So what is a “calorie,” anyway? What are they for? Why do we eat them? And why are too many of them bad for you?
The first important thing to understand is that a calorie simply is a unit of measurement; it’s no more a “thing” than an inch or an ounce is. A calorie is a unit of energy: specifically, it’s the amount of energy you’d need to spend to raise 1 kilogram of water’s temperature by one metric degree.*
And your body needs energy to do... well, anything at all! Things like walking, talking, breathing, pumping blood... every kind of movement requires energy. If you didn’t take in a certain number of calories worth of energy every day, you’d die.
However, the human body has a survival mechanism to prevent that from happening: the body itself functions like a rechargeable battery, where any extra energy that doesn’t get used gets socked away for leaner times... usually in the form of body fat.
This is why the balance of diet and exercise is so important to general health. If you’re constantly taking in more energy (food calories) than you’re spending (movement and exercise), your body is going to store them up as fat. If you want to lose the fat, you have to “drain the battery” by using more calories than you’re taking in, and that’s most often done by decreasing the amount of energy your body is taking in while also increasing the amount of movement and exercise. Sticking to exclusively one or the other is usually not a good recipe for weight loss or fitness.
So how does that energy storage translate into weight? Well, according to the Mayo Clinic, a good rule of thumb is that you’d need to burn an extra 3500 calories of energy to lose one pound of fat from the body. Obviously, like most rules of thumbs, this isn’t consistent; the less you weigh, the less you’ll lose, and the smaller percentage of that weight loss will be from fat rather than from muscle. But 3500 is a good round number, especially since it divides into 7: that’s 500 fewer calories a day to lose one pound per week (anything more than two pounds a week is not only unsafe, but would kick your body into starvation mode, where the battery effect goes into overdrive and would ironically thwart all of your efforts). You can use a calorie calculator to find out how much energy you need to take in per day for your body’s size and activity level. Subtract 500, and that’s what you should cap your daily calories at to lose one pound every week... and that’s if you stayed at your current activity level, which you probably wouldn’t, because you’ll need to be exercising also to keep your muscles strong and insure that the weight loss comes mostly from your fat battery and not your muscle mass.
That sounds really easy. The problem is that calories come into our body via food, and food can be really complicated. Putting aside how certain foods hit the pleasure centers of our brains—and can be comforting, enjoyable, and even addictive—our bodies have a really poor mechanism for telling us how much food we need: weight. If the food in our bodies doesn’t weigh enough, we get hungry. When it does, we feel full. It’s not even volume, because we chew everything down to roughly the same density... it’s mass. But we know from our earlier posts that weight is a poor indicator of energy intake, that different foods have different Calorie Densities. Two foods of the same weight could deliver vastly different energy packages. One will make you feel full with a reasonable amount of calories that makes it easy to stay under your cap, and one will make you feel full after blowing it away... or you’ll stick to your calorie gap and feel hungry. That’s why it’s important to know the Calorie Density of foods.
Next, we’ll talk about some handy Calorie Density numbers to keep in mind, and how we’d like to see those numbers shown on nutritional labels.
*The word "calorie," with a lowercase "c", is often used by scientist as a much smaller unit of measurement than a “Calorie” with a capital “C”; there are 1000 calories in a Calorie. But like most regular folks, we’ll still use the lowercase word to mean the same thing as a dietary Calorie.
