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Etiology

Increased fiber intake in men was associated with reduced MI

ACP J Club. 1996 July-Aug.;125:23. doi:10.7326/ACPJC-1996-125-1-023


Source Citation

Rimm EB, Ascherio A, Giovannucci E, et al. Vegetable, fruit, and cereal fiber intake and risk of coronary heart disease among men. JAMA. 1996 Feb 14;275:447-51. [PubMed ID: 8627965]


Abstract

Objective

To determine the relation between dietary fiber and fatal coronary artery disease (CAD) and nonfatal myocardial infarction (MI).

Design

6-year cohort study of men enrolled in the Health Professionals Follow-up Study.

Setting

United States.

Participants

51 529 men who were health professionals were enrolled in the study in 1986 when they were between 40 and 75 years old. Exclusion criteria were daily energy intake outside the range of 3360 to 17 640 kJ, missing data on food questionnaires, or cardiovascular disease or diabetes reported at baseline. Data from 43 757 men were included.

Assessment of risk factors

Baseline questionnaires were used to gather data on physical activity; frequency of intake of 131 foods; and specific brands of breakfast cereals, multivitamins, and cooking oils. The average daily and energy-adjusted fiber intakes were calculated for each man. The fiber data were divided into 5 quintiles of consumption (median intakes of 12.4, 16.6, 19.6, 23.0, and 28.9 g of fiber/d).

Main outcome measures

Fatal CAD and nonfatal MI were the main outcome measures. They were confirmed by follow-up questionnaires; medical records and autopsy reports; and interviews with men, families, and physicians.

Main results

Relative risks (RRs) were adjusted for age in 5-year categories and other risk factors using multivariate analyses. During follow-up, 229 fatal CAD events and 511 nonfatal MIs occurred; 6 men had both. Only men in the highest quintile of fiber consumption compared with men in the lowest quintile of consumption had reductions in risk. For fatal CAD events, the age-adjusted RR was 0.45 (95% CI 0.28 to 0.72, P for trend < 0.001); for nonfatal MI, the age-adjusted RR was 0.65 (CI 0.49 to 0.88, P for trend = 0.02); and for the combined end points, the age-adjusted RR was 0.59 (CI 0.46 to 0.76, P for the trend < 0.001). When the fiber data were divided into sources of fiber, only the intake of cereal fiber (not vegetable or fruit fiber) was associated with a decreased risk for MI in the highest quintile of consumption (multivariate RR 0.73, CI 0.56 to 0.94, P for trend = 0.02); this pattern remained consistent after controlling for the intake of carotene, folate, and vitamin B6.

Conclusion

Men who consumed high levels of dietary fiber had a reduced risk for fatal coronary artery disease events and nonfatal myocardial infarction.

Source of funding: National Institutes of Health.

For article reprint: Dr. E.B. Rimm, Department of Nutrition, Harvard School of Public Health, 665 Huntington Avenue, Boston, MA 02115, USA. FAX 617-432-2435.


Updated Commentary

Increased fiber intake in men was associated with reduced MI

What we eat affects our risk for developing CAD. The best evidence that supports the "diet-heart" hypothesis comes from the many studies that have examined the effects of saturated fat and cholesterol consumption on the risk for CAD. Other dietary factors, such as intake of alcohol, fiber, omega-3 polyunsaturated fatty acids, and nutrient antioxidants, however, may also affect CAD risk. The studies by Knekt and Rimm and their colleagues examined the role of flavonoid and fiber consumption as predictors of incident CAD.

Dietary flavonoids are water-soluble antioxidants found in fruits (e.g., apples, cranberries, and strawberries); vegetables (e.g., onions and broccoli); red wine; and tea. In the study by Knekt and colleagues, Finnish men and women with very low flavonoid consumption were at increased risk for CAD mortality. The association was stronger among women than men but appeared to be confounded by other dietary factors, particularly dietary fat and fiber. Although this study concurs with 2 previously published reports (1, 2), flavonoids have not been consistently associated with CAD risk (3, 4). Because of the relative weakness of the associations; the inability to control for important CAD risk factors, such as diabetes mellitus, alcohol consumption, and high-density lipoprotein (HDL) cholesterol level; and a study population of Finnish adults who consume very low levels of flavonoids compared with other populations (5) should be interpreted cautiously.

Rimm and colleagues examined the relation between dietary fiber consumption and risk for CAD among men. Because increased dietary fiber intake may lower glucose and cholesterol levels and, perhaps, caloric intake, it may be associated with CAD risk. Previous studies reported an inverse association between fiber consumption and CAD risk (6). After controlling for potential confounders, including dietary fat intake, Rimm and colleagues found that each 10-gram increase in daily fiber intake was associated with an approximately 20% reduction in CAD risk. Unexpectedly, insoluble fiber (rather than soluble fiber) and cereal fiber (rather than fruit or vegetable fiber) accounted for this association. A biologic explanation for the protective association between insoluble fiber and CAD risk is lacking. Although the authors controlled for the effects of many variables, the possibility that increased cereal fiber intake is a marker for a healthy lifestyle cannot be discounted.

Should physicians counsel their patients to consume large quantities of onions and apples for their flavonoid content and cereal products for their insoluble fiber content? These 2 studies provide evidence of the potential importance of specific dietary components, but their findings should be placed in the context of previous research, particularly because the few prospective studies that have examined the relation of flavonoids and CAD have produced inconsistent findings and there is, as yet, no biologic explanation about how insoluble cereal fiber may act to reduce CAD risk. Based on existing evidence, current recommendations about fruit, vegetable, and fiber consumption seem reasonable: Consume 5 or more servings of fruits and vegetables daily, and 6 or more servings of breads, cereals, and legumes daily (3). A decreased risk for CAD was observed by Knekt and colleagues at flavonoid intakes of 4.8 to 5.5 mg/d or greater. Comparable intakes should be readily achievable by following current recommendations for fruit and vegetable consumption. Rimm and colleagues found that men who consumed the most fiber had the lowest risk for CAD. On average, American men and women consume approximately 18 grams and 12 grams of fiber/d, respectively (4). Current guidelines recommend a higher level of consumption: 20 to 30 grams daily. Achieving this goal may be difficult, but most persons should be encouraged to increase their fiber intake.

Joel A. Simon, MD, MPH
San Francisco Veterans Affairs Medical CenterUniversity of California, San FranciscoSan Francisco, California, USA


References

1. Hertog MG, Feskens EJ, Hollman PC, Katan MB, Kromhout D. Dietary antioxidant flavonoids and risk of coronary heart disease: the Zutphen Elderly Study. Lancet. 1993;342:1007-11.

2. Yochum L, Kushi LH, Meyer K, Folsom AR. Dietary flavonoid intake and risk of cardiovascular disease in postmenopausal women. Am J Epidemiol. 1999;149:942-9.

3. Rimm EB, Katan MB, Ascherio A, Stampfer MJ, Willett WC. Relation between intake of flavonoids and risk for coronary heart disease in male health professionals. Ann Intern Med. 1996;125:384-9.Hertog MGL, Swetnam PM, Fehily AM, Elwood PC, Kromhout D

4. Hertog MGL, Swetnam PM, Fehily AM, Elwood PC, Kromhout D. Antioxidant flavonols and ischemic heart disease in a Welsh population of men: the Caerphilly Study. Am J Clin Nutr. 1997;65:1489-94.

5. Hertog MG, Kromhout D, Aravanis C, et al. Flavonoid intake and long-term risk of coronary heart disease and cancer in the Seven Countries Study. Arch Intern Med. 1995;155:381-6.

6. Committee on Diet and Health, Food and Nutrition Board, National Research Council. In: Diet and health: implications for reducing chronic disease risk. Washington, DC: National Academy Press. 1989:19:5-6.