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Even though most of the major controversies regarding intestinal fat absorption have been resolved over the past three decades, our concepts of fat digestion and absorption continue to be modified, and new concepts have emerged. The purpose of this review is to summarize advances in our understanding of fat digestion and absorption since the topic was last reviewed by Johnston in 1968. The discussion will emphasize 1) the role of colipase and its interactions with lipase, bile salt micelle, and triglyceride substrate; 2) the importance of the unstirred water layer in fat absorption; 3) micellar formation and dissociation; 4) the role of fatty acid binding protein; 5) factors influencing the reesterification mechanisms in the intestine; and 6) intestinal contribution to lipoprotein and apoprotein production. The importance of these new concepts and the remaining gaps in our understanding of these complex digestive and absorptive processes are discussed.

A new automated potentiometric method for the determination of colipase was developed, taking advantage of the reactivation of purified lipase, in the presence of bile salt and at pH 6.5. High-fat and high-starch diets induced an opposite regulation of lipase and amylase in the rat pancreas. At the same time, the level of colipase was not influenced by nutrition. During fasting and in alloxan diabetes, the specific activity of lipase almost doubled, that of amylase decreased sharply, and colipase was not affected in the rat pancreas. In obese-hyperglycemic mice, suffering from obesity, hyperinsulinism, and moderate diabetes, there was also no regulation of pancreatic colipase. Thus, at variance with a number of hydrolases, there was no dietary or hormonal adaptation of colipase. However, this was probably without any bearing on intraluminal lipolysis. Indeed, comparison of lipase and colipase activities in pancreas and in small intestine suggests that colipase concentration is not a limiting factor of intraluminal lipolysis. The molecular mechanism of this assumption is discussed on the basis of in vitro studies.