Growing rates of obesity among Americans are clear evidence that even the best intentions and strongest motivations are often not enough to help seriously overweight people lose a significant amount of weight and, more important, keep it off.

But for those who can overcome fears of surgery and perhaps do battle with recalcitrant insurers, there remains another very successful option that experts say is currently vastly underused. That option is bariatric surgery, an approach that is now simpler, safer and more effective than in its early days in the 1990s.

“Only one-half of 1 percent of people eligible for bariatric surgery currently undergo it,” Dr. Anne P. Ehlers, a bariatric surgeon at the University of Michigan, told me.

Bariatric surgery is generally considered a treatment option for people with a body mass index (B.M.I.) of 40 or more who failed to lose weight with diet and exercise alone. It is also recommended for those with lesser degrees of obesity — a B.M.I. of 30 to 35 — who have obesity-related medical conditions.

The underuse of weight-loss surgery has been largely attributed to “the reluctance of the medical community and patients to accept surgery as a safe, effective and durable treatment of obesity,” other experts at the University of Michigan wrote in JAMA in 2018.

They added that patients “may be reluctant to pursue surgical treatment because they may be judged by others for taking the easy way out and not having the willpower to diet and exercise.”

Although willpower is clearly an inadequate tool for millions now struggling with obesity, “many may feel like failures if they opt for surgery,” Dr. Ehlers said in an interview.

Yet this stigma, real or imagined, may be keeping many people from a treatment that not only can result in long-term weight loss but can also significantly improve physical and emotional health and even longevity.

Disorders that can be reduced or reversed by bariatric surgery include Type 2 diabetes, heart disease, high blood pressure, elevated cholesterol, gastroesophageal reflux disease (GERD), obstructive sleep apnea, breast cancer, colorectal cancer, urinary incontinence, infertility and fractures. Death rates may be reduced by nearly 50 percent, especially among people 55 and older.

Although guidelines set in 1991 limit recommendations for bariatric surgery to those most severely affected by obesity, current evidence indicates that young people who are not yet morbidly obese may be especially likely to benefit from weight-loss surgery. Most adolescents who are obese remain obese as adults and have worse medical outcomes than people who became obese as adults. The surgical route is now sometimes offered to adolescents and young adults with obesity-related health problems like Type 2 diabetes that have failed to yield to diet and exercise.

In a study reported by the University of Pittsburgh Graduate School of Public Health that followed 2,221 patients, within three years of bariatric surgery, most experienced less pain and improved ability to walk. But as with any weight-loss program, such benefits as well as lasting weight management depend on whether patients stick to a healthful diet and exercise regimen after the surgery.

The original bariatric technique, called Roux-en-Y gastric bypass, reduces the stomach to the size of an egg and bypasses a major portion of the small intestine to limit caloric absorption. A now-retired friend who underwent this operation 15 years ago lost 160 pounds and has kept all but 10 pounds off despite traveling widely on vacations, a time when people often gain weight.

However, in recent years, gastric bypass has yielded to a newer, less involved operation called sleeve gastrectomy that has fewer complications yet excellent long-lasting results.

According to the American Society for Metabolic and Bariatric Surgery, only 1.5 percent of patients undergoing sleeve gastrectomy require a reoperation because of complications, as against 7.7 percent undergoing gastric bypass and 15.3 percent who have a less effective procedure called lap band surgery, in which a band placed around the stomach divides it into two pouches.

In sleeve gastrectomy, about 85 percent of the stomach is removed, resulting in a banana-shaped pouch that limits the amount of food that can be consumed. In addition to restricting how much a person can eat, the surgery reduces hunger and the desire to overeat by eliminating the portion of the stomach that produces ghrelin, the hormone that stimulates appetite.

Both sleeve gastrectomy and gastric bypass, as well as other albeit less effective bariatric approaches, can be done laparoscopically, with patients spending only a day or two in the hospital.

In a major report involving 33,560 patients treated at 10 national medical centers and followed for five or more years, sleeve gastrectomy resulted in significantly fewer post-operative interventions than Roux-en-Y gastric bypass. The study was published in January in JAMA Surgery.

At most centers today, Dr. Ehlers said, “sleeve gastrectomy accounts for at least 80 percent of the procedures done.”

Even with these seemingly drastic treatments, weight loss occurs gradually, with patients beginning to notice gradual weight loss by the end of a month. Most people can lose up to half their excess weight within a year of surgery and up to 60 percent by 18 months.

However, Dr. Ehlers cautioned, “This operation is not a magic pill. It’s a tool to be used in combination with a proper diet and physical activity. Prior to surgery, patients should be taught how to eat, and after surgery they need to learn how much they can eat before feeling sick. Most people can tolerate any food in small amounts, but they may never be able to eat a full Thanksgiving dinner again.”

Bariatric surgeons recommend that patients skip all sugary and carbonated drinks and not drink water when they eat solid food. Although it is possible to overeat and stretch one’s stomach even back to its original size, this can be avoided if patients learn to stop eating when they feel full.

Patients may have to supplement their diets with certain nutrients, like calcium, iron, vitamin B12 and vitamin D, to compensate for the reduced ability to absorb them after surgery.

As with any operation, bariatric surgery has potential complications, which tend to be lower when performed by experienced surgeons at medical centers that do many of these operations. Rates of both complications and deaths related to the surgery have fallen drastically since 1998 from a peak of 11.7 percent and 1 percent, respectively, to 1.4 percent and .04 percent by 2016.

About a quarter of a million bariatric surgeries were performed in 2018, yet approximately 18 million adults aged 20 or older had B.M.I.s higher than 40, according to the latest available data from the American Society for Bariatric Surgery. The average cost of weight loss surgery ranges from $17,000 to $30,000 and is often covered by insurance. However, untreated obesity costs the nation $1.72 trillion, or 9.3 percent of the gross domestic product, in health care expenses alone, the society reported.

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