Fatty Acids & Dietary Fats — Omega-3/6/9, Saturated & Trans Fats

Nutrition basicsFatty acidsDietary fats

Dietary fats are built from fatty acids — chains of carbon atoms with a string of hydrogen attached. The single most important feature is how many double bonds the chain has, because that decides whether a fat is solid or liquid, how stable it is in heat, and how it affects your heart:

No double bonds → saturated fat (solid at room temperature: butter, coconut, lard).
One double bond → monounsaturated fat — the omega-9 family (olive and rapeseed oil, avocado, nuts).
Two or more double bonds → polyunsaturated fat — the omega-3 and omega-6 families. These include the only fats your body cannot make and must get from food.

← Fat (macronutrient basics) How to choose a good olive oil →

Read first. The fat-composition figures and smoke points below are approximate typical values — real oils vary by variety, refining and brand. They are a guide for everyday choices, not exact analysis, and nothing here is individual medical or dietary advice. If you have heart disease, high cholesterol, diabetes or take medication, follow your clinician's guidance.

The types of fatty acid

Essential fatty acids (EFAs)

Must come from food

What they are: your body can build almost every fatty acid it needs — except two. Linoleic acid (LA, an omega-6) and alpha-linolenic acid (ALA, an omega-3) are essential: you have to eat them. From these two, the body makes the longer fatty acids it needs (with limits — see omega-3 below). Where: LA from vegetable oils, nuts and seeds; ALA from flaxseed, walnuts, rapeseed and chia. A true deficiency causes dry, scaly skin and poor wound healing, but it is rare on any normal diet. What matters more for most people is the balance and quality of fats, covered below.

Saturated fat

Limit: <10% of energyRaises LDL cholesterol

What it is: fatty acids with no double bonds, so they pack tightly and are usually solid at room temperature. The body can make all it needs, so none is "required" in the diet. Where: butter, cheese, fatty and processed meat, lard, coconut and palm oil, and many baked/fried foods.

The evidenceMost saturated fats raise LDL ("bad") cholesterol, a cause of heart disease. Major reviews show that replacing some saturated fat with unsaturated fat (especially polyunsaturated) lowers cardiovascular risk — the swap matters more than the fat alone.¹ ²

Honest nuanceHeadlines that "saturated fat is harmless" overstate the case. The science supports moderation (WHO and most heart bodies advise <10% of calories) and, above all, what you replace it with — swapping it for refined carbs or sugar gives no benefit; swapping for olive oil, nuts and oily fish does.

PracticalKeep butter, fatty cuts, cheese and coconut/palm oil as a smaller part of the plate; lean on olive/rapeseed oil, fish, nuts and seeds instead.

Monounsaturated fat (MUFA)

Favour theseHeart-friendly

What it is: fatty acids with one double bond — chiefly oleic acid, the omega-9 fat. Liquid at room temperature but fairly stable for cooking. Not essential (the body can make it), but a healthy fat to centre your diet on. Where: olive oil, rapeseed (canola) oil, avocado, and most nuts. Why it's good: diets rich in MUFA (the Mediterranean pattern) are linked to better cholesterol balance and lower heart-disease risk.³

Omega-3 (ALA, EPA & DHA)

EPA+DHA ≈ 250–500 mg/dayAnti-inflammatory

What it is: a polyunsaturated family with three key members — ALA (plant form, essential), and the long-chain EPA and DHA (from fish/algae) that the body actually uses for the heart, brain, eyes and to calm inflammation. The catch: your body converts ALA into EPA and DHA only poorly (a few percent), so oily fish or an algae supplement is the reliable way to get them. Where: EPA/DHA in salmon, mackerel, herring, sardines and algae oil; ALA in flaxseed, walnuts, rapeseed and chia.

How muchEFSA sets an adequate intake of 250 mg/day EPA+DHA for adults (≈ two fish meals a week), and ~0.5% of energy as ALA.⁴

EvidenceStrongest for lowering triglycerides. For the general population the two big supplement trials were null (VITAL, ASCEND); one high-dose trial was strongly positive (REDUCE-IT, 4 g/day icosapent ethyl) but is contested because its mineral-oil placebo appears biologically active, and a near-identical trial with a different placebo (STRENGTH) was null and stopped early. Safety: supplemental EPA/DHA raises the risk of atrial fibrillation dose-dependently — roughly 12% at ≤1 g/day and about 50% above 1 g/day — which is the main reason not to self-prescribe high doses. Eating fish carries no such signal, and beats relying on capsules.⁵

Omega-6 (linoleic acid & arachidonic acid)

Essential — but plentiful

What it is: a polyunsaturated family led by linoleic acid (LA), which is essential; from it the body makes arachidonic acid (AA), used in cell membranes and signalling. Where: vegetable oils (sunflower, corn, soybean), nuts and seeds — so most people get plenty.

The "inflammation" claimYou'll read that omega-6 is "pro-inflammatory." In humans this is largely not borne out: controlled trials show higher linoleic acid does not raise inflammatory markers, and higher omega-6 intake is linked to lower, not higher, heart-disease risk.⁶

Sensible takeYou don't need to chase omega-6 or fear it. The useful goal is to get enough omega-3 (fish), not to wage war on omega-6.

Omega-7 & Omega-9

Non-essential

Omega-9 (oleic acid): the main monounsaturated fat (see above) — olive and rapeseed oil, avocado, nuts. The body makes it, so it is not essential, but it's a great fat to build meals around. Omega-7 (palmitoleic acid): a monounsaturated fat found in sea-buckthorn and macadamia. It's sold as a supplement for metabolic and skin health, but human evidence is preliminary — interesting, not established. No need to seek it out.

GLA — gamma-linolenic acid

Omega-6 · supplementEvidence weak/mixed

What it is: an omega-6 the body normally makes from linoleic acid; it converts to anti-inflammatory signalling molecules, which is why it's taken as a supplement. Where: evening primrose oil, borage oil and blackcurrant seed oil (little in everyday food).

EvidenceStudied for eczema, PMS, rheumatoid arthritis and diabetic nerve pain. Honest verdict: a Cochrane review found no benefit for eczema; for rheumatoid arthritis there is some low-quality evidence of symptom relief. Overall modest and mixed — not a proven treatment.⁷

SafetyGenerally well tolerated; caution with blood thinners and before surgery.

CLA — conjugated linoleic acid

Naturally in dairy & beefWeak weight-loss evidence

What it is: a natural family of modified linoleic acids found in the meat and milk of grazing animals (ruminants). As food it is harmless; as a high-dose supplement it is marketed for fat loss.

EvidenceSupplement trials show at most a tiny, clinically meaningless change in body fat, and high doses have been linked to insulin resistance, inflammation and liver effects in some studies. Not recommended as a weight-loss aid.⁸

Trans fats

Avoid — keep as low as possible

What they are: unsaturated fats with a "trans" twist in the chain. Industrial trans fats are made by partially hydrogenating vegetable oil to harden it — once common in margarine, frying fat and packaged baked goods. Why they're the worst fat: they raise LDL and lower HDL cholesterol and are strongly linked to heart disease.

The good newsThe WHO has driven a global push to eliminate industrial trans fats, and the EU caps them at 2 g per 100 g of fat (since 2021). They are now rare in regulated markets — check labels for "partially hydrogenated oil" on imported snacks.⁹

Natural transSmall amounts occur naturally in dairy and beef; these are not considered a significant health concern at normal intakes.

Oils & fats

The fats and oils on your shelf — avocado, olive, rapeseed, coconut, MCT, butter, lard and more — now have their own shelf reference, with each oil's fat profile, best use and smoke point.

Open the oils & fats reference →

← Back to Macronutrients How to choose a good olive oil →

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Bodil Isaksson, Licensed Biomedical Scientist (Sweden)

At Food Health Lab we explain what the science says in plain language, and we cite our sources so you can check for yourself.

References

Fat-composition percentages and smoke points are approximate typical values (chiefly from USDA FoodData Central and standard food-science references); they vary by variety, refining and brand.

World Health Organization. Saturated fatty acid and trans-fatty acid intake for adults and children: WHO guideline (2023). who.int
Hooper L, et al. Reduction in saturated fat intake for cardiovascular disease. Cochrane Database Syst Rev, 2020. cochranelibrary.com
Sacks FM, et al. Dietary fats and cardiovascular disease: a Presidential Advisory from the American Heart Association. Circulation, 2017. ahajournals.org
EFSA Panel on Dietetic Products, Nutrition and Allergies. Dietary Reference Values for fats, incl. essential fatty acids and EPA/DHA (250 mg/day). EFSA Journal, 2010. efsa.europa.eu
Hu Y, Hu FB, Manson JE. Marine omega-3 supplementation and cardiovascular disease: meta-analysis of 13 trials. J Am Heart Assoc, 2019. ahajournals.org · REDUCE-IT (high-dose EPA), NEJM 2019. nejm.org
Marklund M, et al. Biomarkers of dietary omega-6 (linoleic acid) and cardiovascular disease: pooled analysis of 30 cohorts. Circulation, 2019. ahajournals.org
Bamford JTM, et al. Oral evening primrose oil and borage oil for eczema. Cochrane Database Syst Rev, 2013 (no benefit). cochranelibrary.com
Onakpoya IJ, Posadzki PP, Watson LK, Davies LA, Ernst E. The efficacy of long-term conjugated linoleic acid (CLA) supplementation on body composition in overweight and obese individuals: a systematic review and meta-analysis of randomized clinical trials. Eur J Nutr, 2012;51(2):127–34; and US NIH ODS dietary-supplement overview. pubmed
World Health Organization. Countdown to 2023: eliminating industrially produced trans fat; EU Regulation 2019/649 (2 g/100 g fat limit, applied 2021). who.int

This article summarizes nutrition science from official health authorities for education. It is not a substitute for individual medical advice. If you have a heart, cholesterol or metabolic condition, discuss dietary fat changes with your clinician.

Fatty Acids & Dietary Fats — Omega-3/6/9, Saturated, Trans & the Oils on Your Shelf