Over the past few weeks I have increasingly found myself – of my own volition I might add – whack-a-mole-in’ fallacious claims about the Swedish Government recommending a low carbohydrate diet.
I have traced the source of many of these claims as a particularly bad BMJ news article by Anders Hansen, so I thought it might be more productive to cut from the root and write to the BMJ calling for retraction, or substantial correction.
Now I know writing whiny complaint letters is more Clark Kent than Superman, but sometimes a few key points from a moaning pedant is a practical way of tackling the great menace of inaccuracy. So, lets see how we get on with this:
I am writing to express my concern regarding the news article “Swedish health advisory body says too much carbohydrate, not fat, leads to obesity”. 1
While I appreciate this is a now a historical news article from 2013, it contains numerous factual inaccuracies which continue – based on the reputation of the BMJ as a trusted source – to be widely propagated and cited, wrongly, as conclusive evidence that low fat diets are ineffective for the treatment of obesity.
Indeed, despite the attempts of the chair of the HTA committee Nina Rehnquist to clarify matters in her rapid response to the article, it has now influenced a much wider audience, as it was cited in the best selling book ‘The Big Fat Surprise’ as the source of the following erroneous claim:
“…in 2013 in Sweden, an expert health advisory group, after spending two years reviewing 16,000 studies, concluded that a diet low in fat was an ineffective strategy for tackling either obesity or diabetes.”
Having read the english summary of the Health and Technology Assessment, I believe that the level of inaccuracy in this news piece combined with its now wide audience requires the BMJ to either retract the article, or substantially correct both the headline and content. Firstly, the title of the piece is inaccurate:
Swedish health advisory body says too much carbohydrate, not fat, leads to obesity
The Health and Technology Assessment cited did not consider the cause of obesity, only the treatment of obesity a point made clear by both the title of the report 2 and Nina Rehnquist’s rapid response.
As the article metrics show, the vast majority of readers have seen only the abstract of this article and I feel that this inaccurate title leaves the piece open to being mis-cited. With regards to the content of the article, there are a significant number of inaccuracies. The first line claims:
An influential Swedish health organisation has recommended a diet that is low in carbohydrates but not low in fat for people who are overweight or obese or have diabetes.
Unfortunately, the report did not consider the treatment of diabetes because this was the subject of an earlier separate Health and Technology Assessment in 2010.3 It is worth noting however that the earlier report on diabetes did not recommend a diet “low in carbohydrates but not low in fat”, in fact is states something quite different:
In type 2 diabetes, low-fat and moderate low-carbohydrate diets (30–40% of the energy from carbohydrates) have similar, favorable effects on HbA1c (long-term blood glucose) and bodyweight. The absence of sufficient-quality studies in people with diabetes prevents evaluation of the long-term effects of more extreme diets involving low-carbohydrate and high-fat intake, eg, so-called “low-carb, high-fat” (LCHF) diets. Hence, safety aspects become particularly important in clinical follow-up of individuals who choose extreme low-carbohydrate diets (10–20% energy from carbohydrates).
With regards to the claim that a diet “low in carbohydrates but not low in fat” was recommended for the treatment of obesity, this is correct only in the short term, and the report has more nuanced conclusions which suggest a range of equally effective options over the longer term:
Weight loss in adults. A range of advice on alteration of eating and drinking habits can result in obese individuals losing weight or reducing their waist size. In the short term (six months), advice on strict or moderate low carbohydrate diets is a more effective means of achieving weight loss than advice on low fat diets. In the long term, there are no differences in the effect on weight loss between advice on strict and moderate low carbohydrate diets, low fat diets, high protein diets, Mediterranean diets, diets aimed at achieving a low glycaemic load or diets containing a high percentage of monounsaturated fats. Advice on increasing the intake of dairy products (primarily milk) or reducing the intake of sweet drinks may also lead to weight loss.
Hanson further states:
The guideline advises that meat and fish rich in fat, along with nuts and olive oils, should form a large part of a healthy diet, while the consumption of pasta, potatoes, and white bread should be reduced.
No such recommendations are made within the report. In fact there were virtually no findings on individual foods, as the HTA report 2 clearly states:
However, all in all these studies provide no clear evidence for advice on individual foods for obese individuals in order to prevent morbidity or achieve weight loss.
In addition I can find no support in the HTA for the following claim made by Hansen:
The recommendation contradicts the generally held belief that people should avoid foods that are rich in fat, especially those high in saturated fat.
The HTA report 2 itself stating:
The studies relating to strict low carbohydrate diets which were included in the report give no indication of whether low carbohydrate diets should provide small portions or not include saturated fat…[…]…is not possible to draw any conclusions on the link between low carbohydrate diets – irrespective of fat content type – and cardiovascular morbidity. The precautionary principle could be applied here. This may result in restraint on the intake of saturated fat when advice is given on low carbohydrate diets, as long as the documentation on the long-term effects is so inadequate.
I would hope that you agree that there are serious inaccuracies in this article which continue to compromise the reputation of the BMJ. I would ask that you consider a formal retraction, or substantial correction of the article to address the above points.
In response to my letter the BMJ have issued a very substantial correction which can be found here:
In this News story, “Swedish health advisory body says too much carbohydrate, not fat, leads to obesity” (BMJ2013;347:f6873, doi:10.1136/bmj.f6873), the headline and some of the text were incorrect. The report did not say that too much carbohydrate leads to obesity, as stated in the headline. It said that low carbohydrate diets were more beneficial for reducing obesity in the first six months of treatment, when compared with low fat diets, but made no difference at 12 months.
The report said that, in the longer term, “there are no differences in the effect on weight loss between advice on strict and moderate low carbohydrate diets, low fat diets, high protein diets, Mediterranean diets, diets aimed at achieving a low glycaemic load, or diets containing a high percentage of monounsaturated fats.” The report did not conclude that “the scientific evidence did not support a low fat diet.”
In addition, the report made few recommendations with regard to specific foods and did not say that “the consumption of pasta, potatoes, and white bread should be reduced.” We apologise for these errors.
Kudos to the BMJ for making a very full and formal retraction of these erroneous claims.
Finally an errata of my own! – In my original letter when referring to Nina Renquist’s rapid response I state “her” when it should in fact be “his” response. Apologies.