This post is for a friend of mine who is currently struggling with her weight. She called me in a bit of a panic because, after being pretty good on her diet for a while, she went out and splurged and overate. She was discouraged enough to feel like quitting her diet and exercise all together. I want to point out that the math of calories means that one day doesn’t make a whole lot of difference, but it’s the slow steady grind that can bring either health or obesity.

For instance, we’ll start with the scenario my friend was in. Weeks of good habits, and then, maybe you overdo things one day. But, think about it. One pound, either to gain or to lose, takes 3500 calories – and that’s over and above what your body requires just for daily living. So to gain a single pound in one day, you’d have to eat your daily needs (around 2000 calories) plus another 3500 calories. You’d have to eat all day long (or boxes and boxes of donuts) to gain a single pound in a day. If, after making bad choices one day, you just go back to your diet, first you shouldn’t feel guilty, and second, you’re going to be OK. A dozen Krispy Kreme donuts, just the basic glazed ones, are 2400 calories. Even if you ate your daily needs and a whole box of Krispy Kreme donuts, you still wouldn’t gain a pound. You may feel like you’re several pounds heavier, but that’s temporary; the permanent weight gain would be less than a pound.

But on the other hand, just going a little over every single day is how people become overweight. Just an extra 200 calories, which is about a single Hershey’s chocolate bar or a 12 oz. can of Pepsi, every day, over time, adds up to 104 pounds of excess weight in just 5 years. Think about how easy it is to go over 200 calories a day. That’s why the slow grind of overeating is so dangerous, and why it’s so important to manage your calories daily.

My third scenario is one I call “eat your cake and have it, too”, the one my friend might find herself in as she attempts to manage her health and her weight. Eat at, or under your daily needs (maybe giving yourself some wiggle room by being more active and therefore burning more calories) but, once in a while, splurge and have an ice cream cone or a giant chocolate chip cookie. Assuming you’re eating no more than what your body requires, but every week you have a “treat” of 500 calories, in 5 years you will have only gained 37 pounds in 5 years. Which is troublesome, but nowhere near the 100+ pounds you would have gained if you had gone over every day, as my second scenario above, and could be easily countered by simple eating 100 calories under every other “non-treat” day – in fact, in that situation, you would be losing weight, at 100 calories per week, or about a pound and a half a year.

So, take heart. Occasional days of splurging are OK, as long as you try to be good the rest of the time. And since maintaining weight, once you strip out all of the emotions attached to the food (difficult but not impossible for most of us), is just a matter of numbers, once you understand the numbers you have all the tools you need to take control.