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Original Research Communications |
1 From the Center for Cardiovascular Disease Control, University of Mas-sachusetts–Lowell; Research and Development, Medical Foods, Inc, Cambridge, MA; the Department of Psychiatry and the Nutrition and Infection Laboratory, Harvard Medical School; the Centers for the Study of Nutrition and Medicine and for Nutritional Research, and Clowes Surgical Metabolism Laboratory, Beth Israel Deaconess Medical Center, Boston.
2 Conflict of interest: SJB conducted the study while at the Beth Israel Medical Center and is now the vice president of research and development for Medical Foods, Inc, Cambridge, MA, who licensed the application for ß– glucan fiber from Alpha-Beta Technology, Inc, Worcester, MA; RAF received research support from Medical Foods, Inc, and how serves on their Scientific Advisory Board; BRB is a consultant to Medical Foods, Inc and Alpha-Beta Technology, Inc for the cholestrol-lowering properties of the yeast-derived fiber; RN is a consultant to Alpha-Beta Technology, Inc.
3 Supported in part by Alpha-Beta Technology, Inc.
4 Address correspondence to RA Forse, Boston Medical Center Place, Boston Medical Center, Boston, MA 02118.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONSUBJECTS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Objective: The purpose of this study was to evaluate the effect on serum lipids of a yeast-derived ß-glucan fiber in 15 free-living, obese, hypercholesterolemic men.
Design: After a 3-wk period in which subjects ate their usual diet, 15 g fiber/d was added to the diet for 8 wk and then stopped for 4 wk. Plasma lipids were measured weekly during baseline and at week 7 and 8 of fiber consumption, and again at week 12.
Results: Compared with baseline, fiber consumption significantly reduced plasma total cholesterol (by 8% at week 7 and 6% at week 8; P < 0.05 using Bonferroni correction); week 12 values did not differ from baseline. No significant differences were noted between baseline LDL cholesterol and values at weeks 7, 8, or 12 when comparing individual groups by using Bonferroni correction, even though the overall one-way analysis of variance with repeated measures was highly significant (P < 0.001). LDL-cholesterol concentrations did decline by 8% at week 8 compared with baseline. There was a significant effect of diet on plasma HDL-cholesterol concentrations (P < 0.005 by one-way ANOVA with repeated measures). However, a group difference was observed only between baseline and week 12 (16% increase; P < 0.05 by Bonferroni correction). Triacylglycerol concentrations did not change.
Conclusions: The yeast-derived ß-glucan fiber significantly lowered total cholesterol concentrations and was well tolerated; HDL-cholesterol concentrations rose, but only 4 wk after the fiber was stopped.
Key Words: ß-glucan • dietary fiber • oat fiber • serum cholesterol • low-density-lipoprotein cholesterol • high-density-lipoprotein cholesterol • HDL cholesterol • LDL cholesterol
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONSUBJECTS AND METHODSRESULTSDISCUSSIONREFERENCES |
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1.1 million each year. The link between elevated plasma LDL-cholesterol concentrations and the risk of developing coronary artery disease has been clearly established (2). Cholesterol-lowering medications are reserved for patients who have not reduced their cholesterol concentrations sufficiently with dietary management and exercise, have already had an infarction or stroke, or do not meet the American Heart Association guidelines for acceptable serum lipid concentrations (3). The National Cholesterol Education Program (NCEP; 3) recommends that most patients with abnormal serum lipid profiles follow the Step I diet plan. The dietary modifications involved include reducing total fat intake to <30% of total energy intake, total saturated fat to <10% of total energy intake, and dietary cholesterol to <300 mg/d. If serum total cholesterol concentrations are not then reduced to values <6.2 mmol/L (240 mg/dL), then the stricter Step II diet should be followed. This diet plan further restricts saturated fat consumption to <7% of total energy and dietary cholesterol to <200 mg/d (1).
Not included in NCEP guidelines are specific recommendations about dietary fiber, although reports indicate that the addition of certain fibers to the diet reduces total cholesterol concentration (4). Recently, the Food and Drug Administration allowed that claim to be made for products containing 
0.75 g ß-glucan from oat products (5). The decision was based on a meta-analysis of numerous reports of studies in hypercholesterolemic patients consuming oat products (6). Patients in these studies achieved reductions in total cholesterol concentrations of 2–18%, depending on the amount and type of oat product, the amount of ß-glucan, and initial total cholesterol concentrations. A reduction in total cholesterol of just 1% could reduce heart disease mortality by 2% (7, 8).
Spent yeast (from breweries or bakeries) is a rich source of ß-glucans. After processing, the yeast contains 85–90% ß-glucan, consisting of repeating units of ß-D-glucose joined together in ß-(1
3) (16) linkages. Physically, the ß-glucans are discrete, hollow microspheres that are highly miscible in most liquids and will not gel. ß-glucan is composed of both soluble and insoluble fiber. Other soluble fibers such as pectin and psyllium tend to clump and gel when mixed with liquids.
The ß-glucan from oat fiber has been shown to improve lipid profiles. The purpose of this study was to examine the effect on blood lipids of yeast-derived ß-glucan fiber in hypercholesterolemic obese individuals to confirm that the yeast source of this fiber works in a similar way.
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SUBJECTS AND METHODS |
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TOPABSTRACTINTRODUCTIONSUBJECTS AND METHODSRESULTSDISCUSSIONREFERENCES |
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120% of ideal weight, and had serum total cholesterol concentrations >6.21 mmol/L (240 mg/dL). Candidates taking cholesterol-lowering medication or who had conditions that are secondary causes of hyperlipidemia such as hypothyroidism, diabetes mellitus, or renal disease were excluded from the study. The study protocol was approved by the Beth Israel Deaconess Medical Center Institutional Review Board.
Nineteen subjects entered the study but 4 of the 15 subjects dropped out during the 3-wk run-in period. A total of 15 subjects completed the study and had blood lipid data available for basal values, week 7, week 8, and week 12. Of the 15 subjects who completed the study, only 12 had data relating to anthropometry, nutrient intake (Table 1
), and clinical tolerance (Table 2).
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Each week the fiber was consumed, subjects completed questionnaires designed to gauge the effect of the product. Assessment was made of 1) the degree of satiety (when the subject felt fullness and the general feeling of fullness throughout the day), 2) product tolerance (abdominal discomfort, diarrhea, nausea, vomiting, and flatulence), and 3) product acceptability (thickness, consistency, color, flavor, aroma, and aftertaste). Satiety was rated on a scale of 0 to 10, with 0 being "hungry" and 10 being "extremely full." Tolerance was assessed at 4 levels: 0 for no adverse effects, 1 for slight awareness, 2 for moderate discomfort, and 3 for marked discomfort. Product acceptability was rated on a scale of 1 to 9, with 1 being the worst attribute (eg, gritty, chalky consistency) and 9 the best attribute (eg, smooth consistency).
Statistical analyses
Data are presented as means ± SDs, except for satiety, tolerance, and acceptability, which are presented as means and medians. One-way analysis of variance (ANOVA) was used for univariate and multivariate repeated-measures analysis (more than one measurement of each subject) with the SYSTAT statistical software program (SYSTAT, Evanston, IL). Statistical significance was determined at the 95% confidence level. Group comparison between the baseline value and each of the treatment [week 7, week 8, and posttreatment (week 12)] weeks was determined by Bonferroni correction, only when ANOVA, as defined above, was found to be significant.
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RESULTS |
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TOPABSTRACTINTRODUCTIONSUBJECTS AND METHODSRESULTSDISCUSSIONREFERENCES |
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). Nutrient intake during the baseline and fiber-treatment periods was not different (9.23 ± 2.16 MJ at baseline compared with 11.61 ± 1.61 MJ during treatment) except for the fiber supplement during the treatment phase. All subjects consumed 15 g fiber daily in addition to their usual diet during the 8-wk study period. Subjects consumed sufficient energy to maintain their body weight during the study.
Changes in plasma lipids
Significant differences were found in total cholesterol (P < 0.05), LDL-cholesterol (P < 0.001), and HDL-cholesterol (P < 0.005 by one-way ANOVA with repeated measures; Figures 1 and 2) concentrations with ß-glucan supplementation. After 7 wk of supplementation, serum total cholesterol concentration was significantly lower than at baseline (6.38 ± 0.44 compared with 5.90 ± 0.68 mmol/L; P < 0.05 by Bonferroni correction). At week 8, total cholesterol concentration was 5.98 ± 0.57 mmol/L, which was also significantly lower (by 6%) than at baseline (P < 0.01 by Bonferroni correction). There was no significant difference in total cholesterol concentration between baseline and week 12.
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No significant differences were observed for LDL-cholesterol concentrations between baseline and weeks 7, 8, and 12 when individual groups were compared by using Bonferroni correction, even though the overall ANOVA with repeated measures was highly significant (P < 0.001). Compared with baseline values, LDL-cholesterol concentration tended to decline by 5% at week 7 and by 8% at week 8.
The mean ratio of total to HDL cholesterol declined during fiber supplementation, which was marginally significant (P = 0.06 by one-way ANOVA with repeated measures; Figure 3). However, the change in this ratio was significant by the single degree-of-freedom polynomial contrast (P < 0.05). Fiber supplementation led to a reduction in the ratio of total to HDL cholesterol from 8.2 at baseline to 7.3 at week 7 and to 7.0 at week 8 (P < 0.05 with Bonferroni correction). This ratio returned to baseline at week 12.
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). Fiber effects such as diarrhea, nausea, abdominal discomfort, abdominal distension, and flatulence were minimal (<1, indicating slight awareness of symptoms that were easily tolerated). There were no reports of vomiting.
The product was moderately well accepted (Table 2). Each of the 6 attributes rated (thickness, consistency, color, flavor, aroma, and aftertaste) had a mean and median of 4 or 5 on a scale of 0 to 9.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONSUBJECTS AND METHODSRESULTSDISCUSSIONREFERENCES |
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The yeast-derived ß-glucan fiber lowered total cholesterol and raised HDL-cholesterol concentrations significantly. The use of dietary fibers rich in ß-glucans from oats has a similar effect on serum lipids. Hypercholesterolemic subjects similar to those consuming the yeast-derived ß-glucan in this study, who consumed oat products in addition to their usual diets, showed reduced total cholesterol concentrations. A review of 24 studies in which hypercholesterolemic subjects consumed oat products showed that total cholesterol concentrations declined by 0.8–26% (4). Two of these studies reported increases in total cholesterol concentrations. Six reported a decrease of <5% from baseline total cholesterol, 7 reported decreases of 5–10%, 6 reported decreases of >10% and <15%, and 2 reported decreases of 19.3% and 26%. (One study reported no data for total cholesterol.)
Oat products can be expected to reduce LDL-cholesterol concentrations by between 4.6% and 24%; 5 of the 24 studies reported no significant reduction and 4 did not report data on LDL-cholesterol concentration (4). Nine studies reported that subjects experienced reductions in LDL-cholesterol concentrations of 
10%. This is similar to what was found when comparable subjects were given yeast-derived ß-glucan. Only 6 of the studies using oat products showed greater reductions in LDL-cholesterol concentrations.
Unlike the significant increases in HDL-cholesterol concentrations observed 4 wk after the end of the study for subjects receiving the yeast-derived ß-glucan, none of the 24 studies of oat products reported significant changes in HDL concentration. Moreover, psyllium alone does not appear to raise HDL-cholesterol concentration (11). However, when psyllium was consumed in conjunction with an NCEP Step I diet that was low in dietary fat, saturated fat, and cholesterol, HDL-cholesterol concentrations increased in healthy children aged 2–11 y (12). Because higher HDL-cholesterol concentrations are associated with a reduced risk of developing coronary artery disease, there may be unique benefits of using the yeast-derived ß-glucan, and perhaps psyllium, rather than the oat products.
HDL-cholesterol concentrations did not increase immediately with consumption of the yeast ß-glucan fiber, rather, it took 12 wk, which was 4 wk after the cessation of the yeast ß-glucan fiber supplement. The mechanism for the increase in HDL-cholesterol concentrations with the yeast product is unknown. It may be that the amount of ß-glucan is the key determinant of whether HDL-cholesterol concentration increases. Twelve grams of yeast ß-glucan were administered in this study; most of the studies in which oats were evaluated provided only 3 g ß-glucan (4, 6). When 14 healthy subjects consumed a higher amount of ß-glucan from oat gum (9 g), HDL-cholesterol concentrations increased (13). Beer et al (13), however, argued that the solubility and viscosity of the ß-glucan are more important than the amount consumed for the effect on serum lipids. An increase in HDL-cholesterol concentrations was observed when oat gum was used (in contrast with oat bran) and the authors attributed this to the low solubility and the moderate molecular weight of the oat gum, which resulted in low viscosity in the gut (13). The yeast ß-glucan used in this study also had a low solubility and a low viscosity. Thus, it is not apparent whether the high amount of ß-glucan or its low viscosity contributed to the increases in HDL- cholesterol concentrations because we and Beer et al used materials with both properties.
The changes in blood lipid concentrations with supplementation with oat products varied substantially between studies. The wide variation may be due to several factors (4). First, it is likely that baseline serum lipid concentrations affected how much serum lipid concentrations changed. Subjects with baseline serum total cholesterol concentrations >6.2 mmol/L had the greatest absolute reductions. We would expect to observe the same phenomenon with the yeast fiber. Second, subjects received different quantities of oat products (7.2–110 g). The largest quantities of oat products did not always result in the greatest reductions in serum lipid concentrations. Rather, the type, form, and soluble fiber and ß-glucan content dictated changes in serum lipid concentrations. It may be possible to obtain significant reductions in total cholesterol and LDL cholesterol with less yeast fiber. Third, the duration of the study may have influenced the results on serum lipid concentrations, although there was no direct correlation between duration of the study and the percentage change in serum lipid concentrations. Three weeks of oat product use appeared to be adequate to cause an observable effect. Because serum concentrations were not measured before 6 wk, we do not know whether significant reductions occurred sooner than this. To our knowledge, this is the only study published on the yeast ß-glucan product.
Others have reported that the soluble fiber psyllium can reduce serum total cholesterol concentrations (14). Subjects who received 10.2 g psyllium seed husk for 24 wk experienced a 5.3% reduction in LDL-cholesterol concentrations compared with a control group. This is similar to our findings for subjects who used the yeast-derived ß-glucan and to those who used oat products (4). However, in addition to the psyllium, the subjects followed the NCEP Step I diet, which alone reduces LDL-cholesterol concentrations. Thus, it appears that the yeast fiber and oat products may cause a greater reduction in LDL-cholesterol concentrations than psyllium alone. HDL-cholesterol concentrations did not increase in this study of adults (14), unlike the study in children cited earlier (12).
Data were compiled from 5 published studies in which subjects followed the NCEP Step II diet alone (2). This diet is another way to reduce the risk of developing coronary artery disease by lowering serum total cholesterol and LDL-cholesterol concentrations. The average decrease in LDL cholesterol was 18.9% for men (baseline: 3.67 ± 0.88 mmol/L) and 15.6% for women (baseline: 3.44 ± 1.09 mmol/L). This effect was greater than what was reported for oat products and for yeast-derived ß-glucan, but it was negated by a significant decrease in HDL-cholesterol concentrations (P < 0.0001).
The yeast-derived ß-glucan was well-tolerated in modest amounts and produced results similar to those of oat products. More volume and energy from the oat products must be consumed than of the yeast fiber to bring about a significant effect on serum lipid concentrations. The yeast-derived ß-glucan fiber has an added benefit over the NCEP Step II diet because it raises HDL-cholesterol concentrations, whereas the diet reduces them. Thus, the yeast product may be superior to oat products because of its unique effect on HDL-cholesterol concentrations and its greater concentration of the active ingredient, ß-glucan. The relative efficiency of yeast-derived ß-glucan compared with that of the NCEP Step II diet is probably best assessed in terms of the ratios of LDL to HDL cholesterol and of total to HDL cholesterol, which are similar. Yeast-derived ß-glucan reduces LDL-cholesterol concentrations less and increases HDL-cholesterol concentrations more than does the NCEP Step II diet. It would be interesting to study whether there would be additional benefits of yeast-derived ß-glucan fiber when combined with an NCEP Step II diet because LDL-cholesterol concentrations might be lowered further and HDL-cholesterol concentrations may be restored or increased over baseline values. This combination might obviate the need for drugs in some cases.
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ACKNOWLEDGMENTS |
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REFERENCES |
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