Bariatric Surgery Reveals Complexities of Our Hunger Systems

A view inside a filing cabinet. Three large labels read "Obesity," "Weight Loss," and "Bariatric Surgery." Within Bariatric Surgery are multiple subfolders. One is obscured, the two vissible ones say "Gastric Bypass" and "Sleeve Gastrectomy."
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This month, in celebration of the 100th anniversary of the American Physiological Society journal Physiological Reviews, we are highlighting recent research published in the journal. Interested in reading more in celebration of Physiological Reviews’ birthday? Read our Spotlight On: Migraine.

Although individuals who are overweight or obese are widely encouraged to try lifestyle changes to lose weight, research repeatedly demonstrates that dieting rarely leads to permanent weight loss. Most people who rely on dieting alone regain all the weight they lost within three to five years. In contrast, with the help of modern methods of bariatric surgery, people can maintain weight loss for up to 20 years or more.

Bariatric surgery is an umbrella term for a number of procedures that alter the patient’s digestive system to facilitate weight loss and reduce the risk of weight-related health concerns such as type 2 diabetes. When initially developed, scientists hypothesized that limiting the size of the stomach would force a patient to eat less, which would cause them to lose weight.

After decades of research, however, scientists realized these forced smaller meal sizes were not enough to explain all of the metabolic changes sparked by the surgeries. In fact, some experts believe these surgeries should be called “metabolic surgeries” to better explain their effects.

Commonly, people who have undergone bariatric surgeries not only eat significantly smaller portions of food but they also choose lower-calorie foods. Despite this, they report high levels of satiety after eating. Satiety is when someone does not feel the urge to eat. It’s at the opposite end from hunger. This means people don’t merely stop eating because they consciously choose to, but because their body signals for them to stop.

In contrast, when people lose weight by dieting, they are hungrier and don’t feel as full, as the body tries to revert to its previous state But, in those who have had bariatric surgery, researchers have found more is going on in their brains and bodies.

An article published in Physiological Reviews examined the research on modern bariatric surgeries and found that changes in brain signaling, hormones, blood composition and the microbiome work together “to exert a profound influence on eating behavior.” This means the benefits of these surgeries are due to far more than because the person ate less food.

Bariatric surgery is not without its drawbacks, however. The most common complications are abdominal pain and episodes of low blood sugar. Nutritional deficiencies occur in 30–70% of patients, depending on the particular nutrient and the specific type of surgery. Though less common, surgical complications such as bleeding, small holes around the surgery site or leakage are also a possibility.

If scientists can better understand what makes bariatric surgeries successful, they might be able to duplicate that success without the risks that come with surgery. The more we learn about these processes in the body, the better we can help everyone live their healthiest lives.

Claire Edwards

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