Waking Salivary Cortisol Associated with Magnitude of Cholesterol Reduction in Women Fed a Healthy Whole-Food Diet for 8 Weeks.

Background: Diet and cortisol are independently linked to cardiometabolic function and health, but underlying alterations in circulating cortisol may influence beneficial cardiometabolic effects of consuming a healthy diet.

Objective: This study was a secondary analysis to examine whether baseline concentrations of waking salivary cortisol interacted with 8-wk whole-food diet interventions to affect cardiometabolic outcomes.

Methods: A randomized, double-blind, controlled 8-wk diet intervention was conducted in 44 participants. The trial was conducted at the Western Human Nutrition Research Center in Davis, California. Participants were overweight or obese women aged 20-64 y, minimally active, and insulin resistant and/or dyslipidemic. Diets were randomly assigned and based on the 2010 Dietary Guidelines for Americans (DGA) or a typical American diet (TAD). Cardiometabolic risk factors and salivary cortisol were assessed at baseline and at 8 wk. Primary outcome measures included 8-wk change in overnight fasted cardiometabolic risk factors, including blood pressure, BMI, and circulating triglycerides, cholesterol, glycated hemoglobin (HbA1c), nonesterified fatty acids, and high-sensitivity C-reactive protein. This trial was approved by the University of California, Davis, Institutional Review Board.

Results: Baseline waking cortisol concentrations interacted ( = 0.0474) with diet to affect 8-wk changes in fasting total cholesterol. Compared with a TAD, a DGA diet was associated with 8-wk decreases in total cholesterol in participants with low (10th percentile of all participants; 2.76 nmol/L) or average (7.76 nmol/L) but not higher (90th percentile of all participants; 13.44 nmol/L) baseline waking cortisol. Consistent with this finding, there was a DGA-specific positive association ( = 0.0047; b: 2.88 ± 0.94) between baseline waking cortisol and 8-wk increases in total cholesterol.

Conclusions: The underlying status of waking cortisol may explain interindividual variability in total cholesterol responses to whole-food diets. This trial was registered at www.clinicaltrials.gov (https://clinicaltrials.gov/ct2/show/NCT02298725) as NCT02298725.