Table 1.
Demographic, Anthropometric, Glycemic, and Metabolic Characteristics of the Study Groups at Baseline and Follow-Up Visits
| Group | Baseline Visit | Follow-up Visit | Difference (% baseline) | Sig. | |
|---|---|---|---|---|---|
| Age (y) | Chamber | 25.4 ± 5.9 | 30.5 ± 6.8 | +5.1 (20.2%) | <.001a |
| Clamp | 27.7 ± 5.9 | 32.1 ± 6.2 | +4.4 (15.9%) | <.001a | |
| Body weight (kg) | Chamber | 91.7 ± 24.9 | 97.9 ± 26.8 | +6.1 (6.6%) | <.001a |
| Clamp | 95.1 ± 23.2 | 101.4 ± 25.9 | +6.2 (6.6%) | <.001a | |
| BMI (kg/m2) | Chamber | 32.8 ± 8.7 | 35.1 ± 9.2 | +2.2 (6.7%) | <.001a |
| Clamp | 34.3 ± 7.6 | 36.5 ± 8.4 | +2.1 (6.2%) | <.001a | |
| Waist circumference (cm) | Chamber | 105.1 ± 17.9 | 109.9 ± 17.7 | +4.9 (4.6%) | <.001a |
| Clamp | 109.5 ± 17.8 | 114.8 ± 19.0 | +5.6 (5.2%) | <.001a | |
| Thigh circumference (cm) | Chamber | 64.4 ± 8.9 | 64.7 ± 8.6 | 0.3 (0.4%) | .601 |
| Clamp | 65.8 ± 8.9 | 66.8 ± 8.9 | +1.0 (1.5%) | .027a | |
| Body fat (%) | Chamber | 30.8 ± 8.4 | 32.2 ± 7.4 | +1.3 (4.3%) | .002a |
| Clamp | 32.4 ± 8.7 | 34.1 ± 7.8 | +1.7 (5.3%) | <.001a | |
| Fat mass (kg) | Chamber | 29.6 ± 14.8 | 32.7 ± 15.0 | +3.1 (10.3%) | <.001a |
| Clamp | 31.9 ± 13.9 | 35.6 ± 15.3 | +3.7 (11.6%) | <.001a | |
| Fat free mass (kg) | Chamber | 62.1 ± 12.7 | 65.2 ± 14.2 | +3.0 (4.9%) | <.001a |
| Clamp | 63.2 ± 12.5 | 65.7 ± 13.5 | +2.5 (4.0%) | <.001a | |
| Fasting plasma glucose (mg/dL) | Chamber | 85.5 ± 9.8 | 88.3 ± 10.0 | +2.8 (3.3%) | .004a |
| Clamp | 89.1 ± 9.1 | 90.9 ± 9.6 | +1.8 (2.0%) | .002a | |
| 2-h plasma glucose (mg/dL) | Chamber | 111.4 ± 26.4 | 123.4 ± 29.5 | +12.0 (10.8%) | <.001a |
| Clamp | 119.8 ± 28.9 | 131.6 ± 31.8 | +11.7 (9.8%) | <.001a | |
| Glucose tolerance statusb | Chamber | ||||
| NGR | 120 (83.3%) | 92 (63.9%) | −28 (−19.4%) | <.001a | |
| IGR | 24 (16.7%) | 52 (36.1%) | +28 (19.4%) | ||
| IFG | 10 (6.9%) | 13 (9.0%) | +3 (2.1%) | .629 | |
| IGT | 22 (15.3%) | 47 (32.6%) | +25 (17.3%) | <.001a | |
| Glucose AUC (mg/dL · 180 min) | Chamber | ||||
| Total | 21 001 ± 3663 | 22 878 ± 3679 | +1877 (8.9%) | <.001a | |
| Incremental | 5605 ± 2893 | 6992 ± 3358 | +1388 (24.8%) | <.001a | |
| Fasting plasma insulin (mU/L) | Chamber | 39.9 ± 22.8 | 42.5 ± 18.4 | +2.6 (6.5%) | .134 |
| Median and IQR | 33 (25–49) | 37 (28–50) | +4 (12.1%) | .100 | |
| 2-h plasma insulin (mU/L) | Chamber | 168.7 ± 162.0 | 172.6 ± 113.4 | +3.9 (2.3%) | .805 |
| Median and IQR | 127 (72–199) | 140 (86–232) | +13 (10.2%) | .261 | |
| Insulin AUC (mU/L · 180 min) | Chamber | ||||
| Total | 31 638 ± 19 932 | 30 888 ± 14 368 | −750 (−2.4%) | .692 | |
| Incremental | 24 544 ± 17 839 | 23 325 ± 12 288 | −1219 (−5.0%) | .479 | |
| Energy intake (kcal/day) | Chamber | 2235 ± 378 | 2340 ± 395 | +105 (4.7%) | <.001a |
| 24-h EE (kcal/day) | Chamber | 2354 ± 434 | 2496 ± 447 | +142 (6.0%) | <.001a |
| 24-h energy balance (kcal/day) | Chamber | −119 ± 184 | −156 ± 187 | −37 (−30.9%) | .042a |
| SMR (kcal/day) | Chamber | 1639 ± 300 | 1726 ± 269 | +87 (5.3%) | <.001a |
| SPA (%)c | Chamber | 7.8 ± 4.4 | 7.2 ± 3.7 | −0.6 (−8.1%) | .175 |
| EE0 activity (kcal/14 · hrs)c | Chamber | 1253 ± 221 | 1327 ± 211 | +75 (6.0%) | <.001a |
| AFT (kcal/14 · hrs)c | Chamber | 293 ± 110 | 314 ± 110 | +21 (7.3%) | .090 |
| AFT (% of energy intake)c | Chamber | 13.1 ± 4.6 | 13.4 ± 4.3 | +0.3 (2.6%) | .528 |
| 24-h RQ (ratio)d | Chamber | 0.852 ± 0.024 | 0.843 ± 0.026 | −0.008 (−1.0%) | .002a |
| CARBOX (kcal/day)d | Chamber | 1098 ± 269 | 1077 ± 242 | −22 (−2.0%) | .348 |
| FATOX (kcal/day)d | Chamber | 970 ± 315 | 1120 ± 367 | +151 (15.5%) | <.001a |
| RMR (kcal/day)e | Clamp | 1779 ± 310 | 1916 ± 325 | +136 (7.8%) | <.001a |
| EE during clamp (kcal/min) | Clamp | ||||
| Basal period | 1.24 ± 0.22 | 1.33 ± 0.23 | +0.09 (7.7%) | <.001a | |
| Insulin infusion period | 1.24 ± 0.22 | 1.32 ± 0.22 | +0.08 (6.7%) | <.001a | |
| BGO (mg/kg EMBS/min) | Clamp | 1.94 ± 0.23 | 1.97 ± 0.27 | +0.04 (2.1%) | .072 |
| Glucose output suppression (%)f | Clamp | −82.4 ± 20.5 | −76.4 ± 19.4 | 6.0% | <.001a |
| M (mg/kg EMBS/min)g | Clamp | 2.69 ± 1.01 | 2.44 ± 0.81 | −0.26 (−9.8%) | <.001a |
| Median and IQR | 2.4 (2.0–2.9) | 2.2 (1.9–2.6) |
Data are reported as mean±sd. “Chamber”: study group with repeated chamber sessions (n = 144; median time between measurements: 4.2 y., IQR: 2.1–7.6 y); “Clamp”: study group with repeated glucose clamps (n = 261; median time between measurements: 3.8 yr., IQR: 2.0–5.8 y).
P < .05 vs baseline value.
Normal glucose regulation (fasting plasma glucose, FPG <100 mg/dL and 2-h plasma glucose, 2hPG <140 mg/dL); impaired glucose regulation (FPG: 100–125 mg/dL and/or 2hPG: 140–199 mg/dL); impaired fasting glucose (FPG: 100–125 mg/dL); impaired glucose tolerance (IGT, 2hPG: 140–199 mg/dL) according to American Diabetes Association diagnostic criteria (12).
Spontaneous physical activity (SPA) was detected by radar sensors and expressed as the percentage of time over the 15-min interval in which activity was detected. Only chambers with an average daily SPA <15% from 11:00 to 01:00 were included in the analysis. The EE in the inactive state (EE0 activity) was calculated as the intercept of the regression line between EE and SPA between 11:00 and 01:00. Sleeping metabolic rate (SMR) was defined as the average EE of all 15-min intervals between 01:00 and 05:00 AM during which SPA was less than 1.5%. Only chamber sessions with at least four 15-min intervals with SPA <1.5% were considered in the analysis. The awake and fed thermogenesis (AFT), as a measure of the thermic effect of food and the energy cost of being awake, was calculated as the difference between EE0 activity and SMR (27).
Carbon dioxide production (VCO2) and oxygen consumption in liters (VO2) were calculated for every 15-min interval, averaged and extrapolated to the 24-h interval. The 24-h RQ was calculated as the ratio of 24-h VCO2 to 24-h VO2 over the entire day. Carbohydrate (CARBOX) and fat (FATOX) oxidation rates were derived from the 24-h RQ after accounting for protein oxidation, estimated from measurement of 24-h urinary nitrogen excretion.
RMR was calculated as the average EE over 40 min while the subject was instructed to stay awake and motionless, and then extrapolated to 24 h.
Suppression of glucose output at the end of the low-dose insulin infusion was calculated as percent reduction of BGO.
Values of M during the final 40 min of insulin infusion were calculated taking into account variations in steady-state plasma glucose and insulin concentrations and normalized to the estimated metabolic body size (EMBS = fat free mass + 17.7 kg) (40).