Carbohydrates and lipids are both macronutrients and provide several key functions to the human body. These nutrients have similar chemical structures and the body uses carbohydrates and lipids in similar ways. Carbohydrates and lipids each come in a variety of forms and should make up a substantial portion of your daily caloric intake.
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Carbohydrates are molecules composed of carbon, hydrogen and oxygen, with a ratio of one atom of carbon and two atoms of hydrogen for every atom of oxygen. Lipids have the same elements as carbohydrates, but differ in their linkage. While the exact chemical structure of lipids varies, they generally have a much greater ratio of hydrogen-to-oxygen than carbohydrates.
Both carbohydrates and fat play an important role in delivering energy to cells. When you eat carbohydrates, they are quickly broken down into glucose, which fuels all muscle action. Carbohydrates can also be stored as glycogen in the muscles and liver for later use. Lipids are either stored in various fat deposits throughout the body for later energy use or are available in the bloodstream for immediate use.
Carbohydrates and lipids each help promote a feeling of satiety after eating and eliminate hunger pangs. Complex carbohydrates, particularly foods high in fiber, can provide lasting energy throughout the day and a feeling of fullness. Lipids take about 3.5 hours to exit the stomach after eating, leading to a prolonged feeling of fullness as well. The best sources of dietary carbohydrates are whole grain oats and beans, while vegetable oils and fish are the healthiest sources of dietary fat.
The Food and Nutrition Board of the Institute of Medicine maintains acceptable macronutrient distribution ranges, or AMDRs, for all macronutrients, including carbohydrates and lipids. The AMDR for adult men and women is 45 to 65 percent of total caloric intake, while fat should account for 20 to 35 percent of the adult diet. A 2,000-calorie diet should then include about 900 to 1,300 calories from carbohydrates and about 400 to 700 from fat.