Dietary fiber intake might reduce cardiovascular risk factor levels and, in turn, might lower the long-term risk of cardiovascular disease (CVD). A total of 11,113 subjects, aged 20 to 79 years with no history of CVD, from the 2005 to 2010 National Health and Nutrition Examination Survey were included in the present study to examine associations of dietary fiber intake with predicted lifetime CVD risk and C-reactive protein levels. Dietary fiber intake showed a significant gradient association with the likelihood of having a low or an intermediate predicted lifetime CVD risk among young and middle-age adults. In fully adjusted multinomial logistic models, dietary fiber intake was related to a low lifetime CVD risk with an odds ratio of 2.71 (95% confidence interval 2.05 to 3.59) in the young adults and 2.13 (95% confidence interval 1.42 to 3.20) in the middle-age adults and was related to an intermediate lifetime risk of 2.65 (95% confidence interval 1.79 to 3.92) in the young and 1.98 (95% confidence interval 1.32 to 2.98) in the middle-age adults compared with a high lifetime risk. A significant inverse linear association was seen between dietary fiber intake and log-transformed C-reactive protein levels with a regression coefficient ± standard error of −0.18 ± 0.04 in the highest quartile of fiber intake compared with the lowest fiber intake. In conclusion, these data suggest that dietary fiber intake is independently associated with the predicted lifetime CVD risk, especially in young and middle-age adults. A greater amount of dietary fiber intake might be associated with lower C-reactive protein levels.
Epidemiologic studies examining the association of dietary intake and cardiovascular disease (CVD) have reported that greater dietary fiber intake is associated with a lower risk of CVD events in short- and intermediate-term follow-up. However, it is unclear whether a dose-response relation exists between dietary fiber intake and long-term risk of CVD. Knowledge of the association between dietary fiber intake and the predicted lifetime CVD risk could help guide clinical and public health recommendations regarding optimal dietary patterns to improve long-term survival free of CVD. C-reactive protein (CRP), a nonspecific biomarker of inflammation, has been shown to be a consistent risk marker for incident CVD. The available reports have also supported the hypothesis of a potential correlation between dietary fiber intake and CRP levels in selected samples ; however, more contemporary nationally representative data are limited. Thus, the primary objective of the present study was to examine the dose-response associations between dietary fiber intake and the predicted long-term CVD risk and CRP levels in a representative sample of the United States population.
Methods
All participants were from the National Health and Nutrition Examination Surveys (NHANES) data sets. Detailed methods and protocols for the present study have been previously reported. Originally, there were 31,034 participants in the 2005 to 2006, 2007 to 2008, and 2009 to 2010 NHANES cycles. We hierarchically excluded lactating or pregnant women (n = 615), those <20 or >79 years old (n = 15,106), those with a CVD history (n = 1,650), those with an energy intake greater than or less than the plausible intake (<600 or >6,000 kcal/day for women or <800 or >8,000 kcal/day for men; n = 1,298), and those with incomplete data (n = 1,252). A total of 11,113 participants were pooled and included in the analyses.
Race was categorized as non-Hispanic white, non-Hispanic African-American, American Hispanic, or other. Current smoking, diabetic status, physical activity, alcohol drinking, and education and income level were all determined from subject self-response to questionnaires. Low physical activity was defined as <1 min/wk of moderate to vigorous intensity activity. Heavy alcohol drinking was defined as >2 drinks/day for men or >1 drink/day for women. Dietary fiber intake in the NHANES was determined from 2 interviewer-administered 24-hour recalls, developed and validated by the U.S. Department of Agriculture. Each unique food of a listing of the foods recorded during the NHANES data collection was matched to a corresponding food item listed in the U.S. Department of Agriculture nutrient database by name and available nutrient content. Participants’ dietary intake of total fiber (in grams per 24 hours) was calculated. The use of fiber supplements was not included in the daily total because of limited information regarding the type and quantity. Subject height and weight were measured during the clinical examination and used to calculate the body mass index. The CRP level was measured using high-sensitivity latex-enhanced nephelometry for quantitative CRP determination.
The predicted lifetime risk for CVD was estimated using our previously published algorithm ( Table 1 ). This algorithm was developed in the Framingham cohorts, and it has been shown to stratify the lifetime CVD risk in adults. This algorithm has been validated across the spectrum of age, gender, and race using pooled data from numerous United States-based cohort studies in the Cardiovascular Lifetime Risk Pooling Project. The participants were stratified a priori into 3 mutually exclusive groups according to their predicted lifetime risk of CVD: low (“all optimal” or “not optimal risk factors”), intermediate (“elevated risk factors”), and high (“any major risk factors”) predicted lifetime risk group.
| CVD Risk Factor | Optimal RF | Not Optimal RF | Elevated RF | Major RF |
|---|---|---|---|---|
| Systolic/diastolic blood pressure (mm Hg) | <120/<80 | 120–139/80–89 | 140–159/90–99 | ≥160/≥100 or treated |
| And | Or | Or | Or | |
| Total cholesterol (mg/dl) | <180 | 180–199 | 200–239 | ≥240 or treated |
| And | And | And | Or | |
| Diabetes mellitus | No | No | No | Yes |
| And | And | And | Or | |
| Current smoker | No | No | No | Yes |
| Lifetime risk stratification | Low | Intermediate | High | |
∗ Lifetime risk indicates the probability that one will develop CVD in one’s lifetime.
To incorporate the complex, multistage sampling design of the NHANES in the statistical analysis, the SAS procedures SURVEYFREQ, SURVEYMEANS, SURVEYREG, and SURVEYLOGISTIC were used. Dietary fiber intake was used as both continuous and categorical variables (quartiles) in the analysis. Multinomial logistic regression analyses were performed to assess the independent association of dietary fiber intake with predicted CVD risk status (low, intermediate, and high). The analyses were stratified into 3 age groups a priori: young (age 20 to 39 years), middle (age 40 to 59 years), and old (age 60 to 79 years). We used multivariate linear regression models to assess the association of log-transformed CRP and dietary fiber intake. A 2-tailed p value <0.05 was considered statistically significant.
Results
Of the 11,113 participants, representing 156.9 million United States adults, the mean age was 44.5 years, 50.2% were women, and 70.7% were non-Hispanic white. The average dietary fiber intake was 16.8 g/day (range 0 to 80.0). The characteristics of the study participants are listed in Table 2 . Within each age stratum, those with greater dietary fiber intake were ∼1 year older, more likely to be women, less likely to drink alcohol, and more likely to have greater social and economic status and greater physical activity. Furthermore, greater dietary fiber intake was associated with lower intake of total energy and saturated fatty acids, greater intake of whole grains, fruits, and vegetables, and less calorie consumption from sugar-sweetened beverages. The mean dietary fiber intake was ∼1.3- to ∼1.6-fold greater in the highest fiber intake quartile compared with the lowest quartile across all 3 age groups. Overall, <15% of the study participants reported consuming the recommended amount of 25 g/day of dietary fiber intake.
| Variable | Age 20–39 (n = 4,218) | Age 40–59 (n = 4,056) | Age 60–79 (n = 2,839) | |||
|---|---|---|---|---|---|---|
| Q1 | Q4 | Q1 | Q4 | Q1 | Q4 | |
| Age (yrs) | 29.1 ± 0.2 | 30.6 ± 0.3 | 48.1 ± 0.3 | 49.6 ± 0.2 | 67.0 ± 0.3 | 68.1 ± 0.3 |
| Non-Hispanic white | 508 (66.5) | 413 (59.8) | 520 (73.4) | 396 (68.5) | 382 (81.2) | 342 (77.4) |
| Male gender | 663 (64.6) | 446 (41.6) | 623 (62.4) | 423 (37.6) | 376 (53.5) | 264 (35.2) |
| Low physical activity | 289 (23.9) | 252 (19.2) | 387 (33.2) | 342 (26.1) | 371 (47.2) | 266 (29.3) |
| Heavy alcohol drinking | 677 (65.2) | 509 (48.7) | 568 (55.9) | 327 (33.4) | 258 (34.6) | 151 (18.5) |
| Education less than high school | 239 (20.9) | 264 (19.6) | 200 (16.1) | 241 (14.1) | 261 (27.4) | 232 (18.6) |
| Income <$45,000 | 644 (44.2) | 490 (35.9) | 549 (34.1) | 412 (27.1) | 457 (50.9) | 417 (45.4) |
| Energy (kcal) | 2,537 ± 30.8 | 1,972.3 ± 29.9 | 2,436.9 ± 33.7 | 1,873.5 ± 28.1 | 2,013.3 ± 36.3 | 1,653.8 ± 23.4 |
| Saturated fatty acids (g) | 31.6 ± 0.5 | 21.3 ± 0.4 | 33.6 ± 0.7 | 19.8 ± 0.5 | 28.3 ± 0.8 | 17.5 ± 0.5 |
| Sodium (g) | 3,955.9 ± 39.7 | 3,429.4 ± 41.8 | 3,954.9 ± 37.9 | 3,240.6 ± 38.6 | 3,283.5 ± 70.4 | 2,836.3 ± 64.7 |
| Whole grain (serving/day) | 0.27 ± 0.02 | 0.93 ± 0.06 | 0.35 ± 0.03 | 1.17 ± 0.07 | 0.41 ± 0.03 | 1.29 ± 0.07 |
| Sugar-sweetened beverage (kcal/day) | 252.3 ± 15.2 | 82.1 ± 4.0 | 171.2 ± 9.5 | 48.0 ± 3.7 | 123.2 ± 9.9 | 29.0 ± 3.7 |
| Fruit (serving/day) | 0.49 ± 0.03 | 1.44 ± 0.07 | 0.48 ± 0.04 | 1.64 ± 0.07 | 0.58 ± 0.04 | 1.78 ± 0.05 |
| Vegetables (serving/day) | 1.00 ± 0.03 | 1.79 ± 0.05 | 1.13 ± 0.03 | 2.01 ± 0.05 | 1.09 ± 0.04 | 1.99 ± 0.05 |
| Dietary fiber (g/day) | 10.3 ± 0.2 | 23.5 ± 0.4 | 11.1 ± 0.2 | 24.7 ± 0.5 | 11.1 ± 0.2 | 22.7 ± 0.4 |
∗ Q1 represents the lowest quartile of fiber intake, and Q4, the highest.
Greater dietary fiber intake was inversely associated with blood pressure, serum total cholesterol, body mass index, smoking status, and serum insulin levels ( Table 3 ). In contrast, it was positively associated with serum high-density lipoprotein cholesterol levels. Participants with high dietary fiber intake were more likely to have a low or an intermediate predicted lifetime risk. Furthermore, the CRP concentrations decreased with increasing levels of dietary fiber intake.
| Age 20–39 (n = 4,218) | Age 40–59 (n = 4,056) | Age 60–79 (n = 2,839) | ||||
|---|---|---|---|---|---|---|
| Q1 | Q4 | Q1 | Q4 | Q1 | Q4 | |
| Systolic blood pressure (mm Hg) | 117 ± 0.4 | 112 ± 0.4 | 122 ± 0.7 | 119 ± 0.7 | 132 ± 0.9 | 130 ± 1.1 |
| Diastolic blood pressure (mm Hg) | 69 ± 0.4 | 67 ± 0.3 | 74 ± 0.5 | 73 ± 0.4 | 68 ± 0.7 | 67 ± 0.7 |
| Total cholesterol (mg/dl) | 189.3 ± 1.6 | 186.3 ± 1.5 | 208.9 ± 1.7 | 207.7 ± 1.7 | 203.6 ± 2.7 | 203.3 ± 2.3 |
| HDL cholesterol (mg/dl) | 48.9 ± 0.8 | 53.3 ± 0.5 | 52.3 ± 0.8 | 56.1 ± 0.6 | 54.8 ± 1.0 | 58.2 ± 1.0 |
| BMI (kg/m 2 ) | 28.7 ± 0.3 | 26.9 ± 0.2 | 29.2 ± 0.2 | 28.4 ± 0.3 | 29.4 ± 0.3 | 28.0 ± 0.3 |
| Serum insulin (μU/ml) | 13.3 ± 1.1 | 10.6 ± 0.5 | 13.9 ± 0.6 | 12.4 ± 0.9 | 13.6 ± 0.7 | 11.4 ± 0.7 |
| Antihypertensive medication use | 57 (4.4) | 23 (2.2) | 233 (19.5) | 189 (19.9) | 357 (46.3) | 381 (44.7) |
| Lipid-lowering medication use | 21 (2.1) | 16 (1.5) | 118 (12.3) | 117 (12.0) | 219 (33.0) | 231 (30.7) |
| Current smoker | 562 (48.4) | 207 (17.6) | 478 (38.0) | 187 (14.4) | 189 (22.4) | 67 (8.2) |
| Diabetes mellitus | 33 (2.5) | 36 (2.9) | 90 (7.1) | 127 (9.7) | 151 (19.5) | 171 (18.1) |
| Low predicted LTR | 316 (30.0) | 543 (51.8) | 142 (14.0) | 232 (24.6) | 49 (7.7) | 61 (9.1) |
| Intermediate predicted LTR | 149 (13.5) | 201 (20.8) | 158 (16.7) | 242 (23.4) | 83 (10.9) | 96 (14.1) |
| CRP (mg/L) | 2.2 ± 0. 1 | 1.9 ± 0.1 | 2.5 ± 0.1 | 2.0 ± 0.1 | 2.7 ± 0.2 | 2.2 ± 0.1 |
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