Gastric bypass, diet therapy induce similar metabolic benefits after weight loss
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Adults with obesity and type 2 diabetes who underwent bariatric surgery or a low-calorie diet intervention experienced similar metabolic benefits, with no evident clinically important effects independent of weight loss, study data show.
“It is generally believed that Roux-en-Y gastric bypass surgery has weight loss-independent, clinically important effects on metabolic function that contribute to the high rate of remission of type 2 diabetes observed after surgery,” Samuel Klein, MD, the William H. Danforth Professor of Medicine and Nutritional Science and director, Center for Human Nutrition at Washington University School of Medicine, St. Louis, told Healio. “This is an important concept because it implies that bypassing the upper part of the intestinal tract has novel therapeutic metabolic effects and has stimulated research trying to find the mechanisms responsible for this effect. Therefore, we conducted a study to determine whether marked weight loss — induced by Roux-en-Y — really does have beneficial effects beyond the effect of weight loss alone on the major physiological factors that regulate blood glucose control in people with obesity and type 2 diabetes.”
Study design
In a prospective cohort study, Klein and colleagues analyzed metabolic regulators of glucose homeostasis before and after marked weight loss (16% to 24%) induced by Roux-en-Y gastric bypass (n = 11; eight women; mean age, 49 years) or low-calorie diet therapy (n = 11; seven women; mean age, 54 years) among adults with obesity and type 2 diabetes. Participants in the diet group received weekly education sessions on dietary practices; all meals were provided throughout the study as nutritional shakes and prepackaged entrees. A study dietitian consulted with surgery patients weekly to monitor body weight and adjust dietary intake to meet weight-loss goals. After participants achieved targeted weight loss, their energy intake was adjusted to maintain a constant body weight for 3 weeks before repeat testing was performed.
The primary outcome was the change in hepatic insulin sensitivity. Secondary outcomes were changes in insulin sensitivity in muscle and adipose tissue; beta-cell function; metabolic response to mixed-meal ingestion; 24-hour glucose, free fatty acid and insulin profiles, and body composition. Hepatic, muscle and adipose tissue insulin sensitivity were assessed via a 9-hour, three-stage hyperinsulinemic-euglycemic pancreatic clamp procedure.
The mean weight loss was 17.8% in the diet group and 18.7% in the surgery group.
No between-group differences observed
Researchers found that weight loss was associated with increases in mean suppression of glucose production from baseline for the surgery and diet groups during clamp stage 1 (mean, 7.02 vs. 7.04 mol/kg of fat-free mass per minute) and during clamp stage 2 (mean, 5.39 vs. 5.37 mol/kg of fat-free mass per minute), with no between-group differences during either stage.
Weight loss was also associated with increased insulin-stimulated glucose disposal for the surgery and diet groups; there was no significant difference between the groups.
Weight loss increased beta-cell function by 1.83 U (95% CI, 1.22-2.44) in the diet group and by 1.11 U (95% CI, 0.08-2.15) in the surgery group, with no between-group difference.
Similarly, weight loss decreased the areas under the curve for 24-hour plasma glucose and insulin levels in the surgery and diet groups, with no between-group differences.
No major complications occurred in either group.
“We were disappointed, but not surprised,” Klein said of the findings. “We know that weight loss alone has profound beneficial effects on metabolic health. The problem is that it is very difficult for most people with obesity to lose weight and maintain long-term weight loss. In fact, the effect of Roux-en-Y surgery on body weight is what makes this procedure so fascinating, and we do not understand why Roux-en-Y reduces the drive to eat and is so successful in producing long-term weight loss.”
Klein said Roux-en-Y gastric bypass surgery simultaneously improves multiple metabolic factors that regulate blood glucose control and metabolic health, including multi-organ insulin sensitivity, beta-cell function and 24-hour blood glucose and insulin profiles.
“Even though weight loss, itself, is the primary mechanism responsible for the beneficial effects of Roux-en-Y surgery, this does not diminish the importance of bariatric surgery as a therapy for patients with obesity and type 2 diabetes,” Klein said. “Bariatric surgery improves health and reduces, or even completely eliminates, the need for diabetes medications.”
For more information:
Samuel Klein, MD, can be reached at the Center for Human Nutrition, Washington University School of Medicine, Campus Box 8031, 660 South Euclid Ave., St. Louis, MO 63110; e-mail: sklein@wustl.edu.
Perspective
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Steven B. Heymsfield, MD, FTOS
These data will shock a lot of people. There are entire careers built around the independent effects of bariatric surgery. At our institution, three or four scientists have NIH grants looking for the mechanism or mechanisms behind the effects of bariatric surgery.
The question is, is this correct? If one could achieve these metabolic results with diet alone, we would not need bariatric surgery. These are difficult studies to conduct — utilizing hyperinsulinemic-euglycemic pancreatic clamp procedure and microbiome analysis, conducted over 4 years — and I give the authors credit for that part of it. That said, this does not change, in any way, our view toward bariatric surgery as a clinical tool. This was also a very small cohort with unequal numbers of men and women in the two groups.
If you are a patient with morbid obesity considering bariatric surgery, this should have absolutely no influence on your decision.
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