These foods are big contributors of fiber in our diet and fiber helps to lower levels of blood cholesterol. Guess what that means? Yes, you guessed it. There are two types of fiber: soluble and insoluble. Why is topical vitamin C important for skin health? Preventing preeclampsia may be as simple as taking an aspirin. Caring for an aging parent? Tips for enjoying holiday meals. A conversation about reducing the harms of social media. Menopause and memory: Know the facts.
How to get your child to put away toys. Is a common pain reliever safe during pregnancy? Heart Health Fiber-full eating for better health and lower cholesterol June 24, Recipe Notes Cooked and seasoned red lentils 1 cup raw lentils to 3 cups water, bring to a boil and simmer for 15 minutes, then sprinkle with sea salt and lemon juice.
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For example, Bell et al 13 examined the hypocholesterolemic effects of psyllium-and pectin-enriched cereals in a randomized, controlled study. They found that the psyllium-enriched cereal lowered cholesterol more effectively than the pectin-enriched cereal.
Also, trials of oat products suggested that hypercholesterolemic patients are more responsive than normolipidemic persons 14 , Concurrent changes in fat and cholesterol caused by inadequate dietary control can confound the relation between increased fiber intake and blood cholesterol concentrations. For this reason, quantitating the direct effect of fiber on cholesterol lowering, in addition to that attributed to displacement of saturated and trans -unsaturated fat in the diet, is difficult.
In this meta-analysis of controlled trials, we evaluated the cholesterol-lowering effects of several water-soluble fibers. We studied the influence on blood lipid changes of fiber type, dosage, initial cholesterol concentration, concurrent changes in dietary fat and cholesterol, and other aspects of the study designs.
Trials of the effects of dietary fiber on blood cholesterol concentrations in adults were identified by a computerized literature search MEDLINE; National Library of Medicine, Bethesda, MD of articles published from to June and examination of cited reference sources.
Only published trials reported in English were considered; however, we included one unpublished trial by Beling et al ; provided by Quaker Oats, Chicago , which has been previously referenced in the literature For studies with parallel group designs, lipid effects were calculated by subtracting the mean change in the control low fiber group from that in the treatment high fiber group.
In crossover studies, the estimate represents the difference in posttreatment lipid concentrations for the high-fiber and low-fiber periods. The net change was divided by the daily dose of soluble fiber. Individual studies were weighted by the inverse of the variance of the fiber effect.
For each trial, we estimated the SE of the treatment effect for the lipid outcome measures by using the SDs of paired differences follow-up minus initial for the treatment and control groups. The within-study SE was divided by the average daily dose for each study to estimate the SE of the treatment effect per gram fiber. We were unable to calculate the correct within-study SEs for more than two-thirds of the trials on the basis of the published data few reported exact probability values or CIs for the group differences described above.
As an alternative, we estimated the SE by using previously published methods and data from the Lipid Research Clinics 23—28; Appendix A. We computed summary estimates effect sizes of the net lipid changes by combining the mean effect sizes reported by individual studies weighted by the inverse of the individual and between-study variance according to a random effects model Summary estimates were computed for each type of soluble fiber separately and for all fibers combined.
For meta-analyses of each fiber type, we selected one set of lipid results per study to avoid undue weighting of a study. For instance, for the trial by Kestin et al 30 , comparing oat bran, wheat bran, and rice bran, we selected the effect size comparing oat bran and wheat bran because wheat was the most often used control fiber in the studies included in the meta-analysis.
When more than one dose was studied 31 — 33 , the mean lipid change across all doses was used to provide an average effect size. However, each dose was represented separately in the dose-response analysis. Weighted least-squares regression analyses were performed by using the general linear models procedure of the SAS program 34 to test for differences in lipid changes without dividing by the dose of soluble fiber.
In addition to the amount of soluble fiber, the following independent variables were included in the model: initial cholesterol concentration; type of dietary fiber; study design parallel or crossover ; health status of study population healthy, hyperlipidemic, or diabetic ; mean age; background diet low-fat, low-cholesterol diet compared with usual diet ; dietary changes change in the high-fiber period minus change in the low-fiber period in total fat, saturated fat, and dietary cholesterol; type of control low-fiber control product compared with diet only ; and treatment length.
All models were weighted by using the inverse of the variance of each effect estimate. Models of dose response dose of specific fiber and dose response stratified by initial cholesterol concentration were examined by forcing the intercept through zero.
Further modeling was done to determine the effects of variability of these covariates among studies as predictors of changes in blood lipids after the amount of soluble fiber and initial lipid concentrations were controlled for.
We did not assume a zero-intercept model to examine the influence of these other covariates. A two-sided significance level of 0. We calculated predicted changes in blood cholesterol from changes in dietary fatty acids and cholesterol by using the equations of Keys et al 18 and Mensink and Katan 35 when sufficient dietary data were included in the published reports. This calculation was used to determine whether lipid changes could be attributed to dietary changes other than the inclusion of soluble fiber in the diet.
An adjusted effect size for soluble fibers was computed for each trial by subtracting the expected lipid changes from the observed lipid changes the combined effect of fat and fiber. A new summary effect size was then calculated by using the adjusted values for each trial.
We reviewed clinical studies reporting the effects of oat products, psyllium, pectin, or guar fiber on blood cholesterol. A description of the individual trials considered for this meta-analysis may be requested by contacting the corresponding author. Seventy published reports were identified for a quantitative analysis. Three of these studies were included only in the dose-response analysis because they did not use a true low-fiber control but rather compared a high with a lower dose of the same intervention fiber 36 — The 67 trials included in the analysis are summarized in Table 1 and included 25 trials of oat products 30 — 33 , 39 — 59 , 17 of psyllium 13 , 60 — 74 , 7 of pectin 13 , 75 — 80 , and 18 of guar gum 81 — Not all trials of different fiber sources provided total cholesterol, LDL-cholesterol, HDL-cholesterol, and triacylglycerol concentrations.
Summary of trials included in the meta-analysis 1. Not all studies of different fiber sources provided total, LDL-, and HDL-cholesterol and triacylglycerol concentrations. The number of male and female subjects does not equal the total number of subjects because some studies did not specify the sex of the subjects. Meta-analysis included 67 trials; however, studies did not necessarily report measurements of all 4 lipid changes total cholesterol, LDL cholesterol, HDL cholesterol, and triacylglycerol.
The meta-analyses included subjects men, women, sex not specified whose average age was 50 y. The average dose of 9. During the high-fiber intervention, subjects consumed an average of kJ more energy than during the control period. Both groups receiving the high- and low-soluble-fiber interventions lost weight, 0. Soluble fiber intake did not significantly affect triacylglycerol concentrations: 0.
Net change in blood lipids in subjects consuming diets high in soluble fiber compared with low-fiber diets 1. P, parallel study; X, crossover study; T, treated; C, control. Average daily dose of soluble fiber: oat products, 5. Net change expressed as the value during the high-fiber diet minus that during the control low fiber period.
We were unable to analyze guar studies separately because of the limited number of studies within the restricted dose range. The net change in total and LDL cholesterol is plotted against the mean daily dose of soluble fiber in Figure 1.
The plot suggests a nonlinear dose response. To test for nonlinearity, an exponential term for dose natural log of the amount of soluble fiber was used in the weighted least-squares regression models. Relation between dose of soluble fiber and mean lipid changes.
For each study, the net change in total cholesterol and LDL cholesterol expressed as the change during the high-soluble-fiber period minus the change during the low-soluble-fiber period is plotted against the mean daily dose of soluble fiber.
All models were weighted by using the inverse of the variance of each effect size and forcing the intercept through zero. Individual studies with low variance in the meta-analysis are denoted with circles around the point estimates. There was no significant dose-response relation between soluble fiber and changes in HDL-cholesterol or triacylglycerol concentrations. Soluble fiber from oat products, psyllium, pectin, and guar gum each significantly lowered total cholesterol Figure 2 , Table 2.
These values were slightly higher when the meta-analysis was repeated for the practical dose range. Psyllium and guar gum lowered HDL cholesterol significantly but minimally Table 2. None of the soluble fibers affected triacylglycerols. Type of soluble fiber was not a significant predictor of lipid changes after the initial lipid concentration was controlled for by linear regression. Net change in total cholesterol.
The net effect of consumption of different dietary fibers on total cholesterol concentrations for oat products, psyllium, pectin, and guar gum. Note that one guar study 85 did not include measures for total cholesterol.
After dose of soluble fiber and initial lipid concentrations were controlled for, none of the following factors was a significant predictor of changes in blood lipids: type of study design, type of control, treatment length, background diet, type of subject, weight change, or changes in dietary intake of fat and cholesterol. There were 13 oat, 6 psyllium, and 3 pectin studies with doses of soluble fiber ranging between 2. Most of the studies reported reductions in total cholesterol that were greater than predicted from changes in fatty acid or cholesterol intake.
Thus, because the adjusted estimates were similar to the unadjusted estimates, the observed lipid changes cannot be attributed primarily to the substitution of dietary fats and cholesterol for dietary fiber within this subset of trials.
This analysis of 67 controlled clinical trials indicated that diets high in soluble fiber decrease total and LDL cholesterol. Dietary fiber had a small HDL-lowering effect at the borderline of statistical significance and did not affect triacylglycerol concentrations.
There was substantial heterogeneity among individual studies, suggesting that effects of fiber are not uniform. Differences in the dose of soluble fiber accounted for some of the variability in study results. We found significant nonlinearity at higher doses, which may have been due to diminished adherence or a biological maximum being reached at higher doses Our primary dose-response analyses were conducted by assuming a zero intercept.
Analyses allowing a nonzero intercept produced a slightly smaller effect of fiber because the intercepts were negative. This suggests that cholesterol would decrease in the treatment group even if there was no added fiber in the high-fiber group.
This could result from nonlinearity of the relation between fiber intake and change in lipids or residual confounding by other important factors, such as body weight or dietary fat changes, for which we were unable to adequately control. For example, although we found that the changes in blood cholesterol could not be attributed to the substitution of fiber for dietary fats and cholesterol in most of the studies with available data, most of the published reports did not provide sufficient dietary data.
This lack of sufficient data limits our ability to conclusively rule out this possibility. We also cannot rule out chance as an explanation because the intercepts were not significantly different from zero. The mechanism by which fiber lowers blood cholesterol remains undefined. Evidence suggests that some soluble fibers bind bile acids or cholesterol during the intraluminal formation of micelles The resulting reduction in the cholesterol content of liver cells leads to an up-regulation of the LDL receptors and thus increased clearance of LDL cholesterol.
However, increased bile acid excretion may not be sufficient to account for the observed cholesterol reduction Other suggested mechanisms include inhibition of hepatic fatty acid synthesis by products of fermentation production of short-chain fatty acids such as acetate, butyrate, propionate ; changes in intestinal motility ; fibers with high viscosity causing slowed absorption of macronutrients, leading to increased insulin sensitivity ; and increased satiety, leading to lower overall energy intake Our data do not support previous findings that patients with hypercholesterolemia are more responsive to dietary fiber than are healthy individuals 14 , We did, however, find that initial LDL cholesterol was a moderately significant predictor of LDL-cholesterol changes, but the difference in responsiveness was small: 0.
Most of the available epidemiologic studies suggest that dietary fiber is inversely related to coronary artery disease 5 , — Earlier studies suggested that the effects of fiber may be larger than those shown in this meta-analysis. However, methodologic problems including small sample sizes, incomplete dietary measures, and inadequate control of important confounders made it difficult to determine the effects of dietary fiber independently of other dietary components and, more specifically, the contribution of soluble compared with insoluble fiber.
The modest reductions in cholesterol expected from intakes of soluble fiber within practical ranges may exert only a small effect on the risk of heart disease. These findings are consistent with an earlier summary of the cholesterol-lowering effects of oat products Publication bias toward studies that showed positive results is always a potential issue in meta-analyses and could be operating in this study.
If this were true, then the small effect estimates associated with intake of dietary soluble fiber would be further attenuated, further highlighting the need for conservative public health claims. The major benefit from eating fiber-rich foods may be a change in dietary pattern, resulting in a diet that is lower in saturated and trans-unsaturated fats and cholesterol and higher in protective nutrients such as unsaturated fatty acids, minerals, folate, and antioxidant vitamins.
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