Digestive enzymes play key roles in liberating nutrients for absorption. Most animal species modulate activities of digestive enzyme activities according to the nutrient content of their diets. For example, individuals feeding on starch-rich diets tend to express higher activities of starch-degrading enzymes, and low activities of protein-degrading enzymes. This idea is known as the 'adaptive modulation hypothesis', and allows animals to digest the nutrients in their diets while still conserving biosynthetic energy and cell-membrane space.
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