I sent the following to Andrew Sullivan, but I thought it would be useful to post here as well:
I read with interest some of your readers’ responses to your post on my post. I’ve been getting similar comments all The Incidental Economist as well. Here’s the thing. Anecdotes are not the same as studies. Not even a collection of them.
I will concede that you can’t prove a negative. Therefore, I cannot prove that there isn’t a single child out there who is sensitive to sugar. The question is, rather, whether this is a widespread phenomenon or whether parents can identify if they have such as a child.
As to the former, it doesn’t appear to be so. As I said in my post, there have been many randomized controlled trials on this topic. RCTs are the most powerful types of studies, and the only ones that can prove causation. They don’t find a relationship. Yes, one individual author may hedge and say it’s not enough, but the whole sum of them are rather convincing.
Let me give you an example of how they work. We divide kids into two groups. One gets sugar, the other gets a sugar-free substitute. Then we measure hyperactivity. There will be kids in both groups who are hyper and kids who are not. The important question is whether there are more kids in the sugar group than the non-sugar who are hyper.
There aren’t. This means that the hyperactivity, while present in some kids after sugar, isn’t caused by the sugar. Some parents who see hyperactivity in the sugar group will believe so, but there will be just as many in the non-sugar group.
As to the second idea, whether parents can accurately identify those kids who are sensitive to sugar, I point you to the study I summarized:
[C]hildren were divided into two groups. All of them were given a sugar-free beverage to drink. But half the parents were told that their child had just had a drink with sugar. Then, all of the parents were told to grade their children’s behavior. Not surprisingly, the parents of children who thought their children had drunk a ton of sugar rated their children as significantly more hyperactive. This myth is entirely in parents’ heads. We see it because we believe it.
Parents who believe their children are hyper when they get sugar are conditioned to see it, even when their kids aren’t given real sugar. They’re not reliable.
As to the red dyes, the evidence there is not compelling either (emphasis mine):
Adverse behavioral responses to ingestion of any kind of candy have been reported repeatedly in the lay press. Parents and teachers alike attribute excessive motor activity and other disruptive behaviors to candy consumption. However, anecdotal observations of this kind need to be tested scientifically before conclusions can be drawn, and criteria for interpreting diet behavior studies must be rigorous. Ingredients in nonchocolate candy (sugar, artificial food colors), components in chocolate candy (sugar, artificial food colors in coatings, caffeine), and chocolate itself have been investigated for any adverse effects on behavior. Feingold theorized that food additives (artificial colors and flavors) and natural salicylates caused hyperactivity in children and elimination of these components would result in dramatic improvement in behavior. Numerous double-blind studies of the Feingold hypothesis have led to the rejection of the idea that this elimination diet has any benefit beyond the normal placebo effect. Although sugar is widely believed by the public to cause hyperactive behavior, this has not been scientifically substantiated. Twelve double-blind, placebo-controlled studies of sugar challenges failed to provide any evidence that sugar ingestion leads to untoward behavior in children with Attention-Deficit Hyperactivity Disorder or in normal children. Likewise, none of the studies testing candy or chocolate found any negative effect of these foods on behavior. For children with behavioral problems, diet-oriented treatment does not appear to be appropriate. Rather, clinicians treating these children recommend a multidisciplinary approach. The goal of diet treatment is to ensure a balanced diet with adequate energy and nutrients for optimal growth.
Not that I expect this will settle the debate. I’m becoming convinced I will never win this one.