Primary school children who live near to fast food outlets are more likely to gain a significant amount of weight, a study has found.

Researchers from the University of the West of England (UWE Bristol) tracked the weight of more than 1,500 state primary school children.

They used the weights of the children, from south Gloucestershire, between reception year (aged four to five) and Year Six (aged 10 to 11).

The study found children living closer to fast food outlets were more likely to gain a significant amount of weight between the first and last year of school.

Matthew Pearce, a former UWE Bristol public health student now working for the NHS, was the lead researcher on the study.

"We know from national data that the number of children classified as obese doubles between the first and last year of primary school," he said.

"Understanding the reasons for this is important to protect the future health of children.

"Obesity is driven by many complex factors. Our study adds to existing evidence that the neighbourhood environment plays an important role in the development of obesity."

Researchers calculated a 'fast food accessibility score' for each child involved in the study.

This took into account the number of fast food outlets and how many were within a distance of 1km by road of each child's home.

Previous research found that adults and children who live near fast food outlets are more likely to be overweight or obese.

The UWE Bristol study is the first to show an association between accessibility to fast food outlets and weight gain over time.

It also found a higher density of fast food outlets within poorer neighbourhoods.

Dr Issy Bray, public health lecturer at UWE Bristol, said: "While our study tried to control for other factors that might influence a child's weight, at this stage we can only say there is a relationship.

"It may be the association is due to other aspects of these neighbourhoods, such as cycling and walking infrastructure.

"Further research should be undertaken to understand how children and their families interact with the neighbourhood and environment."

The study used data from the National Child Measurement Programme, which involves the annual weighing and measuring of primary school children.

Data was taken from 2006/7 to 2012/13.