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Does a strict diet explain the metabolic effect of gastric bypass surgery?

Thu, 08/13/2020 - 15:47
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Researchers at the Lund University Diabetes Centre (LUDC) and the Centre for Analysis and Synthesis (CAS) have for the first time studied the effects of the strict low-calorie diet and the operation separately, and the results show that the diet alone accounted for the greatest positive effect. The findings are described in the paper, ‘Metabolic Effects of Gastric Bypass Surgery - is it all about Calories?’, published in the journal Diabetes

"What we previously thought was an effect of the operation is actually due to the diet," said associate professor Nils Wierup, who led the study with associate professor Peter Spégel.

By monitoring individuals who underwent a six-week low-calorie diet followed by a bariatric operation, they can for the first time show why several health markers improve.

"More than 90 percent of everything that occurred, happened as a result of the diet. Very little changed after the surgery," added Peter Spégel, who works at LUDC and CAS.

However, the results are not to be interpreted as the low-calorie diet being beneficial in itself or that the operation is unnecessary. The procedure is necessary in order for the patient to maintain a limited food intake for a long period.

Normally, the patient follows a strict six-week diet of fewer than 1,000 calories per day in order to achieve the weight loss. Previous research has studied the combined effect of the diet and surgery. What has been seen, in addition to weight loss, is improved blood sugar control, which has been considered a result of an increase in the hormones GLP-1 and GIP and enhanced insulin release. As a bonus, individuals with type 2 diabetes 'recovered' just days after the procedure.

In the present study, plasma metabolite profiling was conducted in patients with (n=10) and without T2D (n=9) subjected to Roux-en-Y gastric bypass surgery (RYGB). Mixed-meal tests were conducted at baseline, after the pre-surgical very low-calorie diet (VLCD) intervention, immediately after RYGB, and after a six-weeks recovery period. They then compared fasted and post-prandial metabolic consequences of RYGB and VLCD in the same patients.

VLCD yielded a pronounced increase in fasting acylcarnitine levels, whereas RYGB, both immediately and after a recovery period, resulted in a smaller, but opposite effect. Furthermore, they observed profound changes in lipid metabolism following VLCD, but not in response to RYGB.

Overall, by measuring several hundred metabolites in the blood  before and after the low calorie diet and a gastric bypass, the researchers could see that the levels of the various metabolites after the diet went in the direction expected from a reduced food intake and improved health. The surgery itself caused very minor changes.

However, a few unique changes were observed that generally were the opposite of those that happened during the diet. The researchers could link some of these effects to the stress that surgery causes for the patient, and this was supported by the fact that virtually all the changes had disappeared six weeks after the operation.

The one most surprised by the results is Nils Wierup, who previously, unlike Peter Spégel, was convinced that it was the surgical procedure and the hormonal changes that accounted for the improved effect.

"What we previously thought was linked to the gastric bypass surgery is actually not. I have had to change my viewpoint," said Wierup.

"It was very good for this project that at the start we had such differing expectations and hypotheses on the effects bariatric surgery and diet have on metabolism. We have therefore looked very carefully at all the results to elucidate the study from all conceivable angles," explained Spégel. "A low-calorie diet is usually not harmful. The fact that we have now shown the effects previously associated with surgery actually arise during the preceding low-calorie diet, and not as a response to the surgery, may perhaps make gastric bypass surgery less magical.

However, as a result of this, “We can also point to bariatric surgery not having any negative metabolic consequences," added Spégel.

"If you are seriously overweight, calorie restriction is not necessarily harmful. Gastric bypass is a good treatment method for obesity. In addition to the weight loss being more considerable and long-lasting compared to a low-calorie diet, the surgery has the added effect that the patient's diabetes reverses," stated Wierup. "If metabolism is primarily affected by the diet and not the surgery, what then is the function of the hormones GLP-1 and GIP?"

The answers will possibly emerge from forthcoming studies in which the researchers will conduct a long-term follow up and compare their results in a European study.