Though the brain's reward-related responses to food are lower late at night, the researchers believe this may cause us to seek food satisfaction by eating more of it.
Lead author Travis Masterson and colleagues found that at night, the brain's reward-related responses to the look of food are lower, meaning we feel less satisfaction when we eat it.
"You might overconsume at night because food is not as rewarding, at least visually at that time of day," explains Masterson. "It may not be as satisfying to eat at night so you eat more to try to get satisfied."
To reach their findings, which are published in the journal Brain Imaging and Behavior, the team enrolled 15 healthy women to their study.
Using functional magnetic resonance imaging (fMRI), the team monitored the brain activity of each participant as they were shown 360 images of low-calorie foods, such as vegetables, fruits and fish, and high-calorie foods, such as candy, ice cream and fast food.
The participants were shown these images once in the morning (between 6.30 am and 8.30 am) and once in the evening (between 5 pm and 7 pm) over two sessions held 1 week apart.
Findings may have implications for eating behavior, weight management
As expected, the researchers found that participants showed greater reward-related neural activity in response to images of high-calorie foods than in response to images of low-calorie foods.
However, the team was surprised to find that when images of both low- and high-calorie foods were viewed in the evening, the reward-related neural responses were lower than when they were viewed in the morning.
"We thought the responses would be greater at night because we tend to overconsume later in the day," notes study co-author Lance Davidson.
What is more, the researchers found that, despite participants reporting that they were no more hungry in the evening than in the morning, they reported thinking about food more in the evening and felt they could eat more.
The researchers say their results "underscore the role that time of day may have on neural responses to food stimuli," which Davidson says may have implications for eating behavior and weight management.
They caution, however, that their findings are preliminary and further research is required to confirm them.
Still, Masterson says the results have helped him curb the late-night snacking. "I tell myself, this isn't probably as satisfying as it should be," he says. "It helps me avoid snacking too much at night."
In March, Medical News Today reported on a study published in PLOS ONE that found a 15-minute walk may stave off cravings for sugary snacks.