Sugar and the Science of Addiction
It’s one thing to have a sweet tooth, but is sugar really an addictive substance?
When we say that a dessert is addictive, we usually mean it’s very delicious. To those who study the physiological and neurochemical aspects of substance abuse, however, “addictive” is a term with serious health implications.
Yet even those on the front lines of addiction research can’t quite agree on what qualifies as addiction. Witness the debate in scientific journals over whether sugar can be classified as an addictive substance or whether obesity should be added to the Diagnostic and Statistical Manual of Mental Disorders as a form of substance (food) abuse or addiction.
Advocates of treating food as a potentially addictive substance point out that palatable food and drugs like cocaine stimulate some of the same regions of the brain, and both trigger a flood of dopamine and feelings of well-being. In both cases, the euphoria is short-lived and the brain craves more. When these pleasure pathways are powerfully and repeatedly stimulated, the brain adapts and it takes more of the substance to achieve the same high. Abusers will continue to pursue that pleasure despite painful consequences.
Research done by Bart Hoebel, Ph.D., and Nicole Avena, Ph.D., at Princeton University lends support to the concept of food addiction. Like humans, rats prefer sweetened water to plain water. Once rats have habituated themselves to drinking sugar water, they exhibit symptoms of withdrawal once it’s taken away — nearly identical to those observed with other chemical dependencies — and they will binge when sugar water access is restored.
Experiments designed by neuropharmacologist Paul J. Kenny, Ph.D., at the Scripps Research Institute demonstrate that rats will continue to pursue palatable foods despite painful consequences — another hallmark of addiction. Rats will scamper away from regular rat chow when they hear a sound signaling an impending electrical shock, but rats with access to chocolate, cheesecake and sausage will keep eating those foods, even when they know a painful shock is coming.
Opponents argue that there are important differences between humans and rats, and between the world we live (and eat) in and the conditions required to induce sugar addiction in lab animals. Even those who argue for the food addiction model acknowledge that — for humans at least — it’s not sugar that pushes our buttons; it’s the combination of sugar, fat and salt. But as unpleasant as it may be to give up favorite foods, nothing like true drug withdrawal symptoms have ever been observed in dieting humans.
Treating Obesity through the Lens of Addiction
For nutrition professionals, the salient question is whether the concept of food addiction suggests more effective treatments for obesity. If food addiction is a real illness, then drugs developed to combat other addictions might offer some hope.
Drugs that block endorphin activity in the brain have been shown to reduce use of heroin, cocaine and alcohol in addicted humans. They also inhibit the consumption of appetizing food in both humans and rats. Similarly, some appetite-suppressing drugs have the bonus effect of reducing the desire to smoke.
One problem is that response to dopamine-blocking drugs depends a lot on a person’s individual baseline. In someone with elevated production of (or sensitivity to) dopamine, a drug that suppresses dopamine makes the reward less rewarding, making compelling foods a bit easier to resist. But in someone with low production of (or sensitivity to) dopamine, such a drug can suppress feelings of well-being so much that depression or even suicidal thoughts may ensue.
Further complicating matters is that obesity is sometimes characterized both by hyper- and hypo-responsiveness to dopamine. Either state, an exaggerated pleasure response to foods or a reduced ability to derive pleasure from foods, could plausibly lead to overeating. Kenny believes that the production of and responsivity to dopamine and other endorphins may change over the course of the disease, similar to the way in which the body’s production of and responsiveness to insulin changes as metabolic syndrome progresses — first surging and ultimately declining.
Although Kenny is hopeful that pharmaceutical interventions may one day be a potent weapon in the fight against obesity, he’s also quick to point out that — as with any addiction — behavioral modification is a crucial element of successful treatment.
Just as those struggling to maintain sobriety are advised to avoid bars and ex-smokers need an activity to replace the after-dinner cigarette, dieters still will need to modify behaviors and habits. But if an anti-addiction drug could safely improve the dismal success rate for dieters, it would be a welcome addition to the arsenal.
Monica Reinagel, MS, LD/N, is based in Baltimore and is the author of The Inflammation-Free Diet Plan (McGraw-Hill 2007).