Pregnant women who take a daily fish oil capsule can cut their baby’s risk of allergies by 30pc.
Probiotics during pregnancy and breastfeeding can also cut the risk of eczema by 22pc.
The findings are from one of the largest ever research projects into how a pregnant woman’s diet affects her baby’s risk of allergies and eczema .
The women taking part in the study took the fish oil capsules from 20 weeks pregnant and during the first three to four months of breastfeeding.
The probiotic supplements were taken from 36-38 weeks into the pregnancy and for the first three to six months of breastfeeding.
Dr Robert Boyle, from the Department of Medicine at Imperial College London, explained: “Food allergies and eczema in children are a growing problem across the world.
“Although there has been a suggestion that what a woman eats during pregnancy may affect her baby’s risk of developing allergies or eczema, until now there has never been such a comprehensive analysis of the data.”
The scientists also looked at fruit, vegetable and vitamins taken during pregnancy but none of these seemed to have any impact on the eczema or allergy risk.
The researchers found no evidence that avoiding foods like nuts, dairy and eggs during pregnancy made any difference to the baby’s allergy or eczema risk.
One in 20 children
Allergies to foods, such as nuts, egg, milk or wheat, affect around one in 20 children.
They are caused by the immune system malfunctioning and over-reacting to these harmless foods.
This triggers symptoms such as rashes, swelling, vomiting and wheezing.
Eczema affects around one in five children and causes dry, cracked and itchy skin.
The causes of eczema and allergies are not fully understood, but allergies are more common in people who suffer from eczema.
“Despite allergies and eczema being on the rise, and affecting millions of children, we are still hunting for the root causes of these conditions, and how to prevent them,” says Dr Vanessa Garcia-Larsen, co-author of the study.
“This study has provided clues, which we now need to follow with further research,” she added.
Probiotics were taken during pregnancy and breastfeeding as a capsule, powder or drink. Most yogurts do not contain enough probiotic.
They were found to reduce the risk of a child developing eczema – between the ages of six months to three years – by 22 per cent.
The team also assessed around 19 trials of fish oil supplements during pregnancy, involving around 15,000 people.
These studies revealed a 30 per cent reduction in risk of egg allergy by age one.
The team also found that taking fish oil supplements during pregnancy reduced the child’s risk of peanut allergy by 38 per cent.
However they caution this finding was based only on two studies, and not as reliable as the egg allergy and eczema results.
The study also revealed some evidence for links between longer duration of breast feeding and a reduced risk of eczema, and breastfeeding was also linked with a lower risk of type one diabetes.
The results of the study are published in the journal PLOS Medicine.