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Positive metabolic effects of gastric bypass disappear quickly

Photograph of gastric bypass surgery in hospital.
In a new study published in the journal Obesity, the researchers studied the metabolism of overweight individuals before and after they had a gastric bypass operation. Photograph: iStock/herjua

A new study from Lund University in Sweden raises questions about the efficacy of bariatric operations involving gastric bypass. The results show that the biggest metabolic changes happened directly after surgery. Just a year after the operation, the concentration of metabolites and fats had returned to almost the same levels as before the procedure. 

Previous research has shown that the majority of those who undergo surgery regain weight within five years of a gastric bypass operation. It has still not been established what happens to the metabolism of those who have had a bariatric procedure. In a new study published in the journal Obesity, the researchers studied the metabolism of overweight individuals before and after they had a gastric bypass operation. The study shows that the biggest changes happened straight after the procedure. One year later, the concentration of metabolites and fats among all the participants were nearing the same levels as before the operation. 

“Just following up on the weight of people can be a blunt instrument for studying the effects of the procedure. Our study provides a greater understanding of what happens to the metabolism in connection with a gastric bypass operation,” says Peter Spégel, associate professor of molecular metabolism at Lund University Diabetes Centre (LUDC), who led the study.

Rapid changes

The study was based on data from 148 people with and without type 2 diabetes who underwent a gastric bypass operation in Sweden. Blood samples were collected from participants just before the procedure and on at least two occasions after the operation. Their body mass index (BMI) was measured before the operation and on three occasions afterwards. 

The researchers conducted detailed analyses of fats and metabolites in the blood. Just one year after the operation, some of the participants were back at exactly the same levels as before the surgery, whereas the reversion was not as marked for others.

“We could see the changes while the participants still had a low BMI after the operation. By studying metabolism, we can obtain a clear indication that unhealthy changes are on the way. We hope that the knowledge can be used in follow-up so that preventive measures can be put in place,” says Nils Wierup, professor of neuroendocrine cell biology at Lund University and one of the main authors of the article. 

Increased risk of type 2 diabetes

The levels of certain polyunsaturated fats increased straight after the operation to then fall and approach the same levels as previously. Polyunsaturated fats are essential and can reduce the risk of cardiovascular disease. The study also showed a reduction in the concentration of a certain type of amino acids after the operation and then a subsequent rise. The levels of these amino acids are usually high in individuals with insulin resistance and carry an increased risk of developing type 2 diabetes. 

“One conclusion we draw is that the risk of developing type 2 diabetes is considerably reduced after the operation among individuals who do not have the disease, but one year later we see an increased risk again. Among individuals who already had type 2 diabetes at the time of the surgery, we see a remission of the disease, but the risk of the disease returning then increases over time,” says Peter Spégel.

The benefit of bariatric operations

Individuals who undergo surgery for obesity need to lose weight before the operation by means of a diet. A previous study by the same research team examined the effects of a low-calorie diet and a gastric bypass operation separately. The study showed that the diet had the biggest effect on metabolism, whereas the surgery led to quite small changes. The researchers’ latest study now shows that for many people, the positive effects on metabolism subside as soon as one year later.

“We need more and larger studies in order to draw reliable conclusions. One advantage of bariatric operations is that a majority of people with type 2 diabetes see a remission of their disease afterwards. And even though a large percentage of individuals who undergo this procedure gain weight afterwards, it’s usually not a return to the same weight as before. In the future, we want to take a closer look as what happens to metabolism on an individual level, as this can vary,” concludes Nils Wierup.

Bariatric operations 

Bariatric surgery can increase the chances of a longer and healthier life for overweight individuals, but there is also a risk of complications. Gastric sleeve, gastric bypass and duodenal switch are three examples of bariatric surgery procedures. In a gastric bypass, a large part of the stomach and some of the small intestine are removed, resulting in the individual eating less. A bariatric procedure may result in a lower risk of developing cardiovascular disease and type 2 diabetes. People who already have type 2 diabetes may see better blood sugar values after the operation and some may be able to stop taking medication. This is because insulin sensitivity increases when obesity decreases.

Read more about bariatric surgery procedures at

Portrait of Peter Spégel. Photograph.

Peter Spégel, associate professor of molecular metabolism and senior lecturer at Lund University
peter [dot] spegel [at] med [dot] lu [dot] se

Link to Peter Spégel’s profile in Lund University’s Research Portal


Portrait of Nils Wierup. Photograph.

Nils Wierup, professor of neuroendocrine cell biology at Lund University
nils [dot] wierup [at] med [dot] lu [dot] se

Link to Nils Wierup's profile in Lund University's research portal

Facts about the study

Subject: Bariatric surgery
Area of research: Clinical research
Type of publication: Peer-reviewed publication
Study design: Quantitative study, researcher-initiated study
Experimental investigation: In vivo, non-randomised intervention in a group
Observational study: Longitudinal
Number of patients in the study: 148
Patient groups: Patients with obesity/type 2 diabetes

Link to study in the journal Obesity

Funding bodies

The study has received support from the Albert Påhlsson Foundation, Crafoord Foundation, Novo Nordisk Fund, Swedish Diabetes Foundation, Hjelt Foundations, Per-Eric and Ulla Schyberg Foundation, Diabetes Wellness Sverige, Horizon 2020 (T2DSystems), Swedish Research Council and Swedish Foundation for Strategic Research (SSF).