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Late one night in 1999 in a research laboratory on the gothic, ivy-cloaked campus of Princeton University, a student saw something that casts a new light on sugar cravings.

Neuroscientist Bart Hoebel had been studying animals under the influence for years. For a month, the psychology professor and his research team fed rats a regular chow and a sugar solution, comparable to the sweetness of fruit canned in heavy syrup. As the researchers expected, the rats preferred the sugar water to the regular chow. But when a drug was used to block the effects of the sugar in the rats’ brains, the results astounded the researchers.

Carlo Colantuoni, then an undergraduate working with the team, routinely entered the animal lab late in the evening to feed the rats or study their behaviour. On each visit, his arrival elicited a response like a jingling Pavlovian bell. “They would hear me open the door and immediately get excited. Some were so excited that they would rip apart the sipper bottles [filled with a 25 percent glucose solution].” After a month, the rats predictably went into a feeding frenzy when the sugar solution was refilled, consuming twice the amount they had at the beginning of the test.

On this particular night, Colantuoni and another student had arrived to observe the rats’ reactions after the drug had been administered to block the effects of sugar in their brains. Colantuoni found the rats in an unusually agitated state, with their heads shaking, their teeth chattering and their forepaws quivering with tremors–in essence showing the telltale signs of withdrawal. Hoebel and his group had seen similar reactions in rats addicted to morphine and cocaine, but it was an unexpected moment in their experiments with sugar.

For close to 25 years, researchers have known that the human attraction to sugar and addiction to drugs occur in the same pathways of the brain. But the Princeton research now suggests that our attraction to sweeteners may have the potential to extend beyond a simple yearning into the realm of chemical dependence. As sugar consumption rises at an alarming rate, wreaking havoc with the nation’s health, the question of culpability looms. Does overeating sugar constitute a mere failure of willpower or can sugar’s sweet lure actually “hook” us?

Bingeing to Survive

Hard-wired from birth to seek out sweet tastes, the human body evolved a survival instinct two million years ago that steered Homo sapiens to sweet foods dense with energy, such as ripe mangoes, clusters of berries, and honey seeping from the comb.

Thousands of generations later, that primitive impulse, in a land of overabundant processed foods and sedentary lifestyles, works against easy weight control and a healthy energy balance. Scientists are now asking if our natural inclination to eat sweets can go too far. Can we lose control of our hunger for sugar, the very taste that aided our ancestors’ survival?

To understand just what happened in the Princeton lab, enter the brain’s everyday pathways for a moment. When we eat a piece of cake, the sweet taste triggers the brain to produce opioids, chemical messengers that identify this taste as desirable. At the same time, the sweetness triggers the brain to produce dopamine, another chemical messenger that works with memory to urge us to pursue this rewarding taste in the future.

Opioids produce love at first bite. Through its effect on memory, dopamine produces love at first sight. So powerful is the response that the simple sight of a desirable food can elevate our dopamine levels and consequently our motivation to seek out the food, one reason that advertising can be so effective.

Researchers theorize that opioids played a key role for humans who foraged, keeping them alive during periods of famine by encouraging them to eat huge amounts of foods that were available–fruits in season, for example–urging them to gorge beyond satiety. Hominid researchers have observed wild apes bingeing on ripe figs and other fruits abundant during brief seasons. The weight gained because of such gorging helped the animals through leaner times.

Robin Edelman is the clinical nutrition manager at Fletcher Allen Health Care in Burlington, Vermont, and former president of the Vermont Dietetic Association. She lives in Hinesburg, Vermont. This article has been abridged; it is reprinted with permission of EatingWell, The Magazine of Food & Health, a quarterly magazine with delicious, healthful recipes, cooking how-to and nutrition news. For a sample issue, visit eatingwell.com or call toll-free 1-800-337-0402

Source: alive #252, October 2003