Mayo Clinic researchers are studying patients who undergo bariatric weight-loss surgery in an effort to understand why some suffer complications or gain their weight back, while others have no difficulties.

The reasons for these struggles are poorly understood, but as many as 36% of patients regain weight within five years of their procedure, and as many as 70% suffer complications such as food intolerance and vomiting, even when they follow strict diets.

“There’s an aftermath to the surgery that doesn’t get as much attention,” said Dr. Iris Wang, who is leading the study.

Two characteristics of the stomach will be monitored: the rate at which it empties itself of food, and the rate at which it expands to accommodate food intake. Variations in patients after surgery might identify those who are likely to struggle, which would allow doctors to prescribe medications or take other steps to support their health and weight loss, Wang said.

So far, researchers have examined an index group of patients who did not undergo surgery. Now they are recruiting patients to follow after bariatric procedures, which are designed to reduce weight by restricting the stomach and making people feel full faster.

Regaining weight can be hard on patients, Wang said. “It’s frustrating for them to not understand why, especially if they’ve been following all the rules. … It’s frustrating to us as providers, who want to give them answers, but we don’t have the right tools right now to do it.”