High-Fiber Diet or Fiber Supplements?

Summarized by Robert W. Griffith, MD
April 19, 2007

Summary

A high fiber diet or supplemental fiber (psyllium), at an amount equivalent to 30 grams of fiber a day, lowers C-reactive protein (CRP) levels by about 16% (30% in lean normotensives, 10% in obese hypertensives).

Introduction

More attention is being paid these days to increases in C-reactive protein (CRP) levels as an indicator of cardiovascular health. CRP is released into the bloodstream any time there is active inflammation in the body, which can occur in response to infection, injury, or various conditions such as arthritis. Increases are predictive of events such as heart attack or stroke, and it's thought that inflammation in blood vessels is the precursor to atherosclerosis.

Over 25% of the population has a raised CRP level, so that interventions to lower this 'marker' are likely to be healthy steps to take. One of these interventions for which success is claimed involves increasing the amount of fiber in the diet. Now a study has been reported that compares the effect on CRP levels of a high-fiber diet and fiber supplements. It's published in the Archives of Internal Medicine, and summarized here.

What was done

Volunteers for this study were recruited by newspaper and Internet advertisements. They had to be between 21 and 49 years old, and could not be diabetic, taking medications, smokers, or pregnant. Two groups of volunteers were sought: lean normotensive and obese hypertensive patients. The lean normotensives had to have a body mass index (BMI) below 25, waist-to-hip ratios less than 0.8 (women) and 0.85 (men), and blood pressure below 130/85 mm Hg. The obese hypertensives had to have BMIs above 27, have a waist girth more than 40 inches (men) and 35 inches (women), and blood pressures between 130/85 and 159/99 mm Hg.

For the first 3 weeks all subject ate their regular diet. They were then randomly assigned to either a high-fiber diet or a diet supplemented with a fiber source. The high-fiber diet was the Dietary Approaches to Stop Hypertension (DASH) diet, which contains 30 grams fiber a day. The supplemented diet was a diet to which psyllium was added to achieve 30 grams fiber daily. Diets for both groups were balanced to achieve a composition of 50% carbohydrate, 34% fat, and 16% protein.

After the second 3 weeks (i.e. the first special diet period), the participants switched to the other special diet for another 3 weeks, so that the study lasted 9 weeks in all. To ensure compliance, participants were required to photograph all their meals and beverages for 3 days of each 3-week diet period.

CRP levels were measured before and after each dietary period, along with blood fibrinogen levels and white blood cell counts.

What was found

There were 35 participants in the study -18 lean normotensives and 17 obese hypertensives. Mean fiber intake on the 3-week run-in regular diet was 12 grams daily. The fiber intake on the high-fiber diet averaged 27.7 grams daily, and on the fiber supplementation diet 26.3 grams daily. The average CRP level at baseline was 4.4 mg/L.

On the high-fiber diet, the average CRP fell from 4.4 to 3.8 mg/L, and on the fiber supplement from 4.4 to 3.6 mg/L. Both these changes were statistically significant, i.e. they could not have occurred by chance alone.

CRP levels changed more in the lean hypertensives; their starting level (on their regular diet) averaged 2.0 mg/L, and fell by 30% to 1.4 mg/L on the high-fiber diet, and by 40% to 1.2 mg/L on the fiber supplementation diet. In the obese hypertensives, the starting level was 7.1 mg/L, which fell to 6.2 mg/L (13%) with the high-fiber diet, and to 6.5 mg/L (8%) with the supplementation diet.

Fibrinogen and white blood counts did not change with either dietary regimen.

What the findings mean

The two test diets were balanced as far as possible, including similar carbohydrate, fat, and protein make-up, so that the study effectively tested the possibility of different effects of dietary fiber and supplemental fiber on CRP levels. The results, however, showed that fiber consumed either as part of a natural diet or as a separate supplement (psyllium - often taken as Metamucil®) improved CRP levels equally.

CRP levels are being measured more often by physicians. The American Heart Association recommends measuring CRP levels in patients who, based on cholesterol levels, weight, level of exercise, smoking, high blood pressure, and diabetes, appear to have a moderate risk of a cardiovascular event; an elevated CRP would indicate that the risk may very well be greater than 'moderate'. The information from this study, although not surprising, will be useful in advising people with raised levels of inflammatory markers like CRP, interleukin-6, or TNF-alpha. If it's unlikely that such subjects are able to stick to a fiber-rich diet, resorting to a psyllium supplement can be seen as a satisfactory alternative.

Just consuming more fiber (in one form or another) is unlikely to be sufficient to combat effectively the adverse factors that cause the raised CRP in the first place. (It was disappointing to see that the effect was less pronounced in the obese hypertensives than in the lean normotensives.) Increased fiber intake must be seen as one part of a lifestyle change - exercise, weight control, no smoking, and so on - heading towards a healthier future.

Source

• Effect of a high-fiber diet vs fiber-supplemented diet on C-reactive protein level. DE. King, BM. Egan, RF Woolson ,  et al. , Arch Intern Med , 2007, vol. 167, pp. 502--506

Related Links
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