ASK A SCIENTIST
Question: How does fat get transferred to our bodies?
Answer: Fat is just one form of a diverse group of substances called lipids. Lipids are organic substances that are mostly insoluble in water. Lipids that are liquid at room temperature are referred to as oils (like olive oil) and lipids that are solid at room temperature are called fats (like butter). Most people use the term fats instead of lipids so we will stick to the common reference of fats that include both fats and oils. Along with carbohydrates and protein, fat is an essential nutrient that provides energy (calories) to your body. Fat is our most concentrated energy source providing 9 calories per gram compared to the 4 calories provided by carbohydrates and protein.
Transportation of fat in your body is somewhat challenging because of the fact that it is not soluble in water. Think of the salad dressing you make, when you shake the bottle you can disperse the fat but it does not dissolve, when left to set the oil and the water (and vinegar) separate, with the oil floating on top. Because of this property your body has devised creative ways to deal with fat from digestion to absorption to transportation.
Digestion of fats actually begins in your mouth where enzymes called lipase begin to break fats up. In your stomach gastric lipase joins in and further breaks fats down. Digestion is then completed in the small intestines with the help of bile, which is produced in the liver and stored in the gall bladder, and pancreatic lipase. Bile acts like a detergent breaking down globs of fat as they enter the small intestines, helps keep fats suspended in the watery digestive juices, and readies fat for the action of lipase, which prepares fat for absorption. Absorption of fat takes place in your small intestines, more specifically the duodenum and jejunum. The process is highly efficient with a 95% absorption rate. Fat must be transported through the watery environment to the surface of the small intestines and that requires the help of micelles. Micelles are water-soluble structures that encase the fat so that the fat does not separate out into an oily layer. Once at the surface of the intestines, where there are millions of microvilli, fat is diffused into intestinal cells and absorbed into your body. Once absorbed, fats then join with a protein to make a lipoprotein called a chylomicron. These chylomicrons enter your lymph system before they are transported to your blood stream. Once in your blood stream there are 3 primary destinations for fat. 1) If needed for energy fat is transported into your cells for fuel. 2) Fat can be used to make hormones. 3) Fat can be stored for later use in adipose tissue.
After you eat it takes approximately 2 hours for fat to enter your blood stream and they are typically gone within 10 hours. This is why doctors tell you not to eat at least 12 hours before a lipid profile test (a.k.a. Cholesterol test)
Ask a Scientist appears Thursdays. Questions are answered by faculty at Binghamton University. Teachers in the greater Binghamton area who wish to participate in the program are asked to write to Ask A Scientist, c/o Binghamton University, Office of Communications and Marketing, PO Box 6000, Binghamton, NY 13902-6000 or e-mail firstname.lastname@example.org. Check out the Ask a Scientist Web site at askascientist.binghamton.edu. To submit a question, download the submission form(.pdf, 460kb).