Whole grains speed up metabolism and reduce calorie retention, according to a new study.

A US study has shown eating whole grains can help people lose weight.

Whole grains increase calorie loss by decreasing the number of calories retained during digestion, while simultaneously speeding up metabolism, according to new research published in the American Journal of Clinical Nutrition.

Studies have suggested health benefits of whole grains and high dietary fibre intake, including for glycemic control and insulin sensitivity. However there has been a belief that whole grains and fibre aren't beneficial for weight regulation.

"This study helps to quantify how whole grains and fibre work to benefit weight management and lend credibility to previously reported associations between increased whole grains and fibre consumption, lower body weight and better health," said lead author Phil J Karl from the Friedman School of Nutrition Science and Policy at Tufts University.

The study compared two groups of people - 81 men and women aged between 40 and 65 - and followed them for eight weeks.

In the first two weeks, all participants ate the same type of food and individual calorie needs were determined.

They were then divided into two groups: one got a wholegrain diet and the other a refined grain diet.

People who ate a diet with whole grains lost close to an extra 100 calories per day due - the equivalent of a daily brisk walk or eating a small biscuit every day in terms of impact.

Grains are a major food group that include wheat, rice, oats and barley products. Whole grains include the outer nutritious layer of grains and are found in products including whole-wheat flour, oatmeal and brown rice.

Refined grains are starches that have been processed and broken down into a finer texture, primarily to increase shelf life.

The Tufts researchers caution that the effects of a whole grain diet on resting metabolic rate were sensitive to dietary adherence. The study also didn't compare a whole grain diet with a diet with no grains at all.

But when it comes to brown rice or bread compared with their white counterparts then whole grains are superior when wanting to loose weight.