Omega-3: what it is, what it does and where to get it (UK guide)

What are omega-3 fatty acids?

What are omega-3 fatty acids? Omega-3 fatty acids are a family of polyunsaturated fats, and three are most relevant in food: ALA from plants, plus EPA and DHA from marine sources. EPA and DHA are made at the base of the marine food chain by microalgae and other marine microorganisms; fish obtain them mainly from their diet and can make them only to a limited, species-dependent extent [1]. ALA is the plant form, found in foods such as flaxseed, chia, walnuts and rapeseed oil. The body turns ALA into EPA and DHA only in small amounts. In isotope studies, young women given 700 mg labelled ALA converted an estimated net 21% to EPA, 6% to DPA and 9% to DHA over 21 days, while labelled DHA was not detected in 6 young men [3]. In practice, this is the distinction: plant omega-3 is useful, but it is not the same as eating oily fish or taking algal oil.

Omega-3	Full name	Chain length	Main food sources	Net conversion from ALA in young women [%]	In young men
ALA	alpha-linolenic acid	short	flaxseed, chia, walnuts, rapeseed oil	not applicable	not applicable
EPA	eicosapentaenoic acid	long	oily fish, microalgae	21	formed
DHA	docosahexaenoic acid	long	oily fish, microalgae	9	not detected

What does omega-3 do in the body?

What does omega-3 do in the body? What omega-3 does in the body can be stated cleanly only through the GB register wording, because each authorised claim has a daily dose condition. At 250 mg EPA and DHA a day: “EPA and DHA contribute to the normal function of the heart” [30]. At 250 mg DHA a day: “DHA contributes to maintenance of normal brain function” [30]. At 250 mg DHA a day: “DHA contributes to the maintenance of normal vision” [30]. At 2 g EPA and DHA a day: “DHA and EPA contribute to the maintenance of normal blood triglyceride levels” [30]. At 3 g EPA and DHA a day: “DHA and EPA contribute to the maintenance of normal blood pressure” [30]. In a meta-analysis of 64 RCTs, triglycerides fell by about 0.10 mmol/L per gram of omega-3 from fish oil; total cholesterol did not fall [15]. For what the evidence shows for each condition, read omega-3 benefits.

Do omega-3 supplements lower heart attack risk?

Do omega-3 supplements lower heart attack risk? Whether omega-3 supplements lower heart attack risk is mixed in trial summaries, and the overall cardiovascular picture is more mixed. Across 40 trials with 135,267 people, EPA and DHA reduced heart attacks by about 13% (RR 0.87) and coronary death by about 9% (RR 0.91), but total cardiovascular events were not significantly reduced (RR 0.95), with larger effects at higher doses; the meta-analysis was funded by GOED, the omega-3 industry body, and its lead author works for GOED [16]. In VITAL, 1 g a day for a median 5.3 years in 25,871 US adults did not significantly reduce major cardiovascular events (HR 0.92) but reduced total heart attacks (HR 0.72) [17]. REDUCE-IT was not a supplement trial: with 4 g prescription icosapent ethyl, pure EPA, composite events were 17.2% versus 22.0% (HR 0.75), while STRENGTH used 4 g EPA plus DHA versus corn oil and was stopped: 12.0% versus 12.2% (HR 0.99) [18].

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, not all fish, and not every food that contains plant fats. The NHS lists herring, including kippers, pilchards, salmon, sardines, sprats, trout and mackerel as oily fish; fresh and canned tuna do not count as oily fish [25]. A portion is about 140 g cooked, and NHS advises at least 2 portions of fish a week, 1 of them oily [25]. In 1,108 Norwegian farmed salmon samples, median EPA plus DHA fell by more than 60% between 2005 and 2020 as fish oil in their feed was replaced [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]. Flaxseed, chia and walnuts give ALA only. For the food-by-food guide, see omega-3 foods.

How much omega-3 do you need a day?

How much omega-3 do you need a day? In the UK, SACN set 450 mg a day of long-chain omega-3, meaning EPA plus DHA, and raised that population guideline in 2004 from 200 mg. SACN says two portions of fish a week, one white and one oily, contain about 0.45 g, or 450 mg, of long-chain omega-3 a day [26]. The European value is EFSA’s adequate intake of 250 mg EPA plus DHA a day for adults [10]. UK adults aged 19 to 64 ate on average 56 g of oily fish a week in NDNS years 9 to 11, 2016/17 to 2018/19, compared with the recommended 140 g [28]. EFSA saw no safety concerns for supplemental intakes of EPA and DHA combined up to 5 g a day in adults, which is not a recommendation [11].

Body	Type of value	EPA plus DHA [mg/day]	Applies to
SACN (UK)	population guideline, 2004	450	UK population
British Nutrition Foundation [27]	UK dietary reference value	450	adults
EFSA (EU)	adequate intake	250	adults
EFSA (EU)	extra DHA in pregnancy and breastfeeding	100 to 200 (DHA only)	pregnant and breastfeeding women
EFSA (EU)	supplemental intake without safety concerns, not a recommendation	5000	adults

For how much omega-3 per day by age, timing and with food, use the dosage guide.

Which omega-3 supplement: fish oil, krill oil or algal oil?

Which omega-3 supplement: fish oil, krill oil or algal oil? Omega-3 fish oil comes from whole oily fish, krill oil comes from Antarctic krill, and algal oil comes from microalgae. Omega-3 supplements differ in raw material, not in the EPA and DHA molecules themselves. EPA and DHA are made at the base of the marine food chain by microalgae and other marine microorganisms [1]. Algal oil raised blood EPA and DHA as effectively as fish oil in a 2025 randomised double-blind trial in 74 adults measured at 6 and 14 weeks; the trial was run by a producer of algal oil, with 5 dsm-firmenich employees and 1 contracted statistician as authors [5]. Chemical form matters in the short term: in 72 volunteers over 2 weeks, re-esterified triglycerides were absorbed at 124% and ethyl esters at 73% of natural fish oil, a gap that largely disappears with long-term use [14].

Supplement	Raw material	Contains vitamins A and D	Fish free	What the evidence shows
Fish oil	whole oily fish	no	no	largest trial base, e.g. VITAL at 1 g a day
Cod liver oil	cod liver	yes	no	vitamin A and D upper limits apply
Krill oil	Antarctic krill (crustacean)	check the label	no	no comparison trial cited here
Algal oil	microalgae (e.g. Schizochytrium)	no	yes	raises blood EPA and DHA as effectively as fish oil (74 adults, producer-run trial)

For supplements that fit a keto diet, see keto supplements.

Is cod liver oil the same as omega-3?

Is cod liver oil the same as omega-3? Cod liver oil vs omega-3 is not a like-for-like comparison, because cod liver oil is one source of EPA and DHA, not another name for the nutrient family. Cod liver oil also contains vitamins A and D, which fish oil from whole fish and algal oil do not [6]. That changes what you need to check on the label for cod liver oil: EFSA’s tolerable upper intake levels for adults are 100 µg vitamin D and 3 000 µg RE vitamin A a day [6]. NHS advises avoiding fish liver oils such as cod liver oil when pregnant or trying for a baby, because they are high in retinol [25]. Vitamins A and D are also sold as separate drops, so if you use them separately, compare total daily amounts across products; see keto vitamins.

Can you get omega-3 without eating fish?

Can you get omega-3 without eating fish? You can get omega-3 without fish, but you need to separate plant ALA from marine-source EPA and DHA. Flaxseed, chia, walnuts and rapeseed oil give ALA, the short-chain plant omega-3. ALA supplementation raises EPA in blood but has little effect on DHA [4]. 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 [4]. For fish-free EPA and DHA, microalgal oil is the direct route. That is because EPA and DHA are made at the base of the marine food chain by microalgae and other marine microorganisms [1]. For a fish-free guide to labels and sources, read vegan omega-3.

What is the right ratio of omega-3, 6 and 9?

What is the right ratio of omega-3, 6 and 9? There is no agreed right ratio of omega-6 to omega-3, and EFSA deliberately set no value for it. Western diets are estimated at about 15:1 to 16.7:1, but that is a narrative estimate by one author, mainly about US diets rather than a measured UK dietary ratio [8]. Omega-9 fats are not essential, because the body makes them. In practice, a ratio can distract from the question you can answer from your diet: are you getting EPA and DHA from oily fish, or from a fish-free algal oil if you do not eat fish? If your diet is built around plant oils, nuts, meat and dairy, that ratio number still does not tell you your red blood cell omega-3 status. For the full explainer, read omega 3, 6 and 9.

What are the side effects of omega-3?

What are the side effects of omega-3? The side effects of omega-3 depend on dose, product type and your own medical situation. In 8 large RCTs with 83,112 people, omega-3 was linked to more atrial fibrillation: about 12% at up to 1 g a day (RR 1.12) and about 51% above 1 g a day (RR 1.51), mainly in people with heart disease or high risk [19]. Omega-3 reduces platelet aggregation, yet did not increase bleeding in 11 trials with 120,643 people (rate ratio 1.09, not significant) [20]. EFSA reported that EPA plus DHA at 2 to 6 g a day increased LDL cholesterol by about 3% [11]. Dose and background risk matter, so do not skip the serving size on the label. Read the longer safety guide on omega-3 side effects. If you take anticoagulants, ask your GP.

Do you need omega-3 on a keto diet?

Do you need omega-3 on a keto diet? Whether you need omega-3 on keto depends on what you actually eat. Keto with salmon, sardines, mackerel, trout or herring is different from keto built mostly on meat, dairy, nuts and plant oils [7]. We found no human trials of omega-3 supplementation in adults on a ketogenic diet, so there is no keto-specific dose [7]. That leaves the ordinary UK target: SACN’s population guideline is 450 mg a day of long-chain omega-3, meaning EPA plus DHA [26]. If you eat oily fish regularly, food may cover your intake. If you do not eat fish, algal oil is the fish-free source of EPA and DHA. The useful keto question is therefore not whether the diet has a special rule, but whether your own food choices provide EPA and DHA. For the keto-specific guide, read omega-3 on keto.

How do you choose a good omega-3 supplement?

How do you choose a good omega-3 supplement? Choose a good omega-3 supplement by checking four facts on the label: mg of EPA and DHA per daily serving, raw material, chemical form and freshness. Do not judge the product only by total oil weight, because the EPA and DHA amount is the number that matters for dose comparisons. Freshness is often expressed as TOTOX, which equals 2 × peroxide value + p-anisidine value; the voluntary GOED industry monograph sets caps of 5 meq/kg for peroxide value, 20 for p-anisidine value and 26 for TOTOX [9]. For a label checklist, see best omega-3 supplement. In 26 supplements tested in Australia, 38% exceeded the primary oxidation limit, 25% the secondary limit and 33% the total oxidation limit; premium products were not less oxidised, and human harm is not established [12]. In one study simulating consumer use, bottled omega-3 oils oxidised faster than capsules: maximum peroxide value was 44.6 versus 7.6 meq/kg, and maximum TOTOX was 96.9 versus 30.4 [13].

How does BeKeto MEGA Omega compare on these criteria?

How does BeKeto MEGA Omega compare on these criteria? On the label criteria above, MEGA Omega 3 vegan algae oil comes out best for anyone who avoids fish, because one 5 ml teaspoon gives 570 mg DHA and 185 mg EPA, above the SACN 450 mg guideline. One 5 ml serving provides 570 mg DHA and 185 mg EPA [29]. SACN’s UK population guideline is 450 mg long-chain omega-3 a day [26]. Each 150 ml dark glass bottle has 30 servings, and the liquid oil has a Sicilian lemon flavour [29]. The algal oil used in production has a typical TOTOX value below 8, compared with the GOED limit of 26, measured before flavouring [29]. One serving meets the 250 mg condition for “EPA and DHA contribute to the normal function of the heart” [30]. “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.” [29]

Frequently asked questions (FAQ)

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