A new study that takes a closer look at how skipping breakfast or have a late-night snack may contribute to obesity has found that eating later on in the day can make it difficult to resist eating too much, while also making it harder to burn off all the calories you consume.
Although eating snacks after already having dinner has long since been associated with an increased risk of obesity, there isn’t enough information yet about why eating food close to bedtime causes people to gain weight.
During this new study, scientists performed a lab experiment to see how changing “when” people ate, but not “what” they ate, could have an impact on three factors which can play a massive role in weight gain and the risk of obesity. These three factors are ‘food cravings and appetite, the ability to burn calories, and the molecular composition of fat tissue.’
Senior author and director of the Medical Chronobiology Program in the Brigham and Women’s Hospital Division of Sleep and Circadian Disorders in Boston, Frank Scheer, PhD, said, “We wanted to test the mechanisms that may explain why late eating increases obesity risk.”
Scheer also says, “Previous research by us and others had shown that late eating is associated with increased obesity risk, increased body fat, and impaired weight loss success. We wanted to understand why.”
In the study, there were 16 overweight and obese adults that participated in two experiments that required them to live in a lab for a number of days. During one stint in the lab, they were made to eat three meals a day, first was around 9 a.m., the second at 1 p.m., and the last 4:30 p.m. Then during their next lab stay, they consumed exactly the same meals on a later schedule of 1 p.m. with the last meal at 8:30 p.m.
In addition, the scientists also asked the participants to follow a strict sleeping schedule while eating identical diets on the same schedule for three weeks before every lab stay. When the participants were in the lab, they ate the same foods, while documenting their hunger cravings, providing regular blood samples, and doing body-temperature and energy-expenditure assessments. The research team also collected samples of what they refer to as adipose tissue, which is the dangerous fat that tends to accumulate around a person’s midsection, from several of the participants to see how the different eating schedules impacted the gene expression in this tissue.
According to the results of the study, which were published in Cell Metabolism journal, for the later eating schedule, it doubled the odds of being hungry while causing people to crave more food overall.
The study also found that for those that ate later, it also more than doubled the cravings for starchy foods and meat in particular, and increased one’s salt carvings by a large 80 percent. When people ate later, they also had substantially lower levels of the leptin hormone, which is what signals satiety. Moreover, people on the later eating schedule burned 5 percent fewer calories during the day than when they followed the earlier scheduled eating time.
During the analysis of the adipose tissue samples from the participants, they found that the genes expressed also promote fat growth when people ate later in the day.
Although the study was a controlled experiment that was created to help figure out whether eating later may directly contribute to weight gain, there were still limitations to the study. One of the biggest ones was that the study was considered small in size, while also being a relatively shorter period of time for the researchers to follow the participants.
Another limitation is that people that were given unlimited access to food in the lab, like what they could have in their real lives, making it almost impossible to know how much the timing of the meals could directly impact the total amount of calories people may be consuming.
In order to help make the study more precise and to see the impact of meal timing on food cravings, scientists had tightly controlled lab conditions that regulated amounts of sleep, light exposure, calories, and physical activity. However, these conditions aren’t necessarily the same as what happens when these participants leave the lab.
“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,” Scheer says.
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