Calories do count! However pleasurable eating is, its real purpose is to provide the energy your body needs to maintain a constant temperature and perform its basic functions. Anything extra you do uses more calories. Any calories you consume that your body does not need are converted to body fat. It's as simple as that. The goal of this chapter is to help you understand what happens to food after it goes in your mouth. This should combat foolish or dangerous myths about food and weight loss.

The meaning of metabolism

Metabolism is the Sum total of all the chemical and physical processes by which the body breaks down, converts, and uses food, gases, and other substances. For our purposes, we will focus on how the body metabolizes food, converting it into forms that can be used immediately - for energy or to build and repair tissues - or stored for future use.

The digestive system breaks down food into its component parts. Carbohydrates become the simple sugar glucose. Fats are broken down into fatty acids, which are the main type of molecules that make up fats and are not soluble in water. Proteins are broken down into amino acids. These components go to the liver, where they are prepared for use or storage.

Glucose is used immediately for energy or is stored as glycogen. But there is a limit to how much glycogen your cells can store. Once the glycogen "bank" is full, the rest is stored as fat. Amino acids are used to build and repair cells, among many other tasks. Anything left over is stored as fat. Fatty acids go straight to the fat cells. Are you beginning to get the picture? Fat cells are the ultimate destination for all nutrients your body does not need for immediate use.

Do not believe any"expert" who claims to have discovered how to change the way your body uses food, or a magic combination of foods that "work together" to burn more calories.

The metabolism meter

The thyroid secretes hormones that regulate metabolism. People with overactive thyroids (hyperthyroidism) will suddenly lose weight, even though their appetites increase. They will also feel nervous and jumpy. This is because their metabolism has been speeded up. Conversely, an underactive thyroid (hypothyroidism) will cause weight gain and a sluggish, low-energy feeling. These are both serious medical conditions that require accurate diagnosis.

Calories in

Everybody talks about calories, but how many people know what a calorie actually is? We tend to think of calories as something "contained in" food, like sugar or fat. In fact, a calorie is a scientific unit of heat measurement.

What does all this have to do with food? When food is digested, it is broken down into a form the body can either use or store. When used, it is "burned," giving off heat energy that is measurable in calories. When stored, it is potential energy, energy that is able to be burned at some future time. That too is measurable in calories.

How many calories make a pound of fat? The answer is 3,500, whether they're coming or going.

If you eat 3,500 more calories than your body needs, they will be stored and add a pound to your weight. On the other hand, if you burn 3,500 more calories than you eat, they will be drawn from your fat stores and you'll lose a pound. The good and bad news about this is that your body is a remarkably shrewd accountant. Whether you eat those extra 3,500 in a day, a week, a month, or a year, the deposit will always be a pound. The same goes for the withdrawal.

Just as a reminder, the three major nutrients - carbohydrate, protein, and fat - and the quasinutrient alcohol provide energy to the body that is measurable in calories. This energy can be either used immediately or stored for future use. Their calorie content is as follows:

Carbohydrate: 4 calories per gram

Protein: 4 calories per gram

Fat: 9 calories per gram

Alcohol: 7 calories per gram

Storing the excess

If we expended every bit of energy we take in as food, we'd be a skinny bunch, and this book would be collecting dust along with all the other diet books. We'd also be in big trouble if food became scarce or the weather turned very cold or we got sick, because then we wouldn't have stored fat to draw on. But this is theoretical. Except in parts of the world where famine is reality, most of us help ourselves to more calories than we actually need, and we carry the extra on our hips and elsewhere.

It doesn't matter whether you eat too much fat, too much carbohydrate, too much protein, or a combination of the three. The body breaks down all the food so it is ready for use or for storage.

Everybody needs some body fat. You need it in the marrow of your bones, where red blood cells are made. You need it around your organs, to cushion them and to keep them warm. Your brain also needs it, your nerves need it, and women particularly need it to keep their reproductive systems working properly. In fact, as much as 50 percent of the fat in your body is used for these essential purposes. The rest is store directly under your skin, and that's the fat that shows.

There's an important wrinkle in the metabolic process that provides a hint why fat makes you fatter than protein an carbohydrates. It takes considerable energy to fuel the metabolism itself, but it is far easier for the body to metabolize fat than protein or carbohydrate.

Because dietary fat is dose to the form it needs to be in for storage, metabolizing it requires just 3 calories for every 100 you eat. That leaves 97 calories to be stored in your fat cells.

Converting carbohydrates to storable fat is a complex process, taking 23 of every 100 calories. Once the conversion has taken place, only 77 calories remain to be stored. Depending on the exact amino acids involved, metabolizing protein requires fewer calories than carbohydrate but more than fat.

Carbohydrates are your best bet if you want to reduce the amount of excess stored as fat.

People who promote high-fat, high-protein, and low­carbohydrate weight-loss diets are ignoring the basic scientific facts. Now that you know the truth, make sure that you don't fall for their dietary mumbo jumbo.