Hostname: page-component-6b989bf9dc-pkhfk Total loading time: 0 Render date: 2024-04-13T23:25:57.659Z Has data issue: false hasContentIssue false

Low-carbohydrate diets impair flow-mediated dilatation: evidence from a systematic review and meta-analysis

Published online by Cambridge University Press:  14 September 2013

Lukas Schwingshackl
Affiliation:
Department of Nutritional Sciences, Faculty of Life Sciences, University of Vienna, Althanstreet 14 UZA II, A-1090Vienna, Austria, lukas.schwingshackl@univie.ac.at
Georg Hoffmann
Affiliation:
Department of Nutritional Sciences, Faculty of Life Sciences, University of Vienna, Althanstreet 14 UZA II, A-1090Vienna, Austria, lukas.schwingshackl@univie.ac.at
Rights & Permissions [Opens in a new window]

Abstract

Type
Letter to the Editor
Copyright
Copyright © The Authors 2013 

With great interest, we read the meta-analysis of Bueno et al. (Reference Bueno, de Melo and de Oliveira1) ‘Very-low-carbohydrate ketogenic diet v. low-fat diet for long-term weight loss: a meta-analysis of randomised controlled trials’, published ahead of print in the British Journal of Nutrition (Reference Bueno, de Melo and de Oliveira1). In their article, the authors compared the effects of very-low-carbohydrate (VLC) diets v. low-fat (LF) diets on the biomarkers of obesity and their associated disorders. With respect to different outcomes between both the regimens, VLC diets turned out to be more effective in lowering body weight, TAG levels and diastolic blood pressure and in increasing HDL-cholesterol levels. However, one established risk factor of CVD, i.e. LDL-cholesterol, still turned out to be harmfully affected by the VLC regimen, most probably attributable to the larger amounts of saturated fat in the diet(Reference Bueno, de Melo and de Oliveira1). In their discussion, the authors stated that future meta-analyses should investigate the impact of low carbohydrates (LC) v. LF on other important pathological markers, e.g. endothelial function, in order to further assess the safety of LC dietary therapies. This is reasonable, since evidence from prospective cohort studies has shown that endothelial dysfunction represents an independent risk factor for the development of many CVD including atherosclerosis(Reference Inaba, Chen and Bergmann2). We, therefore, carried out a meta-analysis to compare the effects of LC and LF regimens on flow-mediated dilatation (FMD). FMD of the brachial artery is a non-invasive measure of endothelial function, furthermore reflecting the local bioavailability of endothelium-derived vasodilators, especially NO. Inflammation of the endothelium is regarded to play a major role in the destabilisation of atherosclerotic lesions, therefore paving the way for future CVD events(Reference Inaba, Chen and Bergmann2). A literature search was performed using the electronic databases MEDLINE (until April 2013), EMBASE (until April 2013) and the Cochrane Trial Register (until April 2013), with restrictions to randomised controlled trials, but no restriction to language using the following search terms: low fat diet AND endothelial function and low carbohydrate diet AND endothelial function (Supplementary material, available online). Studies were included in the meta-analysis if they met all of the following criteria: (1) randomised controlled design with a minimum intervention period of 3 weeks; (2) comparing a LC diet ( ≤ 45 % carbohydrates of total energy content, TEC) with a LF diet ( ≤ 30 % fat of TEC)(Reference Hu, Mills and Yao3); (3) report of post-intervention values with standard deviations; when the results of a study were published more than once, only the most recent or most complete article was included in the analysis; (4) participants age >18 years; (5) exclusion of subjects with CHD.

A meta-analysis was carried out in order to determine the pooled effect of the intervention in terms of weighted mean differences (WMD) between the post-intervention values of the LC group and those of the LF group. All data were analysed using the Review Manager 5.1 software, provided by the Cochrane Collaboration (http://ims.cochrane.org/revman). Overall, six trials with a sample size of 210 subjects were included(Reference Buscemi, Verga and Tranchina4Reference Wycherley, Brinkworth and Keogh9). Study duration ranged between 3·5 weeks and 12 months. Decreases in FMD (WMD: − 1·01 (95 % CI − 1·83, − 0·19) %, P= 0·02) were significantly more pronounced following consumption of LC diets than following that of LF diets (Fig. 1). The I 2 test showed very low heterogeneity (I 2= 10 %).

Fig. 1 Forest plot showing pooled weighted mean differences (WMD) with 95 % CI for flow-mediated dilatation (%) of six randomised controlled low-carbohydrate diet studies. For each low-carbohydrate trial, represents the point estimate of the intervention effects. The horizontal line joins the lower and upper limits of the 95 % CI of these effects. The area of reflects the relative weight of the study in the respective meta-analysis. At the bottom of the graph, represents the pooled WMD with 95 % CI. (A colour version of this figure can be found online at http://www.journals.cambridge.org/bjn).

In our meta-analysis, LC dietary protocols were associated with a significant decrease in FMD when compared with their LF counterparts. A recent meta-analysis of observational studies including a sample size of 5·547 subjects has observed that a 1 % decrease in FMD is associated with a 13 % increase in the risk of future cardiovascular events(Reference Inaba, Chen and Bergmann2). In another recent meta-analysis of cohort studies carried out by Noto et al. (Reference Noto, Goto and Tsujimoto10), an association between LC diets and increased risk of all-cause mortality could be observed, although not for cardiovascular (CVD) mortality as well as CVD incidence(Reference Noto, Goto and Tsujimoto10). It should be noted that in direct comparison with the meta-analysis carried out by Bueno et al. (Reference Bueno, de Melo and de Oliveira1), we had to modify the inclusion criteria, since only a few dietary intervention trials had reported FMD as an outcome parameter. However, in consideration of the fact that LC was associated with a higher all-cause mortality risk, further trials are required to confirm the mechanisms of FMD impairment following LC regimens.

Supplementary material

To view the supplementary material for this article, please visit http://dx.doi.org/10.1017/S000711451300216X

References

1Bueno, NB, de Melo, IS, de Oliveira, SL, et al. (2013) Very-low-carbohydrate ketogenic diet v. low-fat diet for long-term weight loss: a meta-analysis of randomised controlled trials. Br J Nutr (Epublication ahead of print version 7 May 2013).Google Scholar
2Inaba, Y, Chen, JA & Bergmann, SR (2010) Prediction of future cardiovascular outcomes by flow-mediated vasodilatation of brachial artery: a meta-analysis. Int J Cardiovasc Imaging 26, 631640.Google Scholar
3Hu, T, Mills, KT, Yao, L, et al. (2012) Effects of low-carbohydrate diets versus low-fat diets on metabolic risk factors: a meta-analysis of randomized controlled clinical trials. Am J Epidemiol 176, Suppl. 7, S44S54.Google Scholar
4Buscemi, S, Verga, S, Tranchina, MR, et al. (2009) Effects of hypocaloric very-low-carbohydrate diet vs. Mediterranean diet on endothelial function in obese women. Eur J Clin Invest 39, 339347.CrossRefGoogle ScholarPubMed
5de Roos, NM, Bots, ML, Siebelink, E, et al. (2001) Flow-mediated vasodilation is not impaired when HDL-cholesterol is lowered by substituting carbohydrates for monounsaturated fat. Br J Nutr 86, 181188.Google Scholar
6Phillips, SA, Jurva, JW, Syed, AQ, et al. (2008) Benefit of low-fat over low-carbohydrate diet on endothelial health in obesity. Hypertension 51, 376382.Google Scholar
7Varady, KA, Bhutani, S, Klempel, MC, et al. (2011) Improvements in vascular health by a low-fat diet, but not a high-fat diet, are mediated by changes in adipocyte biology. Nutr J 10, 8.CrossRefGoogle Scholar
8Volek, JS, Ballard, KD, Silvestre, R, et al. (2009) Effects of dietary carbohydrate restriction versus low-fat diet on flow-mediated dilation. Metabolism 58, 17691777.Google Scholar
9Wycherley, TP, Brinkworth, GD, Keogh, JB, et al. (2010) Long-term effects of weight loss with a very low carbohydrate and low fat diet on vascular function in overweight and obese patients. J Intern Med 267, 452461.CrossRefGoogle ScholarPubMed
10Noto, H, Goto, A, Tsujimoto, T, et al. (2013) Low-carbohydrate diets and all-cause mortality: a systematic review and meta-analysis of observational studies. PLOS ONE 8, e55030.Google Scholar
Figure 0

Fig. 1 Forest plot showing pooled weighted mean differences (WMD) with 95 % CI for flow-mediated dilatation (%) of six randomised controlled low-carbohydrate diet studies. For each low-carbohydrate trial, represents the point estimate of the intervention effects. The horizontal line joins the lower and upper limits of the 95 % CI of these effects. The area of reflects the relative weight of the study in the respective meta-analysis. At the bottom of the graph, represents the pooled WMD with 95 % CI. (A colour version of this figure can be found online at http://www.journals.cambridge.org/bjn).