While babysitting in my teens parents always gave me the same instructions: don’t give the kids sharp knives, don’t feed the baby the steak from the freezer, and whatever you do – don’t give the children sugar before they go to bed. The idea that sweets and red cordial makes kids go (sugar) bananas has been around for the last 30 years. But the evidence to prove it is actually pretty scarce.

In fact evidence that sugar can give anyone a “high” is also in short supply. New reviews on old data are saying that the placebo effect and some judgmental parents are to blame for kids missing out their much wanted sweets.

The 70’s: don’t blame the boogie, blame the sugar!

In 1974 a fellow by the name of Crook found that when you took sucrose out of a hyperactive child’s diet their behaviour improved. He then found that when the sugar was reintroduced, hyperactivity and naughty childlike behaviour returned.  Four years later, another study showed the same effect. This led scientists and parents alike to conclude that sugar makes kids go hyper. Many smaller studies have also shown a connection between controlled, healthy diets and decrease in hyperactivity.

It was predicted that because refined sugars and carbohydrates enter the bloodstream quickly and make rapid changes in blood glucose levels it might trigger adrenaline production. Adrenaline is a hormone that increases heart rate and blood pressure, bringing more oxygen to the brain, and making kids more active and alert. But, this idea hasn’t been confirmed by rigorous investigations.

Now: don’t blame the sugar, blame the parents (and the researchers)

More recently, scientists are actually changing their tune about sugar’s effect on the body and brain. In 2004, a review on the topic published in the British Journal of Nutrition found that many of the 1970s studies used poor methods. For one, they didn’t have a control group of kids who hadn’t eaten sugar to compare against. And mistake 2: many of them used parents to judge the children’s behaviour after the parents knew their kids took a sugar hit, and know the myth about sugar. (Tainted results!)

Adding some sweetness to the 2004 conclusions, earlier this year a review on the placebo effect found that when it comes to sugar and parental expectations, parents are quite biased. One study tested this bias directly. Researchers gave one group of kids a sweet, nonsugar drink and a parent was told the child had sugar; while in another group the child was given a sweet, nonsugar drink but the parent told the child was not given sugar.  On average, the parents who thought their kid drank sugar recorded that their child was more hyperactive and noncompliant than those who thought their little dears didn’t ingest any sugar. Alarmingly (and probably coincidentally) the researchers found that the children, who were expected to go hyper (their parents were told they drank sugar), actually had significantly lower activity levels as measured by a wrist actometer.

Dr. Vreeman and Dr. Carroll, two  paediatricians from Riley Hospital for Children wrote in their myth busting book Don’t Swallow Your Gum: Myths, Half-truths, and Outright Lies About Your Body and Health this year (2009, St. Martin’s Press) that there are at least 12 double-blind, randomized, controlled trials (the best, most reliable kind) which examine how children react to diets containing different levels of sugar. According to them, “None of these studies, not even studies looking specifically at children with attention deficit-hyperactivity disorder, could detect any differences in behavior between the children who had sugar and those who did not.”

Sugar and the brain

It also doesn’t make much sense that the human brain and nervous system would be so sensitive to sugar that eating some chocolate or red cordial would significantly change our behaviour. All chemicals that affect our brain are tightly controlled. This makes sure that we keep a (somewhat) constant concentration of different substances in our body. Glucose supply is no different. It’s controlled by complex mechanisms, like hormones and feedback loops. So, for example, if there is too much glucose in the blood from digesting sugar, insulin will be produced to suck it up, keeping a constant concentration of glucose in the blood.

Despite tight control of the chemicals that affect our brain, studies have shown that glucose can actually improve some cognitive tasks, such as attention, information processing, and word recall.

Going red: Could it be the colouring?

If sugar isn’t to blame for hyperactive kids, what is? Maybe it’s the red in the red cordial. In 1977 Feingold hypothesized that additives, like artificial colours and preservatives, caused hyperactivity in children. To test his theory he gave kids a capsule of food dyes, or a placebo for five days and made them perform learning tasks. Some of the children performed worse after receiving the food dyes compared with placebo.

But, the study used a high dose of food dyes (much more than what a child would consume from the regular diet), so we aren’t sure that these results can be generalized to real-life situation. Although an analysis of 15 quality controlled trials of food colourings showed increase in hyperactivity.

The Sweet Conclusion

After all the hype about sugar and hyperactivity there is really not much evidence to back it up. Of course that doesn’t mean that it’s time to ply those kids with candy and cake. Sugar does lead to obesity and can harm your teeth. But no more can parents use the excuse “it’s getting close to bed time” to stop their kids enjoying a late night snack.  And for my next babysitting myth? Can I feed babies steak straight from the freezer?