High Fiber Diet Can Reduce CRP Levels

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Credit to www.medscape.com

March 14, 2007 — Fiber in the diet can reduce C-reactive protein (CRP) levels, a new study suggests. Writing in the March 12 issue of the Archives of Internal Medicine, Dana King, MD, and colleagues from the Medical University of South Carolina in Charleston report that both a high-fiber diet, as well as a fiber-supplemented diet, significantly — if modestly — reduced baseline CRP levels during a 3-week period.

"The study adds prospective trial data to the previous literature on dietary fiber and CRP," Dr. King told heartwire. "The findings support current American Heart Association and other group's guidelines that promote adequate intake of fiber in the diet to promote good health. Clinicians should continue to counsel patients to eat foods high in fiber, or take a supplement to reach their fiber intake goals."

The study is one of the first to specifically examine a cause and effect role for fiber and CRP level in a randomized fashion, the authors add.

Both Fiber Strategies Lower CRP

The study enrolled 28 women and 7 men whose baseline fiber intake was approximately 12 g/day, measured during a 3-week run-in period. The participants were then randomized to either the DASH (Dietary Approaches to Stop Hypertension), high-fiber diet (mean intake, nearly 28 g of fiber per day), or to a fiber supplement (psyllium) on top of their regular diet (mean intake, totaling 27 g/day). After 3 weeks on one diet, participants crossed over to the other fiber diet.

On both diets, CRP levels dropped below baseline values, a statistically significant change in both groups. The absolute reduction was greater in the supplemented diet group, but there were no statistically significant differences in the CRP changes between the 2 groups.

Table 1. CRP Changes by Diet*

GroupChange in CRP: Dietary FiberP From BaselineChange in CRP: Supplemental FiberP From Baseline
All participants (n = 35) -13.7% .046 -18.1% .03

*CRP indicates C-reactive protein.
Source: Arch Intern Med. 2007;167:502-506.

Changes in CRP levels were greater in lean, normotensive subjects than in obese, hypertensive subjects. This finding was "surprising" the authors note, because previous work had suggested that fiber affects CRP levels by modulating metabolism in abdominal fat such that overweight or obese subjects would seem more likely to be affected by fiber consumption.

Table 2. CRP Changes by Diet and Baseline Weight/Blood Pressure*

GroupBaseline CRP (mg/L)Follow-up CRP: High-Fiber Diet (mg/L)P From BaselineChange in CRP: Supplemental Fiber (mg/L)P From Baseline
Lean normotensive patients (n = 18) 2.0 1.4 < .05 1.2 < .05
Obese hypertensive patients (n = 17) 7.2 6.5 NS 6.2 NS

*CRP indicates C-reactive protein; NS, not significant.
Source: Arch Intern Med. 2007;167:502-506.

"The finding of a lower relative reduction in obese participants was both surprising and disappointing," Dr. King told heartwire. "Surprising, because we had not noted a differential impact previously [and] disappointing due to the fact that CRP and inflammatory markers are elevated higher, on average, in people with obesity, so our hope was that fiber would work even better in such individuals. Instead, it appears that dietary fiber has a lesser impact on obese individuals."

A longer intervention period or a higher fiber intake in obese subjects might have led to a greater impact on CRP levels, the authors suggest, noting that future studies could address these questions. "Nevertheless, the findings indicate that modification of dietary fiber may be helpful in modulating inflammation to a certain degree," with possible benefits for cardiovascular risk, they conclude.

Elaborating to heartwire, Dr. King acknowledged, "There has been no cause-and-effect link proven between CRP and cardiovascular risk, thus our cautious but hopeful statement. If a link is more firmly established, dietary fiber may play a role in helping to reduce the cardiovascular risk attributable to CRP and inflammation."

Commenting on the study for heartwire, Paul Ridker, MD, from the Brigham and Women's Hospital in Boston, Massachusetts said, "These data add to a growing knowledge base that diet alone can have a substantive effect on lowering CRP levels. Physicians should remember that advice on diet, exercise, and smoking cessation remains crucial for our high CRP patients."

Arch Intern Med. 2007;167:502-506.

The complete contents of Heartwire, a professional news service of WebMD, can be found at www.theheart.org, a Web site for cardiovascular healthcare professionals.

Clinical Context

Current evidence supports that higher levels of inflammatory markers, such as CRP, are associated with an increased risk for cardiovascular events. Elevation of CRP levels has specifically been linked to insulin resistance, hypertension, the development of diabetes mellitus, and metabolic syndrome. A proposed intervention to lower levels of inflammatory markers is a high-fiber diet.

The aim of this study was to examine whether a high-fiber diet would reduce inflammatory markers and to compare the results from a diet supplemented with fiber vs a diet that is naturally high in fiber.

Study Highlights

  • In this crossover intervention trial, 35 participants (18 lean normotensive and 17 obese hypertensive individuals) were randomized to 2 diets: a high-fiber (30 g/day) DASH diet or fiber-supplemented diet (30 g/day). The diets were implemented after a baseline (regular) diet period of 3 weeks.
  • The study included 28 women and 7 men aged 18 to 49 years; 16 (46%) were black, and the remainder were white.
  • Lean normotensive volunteers had body mass indexes less than 25 kg/m2, waist (abdominal)-to-hip circumference ratios of less than 0.80 for women and less than 0.85 for men; blood pressure consistently lower than 130/85 mm Hg on all 3 visits prior to the first study, fasting glucose level less than 110 mg/dL (< 6.1 mmol/L), glycated hemoglobin (HbA1c) level less than 5.6%, fasting triglycerides level less than 125 mg/dL (< 1.41 mmol/L), high-density lipoprotein cholesterol level greater than 40 mg/dL (> 1.04 mmol/L) for men and greater than 45 mg/dL (> 1.17 mmol/L) for women, and total cholesterol level less than 200 mg/dL (< 5.18 mmol/L).
  • Obese, hypertensive (high normal, stage 1) volunteers had body mass indexes of 27 kg/m2 or greater and had 3 or more of the following characteristics: a waist circumference greater than 40 inches (> 101.6 cm) for men and greater than 35 inches (> 88.9 cm) for women, blood pressure consistently in the range of 130/85 to 159/99 mm Hg on 3 visits prior to the first study day, not taking medications, fasting glucose level less than 126 mg/dL (< 7.0 mmol/L; individuals with diabetes mellitus were excluded, but those with impaired fasting glucose included), HbA1c level less than 7%, and fasting triglyceride levels greater than 150 mg/dL (> 1.70 mmol/L) or high-density lipoprotein cholesterol levels less than 50 mg/dL for women (< 1.30 mmol/L) and less than 40 mg/dL (< 1.04 mmol/L) for men.
  • The mean (SD) fiber intake on baseline diets was 11.9 (0.3) g/day; on the high-fiber DASH diet, 27.7 (0.6) g/day; and on the supplemented diet, 26.3 (0.4) g/day.
  • Overall, the mean CRP level changed from 4.4 to 3.8 mg/L (-13.7%; P = .046) in the high-fiber DASH diet group and to 3.6 mg/L (-18.1%) in the fiber-supplemented diet group (P = .02).
  • CRP levels decreased in the 18 lean normotensive participants in either intervention diet group (2.0 mg/L [baseline] vs 1.4 mg/L [high-fiber DASH] vs 1.2 mg/L [supplemented]; P < .05) but did not change significantly (7.1 mg/L [baseline] vs 6.2 mg/L [high-fiber DASH] vs 6.5 mg/L [supplemented]; P > .05) in obese hypertensive participants.
  • Other inflammatory markers measured included the fibrinogen level and the white blood cell count. However, these levels did not change in either intervention diet group (P = .91).
  • Weight, triglyceride level, cholesterol level, and insulin resistance did not change in either intervention diet group (P > .05 for all).
  • Neither age nor race influenced the response of CRP levels to the diets.
  • No evidence of a crossover effect was detected.
  • Limitations to the study included the short duration of each diet (3 weeks), and the addition of magnesium and potassium to the supplemental fiber may complicate the replication of these results in practice.

Pearls for Practice

  • Elevated CRP levels are associated with the development of cardiovascular disease, insulin resistance, hypertension, the development of diabetes mellitus, and metabolic syndrome.
  • This study demonstrated that fiber intake of about 30 g/day from a diet naturally rich in fiber or from a supplement can reduce levels of CRP.

Submitted by DMorgan on Fri, 03/30/2007 - 10:12pm.

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