Jerry Seinfeld used to have a joke about his two warring halves: “Night Guy” and “Morning Guy.” “Night Guy” wants to stay up late, and “Morning Guy” really wishes he'd gone to bed earlier. Some of us share a similar dualism in our eating habits. While our morning selves are usually able to find contentment with light, nutritious meals, our nighttime personas just can't get enough potato chips and pints of ice cream.
An April 2013 study in the journal Obesity offers an explanation for our dueling selves. A group of researchers from Oregon Health & Science University, Harvard University and Brigham and Women's Hospital concluded that, thanks to our circadian system – aka our internal body clock – we’re hungriest a few hours before bed time and the least hungry when we wake up.
“We've uncovered a rhythm in appetite that we didn't previously know existed,” says the study's senior author Steven Shea, Ph.D., director of the Center for Research on Occupational and Environmental Toxicology at Oregon Health & Science University.
The researchers asked a group of adults to spend 13 days in a laboratory on a strict food and activity regimen. The subjects had to rate their appetites throughout the day. Shea and his colleagues found that people felt hungriest around 8 p.m. and the least hungry around 8 a.m. Their desires for sweet, salty and starchy foods, fruits and meat followed a similar pattern.
Shea thinks that the desire to fill up on food before bedtime may have worked well for our ancestors. “I can understand evolutionarily why it became this way – you don't know when food will come the next day so it's like a bank,” he says. A suppressed morning appetite can also help you sleep through the night and wake up able to focus on other tasks besides eating, notes Shea. But given the abundant food and late bed times of the Western world, late night cravings may be a recipe for obesity.
While Carla Wolper, R.D., a nutritionist and professor at the Center for Eating Disorders at Columbia University Medical Center, would like to see this research examined further – Shea's study only looked at 12 individuals – she acknowledges that a lot of people have trouble with nighttime eating.