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Hugh Sinclair Unit of Human Nutrition, Department of Food Science and Technology, University of Reading, Reading, RG6 6AP
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONLipid responses to inulin...Lipid responses to inulin...Mechanism of lipid-lowering in...CONCLUSIONREFERENCES |
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KEY WORDS: • inulin • triglycerides • human trials
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONLipid responses to inulin...Lipid responses to inulin...Mechanism of lipid-lowering in...CONCLUSIONREFERENCES |
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). Oligofructoses
(OFS)2of varying chain lengths can be obtained from inulin by enzymatic
hydrolysis. Because of their gelling and thickening properties, both
inulin and OFS are useful as food ingredients and have found widespread
application in recent years in items such as bread, processed cheese
and dairy products (Dyssler and Hoffem 1995
); in
addition, they may hold the promise of health benefits. Dramatic
reductions in serum triglycerides have been reported in rats consuming
relatively high doses of OFS, although reductions in cholesterol have
been seen only with long-term feeding (Delzenne et al. 1993
, Fiordaliso et al. 1995
). Recent studies
have shown the effects on serum triglycerides to be due to reduced
secretion of VLDL particles from the liver and to be associated with
reduced activity and gene expression of the key regulatory enzyme,
fatty acid synthetase (Kok et al. 1996a and 1996b
).
Although the data obtained from animal studies suggest convincing
lipid-lowering properties of OFS, much less information is
available from human studies, in which the doses that can be applied
are much lower than those that have been used to elicit effects in
animals. |
Lipid responses to inulin and OFS in subjects with raised blood lipids |
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TOPABSTRACTINTRODUCTIONLipid responses to inulin...Lipid responses to inulin...Mechanism of lipid-lowering in...CONCLUSIONREFERENCES |
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). No effects on other serum lipids or on blood glucose
concentrations were observed. Similar reductions in blood lipids were
reported to have been observed in a group of Japanese subjects with
hyperlipidemia (Hidaka et al. 1986
), but no data were
shown to support this conclusion. More recently, Davidson et al. (1998)
in a randomized crossover trial in subjects with modest
hyperlipidemia, showed significantly lower total and LDL concentrations
during the inulin (Raftiline) phase compared with the placebo phase,
but the authors reported no effects on HDL cholesterol or serum
triglyceride concentrations. |
Lipid responses to inulin and OFS in normal subjects |
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TOPABSTRACTINTRODUCTIONLipid responses to inulin...Lipid responses to inulin...Mechanism of lipid-lowering in...CONCLUSIONREFERENCES |
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)
investigated effects of Neosugar OFS (20 g/d) fed as 100-g cookies in a
randomized crossover design with treatment periods of 4 wk. Sucrose was
used as placebo. No changes in serum triglycerides, cholesterol or
apolipoproteins were observed in either the treatment or placebo
periods, although there was a strong trend in the reduction of free
fatty acid (FFA) concentrations with OFS. In contrast, Canzi et al. (1995)
observed significantly lower triglyceride and
cholesterol concentrations in young male volunteers who consumed 9 g inulin (Raftiline) added to a rice breakfast cereal for a period of 4
wk. The study was a randomized sequential design with a placebo period
(rice cereal) followed by a test period (rice cereal plus inulin).
Total cholesterol and LDL cholesterol levels were reduced by 5 and 7%,
respectively, with the inulin treatment compared with the placebo.
Fasting triglyceride concentrations were reduced by 27% during inulin
treatment and remained significantly lower 4 wk after the end of the
inulin phase. In the group as a whole (test and control periods),
strong and significant associations were observed between fecal
secondary bile acids and serum cholesterol (P < 0.05) and, most notably, triglycerides (P < 0.001).
Pedersen et al. (1997)
reported no effect on blood
lipids of a daily intake of 14 g inulin added to a low fat spread
for a period of 4 wk. The study was a double-blind randomized cross
over design in 66 young healthy women. Although HDL cholesterol and the
LDL:HDL cholesterol ratio were lower at the end of both the control and
test (inulin) periods, there were no significant differences in blood
lipids between placebo and inulin. Although this was a rigorously
designed study, the fact that subjects were required to consume 40 g of spread per day (30 g/d fat) (approximately twice the normal level
of spread intake and 50% of total fat intake for young women) may have
contributed to the negative findings observed in this group. As
discussed below, triglyceride-lowering with inulin may be more
likely if the background diet is high in carbohydrate rather than fat.
In a recently conducted study, 58 middle-aged subjects with
moderately raised blood lipid concentrations consumed 10 g/d of inulin
(Raftiline) or placebo in a powdered form that could be added to
beverages, soups or cereal (Jackson et al. 1998
). The
study was a double-blind parallel control design with equal numbers
of subjects allocated to placebo and inulin groups using stratified
randomization. Subjects consumed the inulin or placebo products for 8
wk with fasting blood samples collected at baseline, 4 and 8 wk of
intervention and 4 wk after the end of feeding. There were no
significant changes in total, LDL or HDL cholesterol or apolipoproteins
B and A in either of the groups over the 8-wk intervention, although 4
wk after the intervention, total and LDL cholesterol levels were lower
than at baseline in the placebo group. Serum triglycerides were 19%
lower at 8 wk than at baseline in the inulin-treated group
(Fig. 1
) and values were significantly lower than in controls
(P < 0.05). Baseline triglyceride values were
identical in the two groups and did not contribute to the lower values
found in the inulin group at 8 wk. Serum triglycerides returned to
baseline values 4 wk after treatment ended. A number of factors may
have contributed to the positive findings for effects of inulin on
serum triglycerides in this study. Subjects were chosen for their
modestly raised triglyceride values at baseline, and the study was
conducted over a longer period than any of the previous human studies.
This appears to be of particular importance because, like the other
studies, no significant differences in fasting serum lipids were seen
at 4 wk, but significantly lower triglyceride values were observed at 8
wk. The method of dietary intervention used was simple, designed to
ensure optimal compliance and to prevent confounding changes in intakes
of other nutrients or foods that might complicate the interpretation of
the findings. Although there were important changes in serum
triglycerides in the group as a whole, it should be noted that not all
subjects showed a positive response to inulin feeding; in ~25% of
subjects, there were no alterations in serum triglycerides, either at 4
or 8 wk. This lack of response may reflect individual differences in
responsiveness to inulin, variations in background diet or lack of
compliance to the product. Individual variation may also explain why,
in a subgroup of subjects who undertook evaluation of postprandial
lipid and glucose responses to standard meals, there were no
significant differences in postprandial plasma triglycerides at 8 wk
compared with baseline in inulin-treated subjects. Fasting and
postprandial FFA levels were significantly lower 8 wk after inulin
treatment compared with baseline. However, lower fasting (but not
postprandial) FFA were also observed at 8 wk in the placebo group.
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Mechanism of lipid-lowering in response to OFS and inulin in humans |
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TOPABSTRACTINTRODUCTIONLipid responses to inulin...Lipid responses to inulin...Mechanism of lipid-lowering in...CONCLUSIONREFERENCES |
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). In
humans, drugs and dietary fatty acids that reduce serum triglycerides
appear to increase triglyceride clearance and fatty acid oxidation;
they also divert fatty acids into hepatic phospholipid synthesis,
rather than inhibit de novo fatty acid synthesis. These observations
suggest that attempts to address the putative triglyceride-lowering
properties of inulin and OFS should use subjects consuming a high
background dietary carbohydrate intake. Investigations conducted in
subjects with NIDDM would be of particular value because in these
individuals, triglyceride rather than cholesterol is the primary lipid
abnormality seen, and a high carbohydrate diet is used as a standard
dietary approach in the treatment of NIDDM. |
CONCLUSION |
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TOPABSTRACTINTRODUCTIONLipid responses to inulin...Lipid responses to inulin...Mechanism of lipid-lowering in...CONCLUSIONREFERENCES |
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FOOTNOTES |
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2 Abbreviations used: FFA, free fatty acids;
NIDDM, noninsulin-dependent diabetes mellitus; OFS,
oligofructose.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONLipid responses to inulin...Lipid responses to inulin...Mechanism of lipid-lowering in...CONCLUSIONREFERENCES |
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1. Aarsland A., Chinkes D., Wolfe R. R. Contributions of de novo synthesis of fatty acids to total VLDL-triglyceride secretion during prolonged hyperglycemia/hyperinsulinemia in normal man. J. Clin. Investig. 1996;98:2008-2017[Medline]
2. Canzi. E., Brighenti, F., Casiraghi, M. C., Del Puppo, E. & Ferrari, A. (1995) Prolonged consumption of inulin in ready to eat breakfast cereals: effects on intestinal ecosystem, bowel habits and lipid metabolism. Cost 92. Workshop on Dietary Fiber and Fermentation in the Colon, 15:17/04. Helsinki, Finland.
3. Davidson M. H., Synecki C., Maki K. C., Drennan K. B. Effects of dietary inulin in serum lipids in men and women with hypercholesterolemia. Nutr. Res. 1998;3:503-517
4.
Delzenne N., Kok N., Fiordaliso M., Deboyser D., Goethals F., Roberfroid M. Dietary fructooligosaccharides modifies lipid metabolism in rats. Am. J. Clin. Nutr. 1993;57:820S(abs.)
5. Dyssler P., Hoffem D. Inulin, an alternative dietary fibre. Properties and quantitative analysis. Eur. J. Clin. Nutr. 1995;49:S142-S152
6. Fiordaliso M. F., Kok N., Desager J. P., Goethals F., Deboyser D., Roberfroid M., Delzenne N. Dietary oligofructose lowers triglycerides, phospholipids and cholesterol in serum and very low density lipoproteins of rats. Lipids 1995;30:163-167[Medline]
7. Hidaka H., Eida T., Takizawa T., Tokunaga T., Tashiro Y. Effects of fructooligosaccharides on intestinal flora and human health. Bifid. Microflora 1986;5:37-50
8. Jackson, K. G., Taylor, G.R.J., Clohessy, A. M., Luff, J. E., Thomas, C. M. & Williams, C. M. (1999) The effect of a daily ingestion of inulin on fasting and postprandial lipid metabolism in middle aged men and women. Proc. Nutr. Soc. (in press).
9. Kok N., Roberfroid M., Delzenne N. Involvement of lipogenesis in the lower VLDL secretion induced by oligofructose in rats. Br. J. Nutr. 1996;76:881-890[Medline]
10. Kok N., Roberfroid M., Delzenne N. Dietary oligofructose modifies the impact of fructose on hepatic traiacylglycerol metabolism. Metabolism 1996;45:1547-1550[Medline]
11.
Luo J., Rizkalla S. W., Alamowitch C., Boussairi A., Blayo A., Barry J.-L., Laffitte A., Guyon F., Bornet F.R.J., Slama G. Chronic consumption of short-chain fructooligosaccharides by healthy subjects decreased basal hepatic glucose production but had no effect on insulin-stimulated glucose metabolism. Am. J. Clin. Nutr. 1996;63:939-945
12. Pedersen A., Sandstrom B., Van Amelsvoort J.M.M. The effect of ingestion of inulin on blood lipids and gastrointestinal symptoms in healthy females. Br. J. Nutr. 1997;78:215-222[Medline]
13. Roberfroid M. Dietary fiber, inulin and oligofructose: a review comparing their physiological effects. Crit. Rev. Food Sci. Nutr. 1993;33:102-148
14. Yamashita K., Kawai K., Itakura M. Effects of fructo-oligosaccharides on blood glucose and serum lipids in diabetic subjects. Nutr. Res. 1984;4:961-966
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