LONDON (Reuters) - People who eat lots of high-fiber and whole grain foods have lower risk of heart disease, stroke, diabetes and other chronic diseases than people whose diets are low in fiber, a study commissioned by the World Health Organization (WHO) says.

For every 8 gram increase in fiber eaten a day, total deaths and incidences of heart disease, type 2 diabetes and bowel cancer fell by 5 to 27 percent, the study said. Protection against stroke and breast cancer also rose.

A good target for those wanting to reap health gains would be to eat 25g to 29g of dietary fiber a day, the analysis found. But the data, published in a series of systematic reviews and meta-analyses in The Lancet medical journal, also suggested higher dietary fiber intakes could give even greater protection.

“Our findings provide convincing evidence for nutrition guidelines to focus on increasing dietary fiber and on replacing refined grains with whole grains. This reduces incidence risk and mortality from a broad range of important diseases,” said Jim Mann, a professor at the University of Otago, New Zealand who co-led the research.

According to the study, most people worldwide currently consume less than 20g of dietary fiber a day. In Britain in 2015, an advisory committee on nutrition recommended an increase in dietary fiber intake to 30g a day, but only 9 percent of British adults manage to reach this target. In the United States, fiber intake among adults averages 15g a day.

Mann said the health benefits of dietary fiber - contained in foods such as whole grains, pulses, vegetables and fruit - come from its chemistry, physical properties, physiology and its effects on metabolism.

“Fiber-rich whole foods that require chewing and retain much of their structure in the gut increase satiety and help weight control, He said. “(And) the breakdown of fiber in the large bowel by the resident bacteria has additional wide-ranging effects including protection from colorectal cancer.”