QUEBEC CITY — Increasing dietary fiber intake might be warranted in patients with diabetes, hypertension, and obesity, Dana King, M.D., said at the North American Primary Care Research Group annual meeting.
He presented a study in which adults with low fiber intake and at least two of the three conditions were twice as likely to have elevated C-reactive protein (CRP) levels, compared with adults with no risk conditions, even after controlling for confounding factors.
Moreover, the influence of fiber on CRP values was greater as the number of conditions increased, said Dr. King, professor at the Medical University of South Carolina, Charleston.
There is some evidence to suggest that dietary fiber reduces cholesterol and influences inflammation. But CRP increases the risk of cardiovascular disease independently from cholesterol, he said.
Both the American Diabetes Association and the American Heart Association suggest adults consume 25–30 g of fiber per day. However, neither group has specific recommendations for higher intake among high-risk patients, Dr. King said.
The cross-sectional study included 7,891 participants in the 1999–2002 National Health and Nutrition Examination Survey at least 20 years of age who had valid high-sensitivity CRP measurements and dietary information. Participants were asked to recall fiber consumption in the previous 24 hours. Fiber supplements were not counted toward total intake.
Individuals with two or more conditions—diabetes, hypertension, or obesity—who consumed 20 g per day or more of fiber had significantly lower median CRP (3.1 mg/L) than people who consumed 8.8 g/day or less (4.5 mg/L).
CRP was four times higher in people with these conditions who consumed less than 8.8 g/day of fiber than people without these conditions (1.4 mg/L).
Even after controlling for age, race, gender, and tobacco use, adults with two or more conditions had double the risk of having elevated CRP (odds ratio 2.3), compared with adults with no risk conditions (OR 1.5).
Only 2%–3% of patients in the study had rheumatoid arthritis, which can raise CRP levels.
Interestingly, only dietary fiber showed a consistent association with CRP. There was no consistent association between CRP and other dietary components such as fat, polyunsaturated fat, protein, carbohydrates, or fish-oil consumption, he said.
It's unclear what biological mechanisms might be at work, but fiber itself might not be the source of the observed benefits.
“We could very well be looking at a surrogate,” Dr. King said. “Fiber may not be changing CRP. There have been a couple of studies, including our own, that have looked at other things that travel along with fiber, other nutrients, such as magnesium.
“There is a high correlation between magnesium intake and fiber intake, and there is a high predictive value of high magnesium intake and lower blood pressure and lower cardiovascular disease. So they may be traveling together. We are still in the process of sorting these things out.”