Proteins, fats and carbohydrates provide the calories your body needs for energy, and a healthy diet contains all three. The trick is to find the right balance and to know which foods contain which source of calories. Whatever your particular calorie requirements are, protein sources should make up 10 to 35 percent of your diet, fat sources 20 to 35 percent and carbohydrate sources 45 to 65 percent, according to the Dietary Guidelines for Americans 2005.
Proteins provide the 20 amino acids which make up the cells, tissues and organs of your body. Your body makes over half the amino acids needed, but your diet must provide the rest -- the essential amino acids. Some foods are "complete" sources of protein and contain all the essential amino acids. Animal-based foods are the main sources of complete protein and include meat, fish, poultry, eggs, milk and cheese.
Plant-based foods also contain protein, but are "incomplete" sources of protein, meaning they contain only some of the essential amino acids. These incomplete proteins include nuts and seeds, rice, beans, corn and tofu. But eating complementary plant-based foods can provide your complete essential amino acid requirement. For example, beans and peas complement rice or nuts and seeds, each providing the essential amino acid the other lacks.
Soybeans are the only plant-based food considered a complete protein, providing all essential amino acids.
A certain amount of fat intake is essential in a healthy diet. Most of your fat requirement should come from unsaturated sources. The main sources of "healthy" fats include nuts and seeds, fish, avocados and most plant-based oils, such as olive oil or canola oil. Healthy fats can help reduce your LDLs or "bad cholesterol."
Saturated fats, on the other hand, increase your bad cholesterol. These fats are usually contained in animal-based foods, such as cheese, meat, milk, butter and cream. The plant-based palm and coconut oils are also sources of saturated fat. You can lessen the amount of saturated fat in your diet by choosing low-fat versions of dairy products or leaner cuts of meat.
The hydrogenation process transforms liquid oils into semi-solid fats, creating trans fats. Trans fats raise your bad cholesterol and put you at risk for heart disease. The Dietary Guidelines for Americans 2005 recommends you keep consumption of trans fats as low as possible. Trans fats are found in commercially-baked desserts, some restaurant fried foods and stick margarine.
Your body turns carbohydrates into glucose for energy. The main sources of healthy carbohydrates are fruits, vegetables, grains and milk products. When you don't use carbohydrate energy right away, your body stores some of it in the liver and muscles, but stores the rest as fat.
Complex carbohydrates, such as those found in whole grain products, beans and root vegetables, contain starch and fiber that your body turns into fat less easily, says the Merck Manual Home Edition. Simple carbohydrates are easily broken down and absorbed – these include fruits, dairy products and natural sweeteners such as honey or maple syrup.
Refined carbohydrates are highly processed, often losing the fiber and nutrients that make them healthy, though they often contain the same number of calories. White flour and white sugar, used to make breads, pastas, cakes, cookies, sweets and sodas, are sources of refined carbohydrates.
- Center for Nutrition Policy and Promotion: Dietary Guidelines for Americans 2005
- Centers for Disease Control and Prevention: Nutrition for Everyone -- Basics: Protein
- University of Illinois: National Soybean Research Laboratory -- Soy Benefits
- Centers for Disease Control and Prevention: Nutrition for Everyone -- Dietary Fats
- Merck Manual Home Edition: Carbohydrates, Proteins and Fats