The ancient Greeks believed all food contained one single ingredient that all bodies needed to sustain life. This single-nutrient theory held for centuries, despite discoveries along the way that connected nutrition with disease, such as curing scurvy among 18th century sailors with citrus fruits. The Golden Age of Nutrition, as described by Purdue University, began with the discovery of vitamin A and continued until the discovery of vitamin B-12 in 1949. After more than a century of research, there is a vast wealth of knowledge regarding what you must eat to get all the nutrients your body needs.

Essential Nutrients

Every body needs five essential nutrients to function properly. These essential nutrients are carbohydrates, proteins, fats, vitamins and minerals. Each nutrient plays at least one role in human physiology. Most foods contain more than one essential nutrient. Eating a variety of healthy foods should provide all the essential nutrients you need without the use of dietary supplements.

Carbohydrates

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Your body uses carbohydrates for energy. Vegetables, whole grains, milk, fruits and beans contain carbohydrates. Whole-grain foods, like whole-wheat bread, nuts and seeds are a source of healthy complex carbohydrates. The body quickly digests simple carbohydrates, like sugar and snack foods, causing unhealthy spikes in blood glucose levels. Get 45 to 65 percent of your daily calories from carbohydrates.

Protein and Fat

Protein is important to muscle function and fat is vital to energy storage, protecting internal organs and for regulating body temperature, among other functions. Meats, like duck and salmon, are high in protein, as are cottage cheese and beans. While protein and fat are essential parts of a nutritious diet, the typical American diet is too high in fat and protein. Most Americans get twice the protein they need, according to according to the University of Iowa Hospitals and Clinics 1. A healthy person should get 10 to 35 percent of her calories from protein and 25 to 35 percent of her calories from fat. Choose foods low in protein and fat, including fresh fruits and vegetables. Opt for healthy fats, like those found in olive oil and salmon, over unhealthy fat from shortening and hamburger.

Vitamins and Minerals

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Your body needs 13 vitamins and more than 80 minerals to function properly. Most Americans do not get enough fiber, vitamin A, vitamin C, calcium or iron, according to the U.S. Food and Drug Administration. Carrots, mustard greens and sweet potatoes are good sources of vitamin A, important to vision, bone growth, reproduction, cell development and regulating the immune system. Vitamin C also contributes to the immune system and for healthy teeth and gums. Citrus fruits, red and green peppers, broccoli, cantaloupe and kiwi are good sources of vitamin C. Iron, found in cereals, beans and tomato products, is a vital component in many proteins and enzymes necessary for human life. Iron plays a role in your respiratory system. Calcium gives you strong bones and teeth. Dairy products, fortified foods and green, leafy vegetables are good sources of calcium.