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Linseed oil instead of salmon? Why there’s no need to go fishing for omega-3

8.7.2025

Translation: Jessica Johnson-Ferguson

Is it true that linseed oil contains hydrocyanic acid and does it become toxic when heated? Or does it make you smarter and reduce the risk of cancer? Here’s a fact check on the most persistent myths about omega-3-rich vegetable oil.

You’ve probably heard that you should eat oily saltwater fish if you want to boost your omega-3 intake. But is this really true? Spoiler alert: yes and no. Although herring, salmon, mackerel and other types of fish undoubtedly contain generous amounts of omega-3, there are certainly alternative sources out there. Linseed oil, for example.

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Small seed, big effect: what makes linseed oil so special

When it comes to omega-3 fatty acids, linseed oil is the silent champion of edible oils. Why’s that? It contains particularly high levels of alpha-linolenic acid (ALA for short) – a plant-based omega-3 fatty acid your body needs, but can’t produce itself. While other edible oils including rapeseed and soybean contain around seven to ten per cent ALA, linseed oil has up to 60 per cent. Just one tablespoon exceeds the recommended daily requirement of 1.5 to two grammes of ALA for an adult.

However, there’s one difference to the healthy fat contained in fish. While salmon and other types of fish contain EPA and DHA, which are omega-3 fatty that are ready to be used, your body first has to produce at least some of them from ALA. The conversion rate isn’t very high and also depends on the person. However, it’s still high enough to meet the basic requirements. So if your diet doesn’t include fish, because you’re a vegan or vegetarian, for example, having linseed in your kitchen is a great ace up your sleeve.

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Linseed oil is good for your heart and blood

Studies show what else this vegetable oil has to offer:

Linseed oil is good for your heart. Studies show that two tablespoons a day for eight weeks can double the omega-3 fatty acids in your blood and improve blood pressure and blood lipid levels at the same time (page in German).

It also seems to have a positive effect on blood sugar levels. A review study showed that ground linseeds can improve fasting and long-term blood glucose levels in people with diabetes or pre-diabetes. However, the study relates to ground linseed, not linseed oil. What’s more, it isn’t comprehensive enough to deliver definitive recommendations despite the promising results.

Another meta-analysis involving over 1,500 participants showed that linseed oil significantly reduces certain inflammation levels in the blood. But this doesn’t mean it’s a miracle cure. Although the positive effect on inflammation levels has been scientifically proven, the improvement wasn’t substantial at around 10 to 20 per cent.

A meta-study found that total cholesterol and especially LDL cholesterol are significantly reduced by linseed. However, this effect has also been primarily associated with ground linseed rather than linseed oil.

Regular consumption of linseed oil could also reduce the risk of cardiac arrhythmia – but this has only been shown in a study on mice so far.

Fact or myth?

With all these positive results, there must be a catch, right? Time for a little fact check.

Myth number 1: Linseed oil reduces the risk of cancer.

The study situation is still too sparse to make a clear statement. But there are some pointers in this direction. The connection between lignans, which are plant substances contained in linseed, and breast cancer has been well studied to date. A large study has proven that women who have particularly high levels of these lignans in their blood are less likely to die of breast cancer – the risk being 42 per cent lower. However, this effect has been linked to lignans contained in linseeds and not linseed oil. Only very small amounts of it are found in oil. Smaller studies have also revealed some positive effects on prostate and bowel cancer, but this still needs to be further confirmed.

Myth number 2: Linseed oil has a short shelf life and tastes rancid quickly.

Is this really true? Yes, in parts. It’s true that linseed oil is indeed sensitive and is best kept in a cool, dark and airtight place. But if you keep it in the fridge and use it within four to six weeks, it’ll stay fresh and tasty. As far as a rancid taste is concerned, this usually comes from poor quality or incorrect storage. So it’s better to buy linseed oil in small bottles so that you can consume it before it goes off.

Myth number 3: Linseed oil contains toxic cyanides.

Although this sounds dramatic at first, there’s no need to panic. Linseeds contain cyanogenic glycosides, which may be converted into toxic hydrogen cyanide in the body – but only if you eat huge quantities of raw seeds. Don’t do that. However, these toxins hardly ever end up in linseed oil. So your spoonful of linseed oil in your breakfast muesli is harmless.

Myth number 4: Never heat up linseed oil or it becomes poisonous.

This is another persistent myth. What’s true is that you should never use linseed oil for frying or baking. When heated, the valuable omega-3 fatty acids are lost and the oil can become rancid more quickly. In addition, it’s true that harmful compounds can form when heated to high temperatures. These are two good reasons to enjoy linseed oil cold – for example on salad, quark or in muesli.

Myth number 5: Linseed oil makes you smarter.

Even if this is often claimed, it’s not as simple as that. Although omega-3 fatty acids are often associated with better memory (page in German), greater brain volume and even a lower risk of Alzheimer’s, this is particularly true of omega-3 fatty acids from fish (EPA and DHA). There’s no significant scientific evidence that linseed oil with its plant-based omega-3 (ALA) has the same effect. In other words, linseed oil is healthy, but there’s no proof it makes you smarter.

Long story short: Linseed oil isn’t a miracle cure, but it’s a real kitchen all-rounder. It provides you with plant-based omega-3, protects your heart and brain, helps against inflammation and could even reduce the risk of cancer – at least that’s what initial studies suggest. Want to know which of the many linseed oils on the market performs best? Here’s the ranking by consumer magazine Stiftung Warentest (page in German).

Header image: Shutterstock

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Anna Sandner

Senior Editor

Anna.Sandner@galaxus.de

Science editor and biologist. I love animals and am fascinated by plants, their abilities and everything you can do with them. That's why my favourite place is always outside - somewhere in nature, preferably in my wild garden.

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