Every time we eat food, our body has to digest and absorb the nutrients the food contains. Some of those nutrients include proteins, carbohydrates and fats. Different enzymes and digestive juices allow different nutrients to be digested and absorbed in the body. For example, fat is a nutrient that must be mixed with an emulsifier in order for it to be effectively digested and absorbed from the intestinal tract .
Fats are hydrophobic, which means they do not dissolve in water. This is evident when you pour a tablespoon of vegetable oil in a cup of water and watch it rise to the top. This property of fat makes it necessary for the body to create an environment in which fat can be digested or broken down.
Bile is what allows fat to be digested in the water environment of the intestines. When fat is present in the intestinal tract, bile is secreted from the gallbladder and is released into the intestines via the common bile duct. Bile has an attraction for both fat and water. Therefore, bile is able to penetrate large fat globules floating around in the intestines and can break them into smaller globules that are now also water soluble with a bile coating. This is called emulsification.
The smaller fat globules or droplets that are combined with bile are technically called micelles. Micelles are important for a couple of reasons. First, the micelles allow enzymes that break down fats to access the fat more easily. Before emulsification, fat digestion is really ineffectual. Second, micelles also allow for transport of the fat molecules from the intestinal tract into the intestinal cells. This allows for the absorption of the fat into the rest of the body.
What Exactly is Bile?
Due to bile, fats are able to form smaller droplets in the small intestines. The bile secretion is actually made of two major components that contribute to its ability to be both hydrophobic and hydrophilic, or water-soluble. Cholesterol is actually used to make bile acid in the liver and is the component that gives bile its non-water-soluble qualities. The bile acid is then combined with an amino acid from protein, which leads to water-soluble qualities.
- Understanding Nutrition Now, 12th edition; Ellie Whitney, Ph.D. and Sharon Rolfes, M.S.
Jennifer Lemacks is an assistant professor at the University of Southern Mississippi with a doctorate in human nutrition from Florida State University, and is a registered dietitian trained in child and adolescent weight management. She has prepared, edited and presented various manuscripts for peer-reviewed journals and professional conferences.