Carbohydrates — Comprehensive Study Notes

Carbohydrate Energy and Role in the Diet

  • Carbohydrates are a macronutrient involved in providing energy; macronutrients (carbohydrate, fat, protein) contain kilocalories, while micronutrients do not.
  • Energy density:
    • Carbohydrates provide E=4 kcal/gE = 4 \ \mathrm{kcal/g}.</li></ul></li><li>Carbohydratesarecomposedofcarbon,hydrogen,andoxygen;theirmetabolisminvolvesglycolysis,theKrebscycle,theelectrontransportchain,andoxidativephosphorylation.</li><li>CarbohydratesfitintotheAcceptableMacronutrientDistributionRanges(AMDR):carbohydratesshouldmakeup</li></ul></li> <li>Carbohydrates are composed of carbon, hydrogen, and oxygen; their metabolism involves glycolysis, the Krebs cycle, the electron transport chain, and oxidative phosphorylation.</li> <li>Carbohydrates fit into the Acceptable Macronutrient Distribution Ranges (AMDR): carbohydrates should make up45\% \text{ to } 65\%oftotaldailykilocalorieintake.</li><li>Whenwerefertogramsinthiscourse,wemeanof total daily kilocalorie intake.</li> <li>When we refer to grams in this course, we mean\text{g of digestible carbohydrate}(i.e.,thecarbohydratethatcanbeenzymaticallydigestedandabsorbed).</li><li>Today’stopicsincludebothdigestibleandnon−digestibleformsofcarbohydrates.</li><li>Insummary:Carbohydratesareenergy−containing;theyaremadeofcarbon,hydrogen,andoxygen;theirmetabolismpowersenergy−yieldingpathways;andtheirintakeisframedbyamacronutrientdistributionrange.</li></ul><h3id="carbohydratefoodsources">CarbohydrateFoodSources</h3><ul><li>Variedsourcesinclude:<ul><li>Grains</li><li>Vegetables</li><li>Legumes</li><li>Nutsandseeds</li><li>Fruit</li><li>Dairyproducts</li></ul></li><li>Carbohydratesarealsopresentinprocessedfoodswithaddedsugars(e.g.,soda,candy).</li><li>Practicalnote:carbohydrate−richfoodsarenotjust“starches”butalsofruits,dairy,andvegetables;processingcanalternutrientdensity.</li></ul><h3id="carbohydratenomenclatureandclassifications">CarbohydrateNomenclatureandClassifications</h3><ul><li>Suffix"saccharide"isusedtonamecarbohydrates;itderivesfromtheLatinword"sacur"meaningsugar.</li><li>Prefixesdescribehowmanysugarmoleculesarebondedtogether:<ul><li>mono−:onesugarunit(monosaccharide)</li><li>di−:two(disaccharide)</li><li>poly−:many(polyaccharide)</li></ul></li><li>Basedoncomplexity:<ul><li>Mono−anddisaccharidesarereferredtoassimplecarbohydrates.</li><li>Oligosaccharidesandpolysaccharidesarereferredtoascomplexcarbohydrates.</li></ul></li><li>Threeimportantmonosaccharides:<ul><li>glucose,fructose,andgalactose.</li><li>Glucoseishighlightedasthebody’sprimaryenergysource.</li><li>Fructoseisthesweetest−tastingmonosaccharide.</li></ul></li><li>Threedisaccharides:<ul><li>Maltose:twoglucosemoleculesbondedtogether.</li><li>Sucrose:oneglucoseandonefructosebondedtogether.</li><li>Lactose:oneglucoseandonegalactosebondedtogether.</li></ul></li></ul><h3id="digestiblevsnondigestiblecarbohydrates">DigestiblevsNon−DigestibleCarbohydrates</h3><ul><li>Digestiblecarbohydrates:thosethatareenzymaticallybrokendownandabsorbed(e.g.,glucosefromstarchandsugars).</li><li>Non−digestiblecarbohydrates:includedietaryfiberandotherpolysaccharidesthatarenotdigestedbyhumanenzymes.</li><li>Wewilldiscussdigestionofstarchesindetailandwhathappenstonon−digestibledietaryfiberthroughtheGItract.</li></ul><h3id="monosaccharidesindetail">MonosaccharidesinDetail</h3><ul><li>Glucose:body’sprimaryenergysource.</li><li>Fructose:sweetestmonosaccharide.</li><li>Galactose:componentoflactoseindisaccharides.</li></ul><h3id="disaccharidesindetail">DisaccharidesinDetail</h3><ul><li>Maltose:twoglucoseunits;foodsourcesincludevariousfruits,vegetables,grains,dairy;honeyalsocontainsmaltose.</li><li>Sucrose:glucose+fructose;foodsourcesincludesugarcane/beets,maplesyrup,honey,andhighfructosecornsyrup(HFCS).</li><li>Lactose:glucose+galactose;dairyproducts(milkandderivativeslikecheese,yogurt,kefir).</li><li>HFCSnote:notnaturallyoccurring;HFCSisafoodadditivechemicallymodifiedtohaveahigherratiooffructosetoglucosethannaturallyoccurringsucrose.</li></ul><h3id="highfructosecornsyrupandfructoseinthediet">High−FructoseCornSyrupandFructoseintheDiet</h3><ul><li>HFCSisnotnatural;itisanadditivewithalteredfructose−to−glucoseratiocomparedtosucrose.</li><li>FoodshighinfructoseincludeHFCS−containingproducts,honey,mostfruits,andsomevegetables.</li><li>Vegetablesandfruitsthattendtobehigherinfructoseincludeartichoke,asparagus,broccoli,leek,mushroom,okra,onions,peas,redpepper,shallots,andtomatoproducts.</li><li>Peoplewithfructoseintolerancemaytoleratesomefructose;lower−fructosefruitoptionsincludeavocados,bananas,cranberries,cantaloupe,lemonsandlimes,oranges,pineapple,andstrawberries.</li></ul><h3id="lactoseanddairyproducts">LactoseandDairyProducts</h3><ul><li>Lactoseisfoundindairyproductsandtheirderivatives(milk,cheese,yogurt,kefir).</li><li>Milkcancomefromcows,goats,sheep,andinsomeregions,waterbuffalo.</li></ul><h3id="polysaccharidesstarchglycogenanddietaryfiber">Polysaccharides:Starch,Glycogen,andDietaryFiber</h3><ul><li>Polysaccharidesaremanymonosaccharidesbondedtogether.</li><li>Humansstoreglucoseasglycogen;plantsstoreglucoseasstarch.</li><li>Starchisamajordietarycarbohydrate;glucoseinstarchcanbeconfiguredastwoforms:<ul><li>amylose</li><li>amylopectin</li></ul></li><li>Dietaryfiberisalsoapolysaccharidebutisstructurallyandmetabolicallydistinctfromstarch.</li><li>Starchanddietaryfiberbothcomefromplants;fiberisnotdigestedbyhumanenzymes.</li></ul><h3id="dietaryfiberindepth">DietaryFiberinDepth</h3><ul><li>Thestructuralpartofplants;typesinclude:<ul><li>cellulose</li><li>hemicellulose</li><li>pectins</li><li>gums</li><li>mucilage</li></ul></li><li>Keydifferencefromstarch:humanslackenzymestodigestdietaryfiber.</li><li>Dietaryfibercategories:<ul><li>Solublefiber:dissolvesinwater;sourcesincludeoats,barley,legumes,citrusfruits.</li><li>Insolublefiber:doesnotdissolveinwater;sourcesincludewholegrainsandvegetables.</li></ul></li><li>Healthassociations:<ul><li>Solublefiberislinkedtolowerratesofheartdiseaseanddiabetesandisfermentablebygutbacteria.</li><li>Insolublefiberpromotesbowelmovementsandhelpspreventconstipationanddiverticulardisease.</li></ul></li><li>Diverticulardisease:formationofsmallpouchesinthebowel,stronglyassociatedwithlong−termconstipation.</li><li>Fluidintakeiscrucialwhenincreasinginsolublefiberintake;inadequatefluidscanworsenconstipation.</li><li>Dietaryfiberrecommendations:(i.e., the carbohydrate that can be enzymatically digested and absorbed).</li> <li>Today’s topics include both digestible and non-digestible forms of carbohydrates.</li> <li>In summary: Carbohydrates are energy-containing; they are made of carbon, hydrogen, and oxygen; their metabolism powers energy-yielding pathways; and their intake is framed by a macronutrient distribution range.</li> </ul> <h3 id="carbohydratefoodsources">Carbohydrate Food Sources</h3> <ul> <li>Varied sources include:<ul> <li>Grains</li> <li>Vegetables</li> <li>Legumes</li> <li>Nuts and seeds</li> <li>Fruit</li> <li>Dairy products</li></ul></li> <li>Carbohydrates are also present in processed foods with added sugars (e.g., soda, candy).</li> <li>Practical note: carbohydrate-rich foods are not just “starches” but also fruits, dairy, and vegetables; processing can alter nutrient density.</li> </ul> <h3 id="carbohydratenomenclatureandclassifications">Carbohydrate Nomenclature and Classifications</h3> <ul> <li>Suffix "saccharide" is used to name carbohydrates; it derives from the Latin word "sacur" meaning sugar.</li> <li>Prefixes describe how many sugar molecules are bonded together:<ul> <li>mono-: one sugar unit (monosaccharide)</li> <li>di-: two (disaccharide)</li> <li>poly-: many (polyaccharide)</li></ul></li> <li>Based on complexity:<ul> <li>Mono- and disaccharides are referred to as simple carbohydrates.</li> <li>Oligosaccharides and polysaccharides are referred to as complex carbohydrates.</li></ul></li> <li>Three important monosaccharides:<ul> <li>glucose, fructose, and galactose.</li> <li>Glucose is highlighted as the body’s primary energy source.</li> <li>Fructose is the sweetest-tasting monosaccharide.</li></ul></li> <li>Three disaccharides:<ul> <li>Maltose: two glucose molecules bonded together.</li> <li>Sucrose: one glucose and one fructose bonded together.</li> <li>Lactose: one glucose and one galactose bonded together.</li></ul></li> </ul> <h3 id="digestiblevsnondigestiblecarbohydrates">Digestible vs Non-Digestible Carbohydrates</h3> <ul> <li>Digestible carbohydrates: those that are enzymatically broken down and absorbed (e.g., glucose from starch and sugars).</li> <li>Non-digestible carbohydrates: include dietary fiber and other polysaccharides that are not digested by human enzymes.</li> <li>We will discuss digestion of starches in detail and what happens to non-digestible dietary fiber through the GI tract.</li> </ul> <h3 id="monosaccharidesindetail">Monosaccharides in Detail</h3> <ul> <li>Glucose: body’s primary energy source.</li> <li>Fructose: sweetest monosaccharide.</li> <li>Galactose: component of lactose in disaccharides.</li> </ul> <h3 id="disaccharidesindetail">Disaccharides in Detail</h3> <ul> <li>Maltose: two glucose units; food sources include various fruits, vegetables, grains, dairy; honey also contains maltose.</li> <li>Sucrose: glucose + fructose; food sources include sugar cane/beets, maple syrup, honey, and high fructose corn syrup (HFCS).</li> <li>Lactose: glucose + galactose; dairy products (milk and derivatives like cheese, yogurt, kefir).</li> <li>HFCS note: not naturally occurring; HFCS is a food additive chemically modified to have a higher ratio of fructose to glucose than naturally occurring sucrose.</li> </ul> <h3 id="highfructosecornsyrupandfructoseinthediet">High-Fructose Corn Syrup and Fructose in the Diet</h3> <ul> <li>HFCS is not natural; it is an additive with altered fructose-to-glucose ratio compared to sucrose.</li> <li>Foods high in fructose include HFCS-containing products, honey, most fruits, and some vegetables.</li> <li>Vegetables and fruits that tend to be higher in fructose include artichoke, asparagus, broccoli, leek, mushroom, okra, onions, peas, red pepper, shallots, and tomato products.</li> <li>People with fructose intolerance may tolerate some fructose; lower-fructose fruit options include avocados, bananas, cranberries, cantaloupe, lemons and limes, oranges, pineapple, and strawberries.</li> </ul> <h3 id="lactoseanddairyproducts">Lactose and Dairy Products</h3> <ul> <li>Lactose is found in dairy products and their derivatives (milk, cheese, yogurt, kefir).</li> <li>Milk can come from cows, goats, sheep, and in some regions, water buffalo.</li> </ul> <h3 id="polysaccharidesstarchglycogenanddietaryfiber">Polysaccharides: Starch, Glycogen, and Dietary Fiber</h3> <ul> <li>Polysaccharides are many monosaccharides bonded together.</li> <li>Humans store glucose as glycogen; plants store glucose as starch.</li> <li>Starch is a major dietary carbohydrate; glucose in starch can be configured as two forms:<ul> <li>amylose</li> <li>amylopectin</li></ul></li> <li>Dietary fiber is also a polysaccharide but is structurally and metabolically distinct from starch.</li> <li>Starch and dietary fiber both come from plants; fiber is not digested by human enzymes.</li> </ul> <h3 id="dietaryfiberindepth">Dietary Fiber in Depth</h3> <ul> <li>The structural part of plants; types include:<ul> <li>cellulose</li> <li>hemicellulose</li> <li>pectins</li> <li>gums</li> <li>mucilage</li></ul></li> <li>Key difference from starch: humans lack enzymes to digest dietary fiber.</li> <li>Dietary fiber categories:<ul> <li>Soluble fiber: dissolves in water; sources include oats, barley, legumes, citrus fruits.</li> <li>Insoluble fiber: does not dissolve in water; sources include whole grains and vegetables.</li></ul></li> <li>Health associations:<ul> <li>Soluble fiber is linked to lower rates of heart disease and diabetes and is fermentable by gut bacteria.</li> <li>Insoluble fiber promotes bowel movements and helps prevent constipation and diverticular disease.</li></ul></li> <li>Diverticular disease: formation of small pouches in the bowel, strongly associated with long-term constipation.</li> <li>Fluid intake is crucial when increasing insoluble fiber intake; inadequate fluids can worsen constipation.</li> <li>Dietary fiber recommendations:25 \text{ to } 35 \mathrm{g/day}.</li><li>USaveragefiberintake(2009–2010,USDA)forindividuals2yearsandolder:.</li> <li>US average fiber intake (2009–2010, USDA) for individuals 2 years and older:16 \mathrm{g/day},wellbelowrecommendations.</li><li>Reasonforlowintake:considerwherefiberisfoundinfoodsandthepracticalimplicationsfordietarypatterns.</li></ul><h3id="wholegrainsvsrefinedgrains">WholeGrainsvsRefinedGrains</h3><ul><li>Wholegrainproductsincludethebran,germ,andendosperm;refinedgrainsremovethebranandgerm,leavingtheendosperm.</li><li>Endospermishighinstarchandhasminimalmicronutrients;branishighinfiberandBvitaminsandtraceminerals;germismicronutrientdensewithBvitamins,vitaminE,fats,andphytochemicals.</li><li>Phytochemicalsareplantchemicalswithpotentialhealthbenefitsbutarenotclassifiedasnutrients.</li><li>Refiningreducesdietaryfiberandmicronutrientswhileleavingprimarilydigestiblecarbohydrate.</li><li>Conclusion:Wholegrainproductsaremoremicronutrient−andfiber−densethanrefinedgrainproducts.</li></ul><h3id="digestionenzymesandmetabolicpathwaysoverview">Digestion,Enzymes,andMetabolicPathways(Overview)</h3><ul><li>Carbohydratenaming:theprefixindicateshowmanymonosaccharidesarebonded;thesuffix"saccharide"isused.</li><li>Enzymaticdigestion:humanspossessenzymestodigestpolysaccharidesfoundinplantstarchbutdonothaveenzymestodigestthepolysaccharidesindietaryfiber.</li><li>Keymetabolicpathwaysforcarbohydrateenergyproductioninclude:<ul><li>glycolysis</li><li>Krebscycle(citricacidcycle)</li><li>electrontransportchain</li><li>oxidativephosphorylation</li></ul></li></ul><h3id="practicalimplicationsandconnections">PracticalImplicationsandConnections</h3><ul><li>Foodchoices:emphasisonavarietyofcarbohydratesources(grains,vegetables,legumes,fruits,dairy)andawarenessofaddedsugarsinprocessedfoods.</li><li>Fructoseconsiderations:someindividualstolerateonlylimitedfructose;chooselower−fructosefruitswhenneeded.</li><li>Fiberandhealth:increasingsolubleandinsolublefibercansupportcardiovascularhealth,glucosecontrol,andguthealth,butmustaccompanyadequatefluidintaketoavoidconstipation.</li><li>Wholegrainsvsrefinedgrains:choosingwholegrainssupportsmicronutrientandfiberintake;refiningreducesnutrientdensity.</li></ul><h3id="summaryofkeyconcepts">SummaryofKeyConcepts</h3><ul><li>Carbohydratesareamacronutrientwithanenergydensityof, well below recommendations.</li> <li>Reason for low intake: consider where fiber is found in foods and the practical implications for dietary patterns.</li> </ul> <h3 id="wholegrainsvsrefinedgrains">Whole Grains vs Refined Grains</h3> <ul> <li>Whole grain products include the bran, germ, and endosperm; refined grains remove the bran and germ, leaving the endosperm.</li> <li>Endosperm is high in starch and has minimal micronutrients; bran is high in fiber and B vitamins and trace minerals; germ is micronutrient dense with B vitamins, vitamin E, fats, and phytochemicals.</li> <li>Phytochemicals are plant chemicals with potential health benefits but are not classified as nutrients.</li> <li>Refining reduces dietary fiber and micronutrients while leaving primarily digestible carbohydrate.</li> <li>Conclusion: Whole grain products are more micronutrient- and fiber-dense than refined grain products.</li> </ul> <h3 id="digestionenzymesandmetabolicpathwaysoverview">Digestion, Enzymes, and Metabolic Pathways (Overview)</h3> <ul> <li>Carbohydrate naming: the prefix indicates how many monosaccharides are bonded; the suffix "saccharide" is used.</li> <li>Enzymatic digestion: humans possess enzymes to digest polysaccharides found in plant starch but do not have enzymes to digest the polysaccharides in dietary fiber.</li> <li>Key metabolic pathways for carbohydrate energy production include:<ul> <li>glycolysis</li> <li>Krebs cycle (citric acid cycle)</li> <li>electron transport chain</li> <li>oxidative phosphorylation</li></ul></li> </ul> <h3 id="practicalimplicationsandconnections">Practical Implications and Connections</h3> <ul> <li>Food choices: emphasis on a variety of carbohydrate sources (grains, vegetables, legumes, fruits, dairy) and awareness of added sugars in processed foods.</li> <li>Fructose considerations: some individuals tolerate only limited fructose; choose lower-fructose fruits when needed.</li> <li>Fiber and health: increasing soluble and insoluble fiber can support cardiovascular health, glucose control, and gut health, but must accompany adequate fluid intake to avoid constipation.</li> <li>Whole grains vs refined grains: choosing whole grains supports micronutrient and fiber intake; refining reduces nutrient density.</li> </ul> <h3 id="summaryofkeyconcepts">Summary of Key Concepts</h3> <ul> <li>Carbohydrates are a macronutrient with an energy density ofE = 4 \ \mathrm{kcal/g}andshouldcompriseand should comprise45\%\text{ to }65\%ofdailycalories.</li><li>Digestiblecarbohydratescontributetoenergyproduction;non−digestiblecarbohydrates(dietaryfiber)arenotdigestedbyhumanenzymesbuthaveimportanthealthroles.</li><li>Monosaccharides:glucose,fructose,galactose;glucoseistheprimaryenergysource;fructoseisthesweetest.</li><li>Disaccharides:maltose(glucose+glucose),sucrose(glucose+fructose),lactose(glucose+galactose);HFCSisnotnaturalandhasahigherfructose−to−glucoseratiothansucrose.</li><li>Polysaccharides:starch(amyloseandamylopectin)andglycogen(animalstorage);dietaryfiberisanon−digestiblepolysaccharideclass.</li><li>Dietaryfibertypes:soluble(fermentable;oats,barley,legumes,citrus)andinsoluble(wholegrains,vegetables);solublefibersupportshearthealthanddiabetesriskreduction;insolublefibersupportsbowelhealthandconstipationprevention.</li><li>Fiberrecommendations:of daily calories.</li> <li>Digestible carbohydrates contribute to energy production; non-digestible carbohydrates (dietary fiber) are not digested by human enzymes but have important health roles.</li> <li>Monosaccharides: glucose, fructose, galactose; glucose is the primary energy source; fructose is the sweetest.</li> <li>Disaccharides: maltose (glucose + glucose), sucrose (glucose + fructose), lactose (glucose + galactose); HFCS is not natural and has a higher fructose-to-glucose ratio than sucrose.</li> <li>Polysaccharides: starch (amylose and amylopectin) and glycogen (animal storage); dietary fiber is a non-digestible polysaccharide class.</li> <li>Dietary fiber types: soluble (fermentable; oats, barley, legumes, citrus) and insoluble (whole grains, vegetables); soluble fiber supports heart health and diabetes risk reduction; insoluble fiber supports bowel health and constipation prevention.</li> <li>Fiber recommendations:25\text{ to }35 \mathrm{g/day};USaverageisaround; US average is around16 \mathrm{g/day}$$ (2009–2010 data).
    • Whole grains provide more micronutrients and fiber than refined grains due to bran and germ removal during refining.
    • Metabolic context: carbohydrate digestion and energy production involve glycolysis, the Krebs cycle, the electron transport chain, and oxidative phosphorylation.
    • Naming conventions: prefixes (mono-, di-, poly-) and suffixes ("-saccharide"); monosaccharides and disaccharides are simple carbs; oligosaccharides and polysaccharides are complex carbs.
    • Practical relevance: dietary patterns influence energy balance, metabolic health, and bowel health; thoughtful choices around fiber and whole grains can impact long-term health outcomes.

    References

    • References for today’s presentation were provided in the transcript.