Omega-3: what it actually does, how much you need, and whether it's worth it

Omega-3 is one of the few supplements with a decent evidence base behind it, and also one of the most commonly underdosed. Most people take three to six times less than they think, because they read the wrong number on the box. Here is what is known, what is not, and how much you actually need.

What it actually is

Omega-3 fatty acids come in three forms. ALA is the plant version (flaxseed, chia, walnuts), while EPA and DHA are the ones your body actually uses, and they come from oily fish and algae. Your body converts only 5–8 percent of ALA into EPA, and under 1 percent into DHA. So whenever anyone talks about omega-3 effects, they are effectively talking about EPA and DHA.

What it actually does

Triglycerides

This is the strongest and least disputed effect. A dose of 2–4 g EPA+DHA per day lowers triglycerides by roughly 15–30 percent, and the higher your starting point, the bigger the drop. It does not meaningfully move LDL cholesterol, and in some people nudges it slightly up. Blood pressure drops a little too, on the order of 1–3 mmHg at 3 g per day.

Inflammation and training recovery

2–3 g per day for at least 4 weeks produces moderately less soreness after a rough session — say 5x5 squats at 80 percent of your max, or 45 minutes of downhill running. The effect is real but modest: hurts less 48 hours later, not no inflammation at all. Strength and jump performance barely change.

Joints

In rheumatoid arthritis, 2.7–3 g per day over 12 weeks reduces morning stiffness and the number of tender joints. For ordinary knees that creak under squats, there is no solid evidence it changes anything.

Muscle in older adults

Around 3 g per day for 6 months alongside strength training gives somewhat better lean mass gains in people over 60. In a healthy 30-year-old already eating 1.6–2.2 g of protein per kilogram of bodyweight, the effect is close to zero.

What it does not do

• It does not burn fat. No dose changes your calorie balance.
• It does not raise testosterone in any measurable way.
• It does not fix a bad diet, bad sleep, and three weeks off training.
• It does not clean out your arteries. Large trials across tens of thousands of people show small to no effect on heart attacks in those already on standard medication.

Dosing, in numbers

• General health, if you don't eat fish: 1–2 g EPA+DHA per day.
• Triglycerides, recovery, joints: 2–3 g per day.
• Above 4 g per day: only with a doctor. Higher doses lengthen clotting time and are linked to a slightly raised risk of atrial fibrillation.

Nothing here is instant. Cell membranes need 8–12 weeks to load up, so judging the results after ten days tells you nothing.

How to read the label

This is where most people go wrong. The front of the box says 1000 mg fish oil — that is the weight of the oil, not the omega-3 dose. Flip it over and look for EPA and DHA.

A typical 1000 mg capsule contains 180 mg EPA and 120 mg DHA, so 300 mg total. To hit 2 g per day you need seven of those capsules, not one.

Concentrated oils carry 500–600 mg EPA+DHA per capsule, so 3–4 capsules do the job. Add EPA and DHA together, divide your target dose by that number — that is the only math that matters here.

Food first

A 150 g cooked portion of oily fish gives roughly: salmon 1.5–2 g EPA+DHA, mackerel 2–3 g, herring about 2 g, sardines about 1.5 g. Two such portions a week average out to roughly 500 mg per day. Canned tuna in water has only 0.2–0.3 g per 100 g, far less than people assume. If you eat oily fish 3–4 times a week, you probably don't need capsules at all.

If you don't eat fish

Algae oil delivers DHA (and increasingly EPA) directly at 1–2 g per day, and it is the only plant source you can actually rely on. A tablespoon of flaxseed oil holds about 7 g of ALA, which converts to maybe 350 mg of EPA and almost no DHA — fine on a salad, useless as a plan.

Practical steps

1. Take it with a meal containing at least 10–15 g of fat; absorption is noticeably better.
2. If you need 6 capsules, split them across 2–3 doses during the day.
3. Keep the bottle sealed and refrigerated. If the oil smells rancid, throw it out — oxidised oil is not worth swallowing.
4. Give it 12 weeks before you judge. If you're tracking triglycerides, get bloodwork before and after.

When to see a doctor

• You take anticoagulants (warfarin, apixaban) or aspirin — clear any dose above 1 g with your doctor.
• Scheduled surgery or a major dental procedure — ask about pausing; a 7-day stop beforehand is commonly requested.
• Triglycerides above 5.6 mmol/L — that is a condition to treat, not to self-experiment on with capsules.
• You notice palpitations or a skipping pulse since raising your dose.
• Pregnancy or breastfeeding — DHA is genuinely useful, but agree the form and dose with your doctor, and avoid cod liver oil because of its high vitamin A content.
• Allergy to fish or shellfish.

The short version

• Only EPA and DHA matter; plant-based ALA converts into them at a negligible rate.
• Aim for 1–2 g EPA+DHA per day for general health, 2–3 g if the goal is lowering triglycerides or easing soreness.
• Read the EPA + DHA total on the label, not the milligrams of fish oil — the gap is often six capsules.
• Two to four 150 g portions of oily fish per week replace the supplement entirely.
• Doses above 4 g per day, blood thinners, upcoming surgery, and very high triglycerides all go through a doctor.