Can consuming lots of calories late in the day put on unwanted pounds?
The answer to that question may be “yes”, based on the findings of two clinical trials, whose results were released earlier this month.
We’ve reported on related research suggesting that big breakfasts and small dinners can aid weight control.
For example, see Mealtimes Matter to Weight and Health, and summarized studies on meal size and timing in Do Fatty Breakfasts Boost Fat-Burning? and Can Larger Breakfasts (or Lunches) and Smaller Dinners Keep Pounds Off?.
But the authors of those investigations cautioned that their findings were preliminary and shouldn’t be considered conclusive.
Dr. Gerda Pot, the co-author of two of those studies, acknowledged lingering uncertainty: “Although the evidence suggests that eating more calories later in the evening is associated with obesity, we are still far from understanding whether our energy intake should be distributed equally across the day, or whether breakfast should contribute the greatest proportion of energy [calories] ...”.
Now, the results of two clinical studies — both published earlier this month — seem to lend weight to the old saying, “eat breakfast like a king, lunch like a prince, and dinner like a pauper”.
Colorado study links eating late to gaining more weight
The most recent findings were presented by University of Colorado researchers five days ago, at the Endocrine Society’s annual meeting (ENDO 2019) in New Orleans.
As that study’s lead author, Adnin Zaman, M.D., said, “Previous studies have suggested that later timing of eating and sleeping are related to obesity.”
She cited a gap in the evidence that her team’s study sought to help fill: “… few studies have assessed both meal and sleep timing … and it’s not clear whether eating later in the day is associated with shorter sleep duration or higher body fat.”
Her team’s week-long study involved 31 overweight and obese adults — 99% of whom were women — whose average age was 36 (Zaman A et al. 2019).
They were enrolled in a weight-loss trial designed to compare the effects of daily calorie restrictions to those of eating only during certain hours of the day (time-restricted eating).
As Dr. Zaman said, “It has been challenging to apply sleep and circadian science to medicine due to a lack of methods for measuring daily patterns of human behavior."
So, all the participants were given electronic devices designed to simultaneously measure their daily sleep, activity, and meal-timing patterns:
On average, the participants consumed food throughout an 11-hour timeframe during the day and slept for about 7 hours a night.
People who ate later in the day also went to sleep later in the day, but they slept for about the same amount of time as those who finished eating earlier.
The study’s results seem to reinforce prior indications that eating later in the day promotes weight gain.
In short, later dinner times were associated with having a higher body mass index and a higher proportion of body fat.
Harvard-led study finds “circadian” time matters more than clock time
A related study examined the effects of meal timing in relation to a person’s “circadian” rhythm, versus time on the clock.
It was led by scientists from Harvard Medical School, and involved researchers from Oregon Health & Science University, Australia’s Monash University, and Spain’s Murcia University.
As the authors wrote in their introduction, “The timing of caloric intake is a risk factor for excess weight and disease. Growing evidence suggests, however, that the impact of caloric consumption on metabolic health depends on its circadian phase, not clock hour.”
A “phase shift” in your circadian rhythms means that your bed and waking times move either earlier in the day (phase advance) or later in the day (phase delay).
Light exposure in the morning advances your circadian rhythm (shifts it earlier), while light exposure in the evening delays that rhythm.
This phenomenon explains the ample evidence that using a digital device (i.e., computer or smart phone) at night can make it more difficult to fall asleep, and why a totally dark bedroom can delay your morning wake time.
(Unsurprisingly, the extent of the impact on your circadian rhythm from exposure to morning and night time light depends in part on the brightness of the light, the length of exposure to that light, and its color — nighttime exposure to the blue light from digital screens is especially capable of impairing your ability to fall asleep.)
In fact, a study published two years ago by the same Harvard-led group showed that the time at which someone consumes 50% or more of their daily calories relative to their own circadian rhythm may influence body composition more than caloric intake relative to the actual hour of the day on a clock (McHill AW et al. 2017).
And, in that 2017 report, they noted that recent laboratory studies showed that calorie-burning and the burning of calories from fat, protein, and carbohydrates depends on the timing of eating relative to someone’s personal circadian rhythm.
Specifically, the 2017 study showed that calorie-burning following an identical test meal was substantially lower when that meal was consumed in the “circadian evening”, compared to eating the same meal during the “circadian morning” — with actual clock timing of the meal exerting smaller effects on calorie-burning.
As they wrote two years ago, “Thus, the specific … [timing of a meal in relation to a person’s personal circadian rhythm] … in real-world settings could play a role in excess body weight if eating predominantly occurs during the circadian evening.”
So, the Harvard-led team set out to identify how people consume calories and macronutrients (carbs, protein, and fat) in relation to the workings of their biological clocks — their so-called circadian rhythm.
The participants in this 30-day study were 106 young adults aged 18 to 22 years, including 45 women and 61 men.
Each participant’s body composition (fat versus muscle) was determined using a bioelectrical impedance scale, and the results placed them into general categories designated as “lean” (53 men and 15 women) or “non-lean” (8 men and 30 women).
And each participant’s typical circadian rhythm was determined by testing body fluids during dim light to determine their individual “dim-light melatonin onset” or DLMO. (The body secretes melatonin in response to darkness, prompting the urge to sleep.)
Then, the participants were assigned to eat meals at a time relative to their individual DLMO, to see whether that timing affected their consumption of total calories, or their consumption of fat, protein, and carbohydrates.
Each participant photographed all the meals and snacks consumed over seven consecutive days, to record the timing of each meal or snack, and allow the researchers to estimate each participant’s intake of calories, fat, protein, and carbohydrates.
The results suggest that eating most of your daily calories later in your personal “circadian day” promotes weight gain:
Accordingly, the Harvard-led team called for studies testing adjustments to the timing of calorie and macronutrient intakes relative to a person’s personal circadian rhythm.