Eating late at night may lead to greater weight gain: new research suggests why

It’s long been popular advice for people trying to lose weight to avoid late-night snacking. No wonder, as numerous studies show that late night eating is associated with higher body weight and an increased risk of obesity.

But until now, few studies have examined exactly why late night eating is associated with higher body weight. That’s what a recent US study found. They found that eating four hours later than normal actually altered many of the physiological and molecular mechanisms that promote weight gain.

This work complements other recently published work which 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 total of six days.

In the first protocol, participants ate their meals early in the day, with the last meal being consumed approximately six hours and 40 minutes before bedtime. In the second protocol, participants ate all of their daily meals approximately four hours later. That meant they skipped breakfast and instead ate lunch, dinner, and supper. Her last meal was eaten just two and a half hours before she went to sleep.

The study was conducted in a controlled laboratory that ensured that the participants in each group ate an identical diet and that all of their meals were evenly spaced about four hours apart.

Specifically, to understand how late eating affects the body, the researchers looked at three different measures associated with weight gain:

1. The influence of appetite
2. The effect of meal time on energy expenditure (calories burned) and
3. Molecular changes caused by adipose tissue.

Appetite was measured using two techniques. The first technique was to have participants rate their feelings of hunger throughout the day. The second technique was to collect blood samples to study the levels of appetite-regulating hormones in the participants’ blood — like leptin (which helps us feel full) and ghrelin (which makes us feel hungry). These hormones were assessed hourly for a 24-hour period on the third and sixth day 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 on a typical day.

To study how nighttime eating affects the way the body stores fat at a molecular level, the researchers performed a biopsy on adipose tissue taken from the abdomen. Only half of the participants agreed.

The team found that eating late compared to eating early not only increased subjective feelings of hunger the next day, but also increased the ratio of “hunger” hormones in the blood — even though participants in both protocols ate an identical diet. Eating late also resulted in a drop in calories burned the next day. In the participants who performed the adipose tissue biopsy, it was also shown that eating late causes molecular changes that promote fat storage.

Taken together, these results indicate that late eating leads to a number of physiological and molecular changes that can lead to weight gain over time.

potential for weight gain

While we don’t understand all of the mechanisms underlying why late-night eating promotes weight gain, this study shows us that it’s likely the result of many factors working together.

One theory for why eating late leads to weight gain could be due to our circadian rhythm. The human body has a natural circadian rhythm that is controlled by the brain to affect the normal ebb and flow of hormones. It is particularly responsive to daylight and food intake.

Mealtime is inextricably linked to human circadian rhythms, as we typically sleep when it’s dark and eat when it’s light. Eating late can challenge the body’s natural circadian rhythm, leading to disruptions in the body’s hunger signals and the way it uses calories and stores fat. However, this connection has so far only been demonstrated in animal studies.

Because the new study was conducted on a limited number of participants and over a very short period of time, more research is needed to further understand if these changes are temporary and what impact long-term nighttime eating may have on weight gain mechanisms. However, we know from other studies that people who tend to eat late in the evening also gain weight more easily.

Other large studies examining the association between disruptions in meal timing and energy balance (eg, skipping breakfast, eating late at night, and shift work) have found that these eating patterns are associated with higher body weight and a greater 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 can be for body weight. Based on what these and other studies have shown, people who watch their weight may want to skip the late-night snacks and prefer to eat most of their meals earlier in the day.

This article was republished by The Conversation under a Creative Commons license. Read the original article.