No Effect of Caloric Restriction on Salivary Cortisol Levels in Overweight Men and Women

ObjectiveThe effect of weight loss by diet or diet and exercise on salivary cortisol levels, a measure of hypothalamic pituitary adrenal activity, in overweight individuals is not known. The objective was to test the hypothesis that 24 weeks of moderate caloric restriction (CR) (25%) by diet or diet and aerobic exercise would alter morning and diurnal salivary cortisol levels.Design and SettingRandomized control trial in an institutional research center.ParticipantsThirty-five overweight (BMI: 27.8 ± 0.7 kg/m2) but otherwise healthy participants (16 M/19 F).InterventionParticipants were randomized to either calorie restriction (CR: 25% reduction in energy intake, n = 12), calorie restriction + exercise (CR + EX: 12.5% reduction in energy intake + 12.5% increase in exercise energy expenditure, n = 12) or control (healthy weight-maintenance diet, n = 11) for 6 months.Main outcome measureSalivary cortisol measured at 8:00, 8:30, 11:00, 11:30, 12:30, 13:00, 16:00 and 16:30. Morning cortisol was defined as the mean cortisol concentration at 08:00 and 08:30. Diurnal cortisol was calculated as the mean of the 8 cortisol measures across the day.ResultsIn the whole cohort, higher morning and diurnal cortisol levels were associated with impaired insulin sensitivity (morning: P = 0.004, r2 = 0.24; diurnal: P = 0.02, r2 = 0.15). Using mixed model analysis, there was no significant effect of group, time or sex on morning or diurnal cortisol levels.ConclusionA 10% weight loss with a 25% CR diet alone or with exercise did not impact morning or diurnal salivary cortisol levels.