The Importance of Caloric Restriction in the Early Improvements in Insulin Sensitivity After Roux-en-Y Gastric Bypass Surgery: Comment on Isbell et al.

We commend Isbell et al. (1) on an important study on the immediate weight loss–independent effects of Roux-en-Y gastric bypass (RYGB) and caloric restriction on glucose metabolism. The study, along with others (2), adds to the increasing understanding of changes in insulin resistance postbariatric surgery. However, the criteria applied to select the patients in the RYGB group were not provided nor were details of the surgery such as duration, the number of open versus laprascopic surgeries in each cohort, or postoperative complications. There is considerable imbalance between the two groups in baseline weight. The effect of confounders including type 2 diabetes and BMI are not sufficiently adjusted for. Insulin and other antidiabetic medication requirements at baseline were not mentioned. It is not clear that outcome measurements were done in a blinded manner. The generalizability of the findings is greatly limited by these shortcomings.

We suggest an alternate study design wherein each subject undergoes caloric restriction first and after complete recovery subsequently undergoes RYGB, thereby serving as his/her own control. We would also suggest limiting the study population to either diabetic subjects alone or to nondiabetic subjects alone, given the metabolic differences among the two states. Without necessarily invalidating the conclusions from the study by Isbell et al., a more rigorous study design could provide greater support to those conclusions.