Digestive enzyme
Digestive enzymes are a group of enzymes that break down polymeric macromolecules into their smaller building blocks, in order to facilitate their absorption by the body. Digestive enzymes are found in the digestive tracts of animals (including humans) and in the traps of carnivorous plants, where they aid in the digestion of food, as well as inside cells, especially in their lysosomes, where they function to maintain cellular survival. Digestive enzymes of diverse specificities are found in the saliva secreted by the salivary glands, in the secretions of cells lining
Discovery and development of gastrointestinal lipase inhibitors
The lipase inhibitors lipstatin and orlistat act locally in the intestinal tract. They are minimally absorbed in the circulation because of their lipophilicity. Hence, they do not affect systemic lipases. 
The mechanism of lipase inhibitors in fat digestion is shown in figure 1. These inhibitors bind covalently as an ester to the serine hydroxyl group at the active site on pancreatic- and gastric lipases and form a stable complex.
This results in a conformational change in the enzyme which causes exposing of the catalytic active site. When the active site is exposed, the hydroxyl group on the serine residue is acylated. This leads to irreversible inactivation of the enzyme. 
The inactive lipase is incapable of hydrolysing fats into absorbable fatty acids and monoglycerides, therefore triglycerides are excreted undigested with faeces. With this mode of action calorie uptake from fat in food is limited, hence body weight is reduced. The main role of lipase inhibitors is therefore to inhibit lipases in the gastrointestinal tract, but they do not have significant activity against proteases, amylases or other digestive enzymes.