The high-protein diet trend in the U.S. peaked in 2004, according to "The Wall Street Journal," but protein continues to provide important functionality in the body. As one of only three macronutrients that provide you with energy, protein also repairs and builds body tissues and organs, and makes enzymes required for digestion and catalyzing metabolic reactions. Primary dietary sources of protein include meat, fish, legumes, dairy products, nuts and seeds. The Food and Drug Administration recommends consuming 50 g of protein each day, or the equivalent of two 3-oz. servings of chicken or two cups of soybeans.
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Protein digestion begins in your mouth, where chewing combines saliva with food, also called mastication, and it breaks down into smaller particles. The surface area of the food multiplies as the pieces become smaller, providing more access for enzymes later in the digestion process that reduce protein into even smaller molecules.
The stomach produces hydrochloric acid, which is needed to activate protein digestion. Food remains in the stomach for two to six hours.
The stomach secretes an enzyme called protease that removes the bonds holding together the long chains of amino acids that make up protein.
The pancreas releases trypsin, another digestive enzyme, into the small intestine. The protein molecules are reduced in size until they can pass through the intestinal wall.
Once the protein molecules are reduced to their smallest component parts, they are ready to enter the bloodstream. The intestinal wall surface consists of folds, or villi, and finger-like projections called microvilli that increase the absorption area where the amino acids move through capillaries that lead to the circulatory system.
Protein Digestion and Aging
The amount of acid the stomach secretes and the enzymes the pancreas and small intestine produce might decrease with age. Bitter herbs stimulate enzyme and stomach acid production, and improve digestion, according to nutritionist Phyllis Balch, author of "Prescription for Nutritional Healing."