Omega 3 is essential to good gut health – this is why you should eat oily fish twice a week
If oily fish is spoken about in relation to your health, it’s usually to do with your brain. And with good reason too. What might surprise you is that it’s also good for your gut microbiome, even though it doesn’t contain any fibre. Fish contain fats called omega-3s that influence your brain and your gut microbiome.
What are Omega-3 foods?
Omega-3s help your gut bacteria to produce more of your helpful short-chain fatty acids. Those who have higher levels of omega-3s in their blood have been shown to have a more diverse gut microbiome and more ‘good’ bacteria, even if they don’t eat much fibre. Surprisingly, fish can also contain a small amount of polyphenols but only because they eat polyphenol-rich algae which can transfer and accumulate in their body.
Let’s circle back to your brain and omega-3s though. Your brain is made up of 75 per cent water, but if you were to hang your brain out to dry, 60 per cent of what remains is made up of fat. And one-third of this fat is omega-3s, or specifically mostly a type of omega-3 called DHA. Omega-3s are crucial in determining how well your brain functions at all stages in life.
There are three main omega-3s:
- Docosahexaenoic acid (DHA)
- Eicosapentaenoic acid (EPA)
- Alpha-linolenic acid (ALA)
It’s DHA that’s particularly important for your brain as it makes up part of the membranes of your brain cells, including your neurons. And you need to get it from food to get enough DHA for your brain.
Fish is a great source of DHA, however, you can find the omega-3 ALA in plant foods like walnuts, flaxseeds and chia seeds. The problem is that ALA converts very poorly to the DHA that your brain particularly needs, so it can be harder to get enough.
So, should we eat more fish?
A 2019 meta-analysis of randomised controlled trials found that supplementing 1g or more of omega-3s (DHA and EPA) a day significantly helped ease depressive symptoms. While a supplement isn’t the same as a piece of fish, it does suggest that perhaps we should be eating more than the current national guidelines of at least one portion of oily fish a week (that only provides half the amount of omega-3s suggested above).
The SMILES trial on food and mood recommended at least two portions of oily fish a week, providing at least 6g of omega-3s – a similar weekly amount to the omega-3 supplements in the meta-analysis on depression.
Regular fish eaters tend to retain more grey matter in key brain regions like the hippocampus and prefrontal cortex in later life, which is linked with better cognitive function and is considered a positive sign of brain health.
Eating more than four portions of fish a week, and not just oily fish (that’s double the national guidelines), is linked to a slower age-related decline in memory. And those who eat more fish tend to have memory abilities in later life similar to those four years younger. In fact, researchers who evaluated the lifestyles of nearly 8,000 participants over five to ten years found that eating fish was one of the most important dietary factors in having better mental faculties than your peers – and who secretly doesn’t want to be mentally running circles around everyone else?
So let’s find your fishy tipple and go for it – be it sushi, fish curry, smoked salmon with scrambled eggs or pulling out all the stops and throwing a whole fish on the summer BBQ stuffed with aromatic herbs and lemon.
DHA omega-3 is nothing without its friends
Fish is not only a great source of protein and omega-3s but also contains B vitamins, choline and iron which are important for brain health and work together with the omega-3 DHA.
DHA, like any superstar, need a behind-the-scenes team to make it shine. DHA relies on B vitamins and choline to be able to do its job – it just doesn’t work as well without them. This likely explains why there’s some frustrating confusion around omega-3 supplements and mood and cognition, with some studies showing an effect, and some nothing.
DHA relies on other nutrients to be able to reach your brain, like B vitamins and choline – because who likes to rock up to a party on their own? Only the very brave – most of us would like at least a friend or two with us before making an entrance. For DHA to be used by your brain it needs to ‘arrive’ as another type of fat called phosphatidylcholine where DHA is bound with choline by your B vitamins – and only then can Cinderella go to the ball. It’s phosphatidylcholine that is important for the cell membranes of the neurons in your brain and is essential for them to function properly. You can also find choline in meat and eggs, and B vitamins in dark-green leafy veg.
I don’t eat fish – how can I get omega-3 foods in my diet?
Plant sources of omega-3s like walnuts, flaxseeds and chia seeds contain ALA, which your body struggles to convert to DHA. Some algae, though, do naturally produce DHA and EPA. Algae oil supplements can be a great choice instead of fish or fish oil omega-3 supplements if you’re a vegan or vegetarian, if you can’t eat fish, choose not to, or simply don’t like it. And try to make sure you’re eating enough foods high in B vitamins like dark-green leafy veggies, whole grains and beans.
This is an edited extract from Genius Gut by Dr Emily Leeming, published on 25 July 2024 (Penguin Michael Joseph), £18.99.
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Omega 3 is critical for your health - yet, according to a global survey, in the UK, we have some of the lowest blood levels of omega 3.
What are the benefits of omega 3?
Omega 3 helps your gut bacteria to produce more short-chain fatty acids. Studies have shown that those who have higher levels of omega 3 in their blood have a more diverse gut microbiome and more 'good' bacteria.
How much omega-3 fatty acids should we have per day?
A 2019 meta-analysis of randomised controlled trials found that supplementing 1g of more of omega 3s a day significantly helped to ease depressive symptoms. While a supplement isn't the same as a piece of fish, it does suggest that perhaps we should be eating more than the current guidelines of at least one oily fish a week.
What foods contain omega-3?
Fish is a great source of omega-3, however, you can find omega-3s in plant foods like walnuts, flaxseeds and chia seeds. It is worth noting, though, that plant sources of omega-3 contain ALA (Alpha-linolenic acid) which your body struggles to convert to DHA (Docosahexaenoic acid) – and it's DHA which is the important omega 3 for your brain.
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