An unclear mechanism
A link between obesity and childhood ADHD could be explained by either a neurobiological or a psychological mechanism, the authors proposed. With the former it is possible that something similar genetically underlies both ADHD and obesity; Castellanos and his colleagues note that dysfunction in the dopamine pathways of the brain have been found among both people who are obese and those with ADHD. As for the psychological mechanism, the impulsive behaviors and diminished inhibitions associated with ADHD “may foster poor planning and difficulty in monitoring eating behaviors, leading to abnormal eating patterns and consequent obesity,” the team wrote.
“One of the aspects of ADHD is this tendency to focus on ‘I want it now’ and not waiting for something, not delaying gratification, so we think that may lead people to eat more than they physiologically might need,” Castellanos says. Eating just an extra 100 calories a day than the total burned can easily lead one to accumulate extra pounds. Appetite regulation is complex but usually balances out in healthy individuals—unless they eat when they’re not actually hungry.
Some researchers are dubious about both the neurobiological and the psychological explanations. Lawrence Diller, a behavioral developmental pediatrician at the University of California, San Francisco (U.C.S.F.), and author of Remembering Ritalin and Running on Ritalin, says he finds the idea of dysregulation in adulthood unlikely for adults who no longer have symptoms of ADHD. “The finding is real—no question about it—but the explanations are poor,” Diller says. “If the ADHD is remitted, then why should the impulsivity and poor judgment still be there?”
Of the 111 men with childhood ADHD in this study, 87 no longer had ADHD symptoms (remitted) and 24 still had ADHD (persistent). Those with remitted ADHD had relatively higher obesity rates than the persistent-ADHD men, although the small number of men with persistent ADHD makes it difficult to draw any substantial conclusions about this difference.
Diller suggested that the long-term impact of ADHD medication may play a part. “We know that stimulants very much affect the satiety thermostat in people who take them,” he says. “There is the question of whether or not the long-term suppression of appetite somehow affects the brain so that when you’re no longer taking the drugs, it takes more [food] to make you feel full.” Diller pointed to research showing that long-term use of ADHD stimulants can lead to 2.5 to five centimeters of lower-than-predicted height in adults, although the adults in this new study showed no significant differences in height. “That doesn’t mean you shouldn’t take the medicine, but in weighing the pros and cons, it’s one more thing for parents to think about in treatment,” Diller says. “The idea that impulsivity and poor judgment may play a role is possible, but I think my idea of adjusting the satiety thermostat long-term is just as plausible as theirs.”
A different possible mechanism, proposed by Juan Salinas, a lecturer specializing in the neuropharmacology of learning and memory at the University of Texas at Austin, resembles the neurobiological hypothesis, given that ADHD involves a dysfunctional release of dopamine in the brain. “From more basic research into the neurobiology of reward, it’s suggestive that maybe somehow these people who do not have ADHD anymore may have an alteration in the dopamine pathways, and maybe some of the eating may be a way to self-medicate to increase dopamine release,” Salinas says. “It’s not so much impulse control, but it’s a self-medicating idea.” The implications of the study, then, Salinas says, are that parents need to train their children with ADHD early to eat healthily, exercise and practice a healthy lifestyle.