Omega-3 foods: which oily fish count in the UK, and what plants really give

Author: Adrianna Kalista

Adrianna Kalista

Passionate about writing and a graduate in clinical dietetics. She is particularly interested in phytotherapy and the effects of ketogenic nutrition on cognitive brain function.

Verification: Dr. Andreia Torres

Dr. Andreia Torres

Clinical nutritionist with a doctorate in health education. International expert in ketogenic nutrition.

Which foods are high in omega-3?

Which foods are high in omega-3? Foods high in omega-3 EPA and DHA are oily fish: the NHS lists herring, including kippers, pilchards, salmon, sardines, sprats, trout and mackerel [9]. The practical split is simple: EPA, DHA and ALA are all omega-3 fats, but the UK oily-fish list is about EPA and DHA, while plants such as flaxseed, chia, walnuts and rapeseed oil supply ALA [1]. Fish get EPA and DHA mainly from their diet, because microalgae and other marine microorganisms at the base of the marine food chain produce them [1]. Fish can produce EPA and DHA themselves only to a limited, species-dependent extent [1]. Tuna has EPA and DHA, but fresh and canned tuna do not count as oily fish in NHS advice [9].

Which fish is the best source of omega-3?

Which fish is the best source of omega-3? The best fish for omega-3 is any oily fish listed by the NHS, but the amount depends on what the fish ate [9]. In an RCT of 51 people eating salmon fed fish oil or rapeseed oil, salmon fed fish oil had 2.1 g EPA plus DHA per 100 g of fillet, salmon fed rapeseed oil had 0.9 g, and health benefits in eaters were not smaller in the rapeseed group [3]. In 1,108 farmed salmon samples from Norway, median EPA plus DHA fell by more than 60% between 2005 and 2020 as fish oil in feed was replaced by plant oils [2]. One 175 g portion of farmed salmon still covers an adult’s weekly adequate intake of EPA and DHA as set by EFSA [2]. For a wider keto view, see which fish to eat on keto.

Does tuna have omega-3?

Does tuna have omega-3? Tuna has some omega-3, but the NHS does not count fresh or canned tuna as oily fish [9]. Tuna also carries more mercury than oily fish: in EFSA data from over 12,000 results in 20 countries, the European mean was 0.29 mg/kg for tuna, against 0.03 mg/kg for salmon and trout [8]. The UK legal maximum for mercury in tuna is 1.0 mg/kg [11]. In the FSA retail survey 2025/26, 2 of 50 raw tuna samples exceeded it, while all 40 ready-to-eat tuna products complied [11]. If you are pregnant or trying for a baby, the NHS says you should have no more than 4 medium cans, about 140 g drained each, or 2 tuna steaks, 140 g cooked, a week [9]. There is no tuna limit when breastfeeding [9].

How much oily fish should you eat a week?

How much oily fish should you eat a week? The NHS advises at least 2 portions of fish a week, 1 of them oily, and a portion is around 140 g cooked [9]. SACN, whose 450 mg long-chain omega-3 a day is a population guideline, not a formal DRV, calculated that two portions of fish a week, one white and one oily, provide about that amount [10]. For the detail behind daily intake, see how much omega-3 per day. There is also an upper limit, because pollutants such as dioxins and PCBs can build up in the body [9]. The NHS says no more than 2 oily portions a week for girls, women who may become pregnant, pregnant women and breastfeeding women, and up to 4 for boys, while SACN (2004) puts the range for men at 1 to 4 portions a week [9][10]. UK adults aged 19 to 64 ate an average of 56 g of oily fish a week in NDNS Years 9 to 11 (2016/17 to 2018/19) [12].

Planning your oily fish portions?

A tin of sardines or a fillet of smoked mackerel makes a quick lunch on keto bread. See the keto breads range in the BeKeto shop.

Shop keto breads

Which plant foods contain omega-3?

Which plant foods contain omega-3? Plant foods such as flaxseed, chia seeds, walnuts and rapeseed oil contain omega-3 as ALA, not EPA or DHA. The body converts little: in isotope studies, young women given 700 mg labelled ALA converted an estimated net 21% to EPA and 9% to DHA over 21 days, while in 6 young men EPA and DPA were formed but labelled DHA was not detected [4]. That is why claims about chia seeds and omega-3 can mislead if they compare ALA with fish EPA and DHA. ALA supplementation raises EPA in blood but has little effect on DHA [5]. In a review of 13 RCTs from 2010 to 2020, high-dose flaxseed or echium oil did not raise the omega-3 index, while microalgal oil raised it in every included study [5]. For fish-free EPA and DHA, read our guide to vegan omega-3.

Can you get enough omega-3 from food on keto?

Can you get enough omega-3 from food on keto? You can get enough omega-3 from food on keto if oily fish is on the menu; a keto diet built on meat, dairy, nuts and plant oils gives far less EPA and DHA [6]. For food-first planning, see omega-3 on keto. We found no human trials of omega-3 supplements in adults on a ketogenic diet [6]. In UK Biobank, 117,108 people had an estimated mean omega-3 index of 5.58%, from plasma NMR rather than red blood cells, in the low range [7]. UK Biobank is not a representative sample, so that is not “the average UK omega-3 index” [7]. In the same analysis, oily fish and fish oil supplements were the strongest positive predictors of the omega-3 index, and oily fish accounted for 7.0% of the explained variation [7]. If food choices leave gaps, compare keto supplements that fit a keto diet, including algal oil.

What if you do not eat oily fish: how does BeKeto MEGA Omega compare?

What if you do not eat oily fish: how does BeKeto MEGA Omega compare? For weeks without oily fish, MEGA Omega 3 vegan algae oil comes out best for keto eaters who avoid fish, because one 5 ml teaspoon gives 570 mg DHA and 185 mg EPA, above the SACN guideline of 450 mg long-chain omega-3 a day, from the same source fish rely on: microalgae [13][10][1]. It is Schizochytrium sp. microalgae oil, with Sicilian lemon flavour, and it is fish-free, free from allergens requiring declaration and vegan [13]. Use the recommended daily 5 ml serving straight from the spoon or in cold dishes; do not exceed it. “This product is intended for adults. Not for use by children or by women who are pregnant or breastfeeding. If you take anticoagulant medication or are due to have surgery, consult your doctor before use.” [13]

Oily fish not on your menu?

Flaxseed and walnuts provide ALA, not EPA or DHA. MEGA Omega 3 Vegan is a fish-free algae oil with 570 mg DHA and 185 mg EPA in 5 ml.

£25.90

Buy MEGA Omega 3

This product is intended for adults. Not for use by children or by women who are pregnant or breastfeeding. If you take anticoagulant medication or are due to have surgery, consult your doctor before use.

Frequently asked questions (FAQ)

Discover more in the BeKeto keto shop

Besides supplements, the shop has keto vitamins, snacks and bread.

Keto Supplements

Shop keto supplements

Keto Vitamins

Shop keto vitamins

Keto Snacks

Shop keto snacks

Keto Breads

Shop keto breads

Bibliography