Academics have discovered that omega-3 fatty acids – found in fish like salmon, mackerel and tuna, as well as walnuts, pumpkin seeds and linseeds – prompt the gut to develop in a way that boosts the immune system.

And they warn that more children could now be at risk of food allergies than in the past because consumption of such foods has fallen.

The team, from France’s National Agricultural Research Institute (INRA), found that when mothers-to-be ate a diet high in a particular group of polyunsaturated fatty acids (PUFAs), the gut walls of their offspring were more permeable.

This allowed more broken down food substances and bacteria to pass into the bloodstream, triggering the baby’s immune system to produce antibodies.

Dr Gaëlle Boudry, from the INRA, explained: “Our study identifies that a certain group of polyunsaturated fatty acids causes a change in how a baby’s gut develops, which in turn might change how the gut immune system develops.”

She continued: “The end result is that the baby’s immune system may develop and mature faster – leading to better immune function and less likelihood of suffering allergies.”

Food allergy appears to be a growing problem, with the number of related hospital admissions in Britain rising six-fold since 1990.

There is considerable debate about how real the reported increase actually is, however. The National Institute for Health and Clinical Excellence (Nice) last year estimated that while more than a third believed they were allergic to some form of food, only a tenth were found to be allergic when properly tested.

Oily fish

Nonetheless, a recent, robust study from the Isle of Wight found one in 20 children did have an allergy. It also found evidence that the real incidence was growing.

Allergy experts do not really know what is behind the rise. One theory is the ‘hygiene hypothesis’: that as homes have become cleaner, children’s immune systems now have less chance to develop fully.

More and more attention is also being paid to the role of early exposure to foods, both in the first years of life and in the womb.

Dr Boudry said: “There is intense research interest in maternal diet during pregnancy. In the Western diet, the group of polyunsaturated fatty acids that we have shown to help gut function are actually disappearing – our dietary intake of fish and nut oils is being replaced by corn oils which contain a different kind of fatty acid.”

Their research, published in The Journal of Physiology, added to evidence that consuming such fatty acids in pregnancy was beneficial for babies, she claimed.

“Other studies have found that a diet containing fish or walnut oil during pregnancy may make your baby smarter – our research adds to this, suggesting such supplements also accelerate the development of a healthy immune system to ward off food allergies.”

She emphasised that their study was in pigs, but the research group believe the animal’s intestine is an “excellent model of the human gut”.

In the study, pregnant and lactating sows were given a dietary supplementation of linseed oil. The permeability of their offsprings’ intestinal walls was than compared with that of piglets from sows not given the supplement.