The effects of marked weight loss, induced by Roux‐en‐Y gastric bypass (RYGB) or sleeve gastrectomy (SG) surgeries, on insulin sensitivity, β‐cell function and the metabolic response to a mixed meal were evaluated.

Fourteen nondiabetic insulin‐resistant patients who were scheduled to undergo SG (n = 7) or RYGB (n = 7) procedures completed a hyperinsulinemic‐euglycemic clamp procedure and a mixed‐meal tolerance test before surgery and after losing ∼20% of their initial body weight.

Insulin sensitivity (insulin‐stimulated glucose disposal during a clamp procedure), oral glucose tolerance (postprandial plasma glucose area under the curve), and β‐cell function (insulin secretion in relationship to insulin sensitivity) improved after weight loss, and were not different between surgical groups. The metabolic response to meal ingestion was similar after RYGB or SG, manifested by rapid delivery of ingested glucose into the systemic circulation and a large early postprandial increase in plasma glucose, insulin, and C‐peptide concentrations in both groups.

When matched on weight loss, RYGB and SG surgeries result in similar improvements in the two major factors involved in regulating plasma glucose homeostasis, insulin sensitivity and β‐cell function in obese people without diabetes.