Eating late at night raises your risk of obesity by slowing your metabolism and making you hungry the following day, a study suggests.
Doctors have been warning against midnight snacking for years because you don’t have chance to burn it off before you go to sleep.
Now Harvard University researchers have shown that it also has a knock-on effect on the body the next day.
People who had their last meal at 10pm burned fewer calories the following day and had higher levels of hunger hormones compared to those who ate at 6pm.
They also had lower levels of chemicals in the body that make us feel full and satisfied after meals, and were more likely to put on weight.
Lead author of the study Dr Nina Vujović, a trainee in circadian rhythms in health and disease, said: ‘In this study, we asked, “Does the time that we eat matter when everything else is kept consistent?”
‘And we found that eating four hours later makes a significant difference for our hunger levels, the way we burn calories after we eat, and the way we store fat.’
Avoiding a midnight snack and early breakfast may be the key to staying slim, another study indicates
The researchers looked at 16 overweight or obese patients aged between 20 and 60.
Each participant followed two schedules in a lab: one where they ate their meals early, with dinner at 6pm, and the other with identical meals but scheduled four hours later in the day, with dinner at 10pm.
For two to three weeks before starting each schedule in the lab, the patients went to bed and woke up at the same time.
OBESITY: WHAT’S THE MEDICAL DEFINITION?
Obesity is defined as an adult having a BMI of 30 or over.
A healthy person’s BMI – calculated by dividing weight in kg by height in meters, and the answer by the height again – is between 18.5 and 24.9.
Among children, obesity is defined as being in the 95th percentile.
Percentiles compare youngsters to others their same age.
For example, if a three-month-old is in the 40th percentile for weight, that means that 40 per cent of three-month-olds weigh the same or less than that baby.
Around two in five men and women in the US are obese.
The condition costs the US healthcare system around $173billion a year.
This is due to obesity increasing a person’s risk of a number of life-threatening conditions.
Such conditions include type 2 diabetes, which can cause kidney disease, blindness and even limb amputations.
Obesity also raises the risk of heart disease, which kills 647,000 people every year in the US – making it the number one cause of death.
Carrying dangerous amounts of weight has also been linked to 12 different cancers.
This includes breast, which affects one in eight women at some point in their lives.
Among children, research suggests that 70 per cent of obese youngsters have high blood pressure or raised cholesterol, which puts them at risk of heart disease.
Obese children are also significantly more likely to become obese adults.
And if children are overweight, their obesity in adulthood is often more severe.
As many as one in five children start school in the US being overweight or obese.
In the final three days, they all ate the same meals at the same times at home.
During the schedules, participants frequently recorded their hunger and appetite, gave blood samples throughout the day and had their body temperature and energy expenditure measured.
In the lab, the researchers strictly controlled environmental factors that may influence someone’s appetite or energy expenditure, including exercise, posture, sleep and exposure to light.
The researchers also took tissue samples from some patients during both schedules to compare their fat stores.
They found that eating later in the day increased levels of the hormone grehlin the following day, which makes us crave food, especially sugary or salty snacks.
Levels of leptin, which makes us feel full and satisfied, were lower.
When the patients ate later, they also burned calories more slowly and had tissue samples showing more fat growth.
In future, the research team wants to study more women, as only five of the 16 participants were female.
Senior study author Dr Frank Scheer, an expert in sleep and circadian disorders, said: ‘This study shows the impact of late versus early eating.
‘Here, we isolated these effects by controlling for confounding variables like caloric intake, physical activity, sleep, and light exposure, but in real life, many of these factors may themselves be influenced by meal timing.
‘In larger scale studies, where tight control of all these factors is not feasible, we must at least consider how other behavioral and environmental variables alter these biological pathways underlying obesity risk.’
The findings were published in the journal Cell Metabolism.
Previous research has found eating late at night increases blood sugar levels – raising the risk of type 2 diabetes, the form linked to obesity.
Levels of melatonin, the hormone central to sleeping, are high around bedtime, and eating disturbs blood sugar control.
A 2021 US survey by the International Food Information Council Survey revealed that roughly 60 per cent of adults aged 18 to 80 admit they are snacking after 8pm.
One poll in 2019 by ice cream brand Nightfood found that 83 per cent of Americans said they snack at least one night a week, and 20 per cent said they snack every night.
The Centers for Disease Prevention and Control recommends four to five smaller meals—breakfast, lunch, dinner, and one or two snacks throughout the day.
The average time people eat dinner in the US is 6.22pm, but it varies between 4.30pm and 10.59pm.