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What Are Macronutrients? - Definition, Functions & Examples

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  • 0:02 What are Macronutrients?
  • 1:06 Carbohydrates
  • 3:31 Proteins
  • 5:34 Lipids
  • 7:29 Lesson Summary
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Lesson Transcript
Instructor: Adrienne Brundage
Macronutrients are energy-providing chemical substances consumed by organisms in large quantities. The three macronutrients in nutrition are carbohydrates, lipids, and proteins.

What are Macronutrients?

Nutrients are environmental substances used for energy, growth, and bodily functions by organisms. Depending on the nutrient, these substances are needed in small amounts or larger amounts. Those that are needed in large amounts are called macronutrients.

There are three macronutrients required by humans: carbohydrates (sugar), lipids (fats), and proteins. Each of these macronutrients provides energy in the form of calories. For example:

  • In carbohydrates, there are 4 calories per gram.
  • In proteins, there are 4 calories per gram.
  • And in lipids, there are 9 calories per gram.

This means that if you look at a food label and it lists 10 grams of carbohydrates, 0 grams of protein, and 0 grams of fat, that food would contain 40 calories.

Carbohydrates

Humans need carbohydrates in the largest amounts. Currently, the USDA recommends that adults get 45-65% of their daily caloric intake from carbohydrates. Carbohydrates are incredibly important to the diet for many reasons.

For starters, carbohydrates are easily metabolized, which just means chemically broken down, and used as the body's main fuel source. All of our bodily tissues have the ability to use the simple carbohydrate, glucose, as energy. When the body uses carbohydrates for energy, it can use other macronutrients for other jobs, like tissue growth and repair.

The brain, kidneys, muscles and heart all need carbohydrates to function properly, and carbohydrates aid in the synthesis of certain amino acids. Furthermore, fats can only be properly metabolized when carbohydrates are present and indigestible carbohydrates, in the form of fiber, are necessary for intestinal health.

Carbohydrates are primarily found in starchy foods, like grain and potatoes, as well as fruits, milk, and yogurt. Other foods like vegetables, beans, nuts, seeds, and cottage cheese contain carbohydrates, but in lesser amounts. Carbohydrates can be simple or complex, which refers to their chemical structure. Simple carbohydrates taste very sweet (like fruit sugar), while complex carbohydrates taste savory (like starch in potatoes).

Fiber is an indigestible form of carbohydrate. Since humans cannot break down fiber carbohydrates, they pass through the digestive system whole and take other waste products with them. Diets low in fiber have problems with waste elimination, constipation, and hemorrhoids. Diets high in fiber have shown decreased risk for obesity, high cholesterol, and heart disease. Fruits, vegetables, and whole grain products all contain high amounts of fiber.

Proteins

Currently the USDA recommends 10%-35% of calories in the human diet come from protein. The typical American diet contains more protein than is strictly necessary. Proteins are also important in the diet for many reasons.

For example, protein is the major constituent of most cells, making up more than 50% of the dry weight. Also, protein defines what an organism is, what it looks like, and how it behaves, because the body is made of thousands of proteins. Proteins are used to produce new tissues for growth and tissue repair and regulate and maintain body functions. Enzymes used for digestion, protection, and immunity are made of protein, and essential hormones used for body regulation require protein. Finally, proteins may be used as a source of energy when carbohydrates are not available.

Protein is found in meats, poultry, fish, meat substitutes, cheese, milk, nuts, legumes, and in smaller quantities in starchy foods and vegetables. People who consume a vegetarian diet can get plenty of protein if they keep a balanced diet.

The body breaks down protein into its building blocks - amino acids. There are 500 known amino acids, 21 of which are needed by humans. Of the 21 necessary for life, nine are considered essential since they cannot be produced by the body and must be eaten. Proteins that contain all nine essential amino acids are considered 'high quality' proteins. These high quality proteins tend to come from animal sources. Proteins that do not contain all nine essential amino acids are considered 'low quality' proteins, and tend to come from plant sources.

Lipids

Lipids, or fats, are substances that do not dissolve in water, and are necessary for survival. Currently, the USDA recommends 20% - 35% of calories should come from lipids. We need this amount of fat for things like the maintenance of cellular membranes, which are made from lipids. They're also a high-density energy source and help us absorb fat-soluble vitamins. In addition, lipids cushion organs and insulate the body. Finally, they provide raw materials for vitamin D and hormones, as well as give taste, consistency, and stability to foods and make us feel full after eating.

Lipids are found in meat, poultry, nuts, milk products, butters and margarines, oils, lard, fish, grain products, and salad dressings. There are three main types of fat: saturated fat, unsaturated fat, and trans fat.

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