While protein’s digestion process occurs in the same way, several factors can affect protein digestion time. One of those factors is the protein consumed. Protein’s simplest types are strings of amino acids held by peptide bonds. Foods that we eat contain proteins in their most complex shape, where amino acids’ protein strings are raveled up. They have to be unraveled and broken apart to absorb the individual amino acids and transfer them into the bloodstream. The stomach acids help unravel all the raveled amino acid chains, allowing digestive enzymes formed by the stomach wall to break apart the peptide bonds. The easier the amino acids enter, the faster the protein can be processed. Therefore, a protein with less-complex composition has higher digestive speeds. Whey protein, found in milk, is a quick-digesting protein example. According to the International Sports Nutrition Journal, its absorption rate was measured at about 10 grams per hour compared to a cooked egg with an absorption rate of about 3 grams per hour. Human Metabolism Nutrients Human Metabolism Nutrients Sugars, lipids, and proteins are the main components of food and act as fuel molecules for the human body. The digestion (breaking down into smaller pieces) of these nutrients in the food system and the resulting absorption (entry into the bloodstream) of the digestive end products render it possible for the tissues and cells to turn the latent chemical energy of the food into usable work. The big consumed end products of food digestion are monosaccharides, primarily glucose (from carbohydrates); monoacylglycerol and long-chain fatty acids (from lipids); and small peptides and amino acids (from proteins). Once in the bloodstream, these nutrients can be metabolized by different cells. We have known it for a long time that these three groups of molecules are fuel sources for human metabolism, but it is a popular misconception (especially among undergraduates) that human cells use only glucose as a source of energy. This misinformation can arise from the manner in which most textbooks describe energy metabolism, underlining glycolysis (a metabolic mechanism for glucose degradation) and omitting fatty acids or amino acid oxidation.