Is the fridge your first port of call when you arrive home from work? You deserve a delicious snack after a busy day at the office, right? Snacking does not bode well for our waistlines, though. But according to a new study, you can blame those "hunger hormones."
Researchers have found that in the evening, we experience alterations in the levels of hormones that influence appetite, which may cause us to overeat.
Unsurprisingly, stress and a predisposition to binge eat were also found to increase hunger levels in the evening. But there may be answer to this problem: eat earlier in the day.
The research included 32 adults, aged 18–50 years, who were overweight.
Each subject was asked to participate in two experiments. The first required the subjects to fast for 8 hours before receiving a "liquid meal," consisting of 608 calories, at 9 a.m.
For the second experiment, participants were again asked to fast for 8 hours, but this time, they consumed the liquid meal at 4 p.m.
Testing how time of day affects appetite
Around 130 minutes after each meal, the participants all underwent a stress test. This required the subjects to place one hand in a bucket of cold water for 2 minutes, while their facial expressions were recorded.
Participants were offered a food and drink buffet, which consisted of pizza, cookies, chips, candy, and water, 30 minutes after the stress test began.
The researchers also took blood samples from the subjects, and these were monitored for levels of the "stress hormone" cortisol, as well as the "hunger hormones" ghrelin and peptide YY (PYY).
Subjects were also asked to report their levels of hunger and fullness prior to each experiment.
The overall aim of this research was to determine how the time of day affects appetite, and whether stress might play a role.
"Eating late in the day is common, and stress can induce eating," the researchers report. "Little is understood about how time of day and stress interact to affect appetite and thereby body weight. These may be particularly important influences in binge eaters, who tend to binge in the evening, and in response to stress."
Stress increases evening hunger
Overall, prior to each experiment, participants reported greater hunger and lower fullness in the evening than in the morning.
Levels of ghrelin, which is the hormone that stimulates appetite, were found to be higher after consumption of the afternoon meal compared with the morning meal, while levels of PYY, which is a hormone that reduces appetite, were found to be lower in the evening.
Upon comparing adults with binge eating disorder with those without the condition, the team found that only adults with binge eating disorder experienced lower fullness in the evening following the afternoon meal.
Furthermore, subjects with binge eating disorder also had higher ghrelin levels in the evening, but lower ghrelin levels in the morning, compared with those who did not have binge eating disorder.
While buffet food intake was similar in both groups, the researchers note that subjects with binge eating disorder "reported greater loss of control and binge resemblance than those without."
Looking at the stress test results, the team found that — in both the morning and evening — all subjects experienced a gradual increase in cortisol and ghrelin levels, though levels of these hormones were higher in the afternoon.
They say that this finding suggests that stress may have greater influence on ghrelin in the evening than earlier in the day.
Taken together, the researchers believe that their study results indicate that we are more likely to overeat in the evening due to changes in our hunger hormones, and that stress and pre-existing binge eating may exacerbate the risk.
That said, first study author Susan Carnell, Ph.D., of the Department of Psychiatry and Behavioral Sciences at Johns Hopkins, notes that there is something we can do to avoid succumbing to evening temptation.
"The good news is that having this knowledge, people could take steps to reduce their risk of overeating by eating earlier in the day, or finding alternative ways to deal with stress."
Susan Carnell, Ph.D.