"A few people in the past have looked at the relationship between fiber and cardiovascular disease, which includes coronary heart disease and stroke," senior author Victoria Burley told Reuters Health.
However, this is the first time all the available results from long-term studies have been pulled together into one analysis, said Burley, a senior lecturer in nutritional epidemiology at the University of Leeds in the U.K.
Burley and her coauthors pooled the results of eight studies conducted since 1990 that included close to 500,000 participants. Those people reported on their dietary fiber consumption and were followed for anywhere from eight to 19 years.
The researchers found the risk of suffering a first stroke fell by 7% for every 7g increase in dietary fiber people reported each day, so that those who ate the most fiber had the lowest chance of stroke, according to findings published in the journal Stroke.
The average U.S. woman gets 13g of fiber per day, and the average man gets 17g, well below the Institute of Medicine recommendation of 24g and 35g, respectively.
An extra 7g could come from two slices of whole wheat bread and a serving of fruit, for example, Burley said. However, even less than that - just 2 or 3 extra grams per day - might affect stroke risk.
Americans suffer almost 800,000 strokes annually, and strokes cause one out of every 18 U.S. deaths, or 130,000 per year, according to the Centers for Disease Control and Prevention. Most happen when a clot blocks blood flow in a brain vessel.
"Stroke is a very common and chronic disease in our society because the risk factors are growing," Dr. Dean Sherzai, a neurologist at Loma Linda University in California, told Reuters Health.
The new results are important because at the moment there are limited treatments and preventive measures available for stroke, but diet changes such as adding more fiber are relatively easy, said Sherzai, who was not involved in the study.
The report did not look at the effects of different types of fiber on people of specific ages, so it is possible some may glean more benefit from eating extra fiber than others, he added.
The findings do not prove fiber directly prevents strokes. Researchers also do not know why fiber would be linked to a lower risk, although they have some ideas.
"There could be all sorts of things going on," Burley said.
Foods high in fiber tend to be low-calorie and help people maintain a healthy weight, which reduces stroke risk, she said. Fibrous foods also have vitamins, minerals and antioxidants including polyphenols and flavonoids, which make blood vessels more elastic.
The findings should serve as more encouragement for people to get their daily recommended fiber, Burley said. She would like to see fiber back on the agenda, since it sometimes falls to the wayside in low-carbohydrate or gluten-free diets.