Does A Cheat Day Boost Metabolism?

Ah, the cheat day, the fabled “get out of jail free” card for nailing your grueling diet for six days out of the week. The weekend rolls around, and you might feel like you’ve earned the right to pig out. And, lo and behold, multiple studies [1, 2] have shown that periods of overfeeding will, in fact, raise your metabolic rate.

Did I just address this whole topic in a single paragraph? Are you now free to (cliché alert) literally have your cake and eat it too?

Well, like most things related to nutrition, it’s not quite that simple. Strictly speaking, cheat days do boost your metabolism, but they don’t come without a hefty cost.

What is a Cheat Day (Or Meal)?

A casual scroll through many popular fitness-related social media accounts will give you the answer here: a cheat day is typically a single day of the week where you break from your traditional “clean” foods and indulge in all the things that you’ve consciously been staying away from in order to meet your calorie/macro goals, usually accompanied by several photos of the food you’re about to gorge on and hashtags about how it’s okay to #LiveALittle.

A cheat meal is the same premise, just reduced in scale from an entire day of gluttony down to a single meal. Some people take this a step further and still stick to their “clean” foods, just eating them in much larger amounts. These are also commonly known as “refeeds” or “diet breaks”, probably to take away the negative stigma around the word cheat.

Regardless of the scale or the food choices, we can concretely define this as willingly overfeeding on calories for a short period of time. At the risk of opening Pandora’s Box, we have to ask: why would we need a cheat day in the first place?

We can address this question in two ways: psychologically and physiologically.

The Psychology of Cheating

The primary component boils down to willpower. No, this doesn’t mean you have to inundate yourself with motivational YouTube videos and podcasts in the name of sticking to your diet for longer. But it’s no secret that we start to feel emotionally and mentally fatigued by consciously restricting our diets over time.

As Menno lays out in his book, The Science of Self-Control, our brains can essentially be divided into two systems: the intuitive, subconscious System 1, and the rational, conscious System 2. These systems, as defined by Nobel-prize winning psychologist Daniel Kahneman, operate in tandem. 

System 1 processes massive amounts of information without any conscious effort and relies on associative reasoning to take “shortcuts,” which can be roughly described as following your emotion or intuition. System 2 operates much more slowly and requires more effort; this system represents logical and rational decision making.

System 1, acting instinctively, will constantly drive you towards pleasure and work to avoid pain. Your brain will predict the present and future enjoyment of something, and will either drive you towards it or away from it. Since food is something that humans derive pleasure and enjoyment from, System 1 will almost always drive you towards it to some degree.

That’s where System 2 comes in; your rational brain might stop and think “well, I’m trying to lose fat, so I’d better not eat that, even though I really want to.” This friction between the two systems is known as cognitive dissonance, which is inherently unpleasant. System 1 is driving you towards something, but System 2 is spending time and effort reigning you in, essentially saving you from yourself, and making you subjectively feel worse in the process. 

This is what we call self-control, meaning the act of self-control is inherently unpleasant to us as well. Your brain registers this decrease in wellbeing, and you gradually begin feeling mental fatigue or boredom. Over time, System 2 essentially shuts down as you become bored of the task you have to do (i.e. control what you eat) and System 1 takes over, pushing you towards things you want to do (i.e. eat a tub of Ben and Jerry’s) that deliver instant gratification and improve your wellbeing.

Put another way, this constant grappling between these two systems while you’re sticking to your diet creates boredom with this specific task (dieting), and given enough time, System 1 will always win and drive you towards something that delivers more immediate gratification.

We can also manufacture motivation to do these certain have-to tasks by giving ourselves a reward at the end of the process. Taking these two phenomena in tandem, you can easily see why some people resort to a cheat day. Their diet is so unnecessarily restrictive and extreme (which is an entirely separate issue) that they need to dangle a carrot in front of them just to get through it. This perceived reward creates enough motivation and self-control during the other six days of the week to keep System 1 at bay, allowing them to stick to their diet.

You should be able to see now that a cheat day/meal is essentially a psychological bandaid on a poorly constructed diet. You set up your diet in a way that’s so taxing, you essentially need a built-in coping mechanism to get through the week. A successful fat-loss diet can minimize this willpower depletion, namely by properly managing your hunger levels, negating the “need” (or, more accurately, the desire) for a period of relief.

How to create that proper diet is explored at length in Menno’s PT Course, but for our purposes here, from a psychological perspective, there’s actually no need for a cheat day in the first place.

What About Physiologically?

Advocates of a cheat day/meal approach might read all of that and try to handwave it away, citing evidence to support that the practice can actually increase your metabolic rate. They may think, “well, if a psychological reward helps me stick to my intense diet and it can boost my metabolism, what have I got to lose?”

As mentioned earlier, it is true that overfeeding can temporarily increase your metabolism. In the studies referenced in the intro, periods of three to four days of consuming more calories than normal resulted in increases of 7-8% Total Daily Energy Expenditure (TDEE), respectively. 

However, you have to take into account the amount of excess calories it took to create that temporary boost in the first place. In the Dirlewanger study, it was a 40% energy surplus over three days; in the McDevitt study, it was a 50% surplus over four days. Once you subtract out the modest increase in caloric burn, you’re still looking at net energy surpluses of over 30% and 40%, respectively. That excess energy doesn’t just disappear because it raises your metabolism, it’s stored in your body just the same as all other energy is.

Additionally, it’s not like that boost to your metabolism hangs around after you stop overfeeding. Any temporary increase can largely be explained by an increase in the thermic effect of food (all forms of energy intake require some level of energy expenditure for your body to process) and a temporary boost to the hormone leptin. 

Leptin is a hormone secreted by fat cells which regulates your energy balance and appetite. This hormone tries to keep your body at homeostasis. More fat cells = more leptin = higher energy expenditure and less appetite. As you diet and lose fat, you secrete less leptin, which lowers your energy expenditure and increases your hunger. This is an expected adaptation to dieting, and you can’t simply “trick” your body and brain into thinking you’re nourished from a single meal/day/few days of overfeeding.

The studies referenced above tracked modest increases in leptin during the overfeeding period of roughly 28%. Just like the increase in thermic effect of food would disappear as soon as you stopped overfeeding, so would any increase in leptin provided you went right back to dieting. Leptin levels respond to energy balance in a matter of hours, and since it’s secreted by fat cells, levels are much more closely tied to the amount of fat in your body than any transient changes in intake. 

It’s no surprise, then, that when you equate total calorie intake, study after study comparing continual dieting vs diets with planned cheat days/diet breaks fail to find any additional benefit to body composition or metabolism by introducing periods of overfeeding [1, 2, 3].

We have to remember to keep the main thing, the main thing. Total energy balance over time is always going to be the primary consideration when dieting, and our metabolisms aren’t going to fall for a little sleight of hand, no matter how much you want to justify deviating from your diet.

The Verdict on Cheat Days

When you really think about it, cheat days likely came into vogue as a way to help people explain away the binge eating episodes that came about as a result of their needlessly restrictive diet. Strictly speaking, having a cheat day boosts your metabolism, but at the cost of essentially undoing days worth of dieting by storing so much excess energy. Any benefit to metabolism or hormone levels would be so short lived that they wouldn’t even move the needle. Not to mention the amount of damage you can do if you really overindulge, which could lay the foundation for harmful eating patterns (i.e. binge eating) down the road.

The absolute best-case scenario for a cheat day, then, is putting your fat loss efforts on pause for a short time while you work off the temporary excess.

But just because cheat days/meals/refeeds aren’t a sound practice doesn’t mean there aren’t intelligent ways to cycle calories throughout the week. A properly constructed diet can aid hypertrophy and increase compliance, all while leading to fat loss. To learn more about dieting principles that actually work, check out Menno’s PT Course, which includes all the information provided here and so much more.