Obese lab rats that have undergone gastric bypass surgery to induce weight loss show a reduced desire for sugar water compared to obese rats that have not had the operation. Researchers at Penn State College of Medicine who observed that outcome also reported that the rats’ preferences for salty, sour, or bitter tastes did not change. Lean rats who were given gastric bypass surgery as a control showed no changes in any of their taste preferences.
The results from the school’s Department of Neural and Behavioral Science and Surgery indicate that obesity, or becoming obese, may alter the brain’s perception of sweetness and the craving for it. If gastric bypass surgery in obese rats somehow changes their brain chemistry and lessens their “sweet tooth,” it confirms the same effect that has been noted in post-operative type 2 human patients.
Previously, scientists thought that changes in humans’ preferences for sweets after bypass surgery were the result of increased dietary awareness, as well as motivation supplied by the surgery’s often dramatic results. The Penn State College lab rat study opens the possibility that unconscious factors are also working to change perceptions of sweetness.
Gastric bypass involves bypassing a portion of the upper small intestine, either surgically or by implanting a sleeve that blocks off part of the upper small intestine. The process produces a dramatic drop in appetite and weight. Usually applied to the morbidly obese (people with a body mass index of 35 or more), the procedure has produced a high percentage of remissions among recipients who have type 2 diabetes. In many cases, the disease’s symptoms disappear within days of successful completion of the surgery.
To prep rats for their study, researchers selected animals lacking a gut hormone, CCK-1, that works to create a feeling of satiation after a meal. Unable to sense when they’d had enough food, the rats ate larger meals than they needed to, eventually becoming obese and developing type 2 diabetes.
Researchers noted that as the rats became fatter, their preference for sweet tastes increased-a tendency also noted in humans who put on large amounts of weight. They observed that taste-receptive neurons in the obese rats’ brains responded more energetically to sucrose water than the same neurons in lean rats.
Like their human counterparts, the gastric bypass rats enjoyed dramatic postoperative weight loss-from 26 to 30 percent of their pre-op body weight-and improved glucose tolerance. The surgery also enabled them to maintain long-term weight loss.
While the Penn State College study confirms that obesity creates changes in the brain that trigger an increased preference for sweets, the exact mechanism remains unknown. Beyond that, its findings bolster the case that gastric bypass should become an approved treatment for type 2 diabetes, even in cases where patients are not morbidly obese.