How Your Eating Schedule Can Affect Weight Gain
A 2019 study of eating schedule habits was recently completed at the University of Barcelona, and published in the scientific journal, Nutrients. Its conclusions were eye-opening! The researchers provided deeper insights into the mechanisms of our 'biological clock', particularly as it relates the relative metabolic capacity our body has to use calories consumed during daytime as opposed to the evening when it's better not to eat at all.
The study's authors also coined a new term: 'eating jet lag', which I'll explain in a bit. The researchers were interviewed by the University of Barcelona. What follows is a summary of the Nutrients publication, the University interview, and the results of a similar study conducted by the University of Pennsylvania that made similar conclusions about the positive health consequences of maintaining a regular eating schedule done earlier in the day.
The Barcelona study monitored eating schedules, specifically the eating schedule, of 1,106 individuals between age ages of 18 and 25, over a two year period. Their weekday eating schedule was compared to their weekend eating schedule, which can be quite different. This is especially true in Southern Europe, where people quite commonly begin their evening meal on the weekends as late as 10 PM. Friends often gather for drinks in a club or bar in the early evening hours, and then ultimately migrate to a nearby restaurant. These cultural patterns made Barcelona an ideal locale for such a study.
In the study, researchers asked each subject to maintain a log in which they entered the start time-of-day of each of their three daily meals. The study had few controls, such as exercise, sleep cycle, and food choice parameters. However, since the population of subjects was large, and the study's duration was long, the results and conclusions reported by the authors are considered to be highly valid.
Once all of the data was collected, the researchers created a daily midpoint, time-wise, for each day's three meals. These mid-points were separated into weekday midpoints and weekend midpoints. These midpoints often differed by as much as three and a half hours. In other words, a person who ate breakfast at 7:30 AM and dinner at 6:30 PM during the week, would eat breakfast at 11:00 AM and dinner at 10:00 PM on the weekends. This irregularity in eating schedules was referred to by the authors as 'eating jet lag', a term I introduced at the outset of this piece.
The University of Barcelona's Eating Schedule Results
The researchers also computed the BMI, or body mass index, of each subject at the outset of the study and at the study's conclusion. BMI is a formula that computes weight and height values to determine whether someone's weight is healthy. What they discovered was that subjects who averaged the largest eating jet lag differential, experienced weight gain, or gain in their BMI. The larger the jet lag differential, the larger the BMI increase. María Fernanda Zerón Rugerio, one of the principal authors of the study, commented on the results, saying;
"Our results show changing the timing of the three meals during the weekend is linked to [greater BMI]. The highest impact on the BMI could occur when there is a 3.5-hour difference in eating schedules. After this, the risk of [excess weight] could increase, since we saw individuals who showed a 3.5-hour eating jet lag increase their BMI by 1.3. kg/m2".
She went on to say, "As a result, when food intake takes place regularly, the circadian clock ensures that the body's metabolic pathways act to assimilate nutrients. However, when food is taken at an unusual hour, nutrients can act on the molecular machinery of peripheral clocks (outside the brain), altering the schedule and thus, modifying the body's metabolic functions."
The researchers demonstrated that our body understands and processes calories differently depending on the time of day. The study concluded that eating late can be related to a higher risk of obesity. Another researcher interviewed by the University of Barcelona, Maria Izquierdo Pulido, stated;
"This difference is related to our biological clock, which organizes our body to understand and metabolize calories consumed during the day. At night, however, it gets the body ready for fasting while we sleep."
Her associate and fellow researcher Trinitat Cambras, stated:
"Our biological clock is like a machine, and is ready to unchain the same physiological and metabolic response at the same time of the day, every day of the week. Fixed eating and sleep schedules help the body to be organized and promote energy homeostasis. Therefore, people with a higher alteration of their schedules have a higher risk of [excess weight]."
The University of Pennsylvania Eating Schedule Study
A similar study, conducted in 2017 by University of Pennsylvania researchers, also concluded that consuming meals later at night can cause weight gain and lead to obesity. The study demonstrated that timing eating patterns later in the day can increase weight and cholesterol levels. It also impairs fat metabolism, hormonal markers related to heart health, and various other health markers. The study is thought to be the first experimental evidence of the metabolic consequences of a pattern of delayed eating.
This study lasted for eighteen weeks and examined only nine healthy-weight adults. But since it was conducted within strict controls, the study's outcomes are considered valid. The controls included a consistent sleep period throughout the entire eighteen weeks (11 PM to 9 AM), a strict schedule of meal timings, and consistent meal and snack food choices. The nine subjects acted as their own control group by engaging in two varying meal patterns:
- An eight week early in the day pattern (8 AM to 7 PM), and
- An eight week later eating pattern (12 noon to 11 PM).
The two testing periods were separated by a two-week washout period to ensure that there was no carry-over effect.
The nine participants had metabolic measures taken and blood drawn at the beginning and end of the first testing period; after the two-week washout period; and at end of the second testing period. This allowed the research team to measure changes in weight, metabolism and energy.
Results of The University of Pennsylvania Study
Researchers learned that when the test subjects ate on the later schedule, compared to the daytime schedule, their weight increased. Their respiratory quotient — the ratio of carbon dioxide production compared to oxygen consumption — also rose during the delayed period. This ratio helped researchers to identify that late eating resulted in the metabolization of fewer lipids and more carbohydrates. They also found several additional negative metabolic profiles including increased fasting glucose, cholesterol, and triglyceride levels.
After conducting a hormonal profile, the University of Pennsylvania researchers discovered that during the daytime period, the hormone ghrelin, an appetite stimulant, peaked early in the day, while leptin, which acts to keep appetite satisfied, peaked later. This suggested that the participants received cues to eat earlier, and that early eating probably helped them to stay satisfied longer. They concluded from this that earlier eating may help prevent overeating and the desire to snack at night.
Kelly Allison, director of the University of Pennsylvania Center for Weight and Eating Disorders, and senior author of the study commented on the study's findings saying;
"While lifestyle change is never easy, these findings suggest that eating earlier in the day may be worth the effort to help prevent these detrimental chronic health effects…We have an extensive knowledge of how overeating affects health and body weight, but now we have a better understanding of how our body processes foods at different times of day over a long period of time ."
Our bodies are pretty smart — smarter than we give them credit for. We intrinsically know that daytime is the time to eat and metabolize calories and that nighttime is the time to fast.
It is clear from these two studies that the formation of a regular, habitual pattern of eating during the daytime on a regular schedule earlier in the day is advantageous to our overall health, and will help us to prevent weight gain and improve important metabolic markers, such as healthy levels of hormones, fasting glucose, cholesterol, and triglycerides. Adjust your eating schedule to match your biological clock, which knows that daytime is the healthiest time to eat, and that nighttime is the time to fast.