Glucose and protein metabolic responses to an energy‐ but not protein‐ restricted diet in type 2 diabetes

Abstract

Aims To test the effect of energy restriction with maintained protein intake on body composition and the insulin sensitivity of glucose and protein metabolism in adults with type 2 diabetes mellitus (T2D). Materials and methods After 3d of an isoenergetic diet with 1.2 g/kg/d protein, obese T2D adults (3 women, 2 men) followed a 5‐week diet providing 60% of energy requirements with 45% carbohydrate, and protein maintained at pre‐intervention level. Isotopic tracers were used to quantify whole‐body glucose (3‐³H‐glucose) and protein (¹³C‐leucine) metabolism pre‐ (day 4) and post‐intervention (day 39), postabsorptive and during a hyperinsulinemic, isoglycemic, isoaminoacidemic clamp. Body composition was measured by dual‐energy x‐ray absorptiometry. Results Post energy restriction, the 6% weight loss was from total body (11%) and visceral fat losses (25%), but lean mass was preserved. Fasting glucose, serum insulin, HOMA‐IR and C‐peptide decreased significantly (29%, 38%, 54% and 38%, respectively) as did other cardiometabolic risk factors. Between clamp studies, postabsorptive protein turnover and oxidation rates decreased (12% and 32%), resulting in less negative net balance, consistent with protein conservation. The rates of glucose turnover decreased, and glucose metabolic clearance rate improved (24%). During the clamp, protein flux was lower (9%) and breakdown suppressed (12%), and net balance became less negative but not different. Though glucose turnover did not differ, metabolic clearance improved 47%. Conclusions In obese adults with T2D, an energy‐restricted diet with maintained protein intake of ~1.2 g/kg/d improved kinetics of protein metabolism (particularly postabsorptive), preserved lean body mass and increased glucose metabolic clearance rate.