Dr Sean Brennan

Diet

Nutritional psychiatry is a young field, but the direction of the evidence is consistent: dietary pattern matters for mood, and improving it produces measurable benefit even in established depression.

What the evidence shows

• Mediterranean-style eating has trial evidence in depression. The SMILES trial (2017) randomised adults with moderate-to-severe depression to dietary support or social support; the diet group had significantly greater improvement, with roughly a third achieving remission. Subsequent trials and meta-analyses point the same way.
• The pattern matters more than any single food. Vegetables, fruit, legumes, wholegrains, nuts, olive oil, fish; less ultra-processed food, refined sugar and takeaway. No single ingredient carries the effect.
• Ultra-processed food is consistently associated with worse mental health in observational data. Causality is harder to prove, but there is no version of the evidence in which eating more of it helps.
• Stability matters. Regular meals stabilise energy, and for people on medications that affect appetite or weight, meal structure is part of managing the medication — not separate from it.

Practical starting points

• Anchor two changes, not ten: oily fish twice a week, and vegetables or legumes at two meals a day.
• Swap, don't just remove — replace refined snacks with nuts or fruit rather than relying on willpower against an empty cupboard.
• If weight has changed on psychiatric medication (mirtazapine, olanzapine, quetiapine and valproate are common culprits), raise it — medication choice and dose are legitimate levers, not just diet.

Dietary change supports treatment; it does not replace it. If eating is entangled with distress — restriction, bingeing or purging — please raise this directly at your appointment rather than attempting a new dietary regime.

Exercise

For mild-to-moderate depression, exercise has effect sizes comparable to antidepressants or psychotherapy in meta-analyses — and unlike either, it also improves cardiovascular health, sleep and cognition. It is treatment, not decoration.

What the evidence supports

• Dose: around 150 minutes per week of moderate activity is the standard target, but benefit begins well below that. Going from nothing to two brisk 20-minute walks a week is the steepest part of the curve.
• Intensity helps. A large 2024 network meta-analysis found walking, jogging, strength training and yoga all effective for depression, with higher-intensity activity tending to work better.
• Strength training is underrated. Resistance exercise two or more times weekly has independent antidepressant and anti-anxiety effects, and preserves muscle and metabolic health — particularly relevant on weight-affecting medications.
• Outdoors adds value. Exercise in daylight combines the activity effect with the circadian light effect. One walk, two mechanisms.
• Consistency beats heroics. The adherence problem is the real problem. Choose the activity you will still be doing in three months, not the optimal one you will abandon in two weeks.

When mood makes it hard

Depression attacks motivation first, which is precisely why "just exercise" is unhelpful advice on its own. Start below what feels meaningful — five minutes counts. Schedule it like an appointment rather than waiting for motivation, which follows action rather than preceding it. If anergia is profound, that is clinical information; tell me, because treating the depression may need to come before the exercise can.

If you have cardiac disease, are markedly deconditioned, or take medications affecting heart rate or blood pressure, see your GP before starting vigorous exercise.

Supplements

The supplement industry is large, loosely regulated and enthusiastic. A small number of compounds have credible evidence in psychiatry; most do not. Below is an honest ledger.

Reasonable evidence

• Omega-3 (EPA-predominant), 1–2 g EPA daily — modest adjunctive benefit in depression in meta-analyses, particularly formulations that are ≥60% EPA. Weak or no evidence as monotherapy or for prevention.
• Vitamin D — if deficient. Correcting deficiency is sensible and cheap; supplementing a replete person has no demonstrated mood benefit. Test first.
• Creatine monohydrate, 3–5 g daily — emerging adjunctive evidence in depression alongside its established benefits for muscle and possibly cognition. Safe in healthy kidneys.
• Magnesium — small trials suggest modest benefit in mild depression and anxiety; plausible for sleep in those with low intake. Glycinate or citrate forms are better tolerated than oxide.
• N-acetylcysteine (NAC), 2–2.4 g daily — mixed but genuine trial evidence as an adjunct in depression, bipolar depression and some compulsive behaviours. Effects are slow, over months.

Use with real caution

• St John's Wort — has genuine antidepressant efficacy, and precisely because of that it interacts dangerously: serotonin syndrome risk with antidepressants, and it induces liver enzymes that lower levels of many drugs, including oral contraceptives. Do not combine with prescribed antidepressants, and always disclose it.
• 5-HTP and SAMe — serotonergic; the same interaction concerns apply when combined with antidepressants. Disclose before use.
• "Nootropic" blends and proprietary formulas — undisclosed doses, untested combinations, and occasionally undeclared pharmaceutical ingredients. Avoid.

Principles

• Treat supplements as drugs: they have doses, interactions and side effects, and I need to know about them to prescribe safely.
• One change at a time, with a defined trial period (8–12 weeks) and a decision at the end — continue or stop.
• Money spent on sleep, food quality and exercise reliably outperforms money spent on capsules.

This information is general in nature and not a substitute for individual medical advice. Always tell your prescriber about every supplement you take, and check interactions before starting anything new — especially alongside antidepressants, lithium or anticonvulsants.