It has long been popular advice for people looking to lose weight to avoid late-night snacking.
It’s no wonder, with a wealth of research showing that eating late at night is linked to higher body weight and a higher risk of obesity.
But until now, few studies have investigated precisely why eating late at night is linked to higher body weight.
This is what a recent study from the United States (US) set out to find out. They found that eating four hours later than normal actually changed many of the physiological and molecular mechanisms that promote weight gain.
This work adds to other recently published work that has found that eating earlier in the day is more beneficial for both appetite and body weight control.
EAT LATE
To conduct their study, the researchers had 16 participants follow two different meal schedules, each for a period of six days in total.
The first protocol had participants eat early in the day with the last meal eaten approximately six hours and 40 minutes before bedtime.
The second protocol had the participants eat all of their daily meals approximately four hours later.
This meant that they skipped breakfast and instead had lunch, dinner, and dinner. His last meal was eaten just two and a half hours before bedtime.
The study was conducted in a controlled laboratory, which ensured that participants in each group ate an identical diet and that all of their meals were evenly spaced about four hours apart.
To understand how eating late affected the body, the researchers looked specifically at three different measures that are associated with weight gain:
- The influence of appetite
- The impact of mealtime on energy expenditure (calories burned), and
- Molecular changes of fatty tissue.
Appetite was measured using two techniques. The first technique was to have the participants rate their feelings of hunger throughout the day.
The second technique involved collecting blood samples to look at the levels of appetite-regulating hormones in the participants’ blood, such as leptin (which helps us feel full) and ghrelin (which makes us feel hungry).
These hormones were assessed hourly over a 24-hour period on the third and sixth days of each trial.
To assess the effect of meal timing on daily energy expenditure, a technique called “indirect calorimetry” was used. This measures both the amount of oxygen a person uses and the amount of carbon dioxide they produce.
This helps researchers estimate how many calories a person’s body uses during a typical day.
To examine how eating late at night affects how the body stores fat at the molecular level, the researchers performed a biopsy of adipose tissue removed from the abdomen. Only half of the participants agreed with this.
The team found that, compared to an early eating pattern, eating late not only increased subjective feelings of hunger the next day, but also increased the ratio of “hunger” hormones in the blood, despite the fact that the participants they consumed an identical diet in both protocols.
Eating late also caused a decrease in the number of calories burned the next day.
In participants who underwent fat tissue biopsy, eating late was also shown to cause molecular changes that promote fat storage.
Together, these results indicate that eating late leads to a series of physiological and molecular changes that, over time, could lead to weight gain.
WEIGHT GAIN POTENTIAL
While we don’t fully understand all of the underlying mechanisms by which eating late at night promotes weight gain, this study shows us that it’s likely the result of many factors working together.
One theory as to why eating late causes weight gain could be due to our circadian rhythm.
The human body has a natural circadian rhythm, which is controlled by the brain to influence the normal ebb and flow of hormones. It is particularly sensitive to daylight and food intake.
Mealtime is intrinsically linked to the circadian rhythm in humans, as we normally sleep when it’s dark and eat when it’s daylight.
When we eat late, this could defy the natural circadian rhythm, causing disruptions in the body’s hunger signals and the way it uses calories and stores fat.
However, this link has only been shown in animal studies so far.
Since the new study was only conducted on a limited number of participants and over a very short period of time, more research will be needed to better understand whether these changes are only temporary and what effect eating late at night may have on long-term these Mechanisms of weight gain.
But we know from other studies that people who tend to eat late at night also tend to gain weight more easily.
Other large-scale studies looking at the relationship between disturbances in meal timing and energy balance (such as skipping breakfast, eating late at night, and shift work) have found that these eating patterns were associated with greater body weight and an increased risk of metabolic disorders (such as high blood pressure or type 2 diabetes).
This study adds to a growing body of evidence showing just how important meal timing can be when it comes to body weight.
Based on what this and other studies have shown, people managing their weight may want to ditch late-night snacking in favor of eating most of their meals earlier in the day. THE CONVERSATION
ABOUT THE AUTHOR:
Alex Johnstone is the Staff Chair for Nutrition at the Rowett Institute at the University of Aberdeen.
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