QVprep Biology Lessons

What are fibers? What are fats? Essential fatty acids



What are fibers? Dietary fiber is a carbohydrate that is incompletely absorbed in humans and in some animals. Dietary fiber consists mainly of cellulose, a large carbohydrate polymer that is indigestible because humans do not have the required enzymes to disassemble it. There are two subcategories: soluble and insoluble fiber. Whole grains, fruits such as plums, prunes, and figs and vegetables are good sources of soluble dietary fiber. There are many health benefits of a high-fiber diet. Dietary fiber helps reduce the chance of gastrointestinal problems such as constipation and diarrhea by increasing the weight and size of stool and softening it. Insoluble fiber is found in whole wheat flour, nuts and vegetables. It stimulates peristalsis – the rhythmic muscular contractions of the intestines which move food along the digestive tract. Soluble fiber is found in oats, peas, beans, and many fruits, dissolves in water in the intestinal tract to produce a gel which slows the movement of food through the intestines. This may help lower blood glucose levels because it can slow the absorption of sugar. Fiber food is thought to lessen insulin spikes, and therefore reduce the risk of type 2 diabetes.

What are fats? A molecule of dietary fat typically consists of several fatty acids bonded to a glycerol. They are typically found as triglycerides - three fatty acids attached to one glycerol backbone. Fats may be classified as saturated or unsaturated depending on the detailed structure of the fatty acids involved. Saturated fats have all of the carbon atoms in their fatty acid chains bonded to hydrogen atoms, whereas unsaturated fats have some of these carbon atoms double-bonded, so their molecules have relatively fewer hydrogen atoms than a saturated fatty acid of the same length. Unsaturated fats may be further classified as monounsaturated and polyunsaturated. Unsaturated fatty acids are classified as omega-3 or omega-6 fatty acids. There are nine kilocalories in each gram of fat. Unsaturated fats such as vegetable oil are considered healthier, while trans fats are to be avoided. Saturated and some trans fats are typically solid at room temperature – example: butter or lard while unsaturated fats are typically liquids – example: olive oil or flaxseed oil. Trans fats are very rare in nature, and have been shown to be highly detrimental to human health, Trans fats are typically created in an industrial process called (partial) hydrogenation and are used as rancidity resistance agents.

Essential fatty acids In humans, at least two fatty acids are essential and must be included in the diet – omega - 3 and omega - 6 fatty acids. They are substrates for a class of eicosanoids known as prostaglandins, which have roles throughout the human body.