They had had medical and psychological tests. They went to counseling and mandatory sessions explaining what was going to happen,   1ffa  and what to expect and how to eat afterward. They learned that the gastric bypass operation both had chosen (it and a procedure called the gastric sleeve are the two main options) leaves patients unable to absorb some vitamins and minerals. They would need to take supplements daily for the rest of their lives. And because the rearranged digestive tracts can dump sugar into the bloodstream too quickly, they would have to be careful about sugar intake or risk “dumping syndrome,” which can cause vomiting, sweating and shakiness. For two weeks before the surgery, Jessica and Keith followed a high-protein liquid diet to shrink their livers. People with obesity often have large, fatty livers that can get in the way during the operation. The day before, Jessica stood at her kitchen counter preparing a mango protein shake with mango flavored Crystal Light and protein powder. It smelled foul. She forced herself to swallow it. “I am excited,” she said. At 6:30 the next morning, a nurse and a surgical resident wheeled Jessica into an operating room on a special wide gurney. They slid her onto an operating table that was set as low as it could go because bariatric patients’ abdomens rise high, as if they were domes. The surgeon, Dr. Oliver Varban, started by inflating Jessica’s abdomen with carbon dioxide to give him more room to work. Then he made seven small holes in her skin and inserted his equipment, including a cylindrical tube containing a tiny light to illuminate her abdominal cavity, lenses, mirrors and a tiny camera to project the scene on a computer monitor above Jessica’s head. The screen showed gleaming golden bubbles of fat that were surprisingly beautiful. Dr. Varban used what looked like a miniature table tennis paddle to push Jessica’s liver aside and give him a clear view of her stomach. Her intestines were obscured by fat, so he used a special surgical grasper to gently push the fat aside. It might seem reasonable for Dr. Varban to simply remove some of the fat from Jessica’s abdomen, but doing that, he said, would result in a bloody, hemorrhaging mess. He explained that there is a mile of blood vessels in every pound of fat. Dr. Varban cut off most of Jessica’s pink and healthy stomach, leaving a pouch the size of an egg. He stapled and sealed the pouch with a device that looked like a saw-toothed pair of shears, leaving a shiny metallic edge of staples. Then he grabbed the top of her small intestine and attached it to the stomach pouch. A couple of hours later, he was done and it was Keith’s turn. The operation was the same, but Keith’s fat looked different, more yellow than golden, and lumpy. And there was much more of it — his organs were buried in it. Men tend to have thicker abdominal fat, Dr. Varban said, and it is slipperier, harder to grasp with the laparoscopic instruments. Jessica and Keith spent two nights in the hospital and then were discharged, with instructions to follow a liquid diet for a couple of weeks and then gradually add solid foods. Jessica was surprised by the pain. When she was home, recuperating, she started to have second thoughts about the surgery. One day, she sat down and cried. “I had like this awful buyer’s remorse,” she said. “I was like, ‘What did I do to my body?’ This is not reversible, there is no going back.”  Improving the Technique For years, surgeons thought weight-loss operations worked because they made the stomach so small that it hardly held any food. And with the bypass operation, they made it even harder for food to be digested. Of course patients lost weight. But some things just did not add up. A simple surgical treatment, the gastric band, which constricts the stomach, was widely used when it was first approved in 2011 but fell out of favor because its effects on weight were variable and almost always smaller than those of the other operations. It still is used (New Jersey’s governor, Chris Christie, had one), but it now accounts for just 5.7 percent of weight-loss surgeries. At a recent meeting of Michigan bariatric surgeons, one doctor asked for a show of hands. Who in the room would refuse to do a gastric band procedure even if a patient asked for it? Just about every hand in the room went up. “The most common operation with the band now is an operation to remove it,” Dr. Varban said. Even leaving aside the gastric band issue, the idea that the bypass and sleeve surgeries were a mechanical fix, by limiting the amount of food a patient could eat, did not seem right. Wiring people’s jaws shut would keep them from eating, noted Randy Seeley, who holds a doctorate in psychology and is a professor of surgery at the University of Michigan. But, he asked rhetorically, “If I wired your jaw shut, would you be more hungry or less hungry?” In contrast, patients who had bypass and sleeve operations reported that they were not particularly hungry afterward, and that their incessant urges to eat vanished. Even more surprising, their taste for food often changed. Dr. Lee Kaplan, an obesity researcher at Massachusetts General Hospital, recalled a patient who asked him: “Are you sure they didn’t operate on my brain? Food does not call out to me anymore.” Another, who used to seek fatty and sugary foods, said, “I crave salads now.” Dr. Justin Dimick, a bariatric surgeon at the University of Michigan, said a woman who lost 200 pounds told him that before the operation, a Reese’s peanut butter cup gave her such a rush that it was, she said, “like an orgasm of pleasure in my brain.” Now, she said: “It’s just peanut butter and chocolate. What’s the big deal?” Experimental data support these reports. Both patients and rodents who had surgery are actually more sensitive to the taste of sweets: Receptors on their tongues detect smaller amounts of sucrose. The data, the patients’ stories, made no sense if all surgery did was make it harder to eat, Dr. Kaplan said. Both the bypass and sleeve operations, he added, “drive the body to want to eat less.” But why? Some, including Dr. Seeley and Dr. Kaplan, looked for answers by studying the surgeries in fat rats and mice. “What you find very quickly is that rats and mice lose weight just the way you see in humans,” Dr. Seeley said. “It’s remarkable.” Surgery changed the weight the animals’ bodies settled into. And, as with patients, their tastes in food changed. For example, Dr. Seeley gave some rodents the exact bariatric surgery operation that humans get while he gave others, which served as controls, sham surgery: Researchers opened the animals’ abdomens and then sewed them shut. The bariatric surgery animals lost most of their excess weight and then stabilized at a lower weight.