Chapter 2 Carbohydrates Copyright 2017 Elsevier Inc All Rights Reserved Lesson 21 Carbohydrates Energy Source Their Structures Role as Fiber Carbohydrate foods provide practical energy sources because of their availability relatively low cost and storage capability ID: 773011
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Chapter 2 Carbohydrates Copyright © 2017, Elsevier Inc. All Rights Reserved.
Lesson 2.1: Carbohydrates: Energy Source, Their Structures, Role as FiberCarbohydrate foods provide practical energy sources because of their availability, relatively low cost, and storage capability.Carbohydrate structures vary from simple to complex, providing both quick and extended energy for the body.Dietary fiber, an indigestible carbohydrate, serves other functions within the gastrointestinal tract.Copyright © 2017, Elsevier Inc. All Rights Reserved.2
Nature of CarbohydratesRelation to energyBasic fuel sourcePlants, through photosynthesis, transform solar energy into carbohydrate, which is the stored fuel form in plants.Energy production systemDigests carbohydrate to produce glucoseAbsorbs glucose and transports it to cellsMetabolizes glucose to ultimately release energyDietary importanceWidely available and easily grownLow costEasily storedCopyright © 2017, Elsevier Inc. All Rights Reserved.3
Classes of CarbohydratesSaccharide = Carbohydrate classSimple carbohydrates have 1 or 2 sugar unitsMonosaccharides (1)Disaccharides (2)Complex carbohydrates have many sugar unitsPolysaccharidesCopyright © 2017, Elsevier Inc. All Rights Reserved.4
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Classes of CarbohydratesMonosaccharidesGlucose: basic single sugar in human metabolismFructose: primarily found in fruits and honeyGalactose: product of lactose (milk sugar) digestionCopyright © 2017, Elsevier Inc. All Rights Reserved.6
Classes of Carbohydrates (cont’d)Copyright © 2017, Elsevier Inc. All Rights Reserved.7Data from U.S. Department of Agriculture, Economic Research Service. Food availability (per capita) data system, sugar and sweeteners (added). Available from: <www.ers.usda.gov/data-products/food-availability-%28per-capita%29-data-system/.aspx#.U7BpG3awXG4>; Accessed June 6, 2015.
Classes of Carbohydrates (cont’d)DisaccharidesSucrose: common table sugar (glucose + fructose)Lactose: sugar found in milk (glucose + galactose)Maltose: product of intermediate digestive breakdown of starch within the body (glucose + glucose)Copyright © 2017, Elsevier Inc. All Rights Reserved.8
Classes of Carbohydrates (cont’d)PolysaccharidesComplex carbohydratesComposed of many single-sugar unitsStarch: most significant polysaccharidesGlycogen: formed within body tissues; crucialDietary fiber: important dietary assetCopyright © 2017, Elsevier Inc. All Rights Reserved.9Courtesy Eileen Draper.
Dietary Fiber Dietary fiber cannot be broken down for energy in humans.Soluble fiberInsoluble fiberSources: Whole grainsLegumesVegetablesFruits with as much skin remaining as possibleDiets high in fiber can help prevent and treat diseaseCopyright © 2017, Elsevier Inc. All Rights Reserved.10
Dietary Fiber (cont’d)BenefitsLowers blood cholesterol levelsPromotes normal bowel function and prevents constipationIncreases satiety, which helps with the prevention of obesityProtects against disorders of the small and large intestinesSlows glucose absorption, thereby reducing blood glucose spikes and insulin secretion.Copyright © 2017, Elsevier Inc. All Rights Reserved.11
Dietary Fiber (cont’d)Health organizations emphasize role of dietary fiberRecommended daily intake for men age 19 - 50: 38 g/day 30 g/day for men > 50For women age 19 - 50: 25 g/day 21 g/day for women > 50Increases should be gradual to avoid gastrointestinal distressCopyright © 2017, Elsevier Inc. All Rights Reserved.12
Case StudyM.H., a 45-year-old female, has made a nutrition goal to increase her intake of dietary fiber to 25 grams per day. She comes for nutrition counseling on food suggestions to assist her in being successful. Copyright © 2017, Elsevier Inc. All Rights Reserved.13
Case Study (cont’d)Before going further with M. H. in giving suggestions for increasing fiber intake in the diet, what questions may you need to investigate?Copyright © 2017, Elsevier Inc. All Rights Reserved.14
Case Study: Recommendations for IntakeAfter reviewing M.H.’s fiber intake for a typical day, you find that she consumes less than half of the recommended intake for women of 25 grams per day.Copyright © 2017, Elsevier Inc. All Rights Reserved.15
Case Study: Follow Up on Fiber IntakeM.H. returns for a follow-up visit to make sure she is following the suggested recommendations for increasing fiber intake.Copyright © 2017, Elsevier Inc. All Rights Reserved.16
CelluloseCellulose: chief component of plant cell walls Holds waterAdds bulk to the dietLigninOnly noncarbohydrate dietary fiberLarge compound, forms woody part of some plantsNoncellulose polysaccharidesAbsorb water and swell to larger size, which aids satiety by slowing stomach emptying of food massBind with bile acidsProvide bulk, thereby preventing spastic colon pressureCopyright © 2017, Elsevier Inc. All Rights Reserved.17
Other SweetenersNutritive sweetenersSugar alcohols (sorbitol, mannitol, xylitol)Nutritive sweeteners that provide 2 to 3 kcal/gNonnutritive sweetenersAlternative or artificial sweeteners used in food productsMost common: acesulfame-K, aspartame, luohan guo, neotame, saccharin, stevia, sucraloseCopyright © 2017, Elsevier Inc. All Rights Reserved.18
Copyright © 2017, Elsevier Inc. All Rights Reserved.Adapted from Fitch C, et al. Position of the Academy of Nutrition and Dietetics: use of nutritive and nonnutritive sweeteners. J Acad Nutr Diet. 2012;112(5):739-758.
Functions of CarbohydratesPrimary energy functionBasic fuel supplyPhysical activitiesWork of body cellsReserve fuel supplyLiver stores about 100 g of glycogenPrimarily maintains blood glucose and ensures brain functionSkeletal muscles can stores 300 to 400 gCopyright © 2017, Elsevier Inc. All Rights Reserved.20
Functions of Carbohydrates (cont’d)Primary energy function (cont’d)Special tissue functionsLiver: glycogen reserves maintain overall energy balanceCentral nervous system depends on constant carbohydrate supplyProtein and fat sparing If dietary carbohydrate is sufficient to meet energy needs, protein does not have to be sacrificed to supply energy and fat is not needed to supply large amounts of energyCopyright © 2017, Elsevier Inc. All Rights Reserved.21
Food Sources of CarbohydratesStarchesMost important carbohydrate in the dietWhole-grain starches such as rice, wheat, corn, and potatoes SugarsNot necessarily badAdded sugars provide empty caloriesModeration is keyCopyright © 2017, Elsevier Inc. All Rights Reserved.22
Digestion of Carbohydrates MouthMechanical functions break food mass into smaller particlesChemical processes in which specific enzymes continue breaking down nutrients (amylase breaks down starch)StomachPeristalsis continues mechanical digestive processGastric secretions mix with food particles to facilitate chemical digestionSecretions do not break down carbohydrates but stop action of salivary amylase Copyright © 2017, Elsevier Inc. All Rights Reserved.23
Digestion of Carbohydrates (cont’d)Small intestinePeristalsis continues to aid digestionPancreatic secretionsPancreatic amylase breaks starches down into disaccharides and monosaccharides.Intestinal secretions (from brush border)Specific enzymes act on their respective disaccharides to render the monosaccharides—glucose, galactose, and fructose—ready for absorption directly into the portal blood circulation.Copyright © 2017, Elsevier Inc. All Rights Reserved.24
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Recommendations for Dietary CarbohydrateDietary Reference Intakes45% to 65% of adult’s total caloric intake should come from carbohydrate foodsLimit added sugar to no more than 25% of calories consumedDietary Guidelines for Americans, 2015-2020Consume at least half of all grains as whole grains.Increase vegetable and whole fruit intake.Choose more nutrient-dense foods and less foods and beverages with added sugar.Reduce the intake of calories from added sugars to less than 10% of total calories.Copyright © 2017, Elsevier Inc. All Rights Reserved.26
Recommendations for Dietary Carbohydrate (cont’d)MyPlateMyPlate Tracker allows users to input personal menu for evaluation on quality of diet Resource for feedback on dietary sources of carbohydrateFiber, whole grain, fruits, vegetables, and added sugarsCopyright © 2017, Elsevier Inc. All Rights Reserved.27
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