Mood, Inflammation and Nutrition

The idea that food affects mood is ancient and intuitive. Its scientific investigation is much newer, and it has produced a field sometimes called nutritional psychiatry. Some of its findings are among the most interesting in modern mental health research; others have been overstated. Alongside it, research into inflammation has offered a biological explanation for why some people’s depression may be linked to their physical health. This article reviews both, with attention to what practitioners can responsibly offer.

Inflammation and depression

Several lines of evidence link inflammation and depression.

• Induced depression. People treated with interferon alpha, an inflammatory cytokine used in the past for hepatitis C and some cancers, frequently developed depressive symptoms, which could be reduced by antidepressant treatment started beforehand. This provides direct evidence that inflammation can cause depressive symptoms.
• Raised markers. On average, people with depression have higher levels of inflammatory markers such as C reactive protein and interleukin 6 than people without it. Meta analyses suggest that roughly a quarter of people with depression have low grade inflammation.
• Sickness behaviour. Inflammatory signals produce a pattern of fatigue, low mood, social withdrawal and reduced motivation, which overlaps with depressive symptoms.
• Treatment response. Raised inflammation has been associated with poorer response to some antidepressants.
• Comorbidity. Depression is more common in inflammatory conditions such as rheumatoid arthritis, inflammatory bowel disease, obesity and cardiovascular disease.

These findings suggest that, for some people, depression may have an inflammatory component. They do not mean that all depression is inflammatory, and anti inflammatory treatments are not established treatments for depression, although trials of them as adjuncts are ongoing.

Diet and depression

Observational evidence

Observational studies have associated Mediterranean style and other healthy dietary patterns with lower risk of depression, and diets high in ultra processed foods, sugar and refined carbohydrates with higher risk. These associations could partly reflect reverse causation, since depression affects appetite and food choice, and confounding by other lifestyle factors.

Intervention trials

The SMILES trial randomised adults with moderate to severe depression to 12 weeks of dietary support from a dietitian, promoting a modified Mediterranean diet, or to social support. The dietary group showed significantly greater improvement in depressive symptoms, and a third achieved remission compared with less than a tenth of the control group. Another trial providing Mediterranean diet education and fish oil supplements to people with depression also reported improvement. These trials were relatively small and could not blind participants, and not every subsequent trial has been positive, but they suggest that dietary improvement can be a useful adjunct to standard treatment.

Specific nutrients

Exercise: a treatment in its own right

Exercise has substantial evidence as a treatment for depression. A large network meta analysis of randomised trials found that walking or jogging, yoga, strength training and mixed aerobic exercise all reduced depressive symptoms, with effects comparable to psychotherapy and medication in some comparisons, and larger effects with more vigorous activity. Exercise also improves sleep, reduces anxiety and benefits physical health, making it one of the most valuable interventions available.

Other lifestyle factors

• Sleep: insomnia is both a symptom of and a risk factor for depression; cognitive behavioural therapy for insomnia can improve mood.
• Alcohol: worsens depression and interacts with medications.
• Social connection: loneliness is a strong risk factor for depression.
• Blood sugar stability: large swings in glucose can affect energy and irritability; regular balanced meals help many people feel steadier.
• Physical health: treating conditions such as hypothyroidism, anaemia and sleep apnoea can improve mood.

Safety and scope

Nutritional and lifestyle approaches complement, rather than replace, evidence based mental health care. Depression can be serious and life threatening. Practitioners should:

• ask about suicidal thoughts when depression is present and know how to respond and refer urgently;
• coordinate with the patient’s doctor or mental health team;
• never advise stopping antidepressants, which should be tapered only under medical guidance;
• check for interactions, for example between St John’s wort and many medicines, including antidepressants, where the combination can cause serotonin syndrome;
• be cautious with restrictive diets in people with a history of eating disorders.

A practical approach

1. Screen for depression using validated tools, and assess risk.
2. Look for physical contributors: thyroid, anaemia, B12 and folate, vitamin D, sleep apnoea, medicines, alcohol.
3. Support dietary improvement towards a Mediterranean style pattern, adapted to the person’s cuisine and circumstances.
4. Prescribe exercise that the person can realistically do.
5. Address sleep and social connection.
6. Consider evidence based adjuncts, such as EPA predominant omega 3, in discussion with the treating clinician.
7. Coordinate care with mental health professionals.

An illustrative case

A 35 year old man with moderate depression is taking an antidepressant with partial benefit. He eats mostly takeaway food, drinks heavily at weekends, rarely exercises and sleeps poorly. His assessment finds a raised CRP, low vitamin D and a waist circumference suggesting visceral adiposity. With his psychiatrist’s agreement, his plan adds dietary support towards a Mediterranean style pattern, a structured walking and strength programme, reduced alcohol and correction of vitamin D. An EPA predominant omega 3 supplement is discussed with his psychiatrist and started. Over 3 months his mood, sleep and energy improve substantially, and his CRP falls. His antidepressant continues, now working alongside a healthier foundation.

Food, movement and mind

The links between nutrition, inflammation and mood are real, and the evidence for dietary improvement and exercise as adjuncts to depression treatment is encouraging. Offered alongside, not instead of, established mental health care, they give practitioners meaningful ways to help people feel better.