Experts have cast doubt on whether omega-3 fats can reduce the risk of heart disease or cancer.
Omega-3 fats are contained in oily fish
What are omega-3 fats?
Omega-3 fats are a type of polyunsaturated fat which has long been thought to be beneficial for health.
The body cannot make its own omega-3 fats, they must be taken in through the diet, or in supplement form.
The fats are naturally found in oily cold water fish like tuna, salmon, and sardines.
Vegetable sources include pumpkin seeds, flax seeds, and walnuts.
Some products, such as margarine, yoghurts and eggs, are now enriched with omega-3 fats.
Why do doctors recommend them?
Large population-based studies have suggested that a diet rich in omega-3 fats can reduce the risk of cardiovascular disease.
Research has shown that they:
- Decrease risk of irregular heart rhythms (arrhythmias), which can lead to sudden cardiac death
- Decrease levels of triglyceride - a type of fat found in the blood which has been linked to heart disease
- Reduce the clumping together of small particles in the blood called platelets which can cause potentially harmful clots
- Decrease growth rate of the fatty plaques that can fur up the arteries
- Lower blood pressure
Do they have other health benefits?
Apparently many. Research has suggested that omega-3 fats can cut the risk of cancers such as prostate and skin.
Other work has suggested that a diet rich in omega-3 can help improve behaviour in violent and antisocial teenagers
The fats have also been touted as a treatment for asthma and inflamed bowels.
Research has also suggested that a lack of omega-3s during foetal development can hinder brain and eye development.
Studies are currently underway to test the possibility that the fats could prevent memory loss and dementia.
What does the latest research say?
Researchers led by a team at the University of East Anglia reviewed 89 studies into the health effects of omega-3 fats.
They found no clear evidence that they are of any use at all.
The findings suggested the fats did nothing to prevent a recurrence of chronic heart conditions.
And they actually found that men with angina given high amounts of oily fish were at a greater risk of heart attack.
Does this mean we should stop taking omega-3 supplements?
No. Even the scientists behind the latest research admit that their work is far from definitive.
They say nutrition guidelines should be regularly viewed.
However, they do argue that it is probably not appropriate to recommend fish oil to people who have angina chest pains, but who have not had a heart attack.
How much should we eat?
The Food Standards Agency recommends that people eat oily fish regularly - but no more than four portions a week.
And it recommends that women who are pregnant, breastfeeding, or planning to have children in the future should limit their intake to a maximum of two portions a week.
This is because of concerns that the fish may be contaminated with pollutants such as mercury, dioxins and PCBs (polychlorinated biphenyls).
High levels of dioxins and PCBs can affect the development of an unborn baby.