Low-carb diet triumphant over low-fat in meta-analysis
I couldn’t believe my eyes when I read the paper a colleague from Europe emailed me this morning. It was from the journal Obesity Reviews, the journal of the International Association for the Study of Obesity (IASO). The IASO is the international academic obesity research society, and as such, it is mired in all the mainstream misconceptions of the causes and proper treatment of obesity. Obesity Reviews is edited by Arne Astrup, the Danish obesity researcher who is a staunch believer in and supporter of the low-fat diet as the best therapeutic tool in the battle against obesity. And Obesity Reviews is the very journal in which George Bray launched his misguided jihad against Gary Taubes and his book Good Calories, Bad Calories.
The paper, which isn’t published yet, is titled:
Systematic review of randomized controlled trials of low-carbohydrate vs. low-fat/low-calorie diets in the management of obesity and its comorbidities
The abstract of this paper pretty much says it all.
There are few studies comparing the effects of low-carbohydrate/high-protein diets with low-fat/high-carbohydrate diets for obesity and cardiovascular disease risk. This systematic review focuses on randomized controlled trials of low-carbohydrate diets compared with low-fat/low-calorie diets. Studies conducted in adult populations with mean or median body mass index of ≥28 kg m−2 were included. Thirteen electronic databases were searched and randomized controlled trials from January 2000 to March 2007 were evaluated. Trials were included if they lasted at least 6 months and assessed the weight-loss effects of low-carbohydrate diets against low-fat/low-calorie diets. For each study, data were abstracted and checked by two researchers prior to electronic data entry. The computer program Review Manager 4.2.2 was used for the data analysis. Thirteen articles met the inclusion criteria. There were significant differences between the groups for weight, high-density lipoprotein cholesterol, triacylglycerols and systolic blood pressure, favouring the low-carbohydrate diet. There was a higher attrition rate in the low-fat compared with the low-carbohydrate groups suggesting a patient preference for a low-carbohydrate/high-protein approach as opposed to the Public Health preference of a low-fat/high-carbohydrate diet. Evidence from this systematic review demonstrates that low-carbohydrate/high-protein diets are more effective at 6 months and are as effective, if not more, as low-fat diets in reducing weight and cardiovascular disease risk up to 1 year. More evidence and longer-term studies are needed to assess the long-term cardiovascular benefits from the weight loss achieved using these diets.
This is all something we long-time low-carbers have known forever, but it’s nice to see it in an international academic journal.
I haven’t gone over this paper my usual critical eye yet (I will; I just haven’t yet. I’m always suspicious of meta-analyses) for a couple of reasons. First, I wanted to get it up so that all the readers of this blog would have a chance to look it over without my input. (I found it on Scribd, so everyone can read the full text version.) And, second, because given the anti-low-carb bias of the editors of this journal, I figured that the peer-review process would have gone over it with a fine tooth comb before approving it for publication.
It will be interesting to watch what happens with this paper. The media is made aware of these papers as soon as the journal announces that they will be published. The media usually waits until right before publication or the day of publication to write articles about the paper for the general press. I will be keen to see if the media picks up on this one from this most august of academic publishers. And I’m curious to see how long it will take for Obesity Reviews to actually publish the paper in its regular journal. Often papers are put up in the soon-to-be-published or early-view sections of the online journal, but then languish there forever before actually being published. I’ll be eager to see the fate of this one.
Enjoy. Use this freely the next time your doctor or a low-carb naysayer comes at you with the old ‘Show me the evidence.’
As always, I welcome your feedback.
I can’t find a flaw in this study that shows low carb diets actually HURT endothelial function.
Please help me figure out why it does not agree with your fast food comparison showing that only carbs effected endothelial heath, in this case its clearly the Low Fat not low carb diet that shows improved endothelial function.
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http://hyper.ahajournals.org/cgi/content/full/51/2/376?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=Gutterman&searchid=1&FIRSTINDEX=0&volume=51&issue=2&resourcetype=HWCIT
Obesity is associated with impaired endothelial-dependent flow-mediated dilation, a precursor to hypertension and atherosclerosis. Although dieting generally improves cardiovascular risk factors, the direct effect of different dietary strategies on vascular endothelial function is not known. The purpose of this study was to test the hypothesis that a low-fat (LF) diet improves endothelial function compared with an isocaloric low-carbohydrate (LC) diet. Obese (n=20; body mass index: 29 to 39; mean systolic blood pressure: 107 to 125 mm Hg) and otherwise healthy volunteers were randomly assigned to either the American Heart Association modeled LF (30% fat calories) diet or an isocaloric LC Atkins’ style diet (20 g of carbohydrates) for 6 weeks (4-week weight loss and 2-week maintenance phase). Brachial flow-mediated dilation and dilation to nitroglycerin were measured with ultrasound using automated edge detection technology (baseline, week 2, and week 6). Blood pressure, weight loss, and cholesterol profiles were measured throughout the study. Weight loss was similar in LF (100±4 to 96.1±4 kg; P (95.4±4 to 89.7±4 kg; P pressure decreased similarly in both groups (LF: 8/5 mm Hg; LC: 12/6 mm Hg) at 6 weeks. After 6 weeks, the percentage of flow-mediated dilation improved (1.9±0.8; P<0.05) in the LF diet but was reduced in the LC diet (–1.4±0.6; P panels was similar at 0, 2, and 6 weeks. Despite similar degrees of weight loss and changes blood pressure, LF diets improved brachial artery flow-mediated dilation over LC diets. LF diets may confer greater cardiovascular protection than LC diets.
I read this study when it first came out. I didn’t put a whole lot of stock in it because of the small number of participants and the fact that the actual diets used weren’t presented. I’d like to know a little more than that one group went on an Atkins diet while the other went on an AHA-type diet. According to the paper, these subjects all got their food from the study center, so it would have been easy to describe the diets better. I’m always a little wary of studies showing an unexpected effect when the authors decide not to include an important part of the data. This missing factor tells us something about the peer-review process where low-carb diets are concerned. I’ll guarantee you that if this study had shown the opposite effect, the peer-reviewers would have insisted that the individual diets be described. But since the study confirms the bias of most reviewers, they didn’t ask that it be included. Another thing that got my antennae up were the differences in caloric intake at the start and at maintenance. According to the study, the group randomized to the LC diet was consuming significantly fewer calories than the members of the group randomized to LF. The LF group cut more calories during the 4 wk weight loss phase than did the LC group, then during maintenance the caloric intake of the LF group didn’t go as high as it was pre-study whereas the LC group went higher. It doesn’t make sense to me how this could happen. It also doesn’t make sense that subjects on a LC diet of 20g CHO per day could eat that many calories, which is why it would have been nice to have seen the actual food choices.
Another problem with this study is the group of people looked at. They are a different group indeed, as even the authors admit. These are obese people with none of the typical lab findings of obesity and/or insulin resistance. Look at the triglyceride numbers alone. Obese people with triglycerides of 77 are unusual. What applies to these people may not apply to the typical obese person.
But, even if we assume that the study were perfectly done (ignoring the fact that there were a tiny number of subjects), it is only one study. And as I’ve said countless times, one study doesn’t prove anything. It would have to be repeated again and again before one could say definitively that LC diets made endothelial function worse.