- Click here for explanation of classification scheme.

The purpose of this study was to conduct a pooled analysis of dietary fiber and its sub-types and risk of coronary heart disease.

 

• Published prospective study
• At least 150 incident coronary cases
• Assessment of usual dietary intake and a validation study of diet assessment method or closely-related instrument.

 

 

• Absence of dietary fiber intake data
• Investigators do not agree to include data.

• Studies were identified through literature searches and inquiring with experts in the field
• Study quality was not assessed.

 

• In all studies, diet was measured at baseline using a food frequency questionnaire (nine studies) or diet history instrument (one study)
• Investigators examined:
  • Total dietary fiber
  • Fiber intake from three different food group sources (cereals, fruits and vegetables)
  • Insoluble fiber (hemicellulose, cellulose and lignins)
  • Soluble fiber (pecans, gums and mucilage)
• *Fiber from cereals, fruits and vegetables was available for all studies with exceptions of two
• *A wide variety of foods contributed to each fiber type with the relative contribution from certain foods varying among studies
• *Starchy vegetables, such as corn and peas, contributed substantially to vegetable fiber in all studies
• *Only six studies had estimates of insoluble and soluble fiber
• Standardized criteria were used to ascertain cases of fatal and non-fatal acute myocardial infarction in all studies.  Because one study had only self-reported data on incidents of CHD, investigators only used fatal coronary cases from this study.
• Three regression models were computed:
  • Model 1: Age (in years), energy intake (kcal per day), smoking status (never or current) and dose (1 to 4, 5 to 15, 15 to 24, and >25 per day), body mass index (<23, 23 to <25, 25 to <27.5, 27.5 to <30 or >30), physical activity (levels 1 to 5), education (less than high school, high school, more than high school), alcohol intake, multiple vitamin use (yes or no), hypercholesterolemia (yes or no) and hypertension (yes or no).
  • Model 2: Covariates in Model 1 and energy-adjusted quintiles of dietary saturated fat, polyunsaturated fat and cholesterol
  • Model 3: Covariates in Model 2 and also energy-adjusted quintiles of dietary and supplement sources of folic acid and vitamin E
• Before performing the regression analysis, dietary fiber and all dietary covariates were adjusted within each study for energy intake
• Investigators analyzed the energy-adjusted dietary fiber as a continuous variable (increment of 10g per day)

 

• 10 articles were included
• 14 articles were identified
• *3 investigators chose not to include data
• *1 did not included data on dietary fiber
• All studies were prospective cohorts:
  • 91,058 men
  • 245,186 women
  • 2,506,581 person-years of follow-up
• Number of cardiovascular events:
  • 5,249 events
  • 2,011 fatal cases.

• In analysis adjusted for all demographic and non-dietary lifestyle factors, for each 10g per day increment in dietary fiber, investigators observed pooled reductions in risk of 12% for all coronary events and 19% for coronary deaths. There was little attenuation of pooled estimates with adjustment for Model 2 and Model 3 (Table 1).
• With adjustment for all demographic, lifestyle and dietary factors: Investigators observed pooled reductions in risk of all coronary events of 10% for each 10g per day increment of cereal and 16% per 10g per day increment of fruit fiber, although the finding for cereal fiber had a CI that included 1.00 (Table 2). 
• Associations were stronger for coronary deaths than for all events, with reductions in risk of 25% for cereal fiber and 30% for fruit fiber for each 10g per day increment. 
• Vegetable fiber was not associated with CHD incidence or mortality
• To determine if the associations observed for cereal and fruit fiber were independent, investigators included these fiber types in the same regression model. The results were similar for:
  • All events:
    • Fruit fiber: RR 0.81; CI 0.69 to 0.95
    • Cereal fiber: RR 0.89; CI 0.76 to 1.05
  • Deaths:
    • Fruit fiber: RR 0.65; CI 0.49 to 0.86
    • Cereal fiber: RR 0.71; CI 0.59 to 0.87 
• Associations were stronger for soluble fiber than insoluble fiber
  • Soluble: 
    • All events: RR per 10g per day increment, 0.72; CI, 0.55 to 0.93
    • Deaths: RR, 0.46; CI 0.28 to 0.74
  • Insoluble: 
    • All events: RR per 10g per day increment, 0.90; CI 0.83 to 0.97
    • Deaths RR, 0.80; CI 0.69 to 0.92 
• The only observation of heterogeneity in RRs was for the analysis of cereal fiber and total coronary events, in which three cohorts of women had RRs greater than 1.00 (Table 2). 

Table 1 Study-Specific and Pooled Multivariate Relative Risks (95% Confidence Intervals) of Coronary Heart Disease per 10g per day increments of Total Dietary Fiber

Studies	All Events			Deaths
	Model 1	Model 2	Model 3	Model 1	Model 2	Model 3
AHS
Men	0.84	0.89	1.04 (0.43-2.57)	0.56	0.22	0.32 (0.05-2.18)
Women	1.39	1.53	1.44 (0.46-4.36)	1.55	1.45	1.85 (0.28-12.1)
ARIC
Men	0.94	1.00	1.02 (0.74-1.40)	0.70	0.71	0.54 (0.19-1.57)
Women	0.66	0.67	0.73 (0.39-1.34)	0.70	---	---
ATBC (men only)	0.96	0.95	0.96 (0.85-1.09)	0.84	0.81	0.84 (0.69-1.03)
FMC
Men	0.89	0.89	0.97 (0.74-1.28)	0.83	0.73	0.74 (0.49-1.12)
Women	0.61	0.58	0.74 (0.42-1.31)	0.59	0.44	0.33 (0.09-1.22)
GPS
Men	0.87	0.83	0.93 (0.54-1.59)	1.00	1.53	1.66 (0.66-4.20)
Women	1.02	1.44	1.00 (0.34-2.98)	0.94	0.81	0.37 (0.04-3.91)
HPFS	0.85	0.84	0.87 (0.78-0.92)	0.77	0.82	0.84 (0.69-1.03)
IWHS	---	---	---	0.78	0.78	0.80 (0.61-1.04)
NHSa	0.95	0.94	0.96 (0.72-1.27)	1.05	1.14	0.96 (0.55-1.67)
NHSb	0.84	0.82	0.87 (0.72-1.05)	0.79	0.81	0.75 (053-1.02)
VIP
Men	0.95	0.82	0.91 (0.63-1.31)	0.69	0.55	0.53 (0.24-1.15)
Women	1.11	2.02	3.18 (0.98-10.37	0.65	---	---
WHS	0.75	0.74	0.77 (0.50-1.17)	1.46	4.70	1.77 (0.24-12.90)
Pooled	0.88 (0.84-0.93)	0.88 (0.83-0.94)	0.81	0.81 (0.74-0.88)	0.81(0.72-0.92)	0.81 (0.73-0.91)
P-value for relative risk	<0.001	<0.001	0.005	<0.001	0.001	<0.001
P-value for heterogeneity	0.42	0.39	0.82	0.85	0.29	0.73
After measurement error correction			0.85 (0.78-0.96)			0.73 (0.61-0.87)
P-value for relative risk†			0.005			<0.001
P-value for heterogeneity ‡			0.93			0.83

  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Abbreviations: Adventists  Health Study (AHS), Atherosclerosis Risk in Communities Study (ARIC), Alpha-Tocopherol Beta-Carotene Cancer Prevention Study (ATBC), Finnish Mobile Clinic Health Examination Survey (FMC), Glostrup Population Study (GPS), Health Professionals Follow-up Study (HPFS), Iowa Women’s Health Study (IWHS), Nurses Health Study 1980 to 1986 (NHSa), Nurses Health Study 1986 to 1996 (NHSb), Vasterbotten Intervention Program (VIP), Women’s Health Study (WHS).

*Model 1 includes age, energy intake, smoking status and dose, body mass index, physical activity, education, alcohol intake, multiple vitamin use, hypercholesterolemia and hypertension. Model 2: Covariates in Model 1 and energy-adjusted quintiles of dietary saturated fat, polyunsaturated fat and cholesterol. Model 3: Covariates in Model 2 and also energy-adjusted quintiles of dietary and supplement sources of folic acid and vitamin E.

  † P-value, test for no association

  ‡ P-value, test for between-studies heterogeneity. 

Table 2. Study-Specific and Pooled Multivariate Relative Risks (95% Confidence Intervals) of Coronary Heart Diease per 10g per day Increments of Cereal Fiber, Fruit Fiber and Vegetable Fiber

Studies	All Events			Deaths
	Cereal	Fruit	Vegetable	Cereal	Fruit	Vegetables
ARIC
Men	0.68	0.90	1.17	0.90	0.20	1.79
Women	1.95	0.54	1.62	---	---	---
ATBC (men only)	1.02	0.72	0.64	0.94	0.41	0.57
FMC
Men	0.95	1.27	1.00	0.82	1.10	0.34
Women	0.75	1.49	0.47	0.44	0.25	1.97
HPFS	0.77	0.76	0.98	0.68	0.74	1.13
IWHS	----	---	---	0.49	0.70	0.98
NHSa	1. 69	0.74	1.07	1.34	0.95	1.10
NHSb	0.66	1.02	1.16	0.61	0.92	0.98
VIP
Men	0.83	1.30	1.24	0.54	0.12	3.11
Women	3.52	8.23	0.09	---	---	---
WHS	0.93	0.45	0.90	0.03	3.93	0.44
Pooled	0.90 (0.77-1.07)	0.84 (0.74-0.88)	1.00 (0.88-1.13)	0.75 (0.63-0.89)	0.70 (0.55-0.89)	1.00 (0.82-1.23)
P-value for relative risk†	0.23	0.04	0.97	0.003	0.004	0.97
P-value for heterogeneity‡	0.02	0.24	0.46	0.30	0.39	0.46

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Abbreviations: Atherosclerosis Risk in Communities Study (ARIC), Alpha-Tocopherol Beta-Carotene Cancer Prevention Study (ATBC), Finnish Mobile Clinic Health Examination Survey (FMC), Health Professionals Follow-up Study (HPFS), Iowa Women’s Health Study (IWHS), Nurses Health Study 1980 to1986 (NHSa), Nurses Health Study 1986 to 1996 (NHSb), Vasterbotten Intervention Program (VIP), Women Health Study  (WHS). 

*Model 1 includes age, energy intake, smoking status and dose, BMI, physical activity, education, alcohol intake, multiple vitamin use, hypercholesterolemia and HTN. Model 2: Covariates in Model 1 and energy-adjusted quintiles of dietary saturated fat, polyunsaturated fat and cholesterol. Model 3: Covariates in Model 2 and also energy-adjusted quintiles of dietary and supplement sources of folic acid and vitamin E.

     † P-value, test for no association

     ‡ P-value, test for between-studies heterogeneity.

• Dietary fiber intake during adulthood is inversely associated with CHD risk. Coronary risk was 10% to 30% lower for each 10g per day increment of total, cereal or fruit fiber. 
• Cereal and fruit fiber had strong inverse associations with CHD risk
• No such associations were observed for vegetable fiber
• These associations seemed to be independent of other dietary factors, sex, age, baseline body mass index, smoking, history of hypertension, diabetes and hypercholesterolemia 
• The only observation of heterogeneity in RRs was for the analysis of cereal fiber and total coronary events, in which three cohorts of women had RRs greater than 1.00.

 

Government:	NIDDK, NIH
Industry:	General Mills Food Company:
Not-for-profit	0 Foundation associated with industry:

• Inverse associations for both types of fiber are presented in the analysis, but only six studies estimated insoluble and soluble fiber, and there is no standard method used to derive these estimates 
• The information from this study is generalizable to the adult population.