Only 16 overweight or obese participants made up the short trial, but the authors stated it was carefully designed to rule out other possible reasons of weight increase.
Frank Scheer is a senior author and the director of the Brigham's Division of Sleep and Circadian Disorders' Medical Chronobiology Program.
All subjects had a regular physical exercise schedule, were in good health, and had no history of diabetes or shift employment, which might alter circadian rhythm. Before the lab experiment started, each participant in the research adhered to a tight, healthy sleep/wake pattern for around three weeks and received prepared meals at set times for three days.
Then participants were divided into two groups at random. For the six days noted in the study, one group consumed calorie-restricted meals at 8 a.m., noon, and 4 p.m., while the other consumed the identical meals four hours later, at midday, 4 p.m., and 8 p.m. Tests for body fat, temperature, and energy expenditure were conducted over the course of three days, while measurements of hunger and appetite were taken 18 times each.
The same individuals then reversed the process, moving the early eaters to the late eaters group and vice versa, utilising each person as their own control.
Hunger increases fat loss decreases: According to the findings, people who eat at night saw a two-fold increase in appetite. People who ate later in the day also reported craving meat, starchy and salty meals, and vegetables and dairy products to a lesser level.
Blood test findings allowed researchers to determine why: Leptin levels, which indicate when we are full, were lower in late diners than among early eaters. Ghrelin levels, which increase our hunger, increased in contrast.
What is novel about our findings, according to Scheer, is that they reveal that eating later increases the ratio of ghrelin to leptin on average across the whole 24-hour sleep/wake cycle.