"We know from our sleep loss studies that when you're sleep deprived, it negatively affects weight and metabolism in part due to late-night eating, but now these early findings, which control for sleep, give a more comprehensive picture of the benefits of eating earlier in the day," said lead author and research associate professor of psychology Namni Goel.
How they conducted the research
The researchers set out to study the metabolic consequences of consistent delayed eating compared to daytime eating.
They instructed nine adults of healthy weights to spend eight weeks eating only during the daytime, which involved consuming three meals and two snacks between 8am and 7pm.
Then the group followed a delayed eating routine - having three meals and two snacks from noon to 11pm - for eight weeks.
There was a two-week break in between to make sure there was no carry-over effect.
Their sleep patterns were kept consistent - between 11pm and 9am - in both phases to eliminate any effect from lack of sleep, which is linked to obesity.
At key points across the study, the researchers measured changes in weight, metabolism and energy used. They also made sure that all measures returned to baseline in the two week break, before the next phase was begun.
Key findings
The research discovered that when participants ate later, compared to when they ate during the daytime, their weight increased.
They found late-night meals caused people to gain weight by reducing their body's fat metabolism - the process by which fats are broken down and used for energy.
Tests revealed that eating later led the participants to metabolise fewer lipids or fats.
It was also found that delayed eating led them to store carbohydrates - which can lead to weight gain and raised blood sugar and insulin levels.
And indeed insulin and fasting glucose were found to be higher when people ate later, and their cholesterol and triglyceride levels rose too.
Eating earlier in the day was found to produce hormone changes that help you feel full longer and therefore not overeat.
For daytime eaters, the hormone ghrelin, which stimulates appetite, peaked earlier in the daytime.
Meanwhile, leptin, which keeps you satiated, peaked later, suggesting that the participants received cues to eat earlier, and eating earlier most likely helped them to feel full longer.
This suggests that eating earlier may help prevent overeating in the evening and at night, say the researchers.
What the experts say
Previous studies have suggested similar results, but this is the first long-term study - albeit a small one - that has analysed the health effects of the timing of eating patterns that also controlled for sleep-wake cycles, exercise and macronutrient intake.
Professor Kelly Allison, senior author on the study, said: "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."
