Sex Differences in Weight Loss Trajectories After One-Anastomosis Gastric Bypass: A Longitudinal Mixed-Effects Analysis

Obesity is a complex condition where the body holds onto more weight than it needs, often leading to serious health problems like diabetes, heart disease, and liver issues. For people with severe obesity, diet and exercise alone sometimes cannot reverse the damage, leading many to seek surgical help. One such procedure is the one-anastomosis gastric bypass, a surgery that reroutes the digestive system to help the body absorb fewer calories. While this operation is known to be effective, doctors have long wondered if it works differently for men and women. The question is not just about who loses more weight, but whether the body's response to the surgery changes over time based on sex. Understanding this is crucial because it helps doctors set realistic expectations for patients and ensures that the path to recovery is tailored to the individual's biology rather than a one-size-fits-all assumption.

A team of researchers set out to answer this question by looking closely at the weight loss journeys of nearly 190 adults who underwent this specific surgery at a university hospital over a ten-year period. They focused on tracking how much weight people lost during the first two years after the operation, comparing the progress of men against that of women. The study included a mix of patients, with women making up the majority of the group, which reflects the reality that more women than men typically seek out weight loss surgery. The researchers gathered data on the patients' starting weight, their medical history, and their weight at several points after the surgery, using a statistical method that allowed them to see the full picture of how weight changed over time rather than just looking at isolated snapshots.

The results revealed a clear pattern in the numbers. Men started the study with a higher average weight than women, and they also carried a heavier burden of related health conditions like type 2 diabetes and sleep apnea. As time went on, men consistently lost more total weight than women. By the end of the two-year period, the average man had shed about 44.4 kilograms, while the average woman had lost about 32.4 kilograms. When the researchers calculated the percentage of total weight lost, men still came out ahead, losing roughly 33.2 percent of their starting weight compared to 29.7 percent for women. Even when the researchers adjusted their analysis to account for differences in age, medications, and pre-existing health conditions, the finding remained the same: being female was independently associated with losing less weight overall.

However, the story of how this weight was lost tells a different part of the tale. While men ended up lighter, the speed and shape of their weight loss journey were remarkably similar to those of the women. The researchers found that the rate at which men and women lost weight over the two years followed parallel paths. It was not that men lost weight quickly at first and then slowed down while women kept going, or vice versa. Instead, the gap between the two groups remained steady from the very beginning. This suggests that the difference in final results is not because men and women react differently to the surgery itself, but because they started from different places. The surgery appears to work in the same way for both sexes, but the men's higher starting weight and body composition meant they had more weight to lose, resulting in a larger total drop.

This distinction is important for how patients understand their own recovery. The study indicates that the surgery does not favor one sex over the other in terms of how the body responds to the metabolic changes it triggers. Instead, the final outcome is largely a reflection of where the patient began. For a man starting at a higher weight, the surgery will likely result in a larger absolute number of kilograms lost, while a woman starting at a lower weight will see a slightly smaller number, even though both are following the same successful trajectory. The researchers noted that this pattern held true even when looking at patients who had undergone previous weight loss surgeries, suggesting the finding is robust. Ultimately, the study provides a clearer picture for doctors and patients alike: while the scale might show different numbers for men and women, the underlying process of healing and weight reduction is a shared experience, driven more by the starting point than by the gender of the person undergoing the procedure.