"An added benefit (of early introduction of solids) is that it seems to confer better sleep for the children", said Gideon Lack, professor of paediatric allergy at King's College London, and a co-author of the research.
Feeding babies solids from three months improves their sleep, according to a study that contradicts NHS advice.
Dr Clare Llewellyn and Dr Hayley Syrad, who have researched baby eating habits for over a decade, said the first foods introduced to children at around six months should be bitter vegetables, as these are the foods most commonly disliked by children.
Professor Lack stressed that mothers should continue to breastfeed their babies until they are at least six months, even if solids are introduced earlier.
One group was exclusively breastfed for six months, the other group was given solid foods in addition to breast milk from the age of three months.
Experts say women should still heed this recommendation, although it is under review. The EAT study showed that introducing small amounts of allergenic foods to younger babies helped reduce food allergy risks.
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The results of the study showed that the babies that started eating solid foods sooner slept longer, woke up less, and had fewer sleeping problems than those that consumed exclusively breastmilk for that six month period.
Feedback about maternal wellbeing showed that sleep problems were reported less frequently in the group introducing solids before six months.
The findings provide some solid data to back up the long-held belief that feeding infants solid food helps them sleep better, Dr Jae Kim, a neonatologist at of the University of California San Diego and the Radey Children's Hospital of San Diego, told Reuters Health in a phone interview.
She said: "These are interesting findings from a large randomised controlled trial".
'However, the evidence base for the existing advice on exclusive breastfeeding is over ten years old, and is now being reviewed in the United Kingdom by the Scientific Advisory Committee on Nutrition and in the EU by the European Food Safety Authority.
A baby's first food should not be mashed banana or rice, with parents advised to wean their children on broccoli. It can take lots of attempts before your baby will accept a new food or texture.
More than 1300 healthy breastfed three-month-olds were split randomly into two groups in one the babies were exclusively breastfed until they were six months old - as current guidelines recommend - while children in the other group were breastfed and given solid foods, including peanuts, eggs and wheat, from the age of three months, in addition to breastfeeding. As part of the study the team also looked the impact on other measures, including growth and sleep.
Despite the official piece of advice, about 75% of mothers gave solid food to their babies before five months - 26% of the babies were waking up at night frequently because of this reason.