Digestibility-reducing substances

While quantitative defenses or digestibility reducing substances are also present In small quantities In the. young needles, they do not seem to be effective In reducing female dry weight, larval density, or level of defoliation. This Is consistent with the reasoning that young tissue development... 

Based on this type of reasoning, investigators have divided defensive substances into (1) the acute toxins (qualitative defenses) that are present in very low concentrations in plant tissues and which exert their effects on herbivores by interfering with some basic metabolic process such as transmission of nervous impulses, and (2) digestibility-reducing substances (quantitative defenses) that are present in higher concentrations in plant tissues, that act in the gut of the animal to reduce its ability to utilize its food, particularly proteins, and whose effectiveness increases directly with their concentration (Cates and Rhoades, 1977 Feeny, 1970, 1976 McKey, 1974 Rhoades and Cates, 1976). Qualitative defenses... 

Pectin, the substance that makes jellies and jams so jelly-like, can help lower blood cholesterol levels by forcing the body to make more bile acids. Pectin is a type of fiber, and like most fiber, pectin cannot be digested by the human body. Instead, the fiber moves slowly through the small intestines. When pectin encounters sugar and acid, its molecules trap water within its long chains, turning into a gel-like mass. This gel traps and eventually eliminates bile acids from the gut. When this happens, the body must make more bile acids, reducing the amount of cholesterol in the blood. 

This resinous material was shown to act as an antiherbivore substance and appeared to reduce digestibility of the plant for several herbivores (103). 

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