The carbohydrates, proteins, and lipids in foods are mostlyin complex forms. For example, the carbohydrates are present as disaccharides, such as sucrose, or polysaccharides, such as starch. The first step in digestion is the breakdown of the larger, insoluble molecules into smaller, soluble forms that can be transported across the intestinal wall into the blood for delivery to the tissues.The breakdown of food begins in the mouth as it is chewed.
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