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Science of the Sweet Tooth

The brain may hold the answer to lessening people’s preference for sweet tastes

Robert Considine, PhD
Photography by Timothy B. Yates/IU Visual Media

Robert Considine, PhD

Occupation
Professor of Medicine at Indiana University School of Medicine

Focus
Endocrinology

American Diabetes Association Research Funding
Innovative Translational Science

The idea that some people have a sweet tooth is well accepted. Studies in twins suggest preference for certain flavors is partially genetic and partially learned. Indiana University’s Robert Considine, PhD, says people who crave sweet flavors may also have different brain chemistry in the reward center of the brain—and, using high-tech scanners, he’s trying to prove it.

The research is driven by more than just curiosity. Understanding why some people get a bigger kick out of sweet tastes than others could help researchers find a way to “turn down” a person’s desire for sweetness. “If it doesn’t taste as good, you may not want it,” Considine says. “At a given time, you will want to eat less.”

With the help of a grant from the American Diabetes Association (ADA), Considine hopes to figure out how brain chemistry regulates our appetite for sweets. He’ll do that by putting people in a brain scanner and watching what happens when he sprays a sweet liquid in their mouths. From there, he’ll look at whether weight-loss surgery might play a role in dampening that desire.

The study draws on decades of research into how addiction works. In trying to understand why some people abuse alcohol or drugs, scientists have developed a much better understanding of the chemical reward system that drives our behavior.

Simply put: When we engage in behaviors that the brain wants to encourage because they help us survive and multiply—eating or having sex, for example—we’re rewarded with a burst of dopamine. The chemical stimulates the pleasure centers of the brain.

Food, Considine points out, is not generally thought of as an addictive substance. “Food is necessary for survival,” he says, “and most addictive substances are not.” But the same dopamine reward that drives some people to alcoholism also prompts us to derive pleasure from food.

The pleasure we get from sweet foods has a deep-seated evolutionary rationale: Sweet foods tend to be high in calories. By releasing dopamine in response to sweet tastes, the brain is teaching us to seek out high-calorie foods. As a result, animals that sought out sweet flavors would be more likely to survive and multiply. But an adaptation that made sense for surviving in some prehistoric jungle is a disadvantage in today’s world, where sugary, calorie-rich foods are easily available all around us.

One reason some people crave sweets and others don’t might be an imbalance in this dopamine reward system. “Either you don’t get enough dopamine for consuming food and so you eat more, or you get a massive response, and you want more,” Considine says.

To better understand this, he is putting three groups of women—120 in all—in a brain scanner. He then looks at what parts of the brain light up when the women are given a spritz of plain or sugary water, about as sweet as a typical cola.

To provide a basis for comparison, he’s testing the responses of 40 lean women. Meanwhile, he’ll test 80 obese women before they undergo one of two types of bariatric surgery: Roux-en-Y gastric bypass, in which a section of the stomach and upper intestine is removed, or sleeve gastrectomy, an alternative procedure that removes a portion of the stomach while leaving the intestine untouched.

The study has two main goals. The first is to see if there’s a difference between the way lean women and presurgery obese women process sweet tastes. “There’s lots of anecdotal stuff out there that obese people like sweet more than lean people,” Considine says. “But there’s no data yet.” His preliminary results suggest that the brains of the obese women in his study had a greater response to sweetness than lean women, perhaps leading them to eat more. Perhaps they don’t process this greater signal correctly, Considine says, or maybe the signal makes them want even more food.

The study’s second element will compare the women who had Roux-en-Y gastric bypass to those who had sleeve gastrectomy.

Ever since the advent of Roux-en-Y gastric bypass, doctors have been reporting a surprising phenomenon: People who had the surgery don’t crave sweets the same way they used to. “Anecdotally, subjects’ taste preferences change,” Considine says.

There have been a few attempts to see if the reports can be confirmed in the lab. In a 2010 study, for instance, researchers performed gastric bypass surgery on rats. After the operation, the rats had less interest in high-sugar drinks. When a different group of researchers followed up with human bypass patients, they found that patients’ tastes changed post-bypass. “Three months after bariatric surgery, patients liked things less sweet than before surgery,” says Considine.

If the change in the brain response and sweetness preference is only found in women who have undergone Roux-en-Y bypass (those who, unlike women who had a sleeve gastrectomy, lost a part of their intestine), it would be a clue that a gut hormone is contributing to the preference for sweetness—and that the gastric bypass literally cuts it out.

Isolating that hormone could help researchers find a way to dial back a patient’s preference for sweetness without an operation. “The goal is to help people lose weight,” Considine says. “We’d like to figure a way to do this without surgery.”

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