Nutrition 101

the role of sugars, starches and fibers in your body and you health

4.1 The Chemist's View of Carbohydrates carbohydrates include monosaccharides, disaccharides, and polysaccharides carbohydrates are made of carbon (C), oxygen (O), and hydrogen (H); each atom forms a specified number of chemical bonds: carbon forms four, oxygen forms two, and hydrogen forms one monosaccharides (glucose, fructose, and galactose) all have the same chemical formula (C6H12O6), but their structures differ. Disaccharides (maltose, sucrose, and lactose) each contain a glucose paired with one of the three monosaccharides. A condensation reaction can bond two monosaccharides together to form a disaccharide and water. A hydrolysis reaction can use water to split a disaccharide into its two monosaccharides hydrolysis = takes water from disaccharide molecule to form a monosaccharide; condensation = bonds two monosaccharides together to form a disaccharide with water. Chains of monosaccharides are called polysaccharides and include glycogen, starches, and dietary fibers. Both glycogen and starch are storage forms of glucose - glycogen in the body, and starch in plants - and both yield energy. glycogen is the storage form of glucose in the body starch is the storage form of glucose in plants Dietary fibers contain glucose (and other monosaccharides), but their bonds cannot be broken by human digestive enzymes; they yield little, if any, energy (dietary fibers are not digestible). Soluble fibers dissolve in water to form gels and are easily digested by bacteria in the colon. Insoluble fibers do not dissolve in water or form gels and are less readily fermented. 4.2 Digestion and Absorption of Carbohydrates The body digests starches into the disaccharide maltose. Maltose and the other disaccharides (lactose and sucrose) from foods are broken down into monosaccharides, which are absorbed. foods must be broken down into monosaccharides to be absorbed Fibers help to regulate the passage of food through the GI tract and slow the absorption of glucose. ​​​​​​​ex: fruits are healthier than their respective juices because the fiber in the fruit negates the negative effects of the sugars. Fibers neutralize sugars. Lactose intolerance occurs when there is insufficient lactase to digest the disaccharide lactose found in milk and milk products. Symptoms include GI distress. 4.3 Glucose in the Body Dietary carbohydrates provide glucose that can be used by the cells for energy, stored by the liver and muscles as glycogen, or converted into fat if intakes exceed needs. All of the body's cells depend on glucose; those of the central nervous system are especially dependent on it. Without glucose, the body is forced to break down its protein tissues to make glucose and to alter energy metabolism to make ketone bodies from fats. ​​​​​​​ex: the reason that not consuming carbohydrates in order to lose weight will take away toned muscles is that the deficiency of glucose requires your body to eat away at your muscle instead. Blood glucose regulation depends on two pancreatic hormones: insulin to move glucose from the blood into the cells when levels are high and glucagon to free glucose from glycogen stores and release it into the blood when levels are low. ​​​​​​​insulin = pancreatic hormone that removes glucose from blood when glucose levels are high glucagon = pancreatic hormone that frees glucose from stores and released into blood when levels are low ex: diabetic patients will receive insulin pumps to neutralize the amount of glucose in their blood 4.4 Health Effects and Recommended Intakes of Sugars Excessive intakes of sugars may increase the risk of dental caries, displace needed nutrients and fiber, and contribute to obesity when energy intake exceeds needs. Concentrated sweets are relatively low in nutrients, high in kcalories, and may need to be limited; sugars that occur naturally in fruits, vegetables, and milk are acceptable. To control weight gain, blood glucose, and dental caries, consumers may use alternative sweeteners...

Practice Questions for chapter 4

1.) A condensation reaction fuses two monosaccharides together to create a disaccharide and molecule of water. A hydrolysis reaction splits a disaccharide into two monosaccharides by taking the molecule of water. 2.) Starch is storage of glucose in the body, whiles glycogen is storage of glucose in plants. Fibers are also polysaccharides, but cannot be digested in the stomach and do not yield as much energy. 3.) Disaccharides include sucrose, maltose, and lactose. (c) (mistake I made: starch, glycogen, and fiber; those are polysaccharides) 4.) The making of a disaccharide from two monosaccharides is an example of condensation. (c) 5.) The significant difference between starch and cellulose is that digestive enzymes can break the bonds in starch, but not in cellulose. (d) (mistake: mistook cellulose for glycogen; cellulose is a type of dietary fiber)