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Researchers Discover Why Gastric Bypass Surgery Really Works

Tim Boyer's picture
Gastric Bypass Surgery

Gastric bypass is a popular weight loss surgical procedure, but did you know that its ability to keep weight off months afterwards is not entirely because the gastric bypass patient is eating less?


In a recent study published in the online journal PloS, researchers from the Sahlgrenska Academy at the University of Gothenburg discovered that reduced food consumption from gastric bypass surgery is not the only reason why weight loss is maintained much later following surgery.

Also See: Lesser Used Surgical Method Actually Results in More Weight Loss

The gastric bypass method (also referred to as “Roux-en-Y” gastric bypass surgery) consists of two parts: The first part is where the stomach is altered to create a small stomach pouch that can hold only about one cup of food. The second part is where the connection from the small stomach pouch bypasses the first part of the duodenum and goes further down the digestive tract directly to the jejunum. The result is that the patient can only eat small portions at a time with less calories being absorbed by the small intestine.

Gastric bypass surgery is especially popular with severely obese patients because it on average causes patients to lose up to 60% of their pre-surgery weight. While decreased calorie consumption does play a role in this weight loss, according to the researchers it does not explain why the weight loss is sustained for many patients. But now according to their latest data, they believe that it is due to more calories being burned during meals as a result of the surgery.

“Parts of the small intestine become more active and require additional nutrition after a gastric bypass,” says Sahlgrenska researcher Malin Werling. “As a result, the blood absorbs fewer nutrients to store as fat. You might say that people burn calories by eating.”

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Data for the study was generated by carefully measuring and comparing the metabolic states before the surgery and afterward in intervals, of six obese study participants who were monitored during 24-hour sessions in a special room called a “metabolic chamber.” The metabolic chamber is an indirect way of determining how much energy is expended by each participant during multiple 24-hour long sessions in a specialized hotel-like room.

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What the researchers found was that following gastric bypass surgery, each weight loss surgery patient exhibited significantly increased energy expenditure than they did before having the surgery. Furthermore, the energy expenditure was observed to occur primarily during meal times.

During meals, the gastrointestinal tract needs energy to break down food and absorb nutrients. The researchers hypothesize that because the anatomy of the digestive system is altered by the surgery that it also changes gastrointestinal and brain-hormone signaling after food is eaten. This in turn may cause an increase in energy expenditure―presumably in the small bowel with increased glucose metabolism.

The researchers report that additional studies will be performed to determine the specific mechanisms that generate the greater meal-associated energy requirements after such operations, and hope that eventually the process can one day be augmented by means of drugs.

For more information about weight loss surgery, here are some select articles:

Obesity Weight Loss: Duodenal Switch Beats Gastric Bypass

Two Weight Loss Surgery Procedures Measure Up after 3 Years

Lesser Used Surgical Method Actually Results in More Weight Loss

Popular Weight Loss Sleeve Surgery Update You Need to Know

Reference: “Roux-en-Y Gastric Bypass Surgery Increases Respiratory Quotient and Energy Expenditure during Food Intake” PLoS ONE 10(6), 2015; Werling M, Fändriks L, Olbers T, Bueter M, Sjöström L, Lönroth H, et al.