It’s more than just your willpower at play.

Why is it that sometimes you can go without eating and wake up in the morning feeling satiated, while other times you graze all day and still find yourself peering into the fridge for food at 9 p.m.?

A recent study published in the International Journal of Obesity found that the nighttime is a high-risk period for overeating, and our hormones may be to blame.

The study examined 32 obese men and women, half of which had the habit of binge eating. Participants were asked to fast for eight hours before a 600-calorie liquid meal. Two hours later, they were subjected to a stressful situation where their non-dominant hand was submerged in freezing water for two minutes.

These tests were completed at 9 a.m. and again at 4 p.m. Afterward, participants were brought to a buffet of pizza, snacks, and sweets. Researchers took blood samples to measure hormone levels and subjects were asked to rate their feelings of hunger and fullness on a scale.

The study suggested three hormones were at play when it comes to hunger: ghrelin, which causes hunger, peptide YY, which is associated with satiety, and cortisol, a hormone linked to stress. All participants were found to be hungrier in the evening, with higher levels of ghrelin and lower levels of peptide YY. Increased amounts of cortisol caused by the stressful situation also increased appetite, specifically in the evening.

Dr. Satchidananda Panda, a professor at the Salk Institute for Biological Studies in San Diego told the New York Times, nighttime hunger “may have been an evolutionary adaptation that helped us get through the night. For millions of years, our nighttime period was a time when we didn’t have access to food, and you also could not just get yourself food as soon as you woke up in the morning.”

Those with binge eating disorders showed lower fullness and higher levels of ghrelin in the evening, and lower levels in the morning. In addition, those with binge eating tendencies reported greater loss of control during the buffet.

Susan Carnell, the first author on the study and an assistant professor of psychiatry and behavioral sciences at Johns Hopkins University School of Medicine told the New York Times, those who struggle with binge eating at night should set a specific time in the evening to stop eating and take extra care to eat properly during the day.

“We definitely know that this pattern of hormone responses increases the risk of overeating in the evening, as opposed to the morning,” Dr. Carnell said. “It implies the people in our study were more vulnerable to overeating in the evening.”

A similar study was published in March 2013 in the journal Obesity which found a person’s peak appetite comes in the evening and is lowest in the morning. Researchers hypothesized this is why evening meals tend to be the largest and many adults skip breakfast.

Our solution? Try these tips for avoiding a fourth meal, and make sure you're eating healthy, balanced meals throughout the day so you're not starving by the time dinner rolls around.