MedicalResearch.com Interview with:
Kirsi-Marja Zitting, Ph.D.
Instructor in Medicine, Harvard Medical School
Division of Sleep and Circadian Disorders
Departments of Medicine and Neurology
Brigham and Women’s Hospital
Boston, MA 02115
MedicalResearch.com: What is the background for this study?
Response: This study is a follow-up study to our previous study where we found that chronic insufficient sleep together with chronic jet lag is associated with adverse changes in metabolism, including increase in blood sugar levels (Buxton et al. Science Translational Medicine, 2012). The present study focuses on the influence of the time of day on metabolism, which has not been investigated in humans independent of the effects of sleep, physical activity and diet.
MedicalResearch.com: What are the main findings?
Response: The main finding of our study is that the time of day affects your resting energy expenditure such that you burn ~10% more calories in the biological afternoon/evening compared to early morning. In other words, a person who habitually wakes up around 7-8 a.m. will burn the most calories around 4-5 p.m. and the least amount of calories around 4-5 a.m. We also found that our body is more prone to burn carbohydrates in the morning and lipids in the evening.
MedicalResearch.com: What should readers take away from your report?
Response: Our metabolism is strongly controlled by the circadian timing system. In order for our circadian rhythms to maintain the optimal timing with respect to our daily behaviors like sleeping and eating, it’s important for us to keep a very regular schedule from one day to the next.
MedicalResearch.com: What recommendations do you have for future research as a result of this work?
Response: The lower resting energy expenditure in the late part of the night and early morning could contribute to weight gain among those with irregular schedules, especially those who stay up late (e.g. night shift workers). It will be important to study whether minimizing caloric intake at night/early morning will help maintain/lose weight.
Because we found that the body is more prone to burn carbohydrates in the morning and lipids in the evening, it would also be important to study whether matching diet with this macronutrient pattern (i.e. eating carbohydrate rich foods in the morning and lipid rich foods in the evening) will help people to maintain/lose weight.
MedicalResearch.com: Is there anything else you would like to add?
Response: Our study provides further evidence that our metabolism is strongly regulated by our internal biological clock (the circadian timing system). Keeping a regular daily schedule is important for your metabolic health.
Kirsi-Marja Zitting, Nina Vujovic, Robin K. Yuan, Cheryl M. Isherwood, Jacob E. Medina, Wei Wang, Orfeu M. Buxton, Jonathan S. Williams, Charles A. Czeisler, Jeanne F. Duffy. Human Resting Energy Expenditure Varies with Circadian Phase. Current Biology, 2018; DOI: 10.1016/j.cub.2018.10.005
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