Chemical Digestion of Fats

Dietary fats or lipids are complex organic compounds composed of carbon, hydrogen and oxygen. Often found in butter, meat or cooking oils, these fats are the most concentrated source of energy in our daily diet. Since they don't dissolve in water, they're not easily broken down in the gastrointestinal tract. It takes longer for these fats to digest than carbohydrates or proteins.

General Digestion

• The human stomach can hold 1.2 liters (about 2.6 pints) of liquid. The digestive juices consist primarily of hydrochloric acid and can dissolve metal. The stomach lining cells cannot tolerate these acidic conditions for long and must replace themselves quickly. Every minute, 500,000 stomach lining cells die and new ones replace them (the entire stomach lining replaces itself every three days). Once an organism dies, the stomach ruptures and the acids begin the final decomposition of the body as it actually digests itself during the putrefaction process.

Fat Digestion

• Bile (which is secreted by the gall bladder) and the enzyme lipase (found in the small intestine) break fats down into fatty acids and glycerol. Fat digestion begins with the action of bile, which emulsifies lumps of fat into thousands of fatty droplets. This process allows lipase to begin its enzyme action and ultimately breaks the fats down into fatty acids and glycerol. Lipase originates in the pancreas and works in the small intestine as it digests the fats. Fats are not water soluble, but their end products---glycerol and fatty acids---will dissolve in water so that the body can easily absorb them.

Fat in the Bloodstream

• It takes 10 to 15 minutes for the structures in the small intestine to absorb fat into the body. Once there, lymph and blood vessels absorb fatty acids and glycerol into the lymphatic system, which then drains into the bloodstream. Here, fatty acids may be oxidized for energy in the muscle cells or stored in the fatty adipose cells. The body prefers glucose rather than fat as an energy source, but it can convert only about 5 percent of the absorbed fat into glucose, so a significant portion of digested fat is stored in adipose or fat cells. The liver absorbs glucose or breaks it down into energy.

Fats as Nutrients

• The term "fats" refers to lipid materials that are solid at room temperature (68 degrees Fahrenheit). Lipid mixtures that are liquid at that temperature are oils. Generally, the hardness of the fat reflects the proportion of saturated fatty acids that are present. A harder fat like a hard cheese or butter contains more saturated fatty acids than a cheese or margarine spread

  Fat generally contains a caloric value that's twice that of carbohydrates. Heart disease is linked with large fat intakes; the excess fat resides in deposits along artery walls and may cause heart attacks. Often digestion converts excess carbohydrates and proteins into fat for storage.

  Fat serves five purposes as a nutrient: It provides an energy source, adds flavor to one's diet, provides basic structural components for cells, provides fatty acids, and carries the fat-soluble vitamins, A, D, E and K.

Fats in Humans

• Once the fats have been broken down into glycerol and fatty acids in the digestive system, they recombine once again in the body. They liberate energy in respiration and are often stored as body fat under the skin, usually around the thighs, belly, buttocks and internal organs. The fat provides an energy reserve and may protect internal organs from physical damage.