It has always been a popular tip for people looking to lose weight to avoid late-night snacking.
No wonder, as a body of research has shown that eating late at night is associated with increased body weight and an increased risk of obesity.
But so far, there are few studies that have specifically investigated why eating late at night is associated with increased body weight.
This is what a recent American (American) study set out to reveal. They found that eating four hours later than normal actually altered many of the physiological and molecular mechanisms that favor 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.
To conduct their study, the researchers had 16 participants follow two different meal schedules, for six days in total.
The first protocol had participants eat their meals early in the day with the last meal about six hours and 40 minutes before bedtime.
The second protocol had participants eat all of their daily meals approximately four hours later.
This means that they skip breakfast and instead have lunch, dinner, and dinner. Their last meal was eaten only two and a half hours before bedtime.
The study was conducted in a controlled laboratory, ensuring that participants in each group ate an identical diet, and that all of their meals were spaced evenly by about four hours between them.
To understand how late eating affects the body, researchers specifically looked at three different metrics associated with weight gain:
- appetite effect
- Effect of eating time on energy expenditure (calorie burn), and
- Molecular changes of adipose tissue.
Appetite was measured using two methods. The first technique was to have participants rate their hunger throughout the day.
The second technique was to collect blood samples to check 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 during the third and sixth days of each experiment.
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 as well as the amount of carbon dioxide they produce.
This helps researchers estimate how many calories a person’s body uses throughout a typical day.
To study how late-night eating affects the way the body stores fat at the molecular level, researchers performed a biopsy of fatty tissue taken from the abdomen. Only half of the participants agreed.
The team found that compared to an early eating pattern, eating later not only increased subjective feelings of hunger the next day, but also increased the proportion of “hunger” hormones in the blood – even though participants ate an identical diet in both protocols.
Eating late also caused fewer calories to be burned the next day.
In participants who had adipose tissue biopsy, late eating was also shown to cause molecular changes that promote fat storage.
Taken together, these findings suggest that delayed eating leads to a number of physiological and molecular changes that, over time, can lead to weight gain.
Possibility of gaining weight
Although we don’t fully understand all of the mechanisms behind late-night eating that promotes weight gain, this study shows us that it is probably 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 the brain controls to influence the natural tides of hormones. It is particularly responsive to daylight and food intake.
Eating time is intrinsically linked to the circadian rhythm in humans, since we usually sleep when it’s dark and eat when it’s daylight.
When we eat late, this may challenge the natural circadian rhythm, causing disturbances in the body’s hunger signals and the way it uses calories and stores fat.
However, this association has only been shown in animal studies so far.
Because 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 understand if these changes are only temporary, and what influences late-night eating in the long term. Mechanisms of weight gain.
But we know from other studies that people who tend to eat later in the evening also tend to gain weight more easily.
Other large-scale studies looking at the relationship between disturbances in meal timing on energy balance (such as skipping breakfast, eating late at night and working shifts) have found that these eating patterns are associated with increased 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 meal timing is when it comes to body weight.
Based on what this and other studies have shown, people who monitor their weight may want to eliminate late-night snacks and prefer eating most of their meals earlier in the day. Conversation
About the author:
Alex Johnston is Head of Nutrition at the Rott Institute, University of Aberdeen.