Take carbohydrates for example. What are good carbs and what are bad carbs? Since your body breaks them all down into individual units, the carbohydrates themselves aren't necessarily good or bad. The problems occur when you eat too many, or if the other ingredients in the food containing the carbohydrates aren't so good.
Look at a chocolate-covered donut, for example, which has lots of sugar and white flour. If you eat too many of them, you'll take in extra calories that will be stored in your body as fat. The donut also contains lots of fats, probably trans-fats, that can raise your risk of heart disease. The donut doesn't provide you with much in the way of vitamins, minerals or other substances, such as natural antioxidantsor healthy fatty acids. When you think of it this way, that donut may not sound so good any more.
A good source of carbohydrates would be almost any fruit or vegetable. These options allow you to get the carbohydrates you need for energy, plus fiber for a healthy digestive system, vitamins, minerals and anti-oxidants. About half of your daily calories should come from carbohydrates. Those carbs should come from fruits, vegetables and 100-percent whole grain breads and cereals -- not from candy, sodas and pastries.
This concept works with proteins and fats, too. A healthy protein source is one that does not add extra unhealthy fats (and maybe offers some fats that are good for you). Navy beens are a good example, They provide protein, fiber, vitamins, minerals and carbohydrates. An example of an unhealthy protein is bacon. Bacon, and other processed meats like it, contain lots of saturated fats and calories which can impact your heart health, expand your waistline, and even increase your risk of cancer.
Healthy fats come from foods that contain polyunsaturated or monounsaturated fatty acids, like olive oil, fish, walnuts, soy, flax seeds and canola oil. While these fats and oils contain a lot of calories, you do need the fatty acids they provide. Unfortunately, there are a lot of unhealthy fats to be aware of. Saturated fats in red meats and trans-fats, found in some stick margarines, baked goods and processed foods, are very bad for your health.
Good Nutrition Means Good HealthA healthy diet will give your body the right amount of energy, enough raw materials and all of the "little helpers" you need to stay healthy. Good nutrition will also provide phytochemicals and antioxidants that will help keep you feeling young, looking great, and perhaps even disease-free. A bad diet will give you too many or too few calories, not enough vitamins and minerals, and will actually make you need more of the antioxidants that you aren't getting.
Gropper SS, Smith JL, Groff JL. "Advanced Nutrition and Human Metabolism." Fourth Edition. Belmont, CA. Wadsworth Pub Co. 2005.