Most dieters know the hard truth: Sticking to a weight loss regimen gets more difficult as the day wears on. But while those who give in to food cravings and binge at night may blame flagging willpower, a new study suggests the problem could lie in the complex orchestra of hormones that drive hunger and signal feelings of satiety, or fullness.
The small study of 32 obese men and women, half of whom had a habit of binge eating, suggests that satiety hormones may be lower during the evening hours, while hunger hormones rise toward nightfall and may be stoked even higher by stressful situations. Overweight binge eaters may be particularly susceptible to the influence of fluctuations in these appetite-regulating hormones, the researchers found.
“There’s more opportunity to eat in the evening, but this study is showing that hormonal responses are setting them up to do this,” said Susan Carnell, an assistant professor of psychiatry and behavioral sciences at Johns Hopkins University School of Medicine who was a first author of the study along with Charlotte Grillot of Florida State University. It’s not clear whether these hormonal patterns precede and cause the binge eating behaviors or are conditioned by an individual’s eating habits, Carnell said. But either way, “you can get stuck in the cycle.”
The study is an important reminder that myriad factors contribute to weight gain, and that shaming and blaming people for their weight problems is inappropriate, said Kelly Costello Allison, director of the Center for Weight and Eating Disorders at the University of Pennsylvania, who was not involved in the new research.
“There is so much bias and judgment about people who are overweight, that it’s their fault or they’re lazy or just don’t have enough willpower,” Allison said. “The bottom line is that people are wired in different ways, and some of that does really depend on these biological markers.”
The new findings were published in the International Journal of Obesity in December. They build on earlier work, including a 2013 Harvard study of normal-weight individuals that found circadian rhythms play a role in regulating appetite, and that hunger peaks in the evening and appetite is, paradoxically, at its lowest in the morning, even though people have not eaten all night.
That research helped explain why so many people skip breakfast, even as evidence mounts that consuming most of one’s calories at the beginning of the day is optimal for weight control and a healthy metabolism.
Evening hunger “may have been an evolutionary adaptation that helped us get through the night,” said Dr. Satchidananda Panda, a professor at the Salk Institute for Biological Studies in San Diego. “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.” In the modern era, with easy access to food at any time of day or night, that evolutionary adaptation may be backfiring, leading to loss of control and nighttime binges.
For the new study, participants were asked to fast for eight hours before consuming a 600-calorie liquid meal.
Then, two hours later, they were subjected to a stress-inducing situation in which they had to submerge their nondominant hand in freezing water for two minutes while they thought they were being filmed (they weren’t). Thirty minutes later, they were offered a buffet of pizza, snacks and sweets.
To gauge the impact that time of day might have on appetite and appetite-regulating hormones, the researchers put the participants through the regimen twice, once starting at 9 a.m. and once starting at 4 p.m. They took blood to measure hormone levels and also asked participants to rate their subjective feelings of hunger and fullness using a numeric scale.
All of the participants reported being hungrier if they started the regimen in the evening compared with the morning. Likewise, they had higher levels of a hormone called ghrelin that makes people hungry and lower levels of a satiety hormone, peptide YY, if they had consumed the liquid meal in the afternoon instead of the morning.
Binge eaters also showed higher initial levels of ghrelin when they started the regimen in the evening, compared to starting in the morning, while those who weren’t binge eaters had the reverse pattern. The binge eaters also reported feeling less sated after the liquid meal and the exposure to the stressor in the evening.
Stress drove up hunger in all of the participants, but the hunger hormone ghrelin rose even higher if participants were subjected to the stressful situation later in the day, suggesting stress may have a more profound effect on hunger in the evening. (There was no group for comparison that had not been subjected to the stressor, however.)
“We definitely know that this pattern of hormone responses increases the risk of overeating in the evening, as opposed to the morning,” Carnell said. “It implies the people in our study were more vulnerable to overeating in the evening.” She suggested that people who know they tend to overeat in the evening and at night make sure to set aside time to eat properly during the day and adopt an “eating curfew,” a set time in the evening when they stop eating for the day.
Allison agreed. “Set a ‘kitchen is closed’ time,” she advised. “Shut off the kitchen light, move away from the kitchen, brush your teeth, and if you want anything after that, have water.”
“At night, in particular, you’re tired, you’ve had cognitive demands to meet during the day, you’re not wanting to regulate yourself as much, and if you have food cravings, there are fewer distractions to help you resist those cravings,” she said.
She and other experts note that hormone levels are responsive to eating patterns and can potentially be reconditioned if people change their eating behaviors. But even if that’s true, “they face a higher hurdle, because they have to change their eating habits first, and wait for their hunger hormones to catch up,” said Courtney Peterson, an assistant professor in the department of nutrition sciences at the University of Alabama at Birmingham.
“It’s not that there’s no hope for helping folks that have these issues,” Allison said. “It just shows there are different starting points for everybody. Some people have more challenges to deal with in terms of how to regulate their food intake because of these biological reasons.”