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 (artificial sweeteners, herbal products, and sugar alcohols) to limit kcalories and minimize sugar intake.
- Weight gain, blood glucose, and dental caries are not necessarily all related, but are caused by the same misuse of sugars

4.5 Health Effects and Recommended Intakes of Starch and Fibers

Adequate intake of fiber fosters weight management, lowers blood cholesterol, and may help prevent colon cancer, diabetes, hemerrhoids, appendicits, and diverticulosis.
Excessive intake of fiber displaces energy - and nutrient-dense foods, causes intestinal discomfort and distention, and may interfere with mineral absorption.
Because starches and fibers help control body weight and prevent heart disease, cancer, diabetes, and GI disorders, the Dietary Guidelines suggest plenty of whole grains, vegetables, legumes, fruits - enough to provide 45 to 65% of the daily energy intake from carbohydrates.

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