It’s 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 eat late at night is linked to higher body weight and an increased risk of obesity.
But so far, few studies have actually investigated precisely why eating late at night is linked to higher body weight. That’s what a recent American study set out to find out.
They found that eating four hours later than normal actually altered many physiological and molecular mechanisms that promote weight gain.
This work adds to others recently published work who found that eating earlier in the day is more beneficial for controlling appetite and body weight.
To conduct their study, the researchers asked 16 participants to follow two different meal schedules, each for a total of six days.
The first protocol instructed participants to eat their meals early in the day, with the last meal eaten approximately six hours and 40 minutes before bedtime.
The second protocol asked participants to eat all of their daily meals about four hours later. This meant that they skipped breakfast and ate lunch, dinner and the evening meal instead. Their last meal was eaten only two and a half hours before sleeping.
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 approximately four hours apart.
To understand how eating late affects the body, the researchers specifically looked at three different measures associated with weight gain:
- The influence of appetite,
- The impact of meal times on energy expenditure (calories burned), and
- Molecular changes in adipose tissue.
Appetite was measured using two techniques. The first technique involved asking participants to rate how hungry they felt throughout the day.
The second technique involved taking blood samples to examine participants’ blood levels of appetite-regulating hormones, 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 days three and six of each trial.
To assess the effect of meal times 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 on fatty tissue taken 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 participants dieting identical food in the two protocols.
Eating late also led to fewer calories burned the following day. In participants who had the fat tissue biopsy, eating late was also shown to cause molecular changes that promote fat storage.
Together, these results indicate that late feeding leads to a number 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 mechanisms behind why late-night eating promotes weight gain, this study shows us that it’s likely the result of many factors working together.
One theory 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.
Timing of eating is intrinsically linked to the circadian rhythm in humans, as we normally sleep when it’s dark and eat when it’s light.
When we eat late, it could challenge the natural circadian rhythm, disrupting the body’s hunger signals and how it uses calories and stores fat. However, this link was only displayed 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, further research will be needed to better understand whether these changes are only temporary and what long-term effect nighttime eating can have on these weights. winning mechanisms.
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 examining the relationship between disruption of meal times on energy balance (such as skipping breakfast, eating late at night and shift work) found that these eating habits were linked to higher 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 how important mealtimes can be when it comes to body weight.
Based on what this study and others have shown, people watching their weight may want to ditch late-night snacking and prefer to eat most of their meals earlier in the day.