The nutrients that provide energy to your body are carbohydrate, protein, and fat. For good health, you should eat foods that include all of these nutrients. National nutrition guidelines recommend that your diet include 45 to 65 percent of calories from carbohydrate, 10 to 35 percent of calories from protein, and 20 to 35 percent from fat.
So, carbohydrate is the type of foods that will be the biggest part of your diet. Carbohydrate includes basic foods such as grains, vegetables, and fruits. Protein, such as milk products, meats, nuts, and beans, also provides energy and are necessary for building body tissue such as muscles and bones. So it’s true that protein is important for building muscles in the body. But it’s important to know that eating protein above the recommended level (10 to 35 percent of your daily calories) does not cause extra muscle growth. Too much protein in the diet (more than 35 percent) can actually cause the body harm. Also, eating protein without doing muscle fitness exercise does not cause strength and muscular endurance above normal amounts. So regular exercise is especially important in building muscles.
Fat is also a source of energy. Certain types of fat (such as fish oil) are good for you, but some (such as saturated fat in butter) are not so good, and you should limit the amount you eat (see page 100). One gram of fat contains 9 calories, and one gram of carbohydrate or protein contains 4 calories. In other words, if you ate the same amount of fat as you ate of carbohydrate or protein, you would take in more than twice the calories. Therefore, it’s important to limit fat in the diet, especially saturated fat. But some fat is necessary for good health.
The key to having a healthy body weight is energy balance. This means taking in no more calories than you expend (such as by doing regular exercise). It’s true that if you eat a lot of fat, you will take in more calories and will have a harder time doing enough activity for energy balance. But all calories consumed in your diet, not just fat calories, are important. So be sure to eat all types of food for energy, but keep the total calories in your diet equal to the total calories that you burn in activity.