We read the paper by Liu et al.1 with interest. The authors conducted a review and meta-analysis of the effects of inulin-type fructans on blood lipid profiles and glucose concentrations from randomized controlled trials. They concluded that the ingestion of inulin-type fructans may provide benefits for low-density lipoprotein (LDL)-cholesterol reduction and glucose metabolism. We have several concerns with the meta-analysis methods, the studies included (and not included) and the conclusions made by the authors.
By comparing the data in the meta-analysis tables to the original publications, we determined that the meta-analysis reported the end of treatment period data, without accounting for differences in baseline values between treatment groups. Since each treatment group had a unique lipid and glucose value at baseline, statistical analyses should account for baseline measures wherever possible (for example, include baseline as a model covariate or analyze the change from baseline). Without accounting for baseline, the reported results could be misleading. There were only two studies included in the inulin-type fructan meta-analysis of LDL cholesterol that reported a significant difference in lipid levels on intervention versus placebo. One of the studies (Dehghan et al.)2 assessed the effects of inulin (10 g per day) in 49 Iranian women with type 2 diabetes. Note that this study reported a 35.3% reduction in LDL cholesterol, which is comparable to effects of a statin drug,3 and far exceeds the effects observed on LDL cholesterol with highly effective gel-forming soluble fibers (for example, beta-glucan and psyllium).4 If this study were removed from the meta-analysis, then it is likely that the statistical test for overall effect would change from P=0.03 to P>0.05, and no longer be statistically significant. While not part of the meta-analysis, a more recent publication by the same author (Dehghan et al.),5 at the same institution (Tabriz University of Medical Science, Iran), and in a similar population (46 Iranian women with type 2 diabetes), reported that oligofructose-enriched inulin (10 g per day) lowered mean LDL cholesterol from 116 mg/dl to 37 mg/dl, a physiologically implausible result that exceeds the effects of a high-dose/high-impact statin drug.6 Given that this is the only research group reporting such highly implausible results, we believe the data from this group should be excluded from meta-analyses.
In summary, the meta-analyses reported in Liu et al.1 were based on post-baseline means without adequate statistical accounting for baseline levels of the end points of interest and, as such, results may not be reliable. Also, the meta-analysis of the LDL-cholesterol effect for inulin-type fructans was statistically significant (P=0.03), but this finding pivots on a study from a research group with multiple reports of highly implausible LDL-cholesterol outcomes. Taken together, these facts lead us to disagree with the authors’ conclusions. The totality of published clinical evidence shows that isolated inulin-type fructans, consumed as a fiber supplement, have no significant beneficial effect on lipid or glucose metabolism.4
Liu F, Prabhakar M, Ju J, Long H, Zhou HW . Effect of inulin-type fructans on blood lipid profile and glucose level: a systematic review and meta-analysis of randomized controlled trials. Eur J Clin Nutr 2017; 71: 9–20.
Dehghan P, Pourghassem GB, Asgharijafarabadi M . Effects of high performance inulin supplementation on glycemic status and lipid profile in women with type 2 diabetes: a randomized, placebo-controlled clinical trial. Health Promot Perspect 2013; 3: 55–63.
Deedwania PC, Hunninghake DB, Bays HE, Jones PH, Cain VA, Blasetto JW et al. Effects of rosuvastatin, atorvastatin, simvastatin, and pravastatin on atherogenic dyslipidemia in patients with characteristics of the metabolic syndrome. Am J Cardiol 2005; 95: 360–366.
McRorie J, McKeown N . An evidence-based approach to resolving enduring misconceptions about insoluble and soluble fiber; understanding the physics of functional fibers in the gastrointestinal tract. J Acad Nutr Diet 2016; 117: 251–264.
Dehghan P, Farhangi MA, Tavakoli F, Aliasgarzadeh A, Akbari A . Impact of prebiotic supplementation on T-cell subsets and their related cytokines, anthropometric features and blood pressure in patients with type 2 diabetes mellitus: a randomized placebo-controlled trial. Complement Ther Med 2016; 24: 96–102.
Law M, Wald N, Rudnicka A . Quantifying effect of statins on low density lipoprotein cholesterol, ischaemic heart disease, and stroke: systematic review and meta-analysis. Br Med J 2003; 326: 1423–1429.
MJW and GRD are full-time employees of the Procter & Gamble Company, which markets fiber products. MNM received grants from the International Life Sciences Institute North America, the General Mills Bell Institute of Health and Nutrition, and an unrestricted gift from Procter & Gamble. She is an unpaid science advisor for the Whole Grains Council.
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McRorie, J., Gibb, R. & McKeown, N. Inulin-type fructans have no significant beneficial effects on lipid or glucose metabolism. Eur J Clin Nutr 71, 677 (2017). https://doi.org/10.1038/ejcn.2017.15
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