As mentioned previously, proteins, carbohydrates, and fat all provide calories to the body. Foods also contain the nutrients that build and repair cells, including vitamins and minerals. Within each of those categories are subdivisions. For example, there are 22 amino acids in proteins; different types of fat, such as saturated and monounsaturated; and there are complex and simple carbohydrates.

Protein

Proteins, which are made up of amino acids, are considered the cell's building blocks for all tissues and cells in the body, including red blood cells, muscle, and hair. A secondary function of protein is to be an energy provider, a backup to carbohydrates. No matter what food it's found in, one gram of protein equals four calories. Protein is found in meat, fish, dairy products (cheeses, milk, yogurt), and legumes (beans and peas).

Legumes are excellent sources of protein; they are high in fiber and low in fat. Animal sources of protein are usually high in fat, although the type of fat and its amount varies widely (you'll read more about fat in a minute). Protein is essential to people who want to get strong and who want to lose weight.

Carbohydrates

One gram of carbohydrates always has four calories. Carbohydrates, sometimes called carbs, should make up 55 to 60 percent of the total calories consumed. The majority of these calories should come from complex carbohydrates. Sugars and starches are carbohydrates, and both of these fuel our brain and muscles. Their primary function is to supply energy quickly. Fiber is also a carbohydrate, but our bodies don't digest it.

• Complex Carbohydrates

  Complex carbohydrates are long connected chains of molecules that are chemically more complex than simple carbohydrates. Complex carbs are found in vegetables, beans, grains, and pasta. They take longer to enter the bloodstream because they are complex and thus take longer to break down into absorbable sugars. Complex carbohydrates are high in fiber, low in calories (compared to fat and alcohol), and low in fat; they have a longer life span than simple carbs, which keeps your energy level up for lengthy periods of time, and give a contented feeling of fullness. They are stored in the liver and muscles as glycogen.

Don't count grams of nutrients. Instead, think about your meals. Here's the ideal proportion of your food intake: Get 55 to 60 percent of your calories from carbs, 30 percent from protein, and 20 percent from fat — the pounds will come off without you doing any other counting.

• Simple Carbohydrates

  Molecularly simple, with their single or double sugar molecules, means they release quickly into the bloodstream but have a short life span. They are found in some fruits, processed sugar, and processed foods. When simple carbs come in the form of processed foods, they are usually lower in fiber and higher in calories than complex carbohydrates.

Like all other calories, calories from carbs are stored as fat only if you eat too many of them, i.e. too many calories in general. And stay away from processed carbs. Studies have shown that the more processed food someone eats, the more they weigh.

Fats

Even though you hear a lot of bad things about fat, it is a necessary nutrient — in the right amounts! Fat supplies essential fatty acids, an important source of energy for aerobic exercise. Free fatty acids make up the main fuel for muscles at rest and during light activity. Stored fat in the body is important for protecting vital organs, insulating against cold, and transporting fat-soluble vitamins (A, D, E, and K). There are two types of fats, saturated and unsaturated.

• Saturated Fats

  Saturated fats are the “bad fats.” These are found in animal foods and products (like beef, pork, ham, and sausage); dairy products, especially whole dairy products (like whole milk, cheese, cream, ice cream); and oils (like coconut oil, cottonseed oil, and palm kernel oils). They are typically solid at room temperature.

• Trans Fatty Acids (TFAs), or Hydrogenated Vegetable Oils

  Although not officially considered saturated fats, trans fatty acids are included with the saturated fats for a good reason. The body responds to TFAs as if they were saturated fats, the harmful kind that raises cholesterol and increases your risk of heart disease. When manufacturers recognized that they could improve the shelf life, flavor, and profit of their processed foods by hydrogenating (adding hydrogen to) polyunsaturated oils, such as corn or vegetable oil, they couldn't act fast enough. Hydrogenation turns polyunsaturated oils into solids.

  Nuts are high in fat but amazingly good for you. They have minerals, fiber, and nice amounts of protein. A great snack food, nuts should be eaten in moderation because they are high in calories; think of a serving as a tablespoon or two. Look for nuts that are unsalted; it's not important whether they are roasted or unroasted. Nuts are great sprinkled on foods high in vitamin C, such as fruit and vegetables, because the vitamin C increases the body's absorption of the iron in nuts.

  Read your packaged food labels carefully; if you eat foods that have TFAs, include them in your saturated fat count. Unfortunately, they are not yet accounted for on the nutrition-facts panel along with the saturated fats, but will be in a few years. You have to look for them in the ingredients listing, where they are listed as partially hydrogenated vegetable (or other) oils. The most commonly used hydrogenated oil is soybean oil. TFAs are found in manufactured cookies, crackers, and fried foods.

Unsaturated Fats

Unsaturated fats are the preferred fats, although they should not be consumed above the recommended level. The two types of unsaturated fats are monounsaturated and polyunsaturated. Monounsaturated fats are found in olive and canola oils. They are touted as the healthiest of the oils. Polyunsaturated fats are found in corn, safflower, soybean, and sunflower oils.