Bariatric surgery may protect against rapid weight gain linked to dieting

It's no secret that people who diet and exercise to lose weight often report struggling to keep the weight off after reaching their goal — and that, a new study says, may be due to dieting's impact on mitochondria. The same effect wasn't linked with bariatric (weight loss) surgery, however, with researchers finding that these surgeries had the opposite effect.

Bariatric surgery refers to a number of surgical procedures like gastric bypass that reduce the size of the stomach and, depending on the procedure, bypass part of the small intestines. Gastric bypass is associated with some benefits beyond reducing the number of calories consumed, including sending type-2 diabetes into remission in a high percentage of patients.

A new international study coordinated by the University of Helsinki has found another benefit associated with bariatric surgery that isn't reflected in calorie-restrictive dieting, one that may explain why dieting is associated with rapid weight regain. Dieting and bariatric surgery, the study found, have different impacts on fat tissue mitochondria metabolic pathways.

The study involved four European datasets, two on weight loss surgery and two on calorie restriction-based diets. The datasets included information on people who were dieting, including their metabolism and weight loss. Of note, the research involved taking fat tissue samples from the dieters at the start of their weight loss and again after the weight loss.

Though both dieting and bariatric surgery resulted in weight loss, the two were found to have opposite effects on the mitochondria metabolic pathways in fat tissue. Calorie restriction dieting was found to send the fat tissue mitochondria 'out of tune' and reduce gene expression. The researchers suggest the impact of calorie restriction on mitochondria in fat tissue may explain why many people rapidly regain the weight they lost.

Bariatric surgery, on the other hand, was found to improve these genes and boost the metabolic pathway activity levels. Commenting on this, University of Helsinki Obesity Research Unit researcher Birgitta van der Kolk said:

Our observations indicate that impaired mitochondrial activity after losing weight by dieting may be the cause of adipose tissue rapidly building up again after weight loss. At the same time, bariatric surgery patients are better protected against regaining weight, which makes us suspect that a recovery of activity by mitochondria in the adipose tissue may be a factor underlying this phenomenon.