The science of the cheat day

What really happens to your body when you let your healthy eating slide.

Inquire into many a health-minded person’s diet, whether a trainer, a professional athlete, or even Beyoncé, and you’ll find that many will say that they take a day off from being regimented about what they put into their bodies. What that looks like may differ from person to person, whether it’s allowing themselves a glass of wine at dinner, a big meal on Friday night, or a hall pass come Sunday. But what actually happens to your body when you, so to speak, cheat?

For people getting enough daily calories (versus someone who is restricting), a little cheating shouldn’t really throw you out of whack, in terms of your appetite-regulating hormones. “Since hormones like leptin and ghrelin exist to prevent starvation, nothing significant would happen to someone who is already getting enough calories on a daily basis,” says Ryan Andrews, a coach with Precision Nutrition. “If someone is consuming an appropriate amount of energy for their body each day, and then they eat slightly more, the body will likely adjust, and nothing remarkable will really happen.”

The needle on the scale should likely stay put, too. "The body seems to have a little bit of wiggle room, calorically speaking,” says Andrews. “And if someone eats a bit below their needs or a bit above their needs, the body compensates and keeps things stable to prevent weight gain or loss. If someone eats a bit too much day after day after day, though, then it can lead to weight gain.”

Which makes a case for a regularly scheduled cheat meal instead of a full-fledged cheat day. “I'm a fan of whatever can help someone eat in a way that allows them control their overall intake,” says Andrews. “If this means they look forward to a larger meal on Sunday or a dessert on Friday—great. I would just challenge people to think about the difference between eating a bit more than usual on Saturday night versus an all-out cheat day with forced overeating. It's when one meal becomes a day that things often spiral out of control."

Another potential downside skews more psychological: You might be stripping all of the enjoyment out of eating a healthy, well-balanced diet. If Sunday becomes fun day, Monday through Saturday becomes food purgatory. “Oftentimes when we restrict a food, we increase its desirability,” he says. “So if someone says I can only have potato chips on my cheat day, that might just fuel the idea of overeating the potato chips because they know they can't eat them for another six days. What if instead they had a reasonable amount of potato chips throughout the week? Might that work better?"