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Glycogenesis
- Increased glycogen levels possible through physical training and dietary manipulations although limited energy source
- Fat storage: conversion of glucose to fat is irreversible
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Carbohydrate Digestion
- Carbohydrates from food tend to be disaccharides (sugars) or polysaccharides (starches) which must be broken down into monosaccharidesfor absorbtion
- Begins in the mouth and ends in the small intestine where intestinal enzymes and pancreatic amylase complete the conversion to monosaccharides
- Enzymes:
- Lactase: lactose
- Sucrase: sucrose
- Maltase: maltose
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Carbohydrate Metabolism
- Primary aspect is maintenance of blood glucose homeostasis (70-100 mg/dL)
- Blood glucose sources may be CHO and non-CHO Dietary starches and simple CHO provide blood glucose after digestion and absorption
- Glycogenolysis: process of converting glycogen stored in liver and muscle back to glucose
- Gluconeogenesis: process of producing glucose from fat and protein
- Results in formation of ketones which can lead to acid base imbalances
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Blood Glucose Regulation: Hypoglycemic hormones
- Insulin
- Pancreas: beta cells
- Lowers blood glucose
- Eases glucose absorption into cells increases glucose use as energy
- Enhances glycogenesis: conversion of excess glucose to glycogen
- Stimulates lipogenesis: conversion of excess glucose to fat
- Inhibits breakdown of fat and protein
- Promotes amino acid uptake in skeletal muscle, increasing protein synthesis
- Influences glucose oxidation
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Blood Glucose Regulation: Hyperglycemic Hormones
- Glucagon
- Pancreas: alpha cells
- Raises blood glucose
- stimulates conversion of liver glycogen to glucose
- Stimulates breakdown of lipids for energy
- Somatostatin
- Released from the Pancreas and Hypothalamus
- Inhibits glucose and glucagon
- Epinephrine
- Raises blood glucose
- Enhances conversion of liver glycogen to glucose Glucocorticoids
- Promote gluconeogenesis and inhibit insulin
- Thyroid hormone Increases insulin breakdown, increases glucose absorption, causes releas of epinephrine
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Glycemic Index
- Measure of the effect of a carbohydrate-containing food on blood glucose level: ranking of how much the food raises glucose levels
- ranking of 100 highest; < 50 low
- Low glycemic index is good!
- Factors affecting glycemicindex
- Physical form such as apple juice compared with apple
- Fat and protein content in addition to CHO, which slows digestion
- Ripeness such as in fruits and vegetables, which increases glucose content
- Fiber content, which slows digestion
- Botanic variety of a food, such as the different glycemic indexes of rice species
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Simple Carbohydrates
- Monosaccharides
- Glucose
- Often called blood sugar,is the simple CHO that circulates in blood
- Found in fruits and honey
- Main energy source for central nervous system and brain
- Rapidly absorbed into bloodstream from intestine, but needs insulin to enter cells
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Sugar: a special disaccharide
- Sugar refers to simple CHO, sucrose, white table sugar, and numerous sweetening agents
- refined white sugar, brown sugar, dextrose, crystalline fructose, high fructose corn syrup (HFCS), glucose, corn sweeteners, concentrated fruit juice, honey, maple syrup, molasses, sorbitol, mannitol, xylitolÂ
- Concerns about sugar focus on (1) sources in the food supply, (2) consumption levels, and (3) health effects
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