No-Carb? Low-Carb? High-Carb?

Transcription

1 No-Crb? Low-Crb? igh-crb? MIKE CIESIELSKI Never before hs the role of crbohydrtes in our diet been so thoroughly discussed. We ll try to cut through the hype to give you the lowdown on... By Brin Rohrig 6 ChemMtters, CTBER

2 Wht re crbs? The word crbohydrte revels tht ll crbs re composed of three elements: crbon, hydrogen, nd oxygen. There re three min ctegories of crbohydrtes monoscchrides, discchrides, nd polyscchrides. Monoscchrides re composed of one sugr unit nd re referred to s simple sugrs. Their empiricl formul is generlly C 2. Some common monoscchrides re glucose nd fructose. Although both hve formul of C , they hve different rrngement of toms. Such compounds re clled isomers. Glucose is produced by plnts during photosynthesis. Glucose cn be found in sports drinks, providing quick energy when C 2 C 2 Glucose Fructose C 2 you need it. Glucose is the body s primry fuel source. It is broken down into energy through the process of cellulr respirtion. Crbon dioxide is relesed s wste product. If glucose is not converted into energy, it is converted into glycogen to be stored. Discchrides, lso known s double sugrs, re composed of two simple sugr molecules. The most common discchride is sucrose or tble sugr. In order to be used by our body s energy, sucrose must first be broken down into glucose nd fructose. Food mnufcturers re more often replcing sucrose in products with fructose, becuse it is cheper to produce, nd becuse it is sweeter, less needs to be used. ther common discchrides re mltose nd lctose (milk sugr). Polyscchrides re complex crbohydrtes. They re polymers composed of long chins of sugr units. A common polyscchride is strch, which is composed of long chins of glucose molecules. Strch is used by plnts s wy to store energy, nd it cn be found in foods such s pottoes, rice, corn, nd whet. ur body must brek down strch into glucose, which it then uses for energy. ther types of complex crbohydrtes re not digestible by our body. Chief mong these re cellulose, which forms the cell wlls of plnt cells, giving them structure nd support. Its glucose molecules re linked together in such wy tht our body lcks the necessry enzymes to brek them down. These indigestible polyscchrides re known s fiber, nd they contribute no clories becuse our bodies cnnot convert them into energy. igh-fiber foods such s ots, brn, nd whole grins re n essentil prt of our diet, iding in digestion. Crbohydrtes nd blood sugr To understnd the effect of crbohydrtes on our body, it is importnt to understnd their role on blood sugr. Just like cr requires fuel, so does our body. The body s mjor fuel source is glucose, or blood sugr. owever, this blood sugr is not utomticlly relesed into the cells. If cr s engine receives too much fuel, the engine becomes flooded, nd it will not strt. In the sme wy, the body must regulte how much blood sugr enters our cells. This occurs through the production of the hormone insulin, which is mnufctured by the pncres. Think of insulin s the gtekeeper to the cells it opens the gtes nd llows glucose to leve the bloodstrem nd enter our cells. C 2 Sucrose C 2 C 2 C 2 C 2 C 2 C 2 C 2 C 2 C 2 nce sugr enters our cells, it cn do one of three things. It cn be converted into energy through cellulr respirtion. r it cn be converted into glycogen in the liver nd muscles, for use s n emergency fuel. Glycogen is similr to strch but is more extensively brnched. Finlly, it cn be converted into ft if there is more sugr vilble thn is needed. Consider wht hppens when you wsh down glzed doughnut with sugry sod. As your bloodstrem is inundted with sugr, temporry spike in blood sugr will occur. Your pncres responds by producing surge of insulin to quickly rid the bloodstrem of this excess sugr. This quick relese of insulin will cuse your blood sugr to then drop suddenly. The sudden drop in blood sugr cn cuse wekness, ftigue, nd intense hunger often leding to crving for more delicious glzed donuts. This cn crete vicious cycle, where our blood sugr constntly rises nd flls, leding to overeting nd eventul weight gin. A well-blnced diet cn help to reduce these sudden peks nd flls in C 2 blood sugr. ver the long term, constnt spikes in blood sugr nd insulin re not good thing. When so much insulin is produced for so long, your body my become immune to the effects of it, creting condition known s insulin resistnce often precursor to type 2 dibetes. For resons not yet fully understood, the cells cn become desensitized to the effects of insulin, with the result tht glucose is not effectively tken into the cells nd converted into energy. The liver then tkes over, tking this excess blood sugr nd converting it into ft leding to obesity. And the overworked pncres my get worn out from producing so much insulin. Why not rdiclly cut crbohydrtes from the diet? Et s much bcon nd eggs s you wnt s long s you forget bout the tost nd ornge juice?! Such suggestion is t the very lest culinry, if not dietry, heresy. But s result of two decdes of rising obesity rtes nd the sheer populrity of low-crb diets, reserchers, doctors, nd dietitins begn re-exmining the theories of Dr. Robert Atkins, who published Dr. Atkins Diet Revolution in e dvocted eting ll of the fts nd proteins you wnted, nd sid tht if you only cut out ll those crbohydrtes, you would lose weight. The polyscchride glycogen is stored form of glucose. C2 R In the United Sttes one teen in seven is overweight. SURCE: SURGEN GENERAL DAN SERB ChemMtters, CTBER

3 PT BY STAFF Numerous modifictions of the Atkins diet, such s the South Bech Diet nd the Zone, hve since ppered. Mny of these modified diets hve more blnced pproch, stressing the importnce of voiding unhelthy sturted fts found in red met nd diry products, nd emphsizing helthier unsturted fts found in nuts, fish, nd vegetble oils. Millions hve tried the diet with success nd testimonils bound. By now, you ve probbly herd friend or fmily member give the low-crb dieter litny: I filed on other diets, but this diet worked for me becuse I wsn t hungry ll the time. I lost weight fster thn on other diets, nd I wsn t hungry ll the time. r even, I filed on this diet, but t lest I wsn t hungry ll the time! ow do low-crb diets work? All diets work ccording to one bsic principle: You must burn more clories thn you consume. ow mny clories you burn depends on both metbolism nd exercise. You cnnot lose weight if you consume more clories thn your body uses. By cutting out crbs, you re cutting bck on lot of clories. Cutting out just sugred sods, potto chips, nd cndy brs cn reduce your overll clorie consumption drmticlly. Another reson low-crb diets re successful is tht fts nd protein hve better stying power. Becuse crbohydrtes re rpidly converted into glucose nd then utilized by your body s energy, they do not keep us stited for long. Ft nd protein re bsorbed more slowly by the body, so they sty with us longer. Even though low-crb diets clim you cn et ll the ft nd protein you wnt, in truth these foods fill us quicker, cusing us to ultimtely et less. Ketosis: An inefficient wy to burn ft Although some clim tht reduced-crbohydrte diet is nothing more thn reduced-clorie diet in disguise, low-crb diets ctully do one thing tht is rdiclly different thn ny other diet. The mjority eliminte most, if not ll, crbohydrtes in the initil induction phse of the diet. When the body becomes crbohydrte-strved, it must find n lternte energy source. The first source it tps is the glycogen found in the liver nd muscle. But the body s glycogen stores cn only lst bout two dys. After this, our body turns to ft for energy. owever, the brekdown of ft in this cse does not produce glucose. Insted, the ft is broken down into ketones, through n unusul process known s ketosis. Normlly, people burn fts without mking ketones. Ketosis only occurs when people re crbohydrte-strved. During ketosis, ft is not completely broken down nd you don t receive the norml cloric vlue from burning it. The excess ketones produced during ketosis re secreted in our urine nd breth. Sometimes this gives your breth fruity odor, since cetone ketone MIKE CIESIELSKI my be relesed by the breth during ketosis. Becuse the kidneys flush out these ketones from the body, it is importnt to drink lot of wter C 3 All diets work ccording to one bsic principle: You must burn more clories thn you consume. C C 2 C Acetocette ( ketone body) on low-crb diet. Dieters often confirm their body is in ketosis by checking their urine with ketone test strips (see Lb on Stick in this issue). Considerble debte hs risen mong medicl experts s to whether or not ketosis is dngerous. Some confuse ketosis with more serious condition known s ketocidosis, which is n extreme form of ketosis sometimes suffered by type 1 dibetics. During ketocidosis, the p of the blood flls to dngerous levels, becuse of excessive buildup of cidic ketones. This cn led to com nd deth if left untreted. Some rgue tht the body functions even better when using ketones s fuel. thers clim tht the brin cnnot function s well on ketones, nd the body will turn to muscle nd orgn tissue to try to scvenge glucose for fuel. owever, most medicl uthorities tody re lening towrd the view tht ketosis is sfe bodily process s long s ketones re not produced fster thn the body cn get rid of them. Are low-crb diets good for you? The low-crb diet phenomenon is still too new to judge its long-term effects. owever, two studies recently published in the New Englnd Journl of Medicine offered some promising news for dult low-crb dieters. These studies found tht prticipnts who lost weight on low-crb diets hd higher levels of DL (good) cholesterol nd lower levels of triglycerides, or fts, thn those who lost weight on different diets. There s no specific reserch on teengers, but you should be wry of going on the diet, especilly if you re still growing. Mny prticipnts scrifice the helth benefits of the nutrients found in milk, fruit, nd whole grins. steoporosis cn result from long-term deficiency of clcium in the diet, which could result if milk ws totlly eliminted from the diet. Pregnnt women should definitely not be on the diet, becuse the developing fetus cn be hrmed by the lck of nutrients. Athletes should lso void lowcrb diets, since pek thletic performnce is dependnt on the quick vilbility of glucose for energy, s well s relying on glycogen reserves. Any diet is only s successful s the bility to remin on it for life. And mke sure you incorporte plenty of exercise in ny weight-loss pln you choose. Brin Rohrig is chemistry techer t Jonthn Alder igh School in Plin City,. is lst rticle for ChemMtters, Lightning: Nture s Dedly Fireworks ppered in the April 2004 issue. PT BY STAFF L 8 ChemMtters, CTBER

4 ctober 2004 Techer s Guide Crb Crzy

5 Student Questions Crb Crzy 1. Wht three elements re in crbohydrte? 2. ow is glucose used in the body? 3. Wht polyscchride is storge form of glucose? 4. Wht is the reltionship between insulin nd blood sugr? 5. By wht bsic principle do ll diets work? 6. ow is ketocidosis different thn ketosis? 7. Why would n thlete wnt to void low crb diet? Copyright 2004, Americn Chemicl Society 2

6 Answers to Student Questions Crb Crzy 1. Wht is crbohydrte? Crbohydrtes re composed of three elements: crbon, hydrogen, nd oxygen. 2. ow is glucose used in the body? Glucose is the body s primry fuel source. It is broken down during cellulr respirtion to relese energy. Crbon dioxide is relesed s wste product. 3. Wht polyscchride is storge form of glucose? Glycogen. 4. Wht is the reltionship between insulin nd blood sugr? Insulin cn be thought s the gtekeeper for blood sugr entering cells. When insulin is relesed by the pncres, blood sugr levels drop. 5. By wht bsic principle do ll diets work? You must burn more clories thn you consume. 6. ow is ketocidosis different thn ketosis? During ketosis, ft is not completely broken down nd your body produces nd excretes ketone bodies. Ketocidosis is n extreme form of ketosis where cid ketone bodies build up fster thn they cn be excreted. The result is dngerous drop in blood p nd, if left untreted, com nd deth. 7. Why would n thlete wnt to void low crb diet? Athletes rely on glucose nd glycogen reserves for quick energy. Most low-crb diets hve n induction phse tht consumes vilble glycogen reserves. Copyright 2004, Americn Chemicl Society 3

7 Content Reding Mterils Ntionl Science Eduction Content Stndrd Addressed As result of ctivities in grdes 9-12, ll students should develop understnding Science s Inquiry Stndrd A: of bilities necessry to do scientific inquiry Science s Inquiry Stndrd A: bout scientific inquiry. Physicl Science Stndrd B: of the structure nd properties of mtter. Physicl Science Stndrd B: of chemicl rections. Life Science Stndrd C: of the cell. Life Science Stndrd C: of mtter, energy, nd orgniztion in living systems. Science nd Technology Stndrd E: bout science nd technology. Crb Crzy Science in Personl nd Socil Perspectives Stndrd F: of personl nd community helth. Science in Personl nd Socil Perspectives Stndrd F: of science nd technology in locl, ntionl, nd globl chllenges. istory nd Nture of Science Stndrd G: of science s humn endevor. istory nd Nture of Science Stndrd G: of the nture of scientific knowledge. istory nd Nture of Science Stndrd G: of historicl perspectives. *QFTC-Question From the Clssroom Copyright 2004, Americn Chemicl Society 4

8 Reding Strtegies These content frmes nd orgnizers re provided to help students locte nd nlyze informtion from the rticles. Student understnding will be enhnced when they explore nd evlute the informtion themselves, with input from the techer if students re struggling. If you use these reding strtegies to evlute student performnce, you my wnt to develop grding rubric such s the one below. Score Description Evidence 4 Excellent 3 Good 2 Fir 1 Poor 0 Not cceptble Complete; detils provided; demonstrtes deep understnding. Complete; few detils provided; demonstrtes some understnding. Incomplete; few detils provided; some misconceptions evident. Very incomplete; no detils provided; mny misconceptions evident. So incomplete tht no judgment cn be mde bout student understnding. Copyright 2004, Americn Chemicl Society 5

9 Crb Crzy Crbohydrtes Monoscchrides Discchrides Polyscchrides Brief Description Exmples Plese put these terms in the boxes below: Ft, glycogen, insulin, ketosis, C 2, 2, glucose, cell. Broken down into gtekeeper Cellulr respirtion Glucose my be converted to Glucose my be converted to ENERGY Strvtion my led to Emergency fuel ketones Copyright 2004, Americn Chemicl Society 6

10 Anticiption Guides Anticiption guides help engge students by ctivting prior knowledge nd stimulting student interest before reding. If clss time permits, discuss their responses to ech sttement before reding ech rticle. As they red, students should look for evidence supporting or refuting their initil responses. Directions for ll Anticiption Guides: In the first column, write A or D indicting your greement or disgreement with ech sttement. As you red, compre your opinions with informtion from the rticle. In the spce under ech sttement, cite informtion from the rticle tht supports or refutes your originl ides. Crb Crzy Me Text Sttement 1. All digestible crbohydrtes re broken down into glucose so the body cn use them. 2. Fructose is more expensive nd less sweet thn sucrose. 3. Indigestible crbohydrtes re unhelthy. 4. Eting sugry sncks cn ctully mke you hungry sooner. 5. To lose weight, you must burn more clories thn you et. 6. Your body burns ft before glycogen. 7. People on low-crb diets should restrict wter intke. 8. Proteins nd fts re bsorbed more quickly in the body thn crbohydrtes. 9. Low crb diets re good for teengers. Copyright 2004, Americn Chemicl Society 7

11 Crb Crzy Bckground Informtion Both strch nd glycogen re importnt polyscchrides which ct to store the simple sugr monomers composing them. Both strch nd glycogen polymerize within cells by form of condenstion synthesis in which hydroxyl group of one monomer rects with the nomeric crbon t the opposite end of second monomer. Molecules of wter re eliminted in the process. Simple sugrs re relesed from storge when the polysccride undergoes the reverse process, hydrolysis, in which molecules of wter re restored. Strch is mde by plnt cells, nd glycogen, by nimls. Both of the polysccrides, with their mny exposed hydroxyl groups, become hevily hydrted in their cellulr environments. Strch molecules huge polysccrides (m.w. often exceeding 1 million) re generlly of two types: mylose consisting of long, unbrnched chins of D-glucose, nd mylopectin, highly brnched. Glycogen, similr to mylopectin, is even more highly brnched. It generlly ppers in grnules tht lso contin enzymes redy to degrde the molecule when conditions re right. Both strch nd glycogen re essentilly insoluble. If the point is to hve glucose redy for instnt use s cellulr fuel, why don t cells simply store the glucose molecules in solution? It turns out tht hving tht mny prticles in solution would crete severe osmotic imblnce tht would either cuse the cells to swell nd burst, or, t the very lest, would rech n equilbrium stte in which no dditionl net gin in glucose molecules would occur. Are ll crbohydrtes creted equl? Do ll crbohydrtes contribute eqully to rise in blood sugr? Fortuntely, no. There re good nd bd crbohydrtes, depending on how quickly tht crbohydrte is converted to glucose in the bloodstrem, s mesured by the glycemic index (GI). The GI rtes glucose t 100, nd foods re rnked ccording to how fst they enter the bloodstrem, reltive to glucose. For exmple, if food hs GI of 50, it is bsorbed into the bloodstrem hlf s fst s tht of glucose. Good crbohydrtes hve low GI, nd bd crbohydrtes hve high GI. White bred, for exmple, hs GI of 70, while pumpernickel hs GI of 41. Wtermelon hs GI of 72, but plum hs GI of only 24. Instnt white rice hs GI of 91, while brown rice only hs GI of 55. Generlly, the more refined the food, the quicker it cn be broken down nd the higher its GI. The more work our body must do to brek down substnce, the slower it will be bsorbed into the bloodstrem. Apple juice hs higher GI thn pples. Bked pottoes hve the highest GI of ll pottoes t 85. To void spikes in blood sugr, with the resultnt insulin spike followed by crsh in blood sugr, choose crbohydrtes with low GI. The GI is not perfect mesure of wht foods to et, however. Fructose, for exmple, hs GI of only 20. Scientists ctully give rts lrge does of fructose to mke them insulin resistnt. Connections to Chemistry Concepts Relting the Cloric vlues of foods to the concepts surrounding ets of Combustion is relevnt to the rticle s discussions bout diet plns. Possible Student Misconceptions Students frequently mistke food Clories (ctully kiloclories) for the unit of energy the clorie. The kilo portion is of course very importnt. Just wrming 200 g cup of wter from room temperture to norml body temperture (25 o C to 37 o C) requires 2400 clories. Is 2400 clorie (not 2400 Clorie or 2400 kiloclorie) diet sufficient to mintin humn body temperture for 24 hours? Copyright 2004, Americn Chemicl Society 8

12 Students my lso wonder bout the term burning food for clories. Misconceptions re compounded by hering foods described s fuels. The wy the cells depend on enzymes to lower the ctivtion energy necessry for breking chemicl bonds during metbolism is bsic topic in mny modern biology curricul. A brief discussion my cler up the confusion if it occurs. Demonstrtions nd Lessons The ACS Chemistry in the Community, 4 th Ed. textbook s well s other bsic high school chemistry textbooks, hs lbortory investigtion in which students construct clorimeter using sod cn contining 100 ml of wter. Students relte the temperture increse in the wter to the weight of prffin consumed by burning cndle in order to determine the et of Combustion of prffin in kj/g. A similr procedure might be devised to determine the het of combustion of smll piece of wood. Comprisons between prffin (lipid) nd wood (crbohydrte) hets of combustion would be relevnt to discussion bout the reltive roles of fts nd crbohydrtes in diet pln. Connections to the Chemistry Curriculum rgnic chemistry, therml energy, nd polymers re topics tht relte to the content of the rticle. In ddition, the wys in which informtion is collected nd nlyzed for mking informed consumer choices is criticl gol of every good high school science progrm. Suggestions for Student Projects 1. Students cn run nlyses of their own diets. The nlysis cn be quick nd simple ctivity such s keeping list of wht is eten on one typicl dy nd then plcing ech food into the pproprite plce on the food pyrmid. A more complex nlysis might involve record of wht ws eten over severl dys followed by detiled nlysis of Cloric content, s well s crbohydrte, ft, nd protein content (on percent by Clorie bsis), including even the mounts of vitmins nd minerls. ChemCom provides rther extensive tble of foods showing this type of nutritionl informtion. See lso the list of suggested Web sites for this rticle. 2. Students cn perform blind tste tests of low-crb or sugr-free food products to compre them to their sugry counterprts 3. Students could exmine one of the current fd diets nd either prepre pper or give clss presenttion on the rtionle behind the diet. Different tems of students could debte the merits of the diet one side rguing in its fvor, the other opposing the diet. Anticipting Student Questions Students will wnt to know if diet like the Atkins diet is good for them. As the rticle points out, there hve been no significnt long-term studies to find out whether minimizing crbs in teenger s diet pln dvisble or even sfe for losing weight. Websites for Additionl Informtion nd Ides Students will be interested in finding out bout, nd perhps, compring other diet plns. For n informtive nd entertining ccount of severl diet fds of the pst go to More of diet plns re found t this site. Be sure to check out the Pleolithic Diet! Copyright 2004, Americn Chemicl Society 9