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Original Paper

Ann Nutr Metab 2006;50:387–393 DOI: 10.1159/000094304

Influence of Daily Consumption of Probiotic and Conventional Yoghurt on the Plasma Lipid Profile in Young Healthy Women

Elisabeth Fabian Ibrahim Elmadfa

Department of Nutritional Sciences, University of Vienna , Austria

ratio. The significant (p ! 0.01) reduction of the average plas-ma LDL cholesterol values found in this period (T1–T3) in the probiotic and the control groups was associated with a sig-nificant (p ! 0.05) improvement of the LDL/HDL cholesterol ratios in both tested groups. Conclusion: Although several lipid parameters changed during the study in both the pro-biotic and the control group, no significant differences be-tween the groups were observed. Therefore, it can be con-cluded that the regular consumption of both probiotic and conventional yoghurt for 4 weeks had a positive effect on the lipid profile in plasma of healthy women.

Copyright © 2006 S. Karger AG, Basel

Introduction

In the past 10 years there has been increased interest in the potential beneficial effects of so-called probiotic bacteria on the plasma lipid profile [1–3] . Many investiga-tions have provided information concerning cholesterol-lowering effects of probiotic bacteria in vitro. However, the mechanism that microorganisms use to lower choles-terol levels and modulate the lipid profile in humans re-mains unclear. Several probiotic bacteria of human ori-gin are known to remove cholesterol from culture media

Key Words Probiotic yoghurt � Lipid profile � Plasma lipoproteins � Plasma cholesterol � Healthy women

Abstract Background: A number of studies have found conflicting results concerning the modulation of plasma lipids induced by probiotics. Therefore, the aim of this study was to verify and compare the effects of probiotic and conventional yo-ghurt on the plasma lipid profile of normocholesterolemic women. Methods: In this study, female volunteers con-sumed 100 g/day of probiotic (n = 17) or conventional yo-ghurt (n = 16) for 2 weeks (T1–T2) and 200 g/day for further 2 weeks (T2–T3). A washout phase lasting 2 weeks followed (T4). Total and HDL cholesterol and triglycerides were deter-mined by enzymatic methods; LDL cholesterol was calcu-lated using the Friedewald formula. Results: The average concentration of total cholesterol was consistent through-out the whole study in the control group, but decreased sig-nificantly (p ! 0.01) in the probiotic group consuming 200 g yoghurt/day (T2–T3). During the period of daily yoghurt in-take (T1–T3) the mean HDL cholesterol level increased sig-nificantly (p ! 0.05) in the probiotic group, resulting in a sig-nificant (p ! 0.05) improvement of the total/HDL cholesterol

Received: June 7, 2005 Accepted: May 28, 2006 Published online: June 30, 2006

Ibrahim Elmadfa Department of Nutritional Sciences, University of Vienna Althanstrasse 14, AT–1090 Vienna (Austria) Tel. +43 1 4277 54904, Fax +43 1 4277 9549 E-Mail ibrahim.elmadfa@univie.ac.at

© 2006 S. Karger AG, Basel 0250–6807/06/0504–0387$23.50/0

Accessible online at: www.karger.com/anm

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Ann Nutr Metab 2006;50:387–393 388

in the presence of bile [4] . A possible mechanism of action relates to the bacteria’s ability to deconjugate bile acids which, when deconjugated, co-precipitate with cholester-ol at a pH ! 5.5 [5–8] . To assume that co-precipitation also occurs in vivo would suggest that increased fecal ex-cretion of bile acids and cholesterol would cause the liver to compensate the loss of bile acids by converting plasma cholesterol into new bile acids. This effect might result in a lowering of serum cholesterol levels [4, 9] .

Furthermore, it is possible that certain probiotic bac-teria are able to take up and incorporate cholesterol for stabilization of their cell membrane in vitro [10, 11] . Per-haps the removal of chymus-cholesterol from the gut also aids in the lowering of plasma cholesterol concentrations in humans [12, 13] . Moreover, propionate, a short chain fatty acid produced during the fermentation of yoghurt, is also suspected to affect the plasma lipid profile in a positive way by modulating lipogenesis and cholesterol-genesis [14, 15] .

Besides their function as adhesion factors and constit-uents of cell membranes in many microorganisms [16, 17] , sphingolipids contained in dairy products [18] may also cause a decrease of total and LDL and an increase of HDL cholesterol levels in plasma. Except for their in-volvement in immunological processes and the regula-tion of the cell cycle (proliferation and apoptosis) [19, 20] , sphingolipids are important for the intake and esterifica-tion of cholesterol in cells, the conversion of cholesterol to bile acids and the regulation of the HMG-CoA-reduc-tase-activity (= hydroxyl-methy-glutaryl-CoA-reduc-tase) in humans [21–24] .

However, a number of studies have presented conflict-ing results concerning the modulation of plasma lipids induced by probiotics. This motivated us to investigate whether daily consumption of probiotic or conventional yoghurt influences the lipid profile in women.

Subjects and Methods

Prior approval for this study was obtained from the Ethical Committee of Vienna. All volunteers gave their written informed consent.

Subjects 33 healthy, non-smoking, normocholesterolemic female sub-

jects aged between 22 and 29 years were recruited for this study. The participants, randomly divided into two groups ( table 1 ), were not allowed to consume any kind of fermented food in the preadjustment phase nor during the whole study. Each group was then provided with either probiotic or conventional yoghurt. One subject had to be excluded because of metabolic anomalies.

Study Design After a preadjustment phase of 1 week, the subjects consumed

100 g/day of probiotic or conventional yoghurt for 2 weeks (T1–T2) and 200 g/day for another 2 weeks (T2–T3). A washout phase lasting 2 weeks followed (T4). Venous blood samples were taken after an overnight fast at the end of each period which amounted to a total of 4 blood collection days during the study ( fig. 1 ).

Yoghurt The probiotic product was a yoghurt drink and comprised the

starter cultures Streptococcus thermophilus and Lactobacillus bul-garicus enriched with the probiotic culture Lactobacillus casei subsp. casei. The control product was a stirred conventional yo-ghurt with the starter cultures S. thermophilus and L. bulgaricus ( table 2 ). Both yoghurts were commercially available products.

Measurements Total , HDL cholesterol and triglycerides were determined by

the enzymatic methods of Siedel et al. [25] , Burstein et al. [26] , and Siedel et al. [27] respectively. LDL cholesterol was calculated according to the Friedewald equation (LDL cholesterol mmol/l = total cholesterol – HDL cholesterol – triglyceride/2.2) [28] .

Body weight was measured with subjects clothed but without shoes. To estimate the intake of energy and various nutrients, all participants completed a 24-hour food record prior to the day the blood sample was taken. Physical activity was not assessed in this study.

Statistical Analysis All data are presented as a mean 8 SD. Differences between

the blood concentrations of the probiotic and the conventional group were compared using the independent t test, those among the groups were determined by paired t tests. A p value of ! 0.05 was considered to be statistically significant.

Results

Mean intake of total energy, dietary fat, cholesterol, and saturated, monounsaturated and polyunsaturated fatty acids was calculated by 24-hour food records and did not change significantly within or between the tested

Table 1. Characteristics of the subjects (at the beginning of the study)

Parameter(mean 8 SD)

Probiotic group(n = 17)

Control group(n = 16)

Age, years 2483 2482Body mass index, kg/m2

Weight, kgHeight, cm

20.783.059.088.5

168.480.05

21.082.759.388.0

167.680.04Contraceptive pill use, nDay of cycle

71286

71387

Effects of Probiotic and Conventional Yoghurt on Plasma Lipid Profile

Ann Nutr Metab 2006;50:387–393 389

groups throughout the investigation. In both groups the average body weight of the individuals remained stable (T1–T4; table 3 ).

Daily consumption of 100 g probiotic or conventional yoghurt (T1–T2) did not have an effect on the plasma lipid profile of either group. In the period in which the amount of yoghurt consumed every day was doubled to 200 g (T2–T3), the average plasma concentration of total

cholesterol decreased significantly (p ! 0.01) to about 6.2% in the probiotic group but remained stable in the control group.

During the 4 weeks of continuous intake of yoghurt (T1–T3) the mean HDL cholesterol concentration in-creased (9.5%) significantly (p ! 0.05) in the probiotic, but did not change in the control group. Nevertheless, the total/HDL cholesterol ratio improved significantly (p !

Fig. 1. Study design. T1 = Collection of the first blood sample after a preadjustment phase of 1 week; T2 = col-lection of the second blood sample after daily consumption of 100 g yoghurt per day for 2 weeks; T3 = collection of the third blood sample after daily consumption of 200 g yoghurt per day for 2 weeks; T4 = collection of the fourth blood sample after a washout phase of 2 weeks.

Yoghurt Starter culture Probiotic culture

Probiotic(Actimel�)

2 ! 108 cfu/g S. thermophilus107 cfu/g L. bulgaricus

3.6 ! 108 cfu/g Lactobacillusparacasei subsp. paracasei(L. casei DN-114 001)

Nutrients (according to the label)

FatProteinCarbohydrate

1.6 g/100 g2.8 g/100 g14.2 g/100 g

Conventional(NÖM� Naturrein)

3.9 ! 107 cfu/g S. thermophilus6.4 ! 107 cfu/g L. bulgaricus –

Nutrients (according to the label)

FatProteinCarbohydrate

3.6 g/100 g3.4 g/100 g3.9 g/100g

Table 2. Bacterial cultures and nutrients contained in probiotic and conventional yoghurt

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Ann Nutr Metab 2006;50:387–393 390

0.05) in the probiotic (13%) and in the control group (8%) throughout the period of continuous yoghurt consump-tion (T1–T3).

After a 4-week period of yoghurt consumption (T1–T3), the mean concentration of LDL cholesterol decreased significantly (p ! 0.01) in the probiotic (14%) as well as in the control group (7.6%). Consequently, the mean LDL/HDL cholesterol ratio declined significantly (p ! 0.05) in the probiotic (21%) and in the control group (13%). After a washout period of 2 weeks (T4) the plasma concentra-tions of total, HDL and LDL cholesterol and the ratios of total/HDL and LDL/HDL cholesterol all returned to their baseline values (T1).

In both tested groups the average plasma level of tri-glycerides remained quite unaffected by daily consump-tion of 100 and 200 g yoghurt for 4 weeks ( table 4 ).

Discussion

The aim of this study was to verify and compare the effects of probiotic and conventional yoghurt on the plas-ma lipid profile of normocholesterolemic women.

Although the average concentration of total and HDL cholesterol improved significantly (p ! 0.01, p ! 0.05) in the probiotic, but not in the control group, there were no significant differences between the two investigated groups at any time. Furthermore, the significant (p ! 0.01) decrease in mean LDL cholesterol levels observed in both the probiotic and the control group did not show any significant differences between the two groups either.

However, the most important result of this study was the significant (p ! 0.05) improvement in the ratio of LDL/HDL and total/HDL cholesterol. The effect was present in the probiotic as well as in the control group

Nutrient T1 T2 T3 T4

Body weight, kgProbiotic groupControl group

58.588.659.487.7

58.388.559.187.7

58.388.459.587.9

58.388.159.587.9

Total energy, MJProbiotic groupControl group

8.6182.158.4682.67

8.6382.128.4982.43

8.6182.548.6182.29

8.2681.388.7282.28

Total fat, gProbiotic groupControl group

81.36830.7279.02833.92

79.64835.7680.05823.83

81.56841.3982.17833.01

82.53828.0679.68828.46

Cholesterol, mgProbiotic groupControl group

234.58125.0208.38127.4

224.1895.7232.38138.7

254.18109.5252.58179.6

265.9889.5226.68146.9

SFA, % of total energyProbiotic groupControl group

15.5385.8815.0483.48

15.1985.4116.2885.88

15.4487.4816.6687.44

16.7483.2615.0984.17

MUFA, % of total energyProbiotic groupControl group

10.3683.6111.2183.55

10.3983.3311.0383.99

9.9382.6811.6784.44

11.7883.2310.9783.50

PUFA, % of total energyProbiotic groupControl group

4.2482.464.9882.80

5.0482.545.2282.49

5.0283.614.3182.00

4.3781.824.2382.14

SFA = Saturated fatty acids; MUFA = monounsaturated fatty acids; PUFA = polyun-saturated fatty acids.

T1 = Collection of the first blood sample after a preadjustment phase of 1 week; T2 = collection of the second blood sample after daily consumption of 100 g yoghurt per day for 2 weeks; T3 = collection of the third blood sample after daily consumption of 200 g yoghurt per day for 2 weeks; T4 = collection of the fourth blood sample after a washout phase of 2 weeks.

Table 3. Body weight of the subjects and daily intake of total dietary fat, cholesterol and fatty acids according to food records

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Ann Nutr Metab 2006;50:387–393 391

during daily intake of yoghurt (T1–T3). According to the results of Gordon et al. [29] the LDL/HDL and total/HDL ratios can be used as index of atherogenicity and to assess the lipid profile in humans, respectively.

The significant (p ! 0.05) improvement of the total/HDL cholesterol ratio observed in the present study could be a consequence of decreased total cholesterol levels, also described by Schaafsma et al. [30] , Anderson and Gilliland [31] and Bertolami et al. [32] , as well as in-creased HDL cholesterol concentrations. The significant (p ! 0.05) change in the LDL/HDL cholesterol ratio in both groups during daily intake of yoghurt (T1–T3) has often been described as a result of lowered plasma LDL cholesterol concentrations [31, 33, 34] . Nevertheless, some authors also observed an improvement of the LDL/HDL ratio caused by an increased concentration of HDL cholesterol when consuming probiotic yoghurt daily for a certain period of time [35, 36] . These investigators sug-

gested the reason for the increased HDL cholesterol con-centration may be the fatty acid distribution of milk fat and sphingolipids contained in yoghurt. In fermented dairy products there are two potential sources of sphin-golipids – milk fat and bacteria (cell membrane constitu-ents and adhesion factors). Full-fat milk contains an aver-age of 120 mg sphingolipids/l [18] and its intake is in-versely correlated with the LDL/HDL ratio [37] .

The yoghurts used in the present study had quite dif-ferent compositions. The probiotic yoghurt contained less fat (1.6 g/100 g) than the control product (3.5 g/100 g); the amount of bacteria was on average higher in the probiotic (5.7 ! 10 8 cfu/g) than in the conventional (10 8 cfu/g) yoghurt.

Although the probiotic and the conventional yoghurt tested in this investigation contained different amounts of milk fat and bacteria, the content of sphingolipids de-rived from both sources could have been similar. If so,

Parameter T1 T2 T3 Alteration in theperiod T1–T3, %(p value)

T4

Total cholesterol, mmol/lProbiotic groupControl group

4.380.74.580.7

4.480.84.580.7

4.180.84.480.7

6.21 (<0.01)1.6 (n.s.)

4.480.94.580.7

HDL cholesterol, mmol/lProbiotic groupControl group

1.680.41.780.3

1.780.31.780.3

1.880.41.880.3

9.5 (<0.05)3.5 (n.s.)

1.880.41.880.3

LDL cholesterol, mmol/lProbiotic groupControl group

2.580.62.780.6

2.580.62.780.5

2.280.72.580.6

14 (<0.01)7.6 (<0.01)

2.480.72.780.5

Total/HDL cholesterolProbiotic groupControl group

2.880.92.780.8

2.680.52.780.6

2.380.52.580.5

13 (<0.05)8 (<0.05)

2.680.62.780.7

LDL/HDL cholesterolProbiotic groupControl group

1.780.91.680.6

1.580.51.680.4

1.380.51.580.4

21 (<0.05)13 (<0.05)

1.580.61.680.4

Triglycerides, mmol/lProbiotic groupControl group

0.6780.20.6580.2

0.6380.20.6480.2

0.6180.20.6180.2

0.9 (n.s.)0.9 (n.s.)

0.6280.20.6280.2

1 Alteration during the period T2–T3.HDL = High-density lipoprotein; LDL = low-density lipoprotein; n.s. = not signifi-

cant. T1 = Collection of the first blood sample after a preadjustment phase of 1 week; T2 = collection of the second blood sample after daily consumption of 100 g yoghurt per day for 2 weeks; T3 = collection of the third blood sample after daily consumption of 200 g yoghurt per day for 2 weeks; T4 = collection of the fourth blood sample after a washout phase of 2 weeks.

Table 4. Concentrations of blood lipid parameters during the study

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subjects of both groups would have consumed similar amounts of sphingolipids and total fat throughout the whole study. The constant intake of energy and nutrients was further supported by the results of 24-hour food re-cords. Although these data were assessed only four times during the investigation, they did not differ significantly within or between both observed groups. Due to the sta-ble body weight of the subjects, it is likely that nutrient intake and physical activity of the individuals were quite similar in both groups throughout the study.

Besides the elevation of HDL cholesterol, sphingolip-ids have been further reported to reduce total and LDL cholesterol [18] , thereby modulating the circulating lipid profile.

According to the literature there are few other expla-nations for the positive changes of lipid parameters found in this study. The bacterial deconjugation of bile acids fol-lowed by their enhanced excretion and the compensation of lost bile acids by converting plasma cholesterol into new bile acids [4, 9], as well as a removal of chymus-cho-lesterol by assimilation and incorporation of cholesterol into bacterial cell membranes, would only have affected the total cholesterol plasma levels [12, 13] . Nevertheless, in our study, alterations were observed in total and also in LDL and HDL cholesterol levels. Additionally, it should be noted that both described mechanisms require lactic acid bacteria (LAB) to remain viable when entering and moving through the gut. This is assumed to occur for probiotic but not for conventional LAB strains. However, in this investigation the positive modulation of the lipid profile was evident in both the probiotic and the control group. Therefore it could be suggested that the two men-tioned mechanisms are not mainly responsible for the positive modulation of the lipid profile observed in this study.

The beneficial effects of propionate on the lipid profile in humans are still under debate, because in contrast to conventional LAB strains, the generation of short chain fatty acids by probiotic bacteria is marginal [38] . If there had been any impact of propionate on the modulation of the lipid profile, any changes should have been more ob-vious for the individuals consuming conventional yo-ghurt; however, this was not the case.

Considering all the discussed mechanisms of action, we suggest that the most probable reason for the modula-tion of the lipid parameters analyzed in this study could be the fatty acid distribution of the milk fat and the sphin-golipids contained in yoghurt. Nevertheless, it is possible that the positive change of the lipid profile found during the period of daily yoghurt consumption in both investi-

gated groups are the result of a combination of several mechanisms, described previously. The modulation of cholesterol metabolism seems therefore to be an effect of fermented dairy products rather than of probiotic bacte-ria.

Conclusion

Although mean concentrations of total, HDL and LDL cholesterol changed among the probiotic as well as the control group, no relevant differences were observed be-tween the two groups. The total/HDL and LDL/HDL cholesterol ratios improved in both groups. The observed modulation of the lipid profile seems more likely to be an effect of the regular consumption of yoghurt as a fer-mented dairy product, rather than related to the intake of probiotic bacteria. Therefore, it can be concluded that daily intake of both probiotic and conventional yoghurt for 4 weeks has a positive effect on the lipid profile in hu-mans.

Acknowledgements

We wish to thank Danone Austria for the generous gift of pro-biotic yoghurt and for their financial support. We would also like to thank NÖM AG Austria for providing the conventional yo-ghurt and Mr. Andrew Bulmer for proofreading the manuscript.

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Ann Nutr Metab 2006;50:387–393 393

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