Everyone knows that getting enough fiber is a secret to staying "regular," but a large new study finds that people who got plenty of fluids were the least likely to suffer constipation.
The results highlight the importance of hydration, but shouldn't discount fiber or other lifestyle factors, according to lead author Alayne Markland, of the Department of Veterans Affairs Medical Center in Birmingham, Alabama.
"I still think that diet, fiber, exercise and increased fluid should remain the recommendations," Markland told Reuters Health.
Estimates of how many people regularly experience constipation are as high as 14 percent worldwide, but they range widely. How researchers define the problem and ask people about it are partly to blame for inconsistent responses, Markland's team writes in the American Journal of Gastroenterology.
Often, constipation is defined as having fewer than three bowel movements a week, the researchers point out. But some studies have found that asking about stool consistency provides a more accurate measure of slow "transit times" of stool through the intestine, which is the source of uncomfortable blockages.
To determine how many people have "hard or lumpy stool consistency" - the type associated with slow transit - and what lifestyle factors might influence that, Markland and her colleagues analyzed responses from more than 8,000 men and women who participated in the National Health and Nutrition Examination Surveys in 2006 and 2008.
Based on survey responses about stool consistency, exercise habits and what participants ate, the researchers found that seven percent of the respondents fit the definition for constipation.
The problem was more common among women and less educated people, but it did not increase with age, as some other studies have suggested.
Neither vigorous exercise nor fiber intake was linked with a person's likelihood of having constipation.
But among the people who consumed the least amount of liquid daily from food and drinks, 8 percent of men and 13 percent of women were constipated, compared to 3 percent of men and 8 percent of women who got the most liquid.
"I scratch my head on that, it's interesting," Dr. Amy Foxx-Orenstein, of the Department of Gastroenterology and Hepatology at the Mayo Clinic in Rochester, Minnesota, told Reuters Health.
Past research indicates that extra fluid only alleviates constipation if the person is dehydrated to begin with, but once you're adequately hydrated more fluid probably just makes you urinate more often, said Foxx-Orenstein, who was not involved in the study.
She encourages patients in her practice to drink enough water and try to get 25 to 30 grams of fiber daily, if not from food then from a supplement, and to eat a breakfast that includes caffeine shortly after waking, as those factors can stimulate bowel movements.
The new study included a large number of participants, but didn't distinguish between different types of fiber and when they were consumed or ask about physical activity in enough detail, Foxx-Orenstein said, and she thinks it's unlikely doctors will change what they tell patients based on these results.
Foxx-Orenstein agreed that the definition of constipation varies widely.
"We used stool consistency, so we took a validated scale and defined constipation as those with the hardest stool," Markland said. That could have made liquids in the diet, which influence stool consistency but not necessarily frequency or amount, seem more important, she acknowledged.
Exercise and fiber may have more of an impact on frequency, Markland added.
The study doesn't mean that those factors are "bogus," she said, just that future studies need to define the weekly thresholds where each factor becomes meaningful.
"It just begs for more research on the role of fiber," Markland said.
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