Carbohydrate and lipid metabolism after 20 days of bed rest

To test the hypothesis that physical inactivity affects carbohydrate and lipid metabolism, we studied the influence of 20 days bed rest in 14 young subjects (9 men and 5 women). There were no changes in body weight or estimated per cent body fat after 20 days bed rest. Total cholesterol, triglyceride, high density lipoprotein cholesterol, and apolipoprotein B levels did not change statistically during bed rest. But apolipoprotein AI levels were significantly lower during and immediately after bed rest compared with control values (p < 0.05). On the 3rd day of bed rest a decrease was found in high density lipoprotein-2 cholesterol (p < 0.05) and an increase in high density lipoprotein-3 cholesterol (p < 0.01) compared with control level. To evaluate the carbohydrate metabolism, each subject underwent a 75 g oral glucose tolerance test. The glucose concentrations in response to glucose ingestion did not change during bed rest, but insulin concentrations increased. The insulin-response curve to glucose ingestion tended to shift to the right during bed rest. From the 3rd day of bed rest an increase (p < 0.05) of total insulin and a decrease (p < 0.05) in blood glucose/insulin ratio were found during the glucose tolerance test which suggested a decrease in insulin sensitivity. These results suggested that physical inactivity impaired carbohydrate- and lipid metabolism.