Dress up your kids like Dracula or Frankenstein, and most likely they'll look more cute than scary.
Let them eat too much candy, and they'll turn into real little monsters.
That's the word, at least, from many parents who fear their trick-or-treaters' sweets success this Halloween will end in wild "sugar highs" -- with energy going through the roof -- followed by moody "sugar crashes" -- with that energy suddenly dropping through the floor.
"I have mothers tell me their child can ingest something sweet, and they know to the minute when the reaction is going to occur," says Jo Ann Hattner, a registered dietitian who teaches nutrition at the Stanford University School of Medicine.
Yet the truth is that experts disagree about whether the sugar high and sugar crash truly exist.
Many say the evidence contradicts such stories. "There is no scientific basis to the idea that sugar and/or candy has any major effect on children's behavior, particularly if they eat OK," says Dian Dooley, professor of human nutrition, food and animal sciences at the University of Hawaii at Manoa.
Others think sugar has plenty of skeletons in its closet. "The bottom line is that the ingestion of too much high-glycemic carbohydrate causes a rapid rise and then fall of blood sugar," says Dr. David Ludwig, professor of pediatrics at Harvard Medical School and director of the Optimal Weight for Life program at Children's Hospital Boston. "This triggers a series of metabolic and hormonal changes that can affect appetite and behavior for hours to come."
Still more experts think that the experience of a sugar high is real -- but only because parents are convinced it exists.
"I would never try to convince parents otherwise," says Dr. Thomas Robinson, professor of pediatrics at Stanford and director of the Center for Healthy Weight at Lucile Packard Children's Hospital. "You can't tell them it doesn't happen because, for them, it does happen."
A little basic physiology implies that sugar highs could happen. Glucose, a digestive byproduct of the sugar we eat, is one of the body's two main sources of energy (along with fat). So it seems feasible that eating a lot of sugar could give a person a quick energy boost.
That's the reasoning behind, say, marathoners eating candy bars en route. It's also the theory behind an old test doctors once got a kick out of: They'd give a pregnant woman a glass of orange juice, Hattner says, and in no time, if the woman's baby was healthy, it would be treating its mom like a soccer ball.
But the body is designed to keep glucose levels in the blood stable. When the levels increase, the pancreas releases insulin, which moves glucose out of the blood and into tissues throughout the body.
If levels have spiked steeply, the pancreas might overreact and release too much insulin, so the glucose level could end up dipping below where it should be. But then the pancreas releases another hormone, glucagon, which moves glucose stored as glycogen out of the liver to bring the levels back up again.
Things can go wrong with this regulatory system. Diabetics don't produce enough insulin, for example. And even in a healthy person, it can take a little time to restore the system to balance once it's gotten off kilter. If glucose levels get dramatically low, that's the physiological basis for a sugar crash. But here the neatness of the theory seems to end. If levels stay high for a while, instead of energizing a person as you'd expect, it actually makes a person sleepy, studies show.
Investigations into the topic date back decades. In the early 1970s, pediatric allergist Dr. Benjamin Feingold found that food additives were related to hyperactivity. His work is widely seen as jump-starting the study of how diet affects behavior, and that field of research soon became very active.
Early studies of sugar searched in vain for proof of the sugar highs that parents and teachers so often complained about. One such finding, published in the New England Journal of Medicine in 1994, compared sugar and the artificial sweetener aspartame -- both of which had been reported to cause hyperactivity and other behavioral problems.
Researchers tested two groups of children: 25 normal preschoolers, 3 to 5 years old, and 23 school-age children, 6 to 10 years old, who were described by their parents as sugar-sensitive.
Each of the children followed three different diets for three weeks each. One was high in sugar but had no artificial sweeteners. A second was low in sugar and used aspartame as a sweetener. And the third was low in sugar and used saccharin as a sweetener. (Because no hyperactivity problems with saccharin had been reported, saccharin was considered a placebo.)
The result: On 39 behavioral and cognitive measures, no significant differences in the three diets were found among the "sugar-sensitive" children. Some differences were found on four of 31 measures among preschoolers, but in no consistent pattern.