One pound of body fat equals about 3,500 calories. One can of soda has about 150 calories. Walking one mile burns about 100 calories. Food has more calories than exercise burns.

A lot of people don’t understand the relationship between calories and their weight. We talk about gaining or losing a pound, but how many calories are in a pound?

One pound of body fat equals about 3,500 calories. That means to lose 1 pound of weight you must somehow burn about 3,500 calories more than you eat. Or another way to look at it is you need to eat 3,500 calories less than you burn.

You may have noticed that walking a mile only burns a puny-sounding 100 calories and drinking a soda costs you a hefty 150 calories. A mile is a long way; it hardly seems fair! Would you walk a mile for a soda? This is why it’s very difficult to lose weight by exercise alone. You can easily eat far more calories than you can exercise off.

I call this the Exercise Problem. You can exercise like crazy and only burn a few hundred calories. Eating a single bowl of ice cream can easily wipe out a day’s hard work. Many people think they can eat more just because they are exercising. Unfortunately, it doesn’t work that way. Food has more calories than exercise burns. One study found that people who ran more than 30 miles a week still gained more than half a pound every year. The number of calories you need to burn through exercise to control your weight is frustratingly large.

Still, it’s not a good idea to lose weight just by cutting calories, because of the starvation response we talked about in The Starvation Threat. Safe weight loss and weight maintenance usually combine both eating fewer calories and burning more calories through exercise.

If you exercise enough to burn an additional 250 calories each day, and you eat 250 calories under your required calorie level, you will lose about one pound per week or about 50 pounds a year. That’s a lot of weight!

It’s clear that exercise combined with eating less is the most effective way to lose weight. But if you can’t exercise, you can still lose weight by controlling your calories. The problem is being thin doesn’t mean you are healthy. Without exercise you could be a TOFI: thin outside yet fat on the inside. Fat on the outside is fat stored under your skin, which is a relatively healthy place to store fat. The fat on the inside is called visceral fat, that’s fat around your internal organs. It’s the visceral fat that’s thought to contribute to heart disease, diabetes, and metabolic syndrome. Sumo wrestlers ripple with fat yet they are healthier than many of their thin, less active spectators. Sumo wrestlers mainly carry their fat under the skin. They exercise enough to burn off the visceral fat, which is some of the first fat to go when you exercise. To get the best of all worlds, you need to work exercise into your life. All is not lost if you don’t see yourself hitting the gym for an hour every day. Later we’ll talk about a lot of way to work exercise into your daily life without becoming a gym rat.

Let’s say every day at breakfast you slather one pat of butter onto a piece of toast. A one teaspoon sized pat of butter is about 35 calories. If you eat an extra teaspoon of butter a day, you gain about 3.5 pounds a year. That adds up over the years. Just eating that one extra teaspoon of butter a day could gain you about 18 pounds in 5 years!

As you can see, your food choices matter. Here’s a table to give you an idea how calories and weight are related.

This table answers the question: how much weight will you gain by eating how many extra calories each day? For example, a Lifesaver® has about 10 calories. If each day you eat an extra Lifesaver you will gain one pound a year. Over 10 years that’s an extra 10 pounds of weight gain just by eating one very small piece of candy you probably wouldn’t give a moment’s thought about eating.

Use the Divide by 10 Rule to Go From Calories to Pounds Gained in a Year

You can quickly calculate the approximate number of pounds you’ll gain in a year from eating a certain number of calories every day by dividing the number of calories by 10.

The math works out so nicely because there are 3,500 calories in a pound and nearly 350 days in year.

Ask yourself: How much will I gain a year if I eat this?

One way to evaluate your food decisions is to think about how much weight you would gain in a year if you ate this food every day. This simple question gives you perspective. It helps you better judge the impact of how your food decisions today will change your waist size tomorrow.

Let’s say you have a choice between two cereals for breakfast. One cereal has 20 more calories per serving than the other. If you eat the cereal with 20 extra calories everyday for a year you will gain an 2 extra pounds a year. That’s a big weight gain for one small choice.

Here’s another situation: if I am strolling down the hall and I see a can of soda sitting on a table and it’s free for the taking, should I drink it?

Let’s see. I know a can of soda has about 150 calories. If I wasn’t sure I would take a look on the can. We’ll also develop some portion judgment related skills in later strategies.

Using the Divide by 10 Rule I think to myself that extra soda will mean about 150/10 = 15 extra pounds a year. That’s a lot for just a soda. I probably wouldn’t drink it. The soda isn’t worth that much to me.

You might argue that you are just having one soda so it’s not fair to say you’ll gain 15 extra pounds a year when it’s really only 150 calories. And you would be correct, but not necessarily right.

These “should or shouldn’t I eat this” situations come up many times each and every day. You make hundreds of food decisions on a daily basis. So really this one decision will have an impact because you make the same type of decision every day.

If today you decide to have the soda because it only has 150 calories, then you’ll probably make the same decision tomorrow, and the day after that, and the day after that. Over a year that adds up to a year’s worth of calories. That’s why its more accurate to make a decision on what you should eat today based on how much you’ll gain over the whole year.

The Lifesaver is a good example of why this way of reasoning works so well. You might not think a second about having a Lifesaver because it has so few calories. But the calories add up over the year. Thinking about the calories over a year shows the real impact each food choice has on your weight.

Just what is a calorie?

We toss the word calorie around a lot, but few people have an idea what it actually is. It doesn’t help that the scientific definition of a calorie is very technical and hard to understand, so it’s often easier for us to act like we know what we are talking about, even when we don’t.

A calorie is simply the measure of the amount of energy available in a food. The more calories in a food, the more energy it has.  This means you can do more work from eating the food. And the more work you can do the better chance you have of surviving.

The energy is in a different form, but energy in food is the same idea as energy in the battery you use in a flashlight. Without the battery¾energy¾the flashlight doesn’t work. Same with your body. It won’t work without energy from food. And because your body demands a constant supply of energy, finding and eating food is the highest of all priorities for your brain. That’s why you think of food so much of the time.

Here are a few examples to help give the idea of calories some meaning. A gallon of gasoline contains about 31,000 calories. It takes about one Big Mac to drive a car four miles. And there is enough energy in 5 pounds of spaghetti to brew a pot of coffee. Yet you can walk a mile using only 100 calories. Humans are pretty efficient users of calories.

Fat is the highest calorie density food at 9 calories per gram. Density is the number of calories that are in the same amount of food, in this case a gram.

In the US, at least, we don’t use grams very often, so it would help to get a better feel for what a gram is. A paper clip weighs 1 gram. A US nickel weighs about 5 grams. Find a nickel and hold it in the palm of your hand for a little while. Get a feel for how much it weighs. You might be more familiar with M&Ms. One M&M weighs about a gram. And 30 grams is equal to about 1 ounce.

Protein and carbohydrates both contain 4 calories per gram. Alcohol has 7 calories per gram. Water contains no calories at all. If you eat food made up of fat, then you’ll be eating a lot more calories than if that food contained water. We’ll use this fact in a later strategy as a way to eat fewer calories while still getting full.

Fat is such a good source of energy that your body has developed a special relationship with it. Your brain is constructed to love fat because sources of fat were scarce in humanity’s past and your body wants you to hunt and eat as much fat as possible. Your love of fat is no accident. It is built-in to your body to help you survive.