Even True Believers Need a Control Group
Sigh. A previously published study – which lacks a control group – is cropping up in a new form to beat the drum of claims that sugar is toxic. Based on a dataset published last year in Obesity, a new publication has just appeared in Atherosclerosis. The first publication from this dataset advanced a claim that holding calories constant while restricting fructose improved metabolic function in children with obesity. In this new publication, the authors report on markers of dyslipidemia and cardiovascular disease risk.
In a letter to the editor published in February, Tauseef Khan and John Sievenpiper explained a key problem with the original study:
It was an uncontrolled before-after study in which children’s baseline self-reported diet, which can be inaccurate, was contrasted to a low-sugar diet provided for 9 days. It is likely that lifestyle and eating behaviors other than sugar intake changed.
What this means is that we now have two publications of one uncontrolled study of fructose restriction.
The problem with this data is that the premise of the study – isocaloric fructose restriction – is not exactly accurate. The authors are claiming that they matched the calories that children consumed during the experiment with fructose to the calories the children consumed before the experiment.
In fact they matched the calories that the children reported consuming. The authors noted the reason this can be a problem in their first publication, saying “recall bias underestimating sugar consumption is the norm in epidemiological studies.”
But then they ignored the issue and continued to claim that they held calories constant during the fructose restriction.
Setting up a valid control group for a study can be a real nuisance. But without well-controlled studies, claims about dramatic benefits from restricting sugar consumption are not valid.
Overstated claims have a way of causing trouble down the road.
Click here for the publication in Atherosclerosis, here for the publication in Obesity, and here for more perspective on problems with this dataset. Click here for perspective on potential problems with multiple publications from the same study.
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July 25, 2016