We've all heard of the "sugar rush." It's a vision that prompts parents and even teachers to snatch candy away from kids, fearing they'll soon be bouncing off the walls, wired and hyperactive. It’s a myth American culture has clung to for decades—and these days, it’s not just a kid thing. Adults are wary of sugar, too. Some of this fear is warranted—diabetes, the obesity epidemic—but the truth is, sugar doesn't cause hyperactivity. Its impact on the body isn’t an up-and-down thing. The science is clear: There is no "sugar rush.”
To find out how and why the myth started, we need to go back to well before the first World War—then pay a visit to the 1970s.
Our Complicated Relationship With Sugar
According to cultural historian Samira Kawash, America has had a long, complex, love-hate relationship with sugar. In Candy: A Century of Panic and Pleasure, Kawash traces the turn from candy-as-treat to candy-as-food in the early 20th century. At that time, the dietary recommendations from scientists included a mix of carbohydrates, proteins, and fats, with sugar as essential for energy.
Not everyone was on board: The temperance movement, for example, pushed the idea that sugar caused an intoxication similar to alcohol, making candy-eaters sluggish, loopy, and overstimulated. In 1907, the chief of the Philadelphia Bureau of Health estimated that the "appetite" for candy and alcohol were "one and the same," Kawash writes. On the flip side, other scientists suggested that sugar from candy could stave off cravings for alcohol—a suggestion that candymakers then used in their advertisements.
While the debate about sugar as an energy source raged in America, militaries around the world were also exploring sugar as energy for soldiers. In 1898, the Prussian war office became the first to commission a study on the sweet stuff—with promising results: "Sugar in small doses is well-adapted to help men to perform extraordinary muscular labor," early researchers wrote. German military experiments introduced candy and chocolate cakes as fortification for the troops, and the U.S. military added sugary foods to soldiers' diets soon after. When American soldiers returned from World War I, they craved sweets, which "propelled an enormous boom" of candy sales that has lasted to this day, Kawash wrote on her blog, The Candy Professor. American advertisers framed candy as a quick, easy source of energy for busy adults during their workday.
As artificial sweeteners moved into kitchens in the 1950s, candymakers struggled to make their products appeal to women who were watching their waistlines. One industry group, Sugar Information Inc., produced a tiny "Memo to Dieters" pamphlet in 1954 designed to fit inside chocolate boxes. "Sugar before meals raises your blood sugar level and reduces your appetite," it claimed. But by the 1970s, the sugar-positivity heyday had started to wane.
The Origins of the Sugar Rush Myth
The idea that sugar causes hyperactivity gained traction in the early 1970s, when more attention was being paid to how diet might affect behavior. One of the major figures studying the possible connection between diet and behavior was an allergist named Benjamin Feingold, who hypothesized that certain food additives, including dyes and artificial flavorings, might lead to hyperactivity. He formalized this into a popular—yet controversial—elimination diet program. Though certain sugary foods were banned from the program for containing dyes and flavorings, sugar itself was never formally prohibited. Still, thanks in part of the Feingold diet, sugar started to become the poster child for diet and hyperactivity.
It wasn't until the late 1980s that serious doubts about sugar's connection to hyperactivity began to be raised by scientists. As FDA historian Suzanne White Junod wrote in 2003 [PDF], the 1988 Surgeon General's Report on Nutrition and Health concluded that "alleged links between sugar consumption and hyperactivity/attention deficit disorders in children had not been scientifically supported." Despite "mothers' mantra of no sweets before dinner," she noted, "more serious allegations of adverse pediatric consequences … have not withstood scientific scrutiny."
A 1994 paper found that aspartame—an artificial sweetener that had also been accused of inducing hyperactivity in children—had no effect on 15 children with ADHD, even though they had consumed 10 times more than the typical amount.
A year later, the Journal of the American Medical Association published a meta-analysis of the effect of sugar on children's behavior and cognition. It examined data from 23 studies that were conducted under controlled conditions: In every study, some children were given sugar, and others were given an artificial sweetener placebo like aspartame. Neither researchers nor children knew who received the real thing. The studies recruited neurotypical children, kids with ADHD, and a group who were "sensitive" to sugar, according to their parents.
The analysis found that "sugar does not affect the behavior or cognitive performance of children." (The authors did note that “a small effect of sugar or effects on subsets of children cannot be ruled out.”)
"So far, all the well-controlled scientific studies examining the relationship between sugar and behavior in children have not been able to demonstrate it," Mark Wolraich, an emeritus professor of pediatrics at the University of Oklahoma Health Sciences Center who has worked with children with ADHD for more than 30 years and the co-author of that 1995 paper, tells Mental Floss.
Yet the myth that consuming sugar causes hyperactivity hasn’t really gone away. One major reason is the placebo effect, which can have powerful results. The idea that you or your children might feel a "sugar rush" from too much candy isn't unlike the boost you hope to feel from an energy drink or a meal replacement shake or bar (which can contain several teaspoons of sugar). The same is true for parents who claim that their kids seem hyperactive at a party. Peer pressure and excitement seem to be to blame—not sugar.
"The strong belief of parents [in sugar's effects on children's behavior] may be due to expectancy and common association," Wolraich wrote in the JAMA paper.
It works the other way, too: Some parents say they've noticed a difference in their kids' behavior once they take out most sugars from their diets. This strategy, like the Feingold diet, continues to attract interest and followers because believing it works has an impact on whether it actually works or not.
Correlation, Causation, and Caffeine
Which isn't to say there are absolutely no links between sugar consumption and poor health outcomes. A 2006 paper found that drinking a lot of sugary soft drinks was associated with mental health issues, including hyperactivity, but the study's design relied on self-reported questionnaires that were filled out by more than 5000 10th-graders in Oslo, Norway. The authors also noted that caffeine is common in colas, which might have a confounding effect.
In another study, conducted by University of Vermont professor of economics Sara Solnick and Harvard health policy professor David Hemenway, the researchers investigated the so-called "Twinkie defense," in which sugar is said to contribute to an "altered state of mind." (The phrase Twinkie defense comes from the 1979 trial of Dan White for killing San Francisco city district supervisor Harvey Milk and Mayor George Moscone. His lawyers argued that White had "diminished capacity and was unable to premeditate his crime," as evidenced in part by his sudden adoption of a junk-food diet in the months before the murders. White was convicted of voluntary manslaughter.)
In their survey of nearly 1900 Boston public high schoolers, Solnick and Hemenway found "a significant and strong association between soft drinks and violence." Adolescents who drank more than five cans of soft drinks per week—nearly 30 percent of the group—were significantly more likely to have carried a weapon.
But Solnick tells Mental Floss the study isn't evidence of a "sugar rush."
"Even if sugar did cause aggression—which we did not prove—we have no way of knowing whether the effect is immediate (and perhaps short-lived) as the phrase 'sugar rush' implies, or whether it’s a longer-term process," she says. Sugar could, for example, increase irritability, which might sometimes flare up into aggression—but not as an immediate reaction to consuming sugar.
Harvard researchers are looking into the long-term effects of sugar using data from Project Viva, a large observational study of pregnant women, mothers, and their children. A 2018 paper in the American Journal of Preventive Medicine studied more than 1200 mother-child pairs from Project Viva, assessing mothers' self-reported diets during pregnancy as well as their children's health during early childhood.
"Sugar consumption, especially from [sugar-sweetened beverages], during pregnancy and childhood, and maternal diet soda consumption may adversely impact child cognition,” the authors concluded, though they noted that other factors could explain the association.
“This study design can look at relationships, but it cannot determine cause and effect,” says Wolraich, who was not involved in the study. "It is equally possible that parents of children with lower cognition are likely to cause a greater consumption of sugar or diet drinks, or that there is a third factor that influences cognition and consumption.”
The Science of the Sugar Crash
Though the evidence against the sugar rush is strong, a "sugar crash" is real—but typically it only affects people with diabetes.
According to the National Institute of Diabetes and Digestive and Kidney Diseases, low blood sugar—or hypoglycemia—is a serious medical condition. When a lot of sugar enters the bloodstream, it can spike the blood sugar level, causing fluctuation, instability, and eventually a crash—which is called reactive hypoglycemia. If a diabetic's blood sugar levels are too low, a number of symptoms—including shakiness, fatigue, weakness, and more—can follow. Severe hypoglycemia can lead to seizures and even coma.
For most of us, though, it's rare. Endocrinologist Dr. Natasa Janicic-Kahric told The Washington Post that "about 5 percent of Americans experience sugar crash."
You're more likely to experience it if you do a tough workout on an empty stomach. "If one exercises vigorously and doesn't have sufficient intake to supplement their use of calories, they can get lightheaded," Wolraich says. "But in most cases, the body is good at regulating a person's needs."
So what you're attributing to sugar—the highs and the lows—is probably all in your head.