Giving children sugar makes them hyperactive.

In June 1973, Benjamin Feingold stood before the American Medical Association's annual meeting in New York and proposed a sweeping explanation for America's epidemic of hyperactive children. Feingold was a senior allergist at Kaiser Permanente in San Francisco, authoritative and seventy years old, and his argument was specific: artificial food colorings, synthetic preservatives, and naturally occurring salicylates in fruits and vegetables were triggering behavioral disturbances in a substantial fraction of American children. His book, Why Your Child Is Hyperactive, reached bookstores in 1975 and became a surprise bestseller. Parent groups organized around his ideas. Journalists covered the theory sympathetically.

And in the popular reception of Feingold's claims, something significant happened: the culprit broadened. Artificial additives slid almost imperceptibly into food itself, and within a few years the dominant folk theory of childhood hyperactivity centered not on Red Dye No. 40 but on sugar. The physiological argument seemed intuitive: sugar enters the bloodstream quickly, blood glucose spikes, the pancreas responds, and some researchers speculated this cascade could trigger adrenal activity, an adrenaline surge that would manifest as agitation and motor overactivity. The biochemistry was plausible enough to sound scientific without being precise enough to test easily. By the early 1980s, a majority of American parents believed that sugar made children wild, and pediatricians were fielding questions about it at nearly every well-child visit.

What the theory had was narrative coherence. What it lacked was evidence. The studies that existed were small, methodologically inconsistent, and almost never blind. Teachers and parents who knew a child had consumed sugar watched that child through the lens of that knowledge. A kid careening around a birthday party after cake and punch seemed causally, obviously wired. That the party itself, the noise, the competition, the other children, the social excitement, might fully explain the behavior was not the hypothesis that came to mind.

The expectation, it turned out, was doing most of the work. Daniel Hoover and Richard Milich at the University of Kentucky designed an experiment, published in 1994, to test what belief alone could produce. They recruited thirty-five mothers of boys aged five to seven whom the mothers described as behaviorally sugar-sensitive. All children received aspartame, a placebo with no sugar. Half the mothers were told their son had just consumed a large dose of sugar; the other half were told the truth. Researchers then observed mothers and children interacting.

The mothers who believed their child had consumed sugar rated those children as significantly more hyperactive. Their behavior changed as well: they stayed physically closer, offered more corrections, and watched their children more intently. The children's actual behavior was identical across both groups. What had shifted was not what the boys were doing but how the mothers were seeing and responding to them. Confirmation bias was not merely coloring the mothers' perceptions, it was reshaping the interaction itself.

The controlled research had been accumulating for years before a definitive synthesis arrived. Mark Wolraich and colleagues at Vanderbilt University published a meta-analysis in JAMA in November 1995, covering twenty-three controlled trials drawn from sixteen published papers. Inclusion required that studies administer a known quantity of sugar, use a blinded placebo condition with artificial sweetener, and report statistics that permitted effect-size calculation. The result, pooled across all those trials, was unambiguous: sugar had no measurable effect on children's behavior or cognitive performance. The effect sizes were negligibly small. No subgroup showed consistent evidence of behavioral change, not children diagnosed with ADHD, not children whose parents considered them sugar-sensitive, not preschoolers.

The problem was never scientific uncertainty. Individual blinded trials throughout the 1980s and early 1990s had returned null results repeatedly. The problem was the asymmetry between how a finding travels through the Journal of the American Medical Association and how a belief travels through a school cafeteria or a pediatrics waiting room. Research requires access, inclination, and a willingness to accept conclusions that contradict experience. A child spinning through a kitchen after Halloween candy requires only a parent watching.

Surveys conducted well into the 2000s found that most parents still believed sugar caused hyperactivity, along with a meaningful fraction of practicing pediatricians. The Hoover and Milich finding helps explain why the belief sustains itself so effectively: parents who expect behavioral change after sugar are primed to find it, respond to it, and remember it. Every birthday party becomes a confirmation. The controlled trial runs in someone else's laboratory, behind a one-way mirror, with placebo-blinded children whose mothers have been carefully deceived. That experiment is not the one most people are running.