The study of 215 mothers and their children showed diet in late pregnancy was most important for increased bone size, bone mineral content (BMC) and bone mineral density (BMD).

A 'prudent' diet of fruit, vegetables, wholemeal bread, rice, pasta, yoghurt and breakfast cereals in the final trimester correlated with good bone health in the children at age nine.

Food frequency questionnaires from early and late pregnancy were used to develop a diet score. A higher score was given to women who followed a prudent diet, and a lower one to those who ate fatty or processed foods.

At age nine, the children were assessed for whole-body and lumbar BMC, BMD and bone area using a bone densitometry technique. Analysis showed children whose mothers followed a prudent dietary score had a significant correlation with increased BMC, BMD and bone area.

A prudent diet in early pregnancy was also associated with improved bone outcomes, but this was not statistically significant after adjustment for confounding factors such as maternal smoking and vitamin D status at 32 weeks gestation.

Lead researcher Dr Zoe Cole, of the Medical Research Council Epidemiology Resource Centre at Southampton, said: 'We've shown there's a very big effect looking at total diet — much more than that seen with individual nutrients alone.'

The team, which will present its research at the British Society for Rheumatology's annual conference in Birmingham in May, is now carrying out a similar analysis of data that should allow them to study the outcomes of 1,000 children.