Lipid digestion begins with triacylglycerols (TAGs), which are the most abundant dietary lipids and serve as a significant energy source. Unlike glucose, which yields only two molecules of acetyl-CoA, TAGs can produce multiple acetyl-CoA molecules, making them a more efficient energy source. The digestion process involves both mechanical and biochemical steps, primarily occurring in the mouth, stomach, and small intestine.
Initially, mechanical digestion occurs in the mouth and stomach, where TAGs are broken down into smaller droplets known as globules. This process involves grinding and churning, which increases the surface area of the lipids, facilitating further digestion. The next step, emulsification, is crucial for lipid digestion and occurs in the small intestine. Bile, which contains bile salts and emulsifying agents, plays a vital role in this process. It transforms the globules into micelles, enhancing their solubility and surface area, which is essential for the subsequent enzymatic action.
Emulsification is followed by the action of pancreatic lipases, which partially hydrolyze TAGs into monoacylglycerols and free fatty acids. This hydrolysis involves breaking the ester linkages within the TAGs, resulting in the formation of monoacylglycerols, where only one ester linkage remains intact. This series of processes—mechanical digestion, emulsification, and enzymatic hydrolysis—ensures that lipids are effectively broken down into absorbable units, allowing for efficient nutrient absorption in the body.