Bed rest worsens impairments in fat and glucose metabolism in older, overweight adults

Background: The effects of bed rest on the dysregulation of fatty acid and glucose metabolism have not been addressed in the older population. Objective: We examined the effect of 10 days of bed rest on fatty acid kinetics and hepatic and peripheral insulin resistance in aging. Methods: We utilized an octreotide, basal glucagon replacement, multistage insulin infusion, and the concomitant infusion of [6,6 ²H₂]glucose to derive insulin-mediated suppression of glucose production and insulin-stimulated glucose disposal in nine older, overweight individuals (body mass index 28.1 ± 1.7 kg m ^-2; 39.9% ± 1.9% fat). During the multistage insulin infusion, we also infused [1-¹³C]palmitate to examine free fatty acid rate of appearance (R_a). Results: Body weight, % body fat, and energy metabolism did not change with bed rest. There was a significant decrease (-2291 ± 316 cm³) in visceral fat, and no change in abdominal subcutaneous fat with bed rest. Insulin-mediated suppression of glucose production was modest prior to bed rest and was further reduced (>15% ± 2%) by bed rest. There was also a minor decrease in the insulin-mediated suppression of free fatty acid R_a after bed rest and, as a consequence, a small variation in plasma free fatty acid from pre-to post-bed rest in the first stage of the multistage insulin infusion. There was also a significant bed rest-induced decline (>2.0 ± 0.6 mg kg FFM ^-1 min^-1) in insulin-stimulated glucose disposal. Conclusions: Preexisting impairments in insulin sensitivity are worsened by bed rest and seem linked to alterations in the regulation of free fatty acid in older, overweight individuals