Gastric bypass can have long-term benefits for adipose tissue

Last Updated: 2016-12-07

By Reuters Staff

NEW YORK (Reuters Health) - In obese women, protective changes in adipose tissue persist long after Roux-en-Y gastric bypass (RYGB), according to researchers at the Karolinska Institute, Stockholm.

The surgery improves long-term insulin sensitivity and white adipose tissue (WAT) factors beyond the baseline state, even if the women regain weight, the researchers found.

Although the molecular mechanisms behind the transition into what the authors call "super-normal" WAT are unclear, they "could be related to changes in the expression of specific WAT genes," the authors suggest in a report online November 16 in Diabetes Care.

The conundrum driving this study is that even if an individual who undergoes RYGB surgery regains considerable weight, some protection against type 2 diabetes remains. To investigate this, the researchers focused on four aspects of WAT that could be involved in a protective effect after bariatric surgery: WAT morphology, secretion of adipokines, WAT inflammation, and lipolysis.

Samples of abdominal subcutaneous fat were taken from 49 obese women before RYGB and at two and five years afterward.

After two years, there was "a dramatic decrease" in mean body mass index (BMI) to a non-obese state, accompanied by significant reductions in waist-to-hip ratio, hip and waist circumferences, and all measures of regional fat depots.

Serum levels of adiponectin, a polypeptide secreted by adipocytes that influences energy expenditure and glucose metabolism/insulin sensitivity, were improved. Adiponectin is inversely correlated with obesity, insulin resistance, and type 2 diabetes, and low levels are associated with an increased risk of type 2 diabetes.

Having fewer but larger fat cells is independently linked to insulin resistance and increased type 2 diabetes risk, while relative hyperplasia (having many small fat cells) is linked to improved insulin sensitivity, according to the authors. After weight loss from gastric bypass, fat cell size decreased markedly while the number of adipocytes remained unchanged.

Lipolysis (determined by glycerol levels), which is increased in WAT of obese individuals, was also markedly reduced two years after surgery.

Previous research has suggested an inverse relationship between WAT lipolysis and insulin sensitivity; altered lipolysis after bariatric surgery thus might influence type 2 diabetes through effects on insulin sensitivity, the authors suggest.

By five years, average BMI had increased by about 2.5 kg/m2, back to an obese state, accompanied by increased fat accumulation in all measured regions and minor changes in the lipid profile, but no change in serum adiponectin.

Lipolysis had increased to levels observed before surgery. Subcutaneous fat cell size did not change, but there was a 30% increase in number of fat cells.

At the five-year follow-up, 30 participants were compared with 30 control women matched for BMI and age; the surgery patients had "markedly better" insulin sensitivity and lipid profiles than the control subjects, as well as higher adiponectin levels.

These findings, the authors concluded, support the idea that long-term improvements in metabolism after gastric bypass involve WAT-specific factors.

"These marked metabolic improvements should encourage people struggling with weight loss," they wrote.

The researchers did not reply to a request for comment.

Funding for the study came from the Swedish Research Council, Novo Nordisk Foundation, CIMED, the Swedish Diabetes Foundation, Stockholm County Council, Erling-Persson Family Foundation, and the Diabetes Research Program at Karolinska Institute.

SOURCE: http://bit.ly/2h7ag7J

Diabetes Care 2016.