Digestive enzymes adapt to the diet when substrate intake is altered. An analysis of experimental works shows that this process includes many enzymes. The intestinal step of digestion is the most important in the enzyme breakdown of dietary components. In the first part of this paper, I have pooled the data on the adaptive potency of pancreatic and intestinal enzymes. When protein, carbohydrate and lipid digestions are considered successively, it is clear that the enzymes involved adapt to any change in substrate intake. For instance, when the amount of starch intake increases, the specific activity of pancreatic amylase is stimulated. At the same time, augmenting the disaccharide level leads to an increase in specific disaccharidase activity, and the absorption rate of some simple hydrolytic products, such as fructose, increases. It thus appears that altering the amount of starch intake leads to a parallel change in the activity of all the enzymes involved in the sequential hydrolysis of the dietary carbohydrates. The second part of the paper discusses the physiological significance of this adaptation in terms of utility to the animal. Two situations are considered in which (i) the nutritional requirements are supplied by food or (ii) they are not supplied either because of a dietary or an enzyme deficiency. When the nutritional requirements, particularly that of protein, are met, adaptation is apparently not useful to the animal. Nevertheless, the role of this adaptation on the hydrolysis rate of different substrates can be supposed. When nutritional requirements are not met, some data show that enzyme adaptation may be advantageous to the animal. If dietary restriction is not too severe and thus the biosynthesis of all the enzymes markedly decreases, then digestive secretions would export considerable nitrogenous material into the gastrointestinal lumen; this material could be a substrate compensating for the essential components lacking in the diet. Any enzyme deficiency leading to substrate decrease is similar to a dietary deficiency. Many experimental studies have shown that in pancreatic deficiency the adaptive potency of the organism is responsible for establishing digestive compensation.