Time-of-day and Meal Size Effects on Clinical Lipid Markers.

Context: Dyslipidemia and cardiovascular disease are common in shift workers and eating at night may contribute to this pathophysiology.

Objective: To examine the effects of eating at different times of day on lipid profiles.

Design: Two 24-hour baseline days with 8 hours of sleep, 3 meals (breakfast, lunch, dinner) and a snack, followed by a 40-hour constant routine (CR) with hourly isocaloric meals.

Setting: Intensive Physiological Monitoring Unit, Brigham and Women's Hospital.

Participants: Twenty-one healthy adults [23.4 ± 2.7 years, 5F].

Intervention: Forty-hour CR.

Main Outcome Measures: A standard clinical lipid panel, consisting of total cholesterol, triglyceride (TG), high-density lipoprotein cholesterol (HDL-C), and low-density lipoprotein cholesterol (LDL-C), was assayed in blood samples collected 4-hourly across ~4 days.

Results: When participants ate at night, levels of TG were similar to eating during the day, however, these levels at night were reached with consuming approximately half the calories. Additionally, 24-hour levels of TG were 10% higher when meals were consumed hourly across 24 hours compared to consuming a typical 3-meal schedule while awake during the day and sleeping at night. The endogenous circadian rhythms of TG, which peaked at night, were shifted earlier by ~10 hours under baseline conditions, whereas the rhythms in total cholesterol, HDL-C, and LDL-C remained unchanged and peaked in the afternoon.

Conclusions: The time-of-day dependency on postprandial lipid metabolism, which leads to hypersensitivity in TG responses when eating at night, may underlie the dyslipidemia and elevated cardiovascular disease risk observed in shift workers.