Of all the fun activities you could spend your time doing, dieting probably doesn’t rank very high.

Dieting involves keeping track of calories, substituting some of your favorite snacks for healthier alternatives, and feeling periodically hungry.  Far from fun – dieting usually feels like hard work.

Then, after weeks and months of keeping your diet, you finally start to see the changes in weight you’ve been working for.  Then a week later, there’s a special event. Maybe it’s someone’s birthday.  Maybe you had a vacation planned. You’ve already lost some weight, and you’re on your way to meeting your goal, so you think, “I can cheat this weekend, just this once. I can just go out and have fun for a couple days and get right back on my diet.”

When Monday comes, you weigh yourself on the scale – just once a week, because you already know that you shouldn’t weigh yourself every day – and you see something that stops you in your tracks: you’ve gained 5 pounds.

The 5 pounds you worked 2 months to get rid of. All your hard work has been erased.

Or has it?

Good news: you almost certainly didn’t gain 5 real pounds, and it’s definitely not 5 pounds of fat.  More than likely, the 5 scary pounds that you see displayed to you by your scale Monday morning is nothing more than 5 pounds of water weight.

How can you tell?

Gaining Fat is "Hard Work"

First of all, let’s get one thing cleared up right now: you can’t gain a pound of fat in a day. Biologically, it would be astounding if you did.  You are probably already very aware of how difficult it is to lose fat, but would you believe that it’s also “difficult” to gain it?

Fat gain and loss has a lot to do with your energy/caloric balance – how many calories you take in vs. how many calories you use during the day.  If you are using more energy than you take in, your body gets some of the energy it needs from your fat stores.  If you’re taking in more energy – overeating beyond your body’s needs – then the opposite happens: you build fat stores.

A commonly held formula in the health and fitness world is that there are 3,500 calories stored in a pound of fat. The theory goes that if you reduce your daily caloric intake by 500 every day of the week, in 7 days you’ll lose a pound of fat.  Conversely, if you overeat by 500 calories a day, you can gain a pound of fat in a week.

Although researchers are still debating how reliable the 3,500 Cal = 1 lb of fat rule is, the point is: you have to actually “work” at gaining AND losing fat. And in both cases, it takes time.

Now, is the “work” you have to do to gain fat easier than the “work” you do to lose it? Of course!  Adding on an extra 500 calories is extremely easy: a large blended coffee-flavored drink will do it right away, for example. So will a 32 oz cup (the kind you get standard at fast food restaurants) of orange soda.

So in order to gain a pound of fat, you would need to add about 500 calories a day on top of your normal diet, every day, for about 7 days.  This makes gaining any amount of fat over a short period such as cheat day extremely difficult and unlikely.  To gain 7 pounds of fat in a day, you’d have to eat about 24,500 calories on top of what you usually eat in a day.  That’s about the entire daily caloric intake of 8 – 10 adult men.

Water Weight


So if that 7 pounds of weight isn’t fat, then what is it? And how long is it going to stick around?  The answer involves your body’s favorite energy source: a molecule called glycogen.

Glycogen is an energy source that is produced primarily from carbohydrates.  Your body loves glycogen because it’s an easily accessible energy source that provides a lot of energy.

Glycogen also has an interesting attribute: it bonds really well with water.  In fact, for every gram of carbohydrate in your body, there are about 3 to 4 molecules of water bonded to it. This can cause some large increases in weight, but weight due to water, not fat. Depending on what kind of diet you were on, loading up on carbs on a cheat day can increase your weight noticeably.

If you were dieting to lose fat, you likely were trying to cut carbohydrates out of your diet.  It’s a very popular dieting technique, and diets structured around low carbohydrate and low caloric intake are about as basic a diet as they come.  The Mayo Clinic notes that a diet targeting low carbohydrate intake constitutes about 60-130 grams of carbs a day.  Some popular diets – such as the Atkins Diet – target extremely low levels of carbohydrates, as low as 18 grams a day.

If you’re taking in 60 grams of carbs a day on your diet, you’re holding onto approximately 210 grams of water. That’s about half a pound of water.

But if on a cheat day, you decide to eat and drink whatever you want and load up to 300 grams of carbohydrates (the average number of carbs eaten by men, according to the US Department of Agriculture), you would be retaining around 1kg of water, or 2.2 pounds.  If you were on a 60 carbs/day diet, you could be a pound and a half heavier already.  If you went up to 400 grams of carbs, you could add on 2 ½ pounds of water.

However, glycogen is far from the only substance or factor that can cause your body to retain extra water.  Excess sodium (salt), something found in a lot of cheat day foods, can also cause your body to hold onto water on top of the water held onto by your glycogen.  Once you factor in the effects of other things you ate and drank, your hormones, and your unique body composition, you can see why your weight can fluctuate so much.

It’s a marathon, not a 100-yard dash

A cheat day every once in a while will not erase weeks and months of hard work.  You can’t gain huge amounts of fat over a day or two.

Changing your body composition and losing weight is a long-term process, but if you do it right, you’ll have results that last.  Quick fixes and crash diets that focus on cutting out nearly all carbohydrates for a short period don’t actually achieve lasting results, and now that you understand a little about glycogen, you also understand why.

However, this doesn’t mean you can get carried away on cheat days.  Extra calories add up over time, a lot faster than you think.

If your cheat day becomes a cheat weekend, and your cheat weekend starts including Fridays too, then before you know it you’re only on your diet just 57% of the time.

Bottom line: it’s OK to give yourself a break. Just make sure after you’ve had your fun, you get back on your fitness journey and keep working towards your goals.

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