A scientific definition of a calorie exists, but what we really want to know when we ask "What is a calorie?" is ...
A calorie is the amount of heat it takes to raise one gram (= one cc, about 1/10 of a typical syringe) of water one degree celsius.
The calories we count in our food are really kilocalories. Sometimes food calories are written as Calorie, with a capital C, to represent the fact that they are really 1,000 calories.
So, a calorie in your food is enough raise one liter (1,000 grams, or roughly 1 quart) of water by roughly 2o fahrenheit.
Thus, if you eat a candy bar, most of which have 200 calories, you have consumed enough energy to boil a half gallon of ice-cold water! With the energy from a 16-oz. steak, your body could boil 2 and 1/2 gallons of ice-cold water.
Yeah, your body's pretty amazing. Think about it. You're mostly water. For me, my 160 pounds is roughly the equivalent of 20 gallons of water. Can you imagine how much energy it takes to keep 20 gallons of water at almost 100o (in fahrenheit) every day? And we're not as insulated as our water heaters are!
photo by Paul Pavao, released to public domain
Scientists may have to know what is a calorie, but we want to know how calories affect us. So let's try this ...
Think of calories as energy, much like the energy you get from your electric and gas company.
Your body needs energy in much the same way your house does. Your house has to run motors on appliances, provide lighting, and maintain a constant temperature.
We all know that heating and cooling—whether that's our stove, dryer, refrigerator, or our heating/cooling unit—is the worst gas hog in our house.
Your body is the same way. A 170-lb. man uses about 2,500 calories a day just to keep the "house" that is his body running well. That's to maintain his 98.6o body temperature, operate all his involuntary systems (like breathing, pumping blood, digesting, etc.), and get up to eat and go to the bathroom. He can sit around all day and burn that much energy.
Our body's energy is not provided by the utility company like our house's energy is. It's not provided by the sun, like our plant's energy is. Instead, it's provided by our food.
And we can measure how much energy our body gets from different kinds of food. Calories are that measurement!
Once I know what is a calorie—it's basically energy—how do I know how many are in my food?
There are two ways:
The nice part is that, believe it or not, if you do this, you will quickly get a feel for the amount of calories in food.
For example, the first time I dieted, I counted calories religiously. As a result I learned that most round fruits—apples, peaches, nectarines, and even tomatoes(!)—are all 50 to 100 calories each. Rice, other grains, and beans are all around 200 calories per cup (cooked). Mayonnaise, butter, peanut butter, and other very high fat spreads are about 100 calories per tablespoon, as are most oils.
Beef is about 60 calories per ounce, and most pieces of chicken, unless they're deep-fried, are 100 calories or less if you take the skin off.
Some things you'll have to look up. Avacados, for example, one of the only fruits with fat in it, are about 200 calories each.
Nuts and seeds have so many calories that they're simply unbelievable. Never eat more than a handful if you're losing weight, but do eat the handful because they're loaded with minerals and the fat is good fat.
Anyway, use the calorie counter and labels, and you'll quickly get a feel for how many calories are in food.
Beware, though, of counting calories in foods like hamburgers or casseroles. Size and ingredients vary, and the calories can vary immensely with it.
Once we know what is a calorie and what effect calories have on us, do we have to count them?
Yes and no.
Your body counts calories whether you do or not. Read any scientifically-based diet book, and it will tell you that only one thing affects a healthy person's weight: Calories in minus calories burned.
If you eat more calories than you burn, then your body will store the extra calories as fat. If you eat less calories than you burn, then your body will burn stored fat, muscle, or organs (in that order) in order to survive.
Thus, if you want to know that you are losing weight, you need to ensure that you eat less calories than you burn.
You can do that two ways:
There are many ways to ensure you eat less calories than you burn besides counting calories. For example, low-carb diets work because it is very difficult to eat enough calories without eating carbs. If I ate only steak on any given day, I'd have to eat 3 pounds of steak in order to match the amount I burn, even if I didn't exercise! When you add vegetables and lower-calorie meats, like pork and chicken, to that mix, you can see why those on low-carb diets lose weight.
Before you just jump on a low-carb diet, though, make sure you see our low-carb diets page because there are other issues to consider.
Eating a lot of fruits and vegetables will also fill you up without giving you many calories, thus helping you to automatically eat less calories than you burn.
Whether you choose to count calories or not, don't believe the fad diets that tell you that you can eat whatever you want and lose weight. It's not true. Calories in minus calories burned is the formula your body is using to determine how much fat it stores.
The comforting news is that most people can eat as much as they want and lose weight. You just can't eat whatever you want and lose weight.
You'll have no problems eating more calories than you burn if you are eating candy bars and covering your food in high-calorie spreads, gravies, and salad dressings. Change what you eat, though, and you'll find you can feast on fruits, salads, and many other foods, including things like chili and pasta dishes! (See our
diet tips page.)