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How Do Carbohydrates & Proteins Affect the Human Body?

By Adam Cloe Ph.D./M.D.

A healthy, well balanced diet provides you with essential nutrients, including carbohydrates and proteins. Although carbohydrates and proteins are important components of your diet, they affect your body in different ways. Carbohydrates are typically used for energy, whereas proteins are broken down to help your body make new proteins.

Carbohydrate Metabolism

Carbohydrates function as the primary energy source for your body. When you eat foods that contain carbohydrates, your digestive tract breaks them down into sugars, which are then absorbed and moved into your bloodstream. Your cells import some of the sugar from your blood and use it for energy. Increases in blood sugar levels prompt your pancreas to secrete insulin, a hormone that helps your muscle, fat and liver cells pull up sugar from your blood. Excess sugar is converted into triglycerides, which are stored in fat cells.

Protein Metabolism

One of the main roles of dietary protein is to allow your body to make new proteins. All proteins are made up of subunits known as amino acids. When you consume protein, your digestive tract breaks it down into component amino acids, which can then be used to make new proteins. Some amino acids, known as "essential" amino acids, cannot be made by the body, so you must get them from your diet to make new proteins.

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Protein as Energy Source

In addition to its role in supplying your body with the building blocks for protein synthesis, dietary protein can also serve as a source of energy. Some of the amino acids in your body can be burned as a fuel source, and when you consume more protein than you need, your body can convert these amino acids into sugars or other molecules to build up your energy reserves. Ammonia is a byproduct of this process, and must be excreted from your body via urine.

Effects on Thermogenesis

Consuming carbohydrates and proteins also increases the speed at which your body burns calories. When you eat, your metabolism increases because you generate more body heat, a process known as thermogenesis. However, proteins and carbohydrates increase thermogenesis at different rates. According to a 2004 article in "Nutrition and Metabolism," protein-rich foods increase thermogenesis more than carbohydrate-rich foods.

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