Is your diet bad for your brain?

02 Dec 2022

If you’re struggling to focus, it may be the food you’re eating – or the food you’re missing out of your diet – that’s behind the problem

Does your concentration drift during the day? Can’t remember what happened in that box-set you binged on last night? You might blame feeling tired or run down, but diet plays an important role in how well your brain ticks over.

Discover some of the most common dietary triggers of ‘brain fog’, and tips to help keep your brain healthy.

Dehydration and concentration

Dehydration can affect your concentration and immediate memory – and you don’t have to be very dehydrated for it to affect your brain health, according to a review of studies by the University of Barcelona in 2012.

The Spanish researchers found that even being 2% less hydrated than the optimum level can affect your cognitive performance. That’s because mild dehydration can interfere with a number of brain processes, including neurotransmitter activity, lowering blood flow to the brain.1 The NHS recommends we drink six to eight glasses of fluid a day2 – try keeping a bottle on your desk to remind you to drink regularly.

Not eating enough omega-3

Omega-3 fatty acids – found in nuts, seeds, rapeseed oil, tofu, soya milk and oily fish – are vital for brain function, and a deficiency is thought to trigger a change in the structure of brain cell membranes.3,4 A 2013 study from Massey University, New Zealand, found that omega-3 improved mental performance and memory in adults.5 Other research has found that increasing your omega-3 intake could boost working memory – the short-term memory that helps you carry out tasks.6

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Overdoing the caffeine

If you rely on a morning coffee to before work, be warned: a review of studies, published in 2015 in the journal Current Neuropharmacology, suggests the ‘brain-sharpening’ effects are purely down to relief from the symptoms of caffeine withdrawal, such as difficulty concentrating, tiredness and low mood.7,8 The study also found too much caffeine – from tea, coffee, chocolate and some soft drinks – can make you anxious and jittery, affecting your concentration.9 Go easy on the lattés and maybe switch to some coffee alternatives instead.

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Missing out on B vitamins

This group of eight vitamins is essential for brain health, but although B vits are found in a wide range of foods – including green leafy veg and wholegrains – deficiency is possible in those consuming western diets rich in refined carbohydrates and low in vegetables.

A 2016 review by Northumbria University found a B-vitamin deficiency can result in short-term problems such as low energy and mood, while in the longer term, reduced levels of B vitamins have been linked with a higher risk of cognitive decline and dementia.11 This may be because lacking B vits results in higher levels of homocysteine, a by-product of protein metabolism which can trigger internal inflammation, affecting everything from your brain to your heart health.12,13

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Too few flavonoids

Flavonoids are a class of polyphenols – active compounds found in fruit, veg and other plant foods that are believed to have benefits for human health and wellbeing.14 A review of emerging studies, published in Nutrients in 2015, reported that flavonoids can help boost many aspects of concentration, including attention, psychomotor processing speed – the relationship between your thoughts and your actions – and working memory, which temporarily holds information to be processed. Tuck into berries, apples, grapes, green tea, oranges and chocolate to get your fill of flavonoids.15

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Advice is for information only and should not replace medical care. Please check with your GP before trying any remedies.

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1. Adan A. Cognitive performance and dehydration. Available from:
2. NHS Choices. Water, drinks and your health. Available from:
3. British Dietetic Association. Omega-3. Available from:
4. Bourre JM. Roles of unsaturated fatty acids (especially omega-3 fatty acids) in the brain at various ages and during ageing. Available from:
5. Stonehouse W, et al. DHA supplementation improved both memory and reaction time in healthy young adults: a randomized controlled trial. Available from:
6. Narendran R, et al. Improved Working Memory but No Effect on Striatal Vesicular Monoamine Transporter Type 2 after Omega-3 Polyunsaturated Fatty Acid Supplementation. Available from:
7. Cappelletti S, et al. Caffeine: Cognitive and Physical Performance Enhancer or Psychoactive Drug? Available from:
8. Healthline. 8 Signs and Symptoms of Caffeine Withdrawal. Available from:
9. As Source 7
10. Kennedy DO. B Vitamins and the Brain: Mechanisms, Dose and Efficacy – A Review. Available from:
11. As above
12. EMedicineHealth. What Are the Health Risks for Elevated Homocysteine Levels? Available from:
13. Wu JT. Circulating Homocysteine Is An Inflammation Marker And a Risk Factor of Life-Threatening Inflammatory Diseases. Available from:
14. Medical News Today. Why are polyphenols good for you? Available from:
15. Bell L, et al. A Review of the Cognitive Effects Observed in Humans Following Acute Supplementation with Flavonoids, and Their Associated Mechanisms of Action. Available from:

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