Amphipathic bile breaks dietary fat into small lipid droplets allowing enzyme access for digestion. Subscribe to Nourishable at    / nourishable  

This video is part 9 of the Lipid Foundations module within a lecture series on the nutrition science of macronutrients.

Lipid Foundations Lecture playlist:    • Lipid Foundations  

Macronutrients Lecture playlist:    • Macronutrients Lectures  

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Lecture Development, Hosting & Post-Production by Lara Hyde, PhD
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Video Production by Robbie Hyde
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Opening Motion Graphics by Jay Purugganan https://www.c9studio.com/WP/

The information in this video is not intended or implied to be a substitute for professional medical advice, diagnosis or treatment. All content, including text, graphics, images and information, contained on or available through this video is for general information purposes only.

References
Chapter 6 Lipids in Wardlaw’s Perspectives in Nutrition, 2019 (Editors: Byrd-Bredbenner, Moe, Berning and Kelley, 11th edition)
Chapter 4 - Lipids, Sterols, and their Metabolites in Modern Nutrition in Health and Disease, 2014 (Editors: Ross, Caballero, Cousins, Tucker and Ziegler; 11 edition)

Images
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Bile is an amphipathic fluid with bile salts that have a hydrophilic water-loving end and an hydrophobic water-fearing end. The liver produces the bile and the gallbladder stores the bile, then secretes the bile when stimulated by the hormone CCK. Approximately 50% of the bile salts secreted into the intestine are reabsorbed and the rest exit through the colon - this is the only way the body has to get rid of cholesterol. Bile acids can break down a large lipid droplet into smaller lipid droplets by orienting the hydrophilic ends towards the outside and the hydrophobic ends towards the center lipid. This allows the lipase enzymes more surface area on the small lipid droplet for digestion. Lipase doesn't stick well onto the small lipid droplets and requires additional docking by co-lipase. The digested fatty acids will get transferred into micelles which are created by one layer of phospholipids with their fatty acid tails oriented towards the fatty acid core and their hydrophilic heads towards the outside watery environment. The micelles can travel through the unstirred water layer by the brush border of the intestine for absorption. The drug orlistat can inhibit gastric and pancreatic lipases; this can help with weight loss because it prevents fat digestion, however all that fat will exit through the colon yielding explosive fatty stools. Similar enzymes called phospholipase A2 and cholesterol esterases can cleave off fatty acid tails from dietary phospholipids and cholesterol esterases.