencing elevated stress and reporting symptoms of depression, much of it due to the uncertainty of the future. More than 2 in 5 Gen Z teens (43%) reported that the amount of stress in their lives has increased in the past year. The survey also reported that stress levels among Gen Z adults have been increasing over the past two years, from 5.6 out of 10 in 2018 and 5.8 out of 10 in 2019 to a high of 6.1 out of 10 in 2020.2

In this article, Today’s Dietitian provides an overview of how diet may have an interrelationship with mental health based on the latest research and explores what strategies RDs can use when counseling clients and patients.

Defining Mental Illnesses
According to the American Psychiatric Association, mental illnesses are health conditions that involve changes in emotions, thinking, or behavior, or a combination of these. Mental illnesses are associated with distress and problems functioning in a variety of settings, including social, work, or during family activities.3 Mental illness includes a wide range of psychiatric disorders such as depression, anxiety disorder, obsessive-compulsive disorder (OCD), and bipolar disorder. The following are definitions of some of the most common mental illnesses RDs may encounter in practice and their relationship with nutrition therapy.

Depression (or major depressive disorder) impacts an estimated 6.7% of adults in any given year, and 1 in 6 individuals will experience depression in their lifetime. Although depression can occur any time throughout life, on average it first appears in the late teens to mid-20s. Females are more likely than males to experience depression. It’s highly heritable, with about 40% of those with depression having first-degree relatives with depression.4

The American Psychiatric Association defines depression as “a common and serious medical illness that negatively affects how you feel, the way you think, and how you act.” Depression symptoms vary from mild to severe and can include sadness, loss of interest in activities once enjoyed, changes in appetite, trouble sleeping or sleeping too much, loss of energy or increased fatigue, feelings of worthlessness or guilt, difficulty concentrating or making decisions, and thoughts of suicide. It also can lead to emotional and physical problems and can decrease the ability to function at work or home. Certain medical conditions can mimic symptoms of depression, so other causes (eg, thyroid issues, vitamin deficiencies, brain tumor) must be ruled out.4

Nutrition matters when it comes to mental health, including depression. A 2017 meta-analysis published in Psychiatry Research examined the relationship between dietary patterns and the risk of depression. Twenty-one studies from 10 countries were examined and researchers concluded that a healthful dietary pattern may decrease risk of depression, whereas a Western-style diet may increase risk.5

A 2020 review looked at diet’s impact on depression in 20 studies. The results showed that high adherence to healthful dietary recommendations, such as fish consumption, exclusion of processed foods, and adequate intake of folic acid and magnesium, were associated with a reduced risk of depression. In addition, several studies showed that inflammatory foods including sweets, refined flour, high-fat foods, and red and processed meats were associated with a significantly increased risk of depression, especially in middle-aged women and those with overweight or obesity. Researchers concluded that diet may have a significant effect on preventing and treating depression, especially one that includes vegetables, fruits, fiber, fish, whole grains, legumes, and less added sugars and processed foods. In addition, researchers found that micronutrients such as magnesium, folic acid, and various B vitamins are important for depression prevention and treatment and should be consumed in adequate amounts.6

Anxiety Disorders
Although anxiousness and nervousness are normal reactions to stress, those with an anxiety disorder experience excessive fear or anxiety. Anxiety disorders are the most common mental disorder and affect close to 30% of adults at some point in their lives.7 In any given year, 2% of US adults have generalized anxiety disorder, 8% to 12% have a specific phobia, and 7% have social anxiety disorder. Women are more likely than men to experience anxiety disorders.

Anxiety disorders can cause individuals to avoid situations that can trigger or worsen symptoms. Often, job performance, schoolwork, and personal relationships are affected. Generalized anxiety disorder involves constant worrying that interferes with daily life and activities. This worry may be accompanied by physical symptoms, including feeling on edge, fatigue, restlessness, difficulty concentrating, problems sleeping, and muscle tension.

Insufficiencies in omega-3 polyunsaturated fatty acids (PUFAs) and tryptophan, as well as high caffeine intake, have been investigated for their potential links to anxiety disorders. Decreased consumption of omega-3 PUFAs also has been associated with depression. A 2018 review examined the effects of PUFAs, specifically omega-6 and omega-3 fats, on anxiety and depression.8 Researchers concluded that low–omega-3 PUFAs may predispose some individuals to depression and anxiety. There’s some evidence that omega-3 DHA supplements may help treat anxiety disorders, but more research is needed.

The research has been less convincing for a relationship between tryptophan and anxiety disorders. A 2021 systematic review of 21 studies examined the link between acute tryptophan depletion (ATD) and anxiety disorders; researchers found no clear indication that ATD provokes anxiety. They concluded that the available studies were of poor quality and higher-quality research is needed to determine an association.9

Caffeine, which is consumed by 80% of American adults daily and considered the most widely used drug in the world, is associated with anxiety.10 Although caffeine boosts alertness, energy, and an overall feeling of well-being, overconsumption can lead to trouble sleeping, jitters, and gastrointestinal irritability and distress. According to the 2020–2025 Dietary Guidelines for Americans, the recommended daily maximum intake for caffeine is 400 mg per day, which is equivalent to four or five cups of coffee.

Caffeine has been shown to have some benefits for brain health; a 2013 study found that individuals who consumed caffeine had overall less cognitive decline compared with those who didn’t consume caffeine.11 However, a 2011 review of eight studies showed that caffeine aggravated symptoms of anxiety and panic disorder. Researchers concluded that individuals with underlying mental health issues may be more susceptible to symptoms caused by higher caffeine consumption.12

OCD is characterized by recurring, uninvited thoughts or ideas (obsessions) that make individuals feel driven to do something repetitively (compulsions).13 These compulsions, such as excessively checking on things, cleaning, or hand washing, tend to significantly interfere with daily activities and social interactions. Individuals with OCD have difficulty disengaging from obsessive thoughts or stopping the compulsive behaviors. Diagnosis of OCD requires experiencing obsessions and/or compulsions for more than one hour per day, which causes significant distress and impairs work or social functioning. OCD affects women more than men and often begins in childhood, adolescence, or early adulthood with an average age of onset of 19 years.13

According to some evidence, a healthful diet may play a role in making OCD symptoms more manageable. A 2021 systematic review examined 33 studies and lifestyle interventions that may be helpful to individuals with OCD. Researchers found that diet appears to be a promising intervention, although additional research is needed.14

Moreover, research has shown that insufficient intake of vitamin D, vitamin B12, omega-3 fats, and probiotics may be associated with OCD. A 2017 study of 82 children and adolescents (52 with OCD and 30 healthy controls) investigated whether vitamin B12, vitamin D, and homocysteine play a role in OCD. Participants were tested for vitamin B12, vitamin D, folate, and homocysteine levels. The results found a significantly lower level of vitamin B12 and vitamin D and higher levels of homocysteine in those with OCD compared with the control group. No significant difference in folate levels was found between the two groups. Researchers concluded that vitamin B12 and vitamin D deficiency and increased homocysteine levels may play a role in the etiology of OCD.15

A 2007 study critically reviewed double-blinded, placebo-controlled clinical trials to determine whether omega-3 PUFAs can be effective in helping to treat mental disorders, including OCD. Researchers found no difference between omega-3 supplementation compared with controls in one study, while other studies did show more positive findings when EPA and DHA were supplemented. Researchers determined that further clinical investigation is needed.16

Probiotic supplementation also has been studied in animals for a potential connection to OCD. A 2014 study examined probiotic pretreatment for OCD-like behavior induced in mice. Mice that received both a two- and four-week probiotic pretreatment experienced a decrease in the development of OCD-like behavior compared with those that received placebo. Researchers concluded that the probiotic appeared to reduce OCD-like behaviors from developing in mice. However, research is needed in humans.17

Bipolar Disorder
Research also has been done on the impact of nutritional interventions on bipolar disorder. This brain disorder causes changes in an individual’s mood, energy, and ability to function. Individuals with bipolar disorder experience episodes of intense emotional states that tend to occur for days or weeks. These episodes are characterized by periods of mania or hypomania (abnormal excitability and overactivity and, in mania, sometimes delusions and/or hallucinations), or depression (with symptoms akin to those seen in major depressive disorder). Mood fluctuations significantly affect daily routines and social interactions, disrupt relationships with family members and close friends, and make it difficult to work and go to school. Bipolar disorder has a strong genetic basis, with 80% to 90% of individuals affected having a relative with bipolar disorder or depression.18 The average age of onset is 25.

Researchers have studied the effects of PUFAs on improving mood symptoms of bipolar disorder. A 2020 study evaluated the efficacy of omega-3 PUFAs on the prevention of bipolar disorder. The study included 80 subjects with bipolar disorder who were randomly assigned to receive EPA and DHA or placebo over 52 weeks. Researchers measured mood episode relapses by the number of hospital admissions and medication changes the subjects experienced. The results showed no significant differences in the number of mood episode relapses or subjects requiring hospital admission or medication adjustments in the omega-3 PUFA group compared with placebo. Researchers concluded that there’s little evidence that omega-3 PUFA supplementation can help prevent bipolar disorder.19

A 2021 study examined the effects of various PUFA ratios on improving mood stability in bipolar disorder. The modified double-blinded randomized controlled 48-week study included 82 subjects. The intervention included a high–omega-3 and low–omega-6 diet vs a usual US level of omega-6 and omega-3 PUFAs (the control diet). Variability in mood, energy, irritability, and pain were reduced in subjects on the high–omega-3 and low–omega-6 diet compared with those on the control diet.20

Recommendations for Dietitians
Given the research on the associations between some dietary factors and certain mental health disorders, RDs have a unique skill set and therefore play an important role in counseling clients and patients, helping them achieve treatment goals and live more healthful and satisfying lives. According to the Academy of Nutrition and Dietetics (the Academy), “optimizing nutritional status improves cognitive and emotional functioning for individuals with mental illness and/or addictions.”21 For mental health nutrition, the Academy recommends a diet that includes complex carbohydrates, foods rich in omega-3 fatty acids, fruits and vegetables, foods limited in added sugars, and noncaffeinated beverages.21

What’s more, the Academy recommends RDs serve as core members of multidisciplinary teams that develop and coordinate treatment plans for patients in their effort to support those with mental illness. Multidisciplinary teams can include RDs, psychiatrists, psychologists, social workers, nurses, nurse practitioners, physician assistants, pharmacists, mental health technicians, substance abuse counselors, foodservice representatives, and therapists (eg, occupational, physical, vocational, and recreational). In addition, the Academy stresses that RDs must recognize the limits and boundaries of nutrition counseling vs psychotherapy and know when referrals to other team members are needed.

When counseling patients who have mental health disorders, RDs should conduct nutrition assessments to identify any possible comorbidities, such as CVD or type 2 diabetes, that may fall under nutrition care and to help pinpoint any risk factors such as unplanned weight loss, food insecurity, disordered eating, and gaps in nutrition knowledge. Once RDs make these necessary nutrition assessments, whether in a one-on-one counseling session, or in a hospital, inpatient, or outpatient setting, they can develop and recommend an appropriate nutrition plan to help improve patient outcomes.

— Toby Amidor, MS, RD, CDN, FAND, is the founder of Toby Amidor Nutrition (tobyamidornutrition.com) and a Wall Street Journal bestselling author. She’s written several cookbooks, including The Best Rotisserie Chicken Cookbook and The Family Immunity Cookbook: 101 Easy Recipes to Boost Health. She’s also a nutrition expert for FoodNetwork.com and a contributor to U.S. News Eat + Run and other national outlets.


1. Substance Abuse and Mental Health Services Administration. Reports from the 2016 National Survey on Drug Use and Health: detailed tables. https://www.samhsa.gov/data/sites/default/files/NSDUH-DetTabs-2016/NSDUH-DetTabs-2016.pdf. Published September 7, 2017. Accessed September 15, 2021.

2. Stress in America 2020: a national mental health crisis. American Psychological Association website. https://www.apa.org/news/press/releases/stress/2020/report-october. Published October 2020.

3. What is mental illness? American Psychiatric Association website. https://www.psychiatry.org/patients-families/what-is-mental-illness. Updated August 2018.

4. What is depression? American Psychiatric Association website. https://www.psychiatry.org/patients-families/depression/what-is-depression. Updated October 2020.

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

6. Ljungberg T, Bondza E, Lethin C. Evidence of the importance of dietary habits regarding depressive symptoms and depression. Int J Environ Res Public Health. 2020;17(5):1616.

7. What are anxiety disorders? American Psychiatric Association website. https://www.psychiatry.org/patients-families/anxiety-disorders/what-are-anxiety-disorders. Updated June 2021.

8. Larrieu T, Layé S. Food for mood: relevance of nutritional omega-3 fatty acids for depression and anxiety. Front Physiol. 2018;9:1047.

9. Schopman SME, Bosman RC, Muntingh ADT, van Balkom AJLM, Batelaan NM. Effects of tryptophan depletion on anxiety, a systematic review. Transl Psychiatry. 2021;11(1):118.

10. Lu S. Too much coffee? American Psychological Association website. https://www.apa.org/gradpsych/2015/11/coffee

11. Arab L, Khan F, Lam H. Epidemiologic evidence of a relationship between tea, coffee, or caffeine consumption and cognitive decline. Adv Nutr. 2013;4(1):115-122.

12. Vilarim MM, Araujo DMR, Nardi AE. Caffeine challenge test and panic disorder: a systematic literature review. Expert Rev Neurother. 2011;11(8):1185-1195.

13. What is obsessive-compulsive disorder? American Psychiatric Association website. https://www.psychiatry.org/patients-families/ocd/what-is-obsessive-compulsive-disorder. Updated December 2020.

14. Brierley ME, Thompson EM, Albertella L, Fontenelle LF. Lifestyle interventions in the treatment of obsessive-compulsive and related disorders: a systematic review. Psychosom Med. 2021;83(8):817-833.

15. Esnafoğlu E, Yaman E. Vitamin B12, folic acid, homocysteine and vitamin D levels in children and adolescents with obsessive compulsive disorder. Psychiatry Res. 2017;254:232-237.

16. Ross BM, Seguin J, Siesweda LE. Omega-3 fatty acids as treatments for mental illness: which disorder and which fatty acid? Lipids Health Dis. 2007;6:21.

17. Kantak PA, Bobrow DN, Nyby JG. Obsessive-compulsive-like behaviors in house mice are attenuated by a probiotic (Lactobacillus rhamnosus GG). Behav Pharmacol. 2014;25(1):71-79.

18. What is bipolar disorder? American Psychiatric Association website. https://www.psychiatry.org/patients-families/bipolar-disorders/what-are-bipolar-disorders. Updated January 2021.

19. McPhilemy G, Byrne F, Waldron M, et al. A 52-week prophylactic randomised control trial of omega-3 polyunsaturated fatty acids in bipolar disorder [published online December 19, 2020]. Bipolar Disord. doi: 10.1111/bdi.13037.

20. Saunders EFH, Mukherjee D, Myers T, et al. Adjunctive dietary intervention for bipolar disorder: a randomized, controlled, parallel-group, modified double-blinded trial of a high n-3 plus low n-6 diet [published online July 4, 2021]. Bipolar Disord. doi: 10.1111/bdi.13112.

21. Girard TA, Russell K, Leyse-Wallace R. Academy of Nutrition and Dietetics: revised 2018 standards of practice and standards of professional performance for registered dietitian nutritionists (competent, proficient, and expert) in mental health and addictions. J Acad Nutr Diet. 2018;118(10):1975-1986.e53.