Carbohydrates and proteins are two key nutrients supplied by the foods you eat. Before your body can benefit, however, your digestive system must process them into useful components. The digestion of carbs and protein shares some general similarities but also certain differences. Understanding how these processes work can increase your overall knowledge of nutrition.
The primary purpose of carbohydrate digestion is to break down the sugars and starches you eat so your body can use them to fuel activities. Although you can also use proteins and fats as energy sources, carbs offer the most direct way of supplying fuel to your cells. By contrast, protein digestion serves to reduce the large protein molecules in the foods you consume down to their individual building blocks, or amino acids. The pool of amino acids resulting from protein digestion then assimilates into new proteins your body manufactures as you need them.
Mouth to Stomach
Carb digestion begins in your mouth as soon as that cracker, piece of bread or mouthful of rice mixes with saliva. An enzyme known as salivary amylase starts to break down starch molecules, made up of a chain of sugars called glucose, into smaller fragments. As these fragments reach your stomach, your stomach acid continues the process. Protein digestion, on the other hand, initiates only when protein-rich foods meet the acid in your stomach. Here, both the acid and an acid-activated enzyme called pepsin begin to split the large protein molecules into smaller pieces known as peptides.
Stomach to Small Intestine
From your stomach, partially digested food moves to your small intestine. Your pancreas also plays a role here, secreting both a buffer to neutralize strong stomach acid and more enzymes to continue carb digestion. In addition, your small intestine releases carb-digesting enzymes, with the net effect of all the sugars and starches you’ve consumed converting to simple sugar molecules, ready for absorption into your bloodstream. Similarly, proteases – the enzymes necessary to complete protein digestion – come from your pancreas and small intestine, and these function to clip individual amino acids from the peptide molecules so they can also travel into your bloodstream.
Fiber is another type of dietary carbohydrate; however, this carb is not digestible. Fiber contains the carb cellulose, and your body lacks the digestive enzyme necessary to break down this molecule into a usable form. Still, fiber is an important part of a healthy, well-balanced diet, as it helps regulate your digestive system and may protect against some diseases, such as colon cancer.
A writer since 1985, Jan Annigan is published in "Plant Physiology," "Proceedings of the National Academy of Sciences," "Journal of Biological Chemistry" and on various websites. She holds a sports medicine and human performance certificate from the University of Washington, as well as a Bachelor of Science in animal sciences from Purdue University.