Fish oil is one of the few supplements almost everyone has been told to take at some point, usually without anyone specifying why, how much, or which one. It is also a category where the gap between the headline and the fine print is unusually wide.
So: what omega-3 actually does, what the large trials found, how much you need, and the thing on the label that decides whether the bottle is worth buying.
What omega-3 actually is
There are three that matter. ALA comes from plants — flaxseed, chia, walnuts, mustard oil. EPA and DHA come from marine sources, and they are the two doing most of the work the research is about.
Your body can convert ALA into EPA and DHA, which is the line every vegetarian supplement leans on. The conversion rate is the problem: it is poor, commonly cited in the low single-digit percentages for EPA and lower still for DHA. Eating flaxseed is good for you. It is not a reliable substitute for EPA and DHA.
What the large trials actually found
VITAL is the trial to know. Nearly 26,000 adults, 1 g of marine omega-3 daily or placebo, followed for a median of over five years.
The headline result was negative. No significant reduction in major cardiovascular events. No reduction in invasive cancer.
But the subgroup that matters here: among people eating less than about one and a half servings of fish a week, supplementation was associated with a meaningful reduction in major cardiovascular events, including a substantially lower rate of heart attack. Subgroup findings need caution — they generate hypotheses rather than settle them — but the direction is consistent with the idea that you are correcting a deficit rather than adding a drug.
That reframes the whole question. Omega-3 is not a cardiovascular medication for everybody. It is a nutrient, and nutrients help the people who are short of them.
Not sure whether your diet actually needs a fish oil, or which one is worth the money? Send me a photo of the label and what you eat in a week.
Where omega-3 actually comes from in an Indian diet
| Source | Type | Practical note |
|---|---|---|
| Hilsa, mackerel (bangda), sardine | EPA and DHA | Among the richest and cheapest sources here |
| Rohu, katla, surmai | EPA and DHA, lower | Still contributes meaningfully twice a week |
| Eggs, especially enriched | Small amounts of DHA | Helpful, not sufficient alone |
| Flaxseed (alsi), chia, walnuts | ALA only | Good food, poor conversion to EPA and DHA |
| Mustard oil | ALA only | Common cooking oil, same conversion limit |
| Algal oil supplement | EPA and DHA | The only vegetarian route to the forms that matter |
Who is most likely to actually need a supplement
- Vegetarians and vegans, for whom the dietary supply of EPA and DHA is effectively zero
- People who genuinely dislike fish or never eat it, which the VITAL subgroup suggests is the group most likely to benefit
- People with high triglycerides, where prescription-strength doses are an established treatment
- Pregnancy and breastfeeding, where DHA matters for foetal brain and eye development and intake is often low
And the group that probably does not need one: somebody already eating oily fish twice a week. For them the trial evidence does not support adding a capsule, and the money is better spent elsewhere.
The label detail that decides everything
This is the single most useful thing in this article, and almost nobody checks it.
A capsule marked 1000 mg fish oil does not contain 1000 mg of omega-3. That figure is the weight of the oil. The amount that matters is the combined EPA and DHA, printed in smaller type, and in cheap products it is often 300 mg or less per 1000 mg capsule.
| What the label says | What it means | What to do |
|---|---|---|
| 1000 mg fish oil | Weight of oil, not omega-3 | Ignore it |
| EPA 180 mg, DHA 120 mg | 300 mg combined — a low-strength capsule | You would need 3–4 for a standard dose |
| EPA 400 mg, DHA 200 mg | 600 mg combined — a concentrate | Reasonable |
| Triglyceride form | Better absorbed than ethyl ester | Mildly preferable, costs more |
| Algal oil | Marine EPA/DHA without fish | The correct choice for vegetarians |
| No EPA/DHA breakdown at all | The manufacturer does not want you comparing | Put it back |
How much, and for what
| Goal | Typical combined EPA + DHA | Evidence |
|---|---|---|
| General intake if you rarely eat fish | 250–500 mg daily | Reasonable; aligns with general intake guidance |
| Raising triglycerides down | 2–4 g daily, prescribed | Well established, and belongs with a doctor |
| Pregnancy (DHA for foetal development) | DHA-weighted, per obstetrician | Established, dose set clinically |
| Joint pain in inflammatory arthritis | Higher doses studied | Modest, adjunctive |
| Depression, cognition, skin | Various | Inconsistent — do not buy on these claims |
Two practical problems with fish oil
Rancidity. Omega-3 oxidises easily, and oxidised oil is the thing causing the fishy burps people complain about. Testing of retail fish oil has repeatedly found a meaningful share exceeding accepted oxidation limits. Buy from a shop with turnover, check the expiry, keep it in the fridge, and if a capsule smells strongly fishy when you break it, the batch is off.
Bleeding risk, in context. Omega-3 mildly inhibits platelets. At ordinary doses in healthy people this does not matter. It becomes a genuine conversation if you take warfarin, clopidogrel, or another blood thinner, or if you have surgery coming up — tell your surgeon, because it is routinely forgotten.
Food first, as always
Two portions of oily fish a week gets most people to the intake the guidance describes, and does it with protein, vitamin D and selenium attached. In India that means the fish people already eat — rohu, hilsa, mackerel, sardine, surmai — not an imported salmon fillet.
If you are vegetarian, this is one of the places where a supplement genuinely earns its place, and the right one is algal oil rather than flaxseed capsules. It is the same argument as B12 in a vegetarian diet: the food simply does not contain it.
How to tell if your bottle has gone off
Oxidation is the quiet problem in this category, and it is easy to check at home.
- Break one capsule open and smell it. Fresh fish oil smells faintly oceanic. Rancid oil smells sharply fishy, like an old aquarium
- Taste a drop. Bitter or sour means oxidised
- Persistent fishy repeat after swallowing is usually the oil, not you
- Check the manufacture date, not just the expiry. Oxidation begins from production, and Indian supply chains can be slow and warm
- Store it in the fridge once opened, and buy smaller bottles you will finish
A product with added vitamin E as an antioxidant, sold in an opaque bottle, is a reasonable sign the manufacturer has thought about this.
What I will not tell you
That fish oil protects your heart regardless of your diet. The largest trial says otherwise for people already eating fish.
That more is better. Beyond the doses above you are buying bleeding risk and burps.
That flaxseed is the same thing. It is a good food with a conversion problem.
Questions I get asked about this
Should I take it on an empty stomach? No. Take it with a meal containing some fat. Absorption is better and the fishy repeat is less likely.
Is cod liver oil the same thing? No. It contains EPA and DHA but also large amounts of vitamin A and D, which accumulate. Do not use it as a general omega-3 source without checking the doses.
Krill oil instead? Absorption may be marginally better per gram, but it is expensive and usually supplies less EPA and DHA per capsule. Compare on combined EPA plus DHA per rupee.
Does it thin the blood dangerously? Not at ordinary doses in healthy people. It matters if you take a blood thinner or have surgery coming, which is why both are worth mentioning.
Will it help my joints? Higher doses have modest support in inflammatory arthritis. For ordinary wear-and-tear joint pain, expect little.
The short version
- EPA and DHA are the two that matter; ALA from plants converts to them poorly
- In a 26,000-person trial, supplementation did not reduce cardiovascular events overall — but appeared to help those eating little fish
- The number on the front of the bottle is the oil weight, not the omega-3; read combined EPA + DHA
- 250–500 mg combined daily is a reasonable general intake; gram-level doses for triglycerides belong with a doctor
- Oxidised fish oil is common and is what causes the fishy repeat — buy fresh, store cold
- Vegetarians should use algal oil, not flaxseed capsules
- Tell your doctor before surgery or if you are on a blood thinner
Before you act on any of this
I am a pharmacist and a nutritionist. I am not your doctor, and this article is general information rather than advice about you specifically. If you take a blood thinner, are pregnant, or have surgery planned, check before starting or continuing fish oil. Nothing here is a reason to start, stop or change a prescribed medicine. What this article can do is tell you which questions are worth asking at your next appointment.
