A landmark study used MealLogger toexplore the relationship between when we eat and our body fat levels (1). Theresults showed that paying attention to one type of clock, but not another, maybe particularly important to anyone interested in maintaining less body fat andlowering their risk of cardiovascular disease (CVD), the leading cause of deathacross the United States (2) and globe (3).
We have an internal clock, or circadian timing system, that supports alertness and physical activity during the day, and sleep and fasting at night. We can influence this system with electrical lighting and thermostats, but these other modern luxuries can also lead to misalignments between our natural rhythms and behaviors. This uncoupling, in turn, is linked to a lower metabolism, problems with blood sugar, and increased risk of CVD, and set out to learn more.
A team of international researchers from Harvard Medical School and other prestigious institutions explored this topic in a study they published in the American Journal of Clinical Nutrition (1). They observed the habits of 110 college-age participants for one month, documented their sleep and daily routines, and “MealLogger allowed participants to take a time-stamped photograph of their meal, include a detailed description of the meal content, and identify which meal they were eating (i.e., breakfast, lunch, dinner, beverage, or snack).” Over 90% of the subjects agreed to photograph their meals and snacks, a particularly high percentage for research settings. Subjects also reported to Brigham and Women’s Hospital Center for physiologic monitoring. What the researchers found was fascinating: While the clock hour (e.g., 8pm dinner) of food intake didn’t predict body fat levels, the circadian clock (specifically, the timing of food intake relative to production of the sleep hormone melatonin) was significantly linked to body fat stores. This held true regardless of which foods people ate and their activity levels.
"In summary, our findings are the first, to our knowledge, to highlight eating patterns in real-world settings by using advanced food diary techniques and reveal that the timing of caloric consumption relative to melatonin onset is associated with increased body fat percentage, whereas caloric intake, the macronutrient content of the calories consumed, the amount of sleep obtained, and clock hour of the caloric consumption were not associated with body composition.”
References:
(1) McHill AW, Phillips AJ, Czeisler CA,et al. Later circadian timing of food intake is associated with increased bodyfat. Am J Clin Nutr.2017;106(5):1213-1219. doi:10.3945/ajcn.117.161588[1]
(2) Centers for Disease Control andPrevention. Heart Disease Facts. Available at:https://www.cdc.gov/heartdisease/facts.htm. Accessed on June 6, 2022.
(3) World Health Organization.Cardiovascular Diseases. Available at: https://www.who.int/health-topics/cardiovascular-diseases#tab=tab_1. Accessedon June 6, 2022.