|
|
||||||||
ORIGINAL RESEARCH COMMUNICATION |
1 From the Department of Human Biology, Maastricht University, Maastricht, Netherlands (EK, ABvR, and RPM); the Division of Biomedical Nutrition, Centre for Chemistry and Chemical Engineering, University of Lund, Lund, Sweden (GÖ); CEBA AB, Lund, Sweden (RÖ); and Döhler GmbH, Darmstadt, Germany (MW)
2 This study does not necessarily reflect the views of the European Commission and in no way anticipates the Commissions future policy in this area.
3 Supported by grant no. QLK1-CT-2000-00535 from the European Commission, as part of a European Union project entitled "Design of foods with improved functionality and superior health effects using cereal ß-glucans."
4 Reprints not available. Address correspondence to RP Mensink, Department of Human Biology, Maastricht University, PO Box 616, 6200 MD, Maastricht, Netherlands. E-mail: r.mensink{at}hb.unimaas.nl.
| ABSTRACT |
|---|
|
|
|---|
Objectives: We examined the effects of a ß-glucanenriched fruit juice on serum lipids and lipoproteins and on markers of cholesterol absorption (serum concentrations of plant sterols) and synthesis (serum concentrations of lathosterol). In addition, we measured effects on lipid-soluble antioxidants.
Design: After a 3-wk run-in period, healthy subjects consumed daily a fruit drink providing 5 g rice starch [placebo (control) group; n = 22] or ß-glucan from oats (n = 25) for 5 wk (parallel design). At the end of the run-in period and at the end of the intervention, blood samples were taken for analysis of lipids and lipoproteins, noncholesterol sterols, and fat-soluble antioxidants. Changes between the end of the run-in period and the end of the intervention were calculated for each subject. Differences in changes between the groups were analyzed statistically.
Results: The differences between the control and ß-glucan groups in the change in serum concentrations of total and LDL cholesterol, respectively, were 4.8% (P = 0.012) and 7.7% (P = 0.005). The differences between the groups in the change in serum concentrations of lathosterol and sitosterol were 13% (P = 0.023) and 11% (P = 0.030), respectively. No significant effects were found on fat-soluble antioxidants.
Conclusions: ß-Glucan lowers serum concentrations of total and LDL cholesterol when incorporated into a fruit drink. A reduced cholesterol absorption contributes to the cholesterol-lowering effect of ß-glucan without affecting plasma concentrations of lipid-soluble antioxidants.
Key Words: ß-Glucan cholesterol lathosterol sitosterol campesterol antioxidants healthy subjects
| INTRODUCTION |
|---|
|
|
|---|
4)linked glucose units separated every 23 units by ß-(1
3)linked glucose. This soluble fiber, which is present in oats, has received much attention, because of its potential to reduce LDL cholesterol. In 1997, therefore, the Food and Drug Administration allowed the health claim that a diet high in soluble fiber from whole oats (oat bran, oatmeal, and oat flour) and low in saturated fat and cholesterol may reduce the risk of cardiovascular disease (1). Indeed, many studies showed the LDL cholesterollowering effects of products enriched with ß-glucan (2), although some studies did not (3, 4). Differences in solubility and molecular weights of the ß-glucans used may explain these contrasting findings, because those characteristics affect intestinal viscosity (57). A greater intestinal viscosity and the subsequently lower bile acid absorption constitute one of the proposed mechanisms by which ß-glucan reduces serum cholesterol concentrations (810). In addition, the increased intestinal viscosity may lower cholesterol absorption (9, 10), although reduced cholesterol absorption was not found in other studies (8, 11). It has also been suggested that intestinal viscosity depends on the method of food processing or on the food matrix of the ß-glucanrich product (12). If this is true, then it is difficult to predict the cholesterol-lowering effect of a food product enriched with ß-glucan. In the current study, we therefore examined the effects of a fruit drink enriched with ß-glucan on the serum lipoprotein profile. To further elucidate the mechanism of action, we examined effects of the fruit drink on markers of cholesterol absorption (serum concentrations of plant sterols) and synthesis (serum concentrations of lathosterol). A greater intestinal viscosity may enlarge the intestinal unstirred-water layer (13), which suggests that ß-glucan may also affect the absorption of other fat-soluble components. Therefore, plasma concentrations of lipid-soluble antioxidants were also analyzed. | SUBJECTS AND METHODS |
|---|
|
|
|---|
5% in the previous 3 mo), no intention to change the physical activity pattern during the study, no use of medication or a prescribed diet known to affect lipid metabolism, no current pregnancy or breastfeeding, no participation in another biochemical trial at the same time, willingness to stop the consumption of vitamin supplements or products enriched with plant stanol or sterol esters 3 wk before the start of the study, and no holiday planned in the weeks of blood sampling. During the screening visits, blood pressure, body weight, and height were measured and a urine sample was analyzed for the presence of glucose. Blood samples were taken from fasting subjects for lipid and lipoprotein analysis at intervals of
3 d. All subjects completed a medical questionnaire. Forty-eight subjects were included in the study. They had mean serum concentrations of
8.0 mmol total cholesterol/L and
4.0 mmol triacylglycerol/L; no indications for treatment for hyperlipidemia according to the Dutch Cholesterol Consensus (14); diastolic and systolic blood pressure
95 mm Hg and
160 mm Hg, respectively; no presence of glucosuria; no clinical condition known to affect lipid metabolism; no drug or alcohol abuse; and no history of coronary artery disease, decompensatio cordis (class III or IV), cardiomyopathy or kidney, liver, or pancreatic disease or malignancy <5 y ago. At the start of the trial, one man decided for personal reasons not to participate. Thus, 47 subjects (18 men and 29 women) began the study.
The women were
± SD 49 ± 16 y old and had a BMI of 23 ± 3. Their mean serum concentrations of total, LDL, and HDL cholesterol and triacylglycerol were 6.71 ± 0.77, 4.33 ± 0.68, 1.63 ± 0.40, and 1.66 ± 0.64 mmol/L, respectively. Eight women smoked, 9 used oral contraceptives, and 12 were menopausal. The men were aged 56 ± 9 y and had a BMI of 26 ± 2. Their mean serum concentrations of total, LDL, and HDL cholesterol and triacylglycerol were 7.25 ± 0.61, 4.97 ± 0.53, 1.53 ± 0.23, and 1.62 ± 0.49 mmol/L, respectively. Two of the men were smokers.
All subjects gave written informed consent before entering the study. The study protocol was approved by the Ethics Committee of Maastricht University.
Study design
The study was a placebo-controlled, double-blind parallel design. During the first 3 wk of the study (run-in period), subjects consumed 2 packages (250 mL each) of a fruit drink, which provided 5 g rice starch (placebo) per day. Then, the volunteers were randomly allocated to 1 of 2 treatment groups. For the next 5 wk of the study, one group continued to consume daily 500 mL of the placebo fruit drink (n = 22), and the other group received daily the fruit drink enriched with 5 g ß-glucan from oats (n = 25). Subjects were required to consume the beverages during 2 of the 3 main meals (breakfast, lunch, and dinner) and to record in their diaries the daily time of consumption and any signs of illness or physical discomfort.
ß-Glucan preparations were manufactured by CEBA AB (Lund, Sweden). The fruit drinks, with an apple or pear taste, were produced by Döhler GmbH (Darmstadt, Germany; Table 1
). The beverages were sent to Maastricht at regular intervals during the study. Subjects visited the department at least every other week to receive a supply of experimental beverages or for blood sampling. Subjects received exactly the amount of fruit drink that they were to consume between 2 visits at the department.
|
Methods
At weeks 0, 2, 3, 7, and 8, subjects were weighed after an overnight fast, while they were wearing light indoor clothing and no shoes, and fasting blood samples were taken. At each occasion, a 10-mL serum tube (Becton Dickinson Vacutainer Systems, Franklin Lakes, NJ) was used. To obtain serum, the tube was left for
1 h after venipuncture at room temperature. Serum was prepared by centrifuging the tube at 2000 x g for 30 min at 4 °C. Serum samples were stored at 20°C until the end of the study. In all serum samples, total cholesterol (ABX Diagnostics, Montpellier, France), HDL cholesterol (precipitation method; Roche Diagnostics Corporation, Indianapolis, IN), and triacylglycerol with correction for free glycerol (Sigma Aldrich Chemie, Steinheim, Germany) were analyzed enzymatically. Serum LDL-cholesterol concentrations were calculated by using the formula of Friedewald et al (16). Serum concentrations of plant sterols were analyzed as described elsewhere (17). At weeks 2, 3, 7, and 8, blood was also sampled in a 10-mL EDTA-coated tube (Becton Dickinson). To obtain plasma for measurements of concentrations of lipid-soluble antioxidants (ie,
-carotene, ß-carotene, lycopene, lutein, canthaxanthin, ß-cryptoxanthin,
-tocopherol, ß+
- tocopherol,
-tocopherol, and phytofluene) and retinol, the EDTA-coated tube was centrifuged at 2000 x g for 30 min at 4°C. Plasma concentrations of retinol and these lipid-soluble antioxidants were analyzed as described elsewhere (17). Before analyses, plasma samples from weeks 2 and 3 and from weeks 7 and 8 were pooled. At weeks 0, 3, and 8, hematologic variables (ie, the number of white blood cells, red blood cells, and platelets) were analyzed in blood from the EDTA-coated tubes on a Coulter Counter (MD series; Beckman Coulter, Inc, Miami, FL), and variables of liver function (eg, alanine aminotransferase, aspartate aminotransferase, bilirubin,
-glutamyltransferase, and alkaline phosphatase), kidney function (creatinine), and inflammation (C-reactive protein) were analyzed with the use of a Beckman Synchron CX7 System (Beckman Instruments, Inc, Palo Alto, CA).
Statistical analysis
Before the start of the study, it was calculated that the power needed to detect a difference of 0.30 mmol/L between the treatment groups was 80%. For lipids and lipoproteins, results of the serum samples taken at the end of the run-in period (weeks 2 and 3) and at the end of the intervention period (weeks 7 and 8) were averaged before statistical analysis. For each subject, responses to the fruit drinks were calculated as the change between values at the end of the run-in period and those at the end of the intervention period. Differences between groups in serum concentrations of lipids and lipoproteins, plant sterols and stanols, and body weight and nutrient intake were evaluated by analysis of variance. Differences between groups in variables that were not normally distributed (eg, lipid-soluble antioxidant concentrations, hematologic variables, and variables of liver function, kidney function, and inflammation) were analyzed by using the Mann-Whitney test.
Statistical analyses were performed by using SPSS for MACINTOSH software (version 11.0; SPSS, Chicago, IL). Values are presented as mean (±SD), and nonnormally distributed values are presented as median (range). P < 0.05 was considered significant.
| RESULTS |
|---|
|
|
|---|
Inspection of the diaries showed no serious deviations from the protocol, except by one subject in the ß-glucan group, who did not consume 4 drinks during the run-in period (week 3) or 8 drinks during the intervention period (weeks 4 and 5). Exclusion of this subject did not change the outcomes of the study.
Changes in body weight were 0.2 ± 1.1 kg for the control group and 0.5 ± 1.0 kg for the ß-glucan group (P = 0.363). There were no significant differences between the groups in the number of white blood cells, red blood cells, or platelets or in serum concentrations of alanine aminotransferase, aspartate aminotransferase, bilirubin,
-glutamyltransferase, alkaline phosphatase, creatinine, and C-reactive protein (data not shown).
Serum lipids and lipoproteins
Mean changes in serum concentrations of lipids and lipoproteins are shown in Table 2
. Compared with the changes in the control group, the changes in serum concentrations of total and LDL cholesterol in the ß-glucan group were 0.30 mmol/L or 4.8% (95% CI for the difference: 0.07, 0.52 mmol/L) for total cholesterol and 0.31 mmol/L or 7.7% for LDL cholesterol (95% CI for the difference: 0.10, 0.52 mmol/L). No significant differences between the groups were observed in changes in serum concentrations of HDL cholesterol (95% CI for the difference: 0.02, 0.08 mmol/L) or triacylglycerol (95% CI for the difference: 0.32, 0.24 mmol/L) or in the ratio of total to HDL cholesterol (95% CI for the difference: 0.03, 0.41). Except for total:HDL (P = 0.033), variables at the end of the run-in period did not differ significantly between the groups.
|
|
-carotene, ß-carotene, and lycopene) tended be lower in the ß-glucan group than in the control group. No differences in LDL cholesterolstandardized plasma concentrations of antioxidants were observed between the groups. | DISCUSSION |
|---|
|
|
|---|
Why ß-glucan can lower serum LDL-cholesterol concentrations is not clear. One of the proposed mechanisms is that ß-glucan binds bile acids or increases intestinal viscosity, which results in a decreased reabsorption of bile acids and increased fecal bile acid excretion (810). As a consequence, bile acid synthesis and excretion into the intestine are increased (23). At the same time, hepatic cholesterol synthesis will also increase (8) because of a higher need for cholesterol in the liver for bile acid production (8). Indeed, in a study with ileostomy subjects (8), a strong positive correlation was found between changes in lathosterol concentrations and bile acid excretion. Thus, the increased cholesterol synthesis after ß-glucan consumption in the current study may be due to increased bile acid excretion. However, higher choleterol synthesis can also be due to lower cholesterol absorption. We measured cholesterol-standardized campesterol and sitosterol concentrations as markers of cholesterol absorption. Concentrations of both markers decreased, which suggested less cholesterol absorption, although only the effect on sitosterol was statistically significant. Our findings agree with the increased excretion of plant sterols and the reduced cholesterol absorption found in ileostomy subjects after consumption of ß-glucan (9). On the other hand, Lia et al (8) did not find changes in cholesterol absorption in ileostomy subjects after consumption of ß-glucan, but they mentioned that this finding should be interpreted with caution because of a low statistical power. In addition, Uusitupa et al (11) did not find any significant change in serum concentrations of campesterol or sitosterol during consumption of 10 g ß-glucan/d for 8 wk. However, serum concentrations of total cholesterol also did not change. On the basis of these findings, we conclude that not only increased bile acid synthesis but also decreased cholesterol absorption contributes to the cholesterol-lowering effect of ß-glucan.
Because ß-glucan may enlarge the intestinal unstirred-water layer (13), the absorption of lipid-soluble antioxidants may also be affected. However, we did not observe any change in absolute or LDL cholesterolstandardized concentrations of lipid-soluble antioxidants, although absolute plasma concentrations of lycopene and total hydrocarbon carotenoids (ie,
-carotene, ß-carotene, and lycopene) tended to decrease in the ß-glucan group. Information from other studies of the effects of ß-glucan on lipid-soluble antioxidants is limited. Kerckhoffs et al (24) reported decreases in absolute plasma concentrations of tocopherols and hydrocarbon carotenoids. However, LDL cholesterolstandardized plasma concentrations were not affected by ß-glucan, which is agreement with the findings of the current study.
To summarize, results of the current study indicate that our ß-glucan preparation lowers serum concentrations of total and LDL cholesterol when incorporated into a fruit drink. Not only an increase in bile acid synthesis (8, 10, 23) but also reduced cholesterol absorption contributes to the cholesterol-lowering effect of ß-glucan without affecting plasma concentrations of lipid-soluble antioxidants.
| ACKNOWLEDGMENTS |
|---|
| REFERENCES |
|---|
|
|
|---|
lrd/tpoats.html. Accessed 27 April 2001.
-hydroxy-4-cholesten-3-one. Am J Clin Nutr 2002;76:11116.This article has been cited by other articles:
![]() |
K. N. Smith, K. M. Queenan, W. Thomas, R. G. Fulcher, and J. L. Slavin Physiological Effects of Concentrated Barley {beta}-Glucan in Mildly Hypercholesterolemic Adults J. Am. Coll. Nutr., June 1, 2008; 27(3): 434 - 440. [Abstract] [Full Text] [PDF] |
||||
![]() |
A. M Zivkovic, J B. German, and A. J Sanyal Comparative review of diets for the metabolic syndrome: implications for nonalcoholic fatty liver disease Am. J. Clinical Nutrition, August 1, 2007; 86(2): 285 - 300. [Abstract] [Full Text] [PDF] |
||||
![]() |
E. Theuwissen and R. P. Mensink Simultaneous Intake of {beta}-Glucan and Plant Stanol Esters Affects Lipid Metabolism in Slightly Hypercholesterolemic Subjects J. Nutr., March 1, 2007; 137(3): 583 - 588. [Abstract] [Full Text] [PDF] |
||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |