What is bariatric surgery? How it helps people lose weight

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By altering the stomach, and sometimes the small intestine, bariatric surgery can help people who struggle with obesity lose significant amounts of weight, and keep it off. Doctors recommend it to patients who have tried unsuccessfully to lose weight through other means, including diet, exercise, and medication.

"A lot of people think it is the easy way out. It is not," says Fatima Cody Stanford, MD, an obesity medicine physician at Massachusetts General Hospital's weight center. "It is a tool that we know, based on evidence, can help people that have moderate to severe obesity achieve and maintain a healthy weight."

How bariatric aids weight loss

It's common to think that a person's weight is determined by the number of calories that one eats versus the number they burn, but the reality is much more complicated, Stanford says.

The body's metabolism is very complex and will change if you lose weight - either from diet or bariatric surgery - which can make long-term weight loss challenging. One theory for why keeping the weight off is so difficult suggests that our bodies and brains fight to keep our weight close to a set point by altering the rate at which our metabolism burns calories.

For example, many contestants on the reality TV show The Biggest Loser struggled to keep all the weight off that they had lost on the show. Later, a study published in Obesity in 2016 found that their metabolism had adjusted to burn fewer calories than they did before losing weight.

Bariatric surgery works differently because it disrupts the normal signals sent between the gut and the brain. When part of the stomach is removed or made inaccessible, it alters this communication in a number of ways, including by reducing appetite-inducing signals related to the hormone ghrelin, which is produced in the stomach. After surgery, the reduction in ghrelin levels is thought to be related to less hunger, which can help people better reach their weight loss goals.

The different types of bariatric surgery

The American Society of Metabolic and Bariatric Surgery (ASMBS) estimates that 252,000 bariatric surgeries were performed in 2018 in the US. These procedures include:

Sleeve gastrectomies, in which about 80% of the stomach is removed to leave a banana-like pouch, was most common, accounting for about 61.4% of bariatric surgeries in 2018.

Roux-en-Y gastric bypasses, in which food is rerouted to skip part of the stomach and the beginning of the small intestine, accounted for 17% of procedures. It is the "gold standard" procedure, according to ASMBS.

Revisions, or follow-up surgeries to fix problems, accounted for 15.4%.

Gastric bands, which create a small pouch at the top of the stomach using an adjustable band accounted for 1.1%. The band has lost favor because it requires adjustment and simply isn't as effective as the other procedures, Stanford says.

How much weight you can lose from bariatric surgery

A number of studies have shown that bariatric surgery can be effective not only for weight loss but also for improving conditions associated with obesity, such as type 2 diabetes, hypertension, and high cholesterol.

In a study in the New England Journal of Medicine in 2017, for example, researchers followed 1156 people with severe obesity, including 418 who had bypass surgery, for 12 years. At the end of the study, those who had the surgery still weighed on average about 77 pounds less. Meanwhile, their counterparts who did not have surgery had much less or no weight loss.

The benefits extended to diabetes. Of those who had type 2 diabetes at the time of surgery, about 75% had normal blood sugar readings two years later. After 12 years, it had decreased to about half.

Stanford, however, cautions patients to temper their expectations, because after surgery, many people still have obesity, just a lesser degree of it.

"A lot of people come in assuming they will get to exactly whatever number they want to get to," Stanford says. "The body doesn't quite work that way, it gets to where it gets to."

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