Kirsten Granados

Effects of 1 day of inactivity on insulin action in healthy men and women: interaction with energy intake

Prolonged periods of limited muscle activity can reduce insulin action. Acute changes in low muscle activity (ie, sitting) have not been assessed. In addition, unless energy intake is reduced during sitting to match low expenditure, the concurrent energy surplus may explain lower insulin action. The objective of the study was to evaluate the acute effect of sitting, with and without energy surplus, on insulin action. Fourteen young (26.1 ± 4.5 years, mean ± SD), nonobese (23.7% ± 7.1% fat), fit (peak oxygen consumption = 49.1 ± 3.3 mL·kg(-1)·min(-1)) men (n = 7) and women (n = 7) completed three 24-hour conditions: (1) an active, no-sitting condition (high energy expenditure of 2944 ± 124 kcal with energy intake matched to expenditure) = NO-SIT; (2) low energy expenditure (sitting) of 2195 ± 121 kcal with no reduction in energy intake (energy surplus) = SIT; and (3) sitting with energy intake reduced to 2139 ± 118 kcal to match low expenditure (energy balance) = SIT-BAL. Insulin action was measured the following morning during a continuous infusion of [6,6-(2)H]-glucose. Data were analyzed using linear mixed-effects models with planned contrasts. Compared with NO-SIT, insulin action, defined as whole-body rate of glucose disappearance normalized to mean plasma insulin, was reduced by 39% in SIT (P < .001) and by 18% in SIT-BAL (P = .07). Insulin action was higher in SIT-BAL compared with SIT (P = .04). One day of sitting considerably reduced insulin action; this effect was minimized, but not prevented, when energy intake was reduced to match expenditure. Strategies to limit daily sitting may reduce metabolic disease risk.

Effects of subtracting sitting versus adding exercise on glycemic control and variability in sedentary office workers

Recent evidence suggests that, like adding exercise, reducing sitting time may improve cardiometabolic health. There has not been a direct comparison of the 2 strategies with energy expenditure held constant. The purpose of this study was to compare fasting and postmeal glucose and insulin concentrations in response to a day with frequent breaks from sitting but no exercise versus considerable sitting plus moderate exercise. Ten sedentary overweight/obese office workers were tested in 3 conditions: (i) walking per activity guidelines (AGW): sitting for majority of workday with a 30 min pre-lunch walk; (ii) frequent long breaks (FLB): no structured exercise but frequent breaks from sitting during workday with energy expenditure matched to AGW; and (iii) frequent short breaks (FSB): number of breaks matched to FLB, but duration of breaks were shorter. Plasma glucose and insulin areas under the curve were measured in response to a meal tolerance test (MTT) at the end of the workday and interstitial glucose was evaluated throughout the day and overnight using continuous glucose monitoring. Using repeated-measures linear mixed models, area under the curve of plasma glucose or insulin after the MTT was not different between conditions. Glycemic variability was lower in FLB compared with AGW (p < 0.05), and nocturnal duration of elevated glucose (>7.8 mmol/L) was shorter after FLB (2.5 ± 2.5 min) than AGW (32.7 ± 16.4 min) or FSB (45.6 ± 29.6 min, p = 0.05). When energy expenditure was matched, breaks from sitting approximated the effects of moderate-intensity exercise on postmeal glucose and insulin responses and more effectively constrained glycemic variability.

Effects of a Single Exercise Bout on Insulin Sensitivity in Black and White Individuals

BACKGROUND Previous research suggests non-Hispanic blacks (blacks) are more insulin resistant than non-Hispanic whites (whites). Physical activity can play an important role in reducing insulin resistance. However, it is unknown whether racial differences exist in response to exercise. Therefore, the purpose of this study was to compare metabolic responses to a single bout of exercise in blacks and age-, sex-, and body mass index-matched whites. METHODS Whole-body insulin sensitivity, glucose storage, glucose oxidation, and respiratory exchange ratio (RER) were assessed during a hyperinsulinemic-euglycemic clamp in normoglycemic blacks (n = 11) and whites (n = 10). Outcome measures were evaluated in a sedentary control condition and 12 h after treadmill walking at 75% of maximal heart rate for 75 min. RESULTS In the control condition, there were no differences in insulin sensitivity between blacks and whites (P = 0.54). During the clamp, glucose oxidation and insulin-stimulated RER values were significantly higher in blacks compared with whites (P = 0.04 and P < 0.01, respectively). Despite similar RER values during exercise, RER values at 60, 90, and 120 min after exercise in blacks were also significantly higher compared with whites (P < 0.05). After exercise, there were no significant improvements in insulin sensitivity (P = 0.57) or glucose storage (P = 0.42) in blacks or whites; however, glucose oxidation was significantly lower in both racial groups (P < 0.05). CONCLUSIONS These data suggest that insulin sensitivity is similar in blacks and age-, sex-, and body mass index-matched whites, but the glucose disposal pathways (storage vs. oxidation) are somewhat different. Compared with whites, blacks appear to have a greater capacity to increase glucose oxidation immediately after exercise and during insulin stimulation.