Many people find that the temptation to binge on snack food becomes overpowering at night. The reasons are likely varied and could include, depending on the person, the mindless habit of chomping in front of the TV, the fact that we’ve been exercising our self-control all day and the dam of resistance has finally given way, or hunger pangs that kick in after a night out partying. Recent headlines, however, would have you believe there is a simpler and more powerful explanation: It’s all your brain’s fault.
“Your brain is wired to love late-night snacks” proclaimed the Huffington Post. “Got a bad case of late-night munchies? Blame that snack attack on your brain, say scientists” was the headline in the Tech Times. These publications and many others were referring to a new brain-imaging study conducted by Brigham Young University researchers and published in the respected journal Brain Imaging and Behavior. But the thing is, the study provided no grounds for blaming your brain at all.
First, let’s clear up a few mundane but important details: No one in this study ate anything at midnight. In fact, they had their brains scanned one day in the morning between 6:30 and 8:30 and on another day between 5:30 and 7:30 in the evening, before their final meal of the day. The participants didn’t eat anything in the scanner; they just looked at pictures of either low-calorie food like vegetables or high-calorie food like candy. So this “midnight snacking” study involved neither midnight nor snacking. Plus, the 15 participants were all (non-dieting) women — not a single man’s brain was scanned — which further limits what can be generalized from this study. (None of which stopped Men’s Fitness from running the story with the headline “Why you crave that midnight snack” and a photo of a man peering into fridge.)
The study’s actual finding is that looking at high-energy foods (in the morning or evening) was associated with more activity in reward-related areas of the women’s brains than looking at low-energy foods. No surprise there — we know that for most people, candy and ice cream are more tempting than fruit and vegetables.
But this wasn’t really the purpose of the study. The researchers, led by Travis Masterson, were more interested in how brain activity in response to food might vary by time of day. We already know based on past research that sleep deprivation can increase the brain’s response to pictures of food. Masterson and his collaborators specifically predicted that food would prompt more reward-related brain activity in the evening than in the morning. And, given that the “[neural] reward response may index how motivated a person is to seek food,” they reasoned that such a finding might help explain why people are especially prone to snacking in the evening.
To their surprise, the researchers actually found that pictures of high and low-energy food provoked less activity in the women’s brains in the evening than in the morning — the complete opposite of what they expected. Following their logic of neural reward response being an indicator of desire for food, this finding would suggest the women were less tempted by food in the evening. A suitable headline might be: “Enjoy nighttime snacks? Don’t blame your brain.”
But having uncovered this null result, the researchers performed a switch. Perhaps, they surmised, the failure of food to trigger as much reward-activity in the brain in the evening somehow translates into greater motivation to eat, as a way to compensate. They (or whoever runs publicity for their department at BYU) also pushed this line in a press release, encouraging the misplaced media headlines. By twisting their own logic, these neuroscientists wanted to — sorry — have their cake and eat it too.
Unsurprisingly, all this jumbled reasoning led to some confused and contradictory reporting. “Certain areas of your brain are more receptive to food at night,” said the New York Daily News, directly contradicting the idea that “… some areas of the brain don’t get the same ‘food high’ in the evening,” as reported at Neurosciencenews.com.
So what’s a more reasonable explanation for why the women’s brains show less activity in response to food in the evening? One can only speculate, but perhaps this was simply a general effect of tiredness, and brain activity would be reduced to all different kinds of pictures. Alternatively, maybe in the evening, the women were more in the mood for alcohol than food. It wasn’t that late, after all, so they might not be that hungry. On the other hand, complying with the research protocols, they’d not had alcohol or caffeine for 24 hours.
Even if the researchers had found the result they’d hoped for, it’s debatable whether the brain is the right place to look for why we snack at night. Certainly blaming any behavior purely on the brain is overly reductionistic. Some neuroskeptics refer to such logic as the “mereological fallacy”: because of course, in this case, it is your whole person, including your body and brain, which snacks, and the reasons are likely to be manifold, including hormonal influences, circadian rhythms, cultural customs, insomnia, and plain old bad habits.
Speaking of which, it’s getting late and I’m off for a nibble.
Dr. Christian Jarrett is editor of the British Psychological Society’s Research Digest blog. His latest book is Great Myths of the Brain.
