As the clocks go back and the evenings draw in, many of us notice a shift in how we feel. Energy dips, sleep changes, and motivation can be harder to find. For some people this is a passing seasonal lull, and for others it develops into seasonal affective disorder (SAD), which is worth discussing with your GP.
Less daylight affects the body clock and the hormones that regulate sleep and mood, including melatonin and serotonin. Light is the first lever (a morning walk counts, even on grey days), and what we eat shapes how well the brain copes with the change.
Your brain is built from food
Every part of the nervous system is made and maintained from what we eat.
Cell structure. The membranes around brain cells are built from fats, including the omega-3 fat DHA, which affects how well those cells send and receive signals.
Myelin. The fatty sheath that insulates nerve fibres and speeds up signals depends on vitamin B12 and iron to form and repair.
Neurotransmitters. Serotonin is made from the amino acid tryptophan, and dopamine from tyrosine. Each step needs helpers such as vitamin B6, folate, iron, zinc and magnesium.
Hormones. Stress and thyroid hormones, both closely tied to mood, rely on nutrients including iodine, selenium and zinc.
The gut-brain axis. Gut microbes ferment fibre into short-chain fatty acids and communicate with the brain through the vagus nerve, the immune system and tryptophan metabolism (Cryan et al., 2019). Two groups of these fibre-fermenting bacteria are consistently lower in people with depression, even after accounting for antidepressant use (Valles-Colomer et al., 2019).
What food can and can't do
Nutrition helps the brain respond to what life brings, from inside and outside the body. It can't change our circumstances, the beliefs we hold, or the genes we were born with. It works best as one part of a wider picture that may include movement, time with people we care about, a sense of purpose and, for some, prescribed medication. (If you take antidepressants, please talk to your GP before changing anything.)
Most of the research looks at whole ways of eating, and the Mediterranean diet is the most studied. A 2025 meta-analysis of five trials in adults with depression found it reduced symptoms by a moderate amount (Bizzozero-Peroni et al., 2025), including the SMILES trial, where 32% of participants reached remission compared with 8% in the control group (Jacka et al., 2017). A second review, limited to people diagnosed with major depression, found no clear effect (Tavakoly et al., 2025). The trials are small, so the picture is still forming.
Across 42 trials of anti-inflammatory diets, improvements were most consistent for depression and in people who already had symptoms, with mixed results for anxiety (Sprengel et al., 2026). The ketogenic diet is newer to this field. In an Oxford trial of adults with treatment-resistant depression, both a ketogenic diet and a vegetable-rich comparison diet led to large improvements, with the ketogenic group slightly ahead at six weeks (Gao et al., 2026).
Foundations first: protein, fats and fibre
Micronutrients get most of the attention, yet they work on top of a foundation of protein, fats and fibre.
Protein supplies the amino acids the brain uses to make neurotransmitters, and steadies blood sugar, which keeps energy and mood more even through the day. Include some at each meal (eg, eggs, fish, chicken, Greek yoghurt, tofu, tempeh or lentils). If breakfast is usually toast or cereal, that is the easiest place to start.
Healthy fats. Omega-3 fats become part of brain cell membranes and help regulate inflammation. In a meta-analysis of 26 trials, omega-3 supplements with a higher proportion of EPA improved depressive symptoms (Liao et al., 2019). The richest food sources are oily fish (eg, salmon, mackerel, sardines). Walnuts, chia and flaxseeds provide a plant form, which the body converts into EPA and DHA only in small amounts. Olive oil, avocado, nuts and seeds add other healthy fats.
Fibre feeds the gut bacteria that produce short-chain fatty acids. Variety matters as much as quantity, because different bacteria thrive on different plant foods (eg, oats, beans, vegetables, berries, nuts and seeds).
Fermented foods bring live bacteria of their own (eg, kimchi, sauerkraut, miso, kefir, live yoghurt, kombucha). In a 17-week trial, a diet rich in fermented foods increased gut microbiome diversity and lowered markers of inflammation (Wastyk et al., 2021).
The micronutrients that matter most
Once the foundation is in place, a handful of micronutrients stand out in the research.
Magnesium plays a part in the stress response and supports GABA, the brain's main calming messenger. In adults with mild to moderate depression, magnesium improved depression and anxiety scores within two weeks, though participants knew what they were taking (Tarleton et al., 2017). Good sources include leafy greens, pumpkin seeds, almonds, beans and wholegrains.
Zinc supports neurotransmitter signalling and the brain's ability to adapt. People with depression tend to have lower zinc levels, and lower levels track with more severe symptoms (Swardfager et al., 2013). Good sources include shellfish, red meat, pumpkin seeds, chickpeas and cashews.
B vitamins (B6, folate, B12) help make serotonin and dopamine, and maintain myelin. B12 deficiency becomes more common with age, with plant-based diets, and with some medications, including metformin and acid-reducing drugs. Good sources include eggs, meat, fish, leafy greens and pulses.
Iron is the less obvious one. It carries oxygen to the brain and helps make serotonin and dopamine. Adults with iron deficiency anaemia have a higher risk of depression, anxiety and sleep disorders, and treatment with iron is linked to a lower risk (Lee et al., 2020). This is particularly relevant for women with heavy periods, and iron is one to test (ask for ferritin by name) rather than supplement on a hunch. Good sources include red meat, sardines, eggs, lentils and dark leafy greens.
Vitamin D: the exception
Vitamin D is the one nutrient where food alone falls short. We make most of it in our skin from sunlight, and between October and March the UK sun is too weak for that. Oily fish and egg yolks provide only small amounts.
For people who already have low mood, the evidence is encouraging. A meta-analysis of 31 trials found vitamin D3 reduced depressive symptoms, with a larger effect in people who had symptoms to begin with, and the clearest benefit within the first six months (Ghaemi et al., 2024). A 2026 meta-analysis of 15 trials in people diagnosed with depression reached a similar conclusion, although results varied considerably between studies (Liu et al., 2026). Neither showed a clear effect on anxiety. Because starting levels vary so much, vitamin D is worth testing before deciding how much you need.
Putting it on the plate
A few things are worth reducing:
Sugar and refined carbohydrates. Fast rises and falls in blood sugar trigger stress hormones such as adrenaline and cortisol, which can show up as irritability, anxiety and an afternoon crash.
Ultra-processed foods. A review of 45 meta-analyses linked higher intake with a higher risk of anxiety and depression (Lane et al., 2024). These are associations, though ultra-processed foods also crowd out the whole foods that supply the nutrients above.
Alcohol. It is a depressant, it breaks up sleep in the second half of the night, and it increases the loss of magnesium and B vitamins.
Then build meals around protein and healthy fats from whole foods, which bring many of the key micronutrients with them.
Oily fish (eg, salmon, mackerel, sardines) provides protein, omega-3 fats, vitamin D and B12, and eggs offer protein, B12 and a little vitamin D. Red meat (eg, beef or lamb) is one of the richest sources of iron, zinc and B12. Pulses (eg, lentils, chickpeas, beans) combine protein and fibre with folate, magnesium and iron, which makes them useful for plant-based eaters too.
Avocado, nuts (eg, almonds, walnuts) and pumpkin seeds add healthy fats alongside magnesium, with pumpkin seeds also providing zinc and iron. Leafy greens (eg, spinach, kale), oats and wholegrains bring fibre, folate, magnesium and B vitamins. Adding fermented foods (eg, kimchi, sauerkraut, miso or kefir) brings live bacteria, and kefir and yoghurt add protein as well.
Going further with personalised nutrition
General guidance is a good place to start, and for many of us it covers a lot of ground. A personalised protocol goes further. It takes into account your stress load, any medication (some affect nutrient levels or interact with supplements), your lifestyle, medical history and test results, and, where useful, genetics. Standard NHS blood tests rarely include magnesium or zinc, and functional testing can fill those gaps if necessary. My work supports mood, energy and resilience alongside medical care, never instead of it.
From there, I bring dietary, supplement and lifestyle recommendations together into a plan that fits your life and changes as you do. If you would like to explore what that could look like for you, you can book a free clarity call.
