Use and storage Jean-Pierre ABSTRACT at rates Starch, appropriate matching sugars, body’s stores is regulated carbohydrate are fat tissue mass, which one eats. oxidation so small J Clin be Nutr alter and to because free oxidize as WORDS acid con- Fat intake and in determining fat as one 1995;61(suppl):952S-9S. body fat content, respiratory Dietary carbohydrate, weight maintenance, quotient, obesity, dietary fat, glycogen, macronutrient balance, exercise The distributed with fatty their other energy most to These the which must by the nervous use therefore are are used used central cannot they fuels ATP the cells energy, in which metabolic However, The human body adjusts in the relative proportions dietary form regenerate specialized needs, of the are the main activities. a few glucose. ferences provide the body. efficiency metabolic and meet fats acids throughout similar body’s tem and and fatty sysacids be supplied to with readily to considerable of canbohydnate and fat difin the diet, even when major changes in the carbohydrate-to-fat ratio occur (1). Because the fraction of total dietary energy provided by protein is relatively small and relatively constant, and because stant amino protein acid termined The the body spontaneously maintains content by adjusting amino intake, body weight maintenance by the intake regulation many factors some are are and utilization of body weight in preventing inherited, and others a nearly is a complex are and problem or causing solve is to review olism for ents play 9525 and the a better in the dietary main variables related features understanding maintenance (2). aim of carbohydrate J Clin evaluation dietary of in various carbohydrate forms of edible and carbohydrates tubers. They energy needs, except in affluent is a major source of energy almost the when and fat as much particular processing important rate of provide are the the bulk Western and where societies sucrose energy as starch (3). It is helpful problem that the organism has carbohydrates. For first be broken exert a powerful that starch carbohydrates to to to be down into monosaccharosmotic effect and it is intestinal absorption be able hydrolysis. Furthermore, to keep up absorption with the must be completed before tenial fermentation; otherwise, such as those experienced after lactose ingestion by individuals low intestinal lactase activity. Meals commonly supply carbohydrates g carbohydrate. glucose there This present in the is much rapidly cells. transferred into state are blood glucose expended glucose of glucose must Glycogen incorporate rise 1 trapped fat. carbohydrates, and glycogen. much be expended molecules in the cells mol The (4). Two they ATE glycogen. are thus made of the associated effectively without creating hydrophilic with of glycogen density moles into complete oxidation of of the energy content were In view is energy in the of the glucose it as glycogen. large; they effect. glycogen oxidation most glucose to store are very in which of an osmotic of glucose must be conversion to glycogen, primarily uptake and glycogen synthesis are the secretion of which increases concentrations to effects, the 15-25 g 5 g is in the than spillage circulation 10 g/h, to bac- side only and the into only taken up must be stoned by in liver and muscle. Glucose greatly stimulated by insulin, when more Because consumes subjected of which hyperglycemia transferred postprandial are are unpleasant body, blood itself. To avoid into the urine, glucose to de- and of this to and fat article nature ‘3 stores g of water/g is thus only Nuir From the University of Massachusetts Medical School, Department of Worcester, MA. metab- of the roles these macronutniof stable body weights and Am stabiliza- important obesity- to lifestyle The the of by grains absorbed, they must ides. Small molecules I socioeconomic for weight is Because 36 ATP are gained during the one molecule of glucose, 2/36, or ‘“5% con- acid oxidation is primarily of carbohydrate involved basis effect abundant provided supplies understand free glucose understanding storage most starches 50-150 Introduction Carbohydrates at which Such regulation. Carbohydrate with and the weight therefore KEY rational about body of human where fat in adipose much a composition mech- fatty fat oxidation. are important occur. on cumulative to changes body to tends arguments pertaining to the by fat intake. Ad- occurs time the tion mix in the diet. regulatory influencing providing of a fuel that events than substantially to the of the later carbohydrate oxidation through evolution. Fat by rather oven sensitivity, concentnations has Am lead can provide distribution to intake balance insulin glycogen fat the adjusting developed primarily economy, of fat oxidation in the centnation, habitual about of efficiently intake have errors triglycerides the macronutnient glycogen justment and preserve homeostasis, most must be stored to be mobilized in 1995;61(suppl):952S-95. 2 Supported 3 Address University by NIH reprint requests of Massachusetts Printed grant in USA. DK 33214. to I-P Medical © 1995 Flatt, Center, American Worcester, Society for Biochemistry, MA Clinical 01655. Nutrition Downloaded from ajcn.nutrition.org by guest on August 29, 2014 oxidation body’s To to bring on average anisms capable to carbohydrate how and fat3 Flatt bulk of dietary energy. glucose and fat absonbed The of carbohydrate USE “4.2 kJ/g 1 kcal/g), (:: of energy glycogen. imposing that can Glycogen typically ‘‘4% definite conveniently concentrations after STORAGE limits fast, and OF on the be carried are highest an overnight (5). AND amount in the in the up to 8% AND of tissue, form liver, after CARBOHYDRATE of ie, carry making weighs “‘1.5 kg, hepatic glycogen to “‘120 g. Glycogen amounts in bile and and intestinal muscle reesterified necessary muscle much lower and deliberate to raise them much above accounts of glycogen that for 20-30% stored in the Total glycogen the day glycogen the amount maintenance effective carbohydrate Marked liver to ensure trations, which of depletion adequate requires can creted amount form on body and vary and much times thus be size and substantially on exertion. greater degraded lipases. into into the circulation. few hours femned These coating after cells, the an enzyme produced of adipose tissue causes a threat to the blood glucose release of to ability of concen- 5 g glucose/h (or are most fatty acids able as a metabolic (10), fatty fat up by the the in which fuel. Dietary in adipose a be trans- chylomicrons must lipase be (LPL), endothelial cells acids produced by LPL cells and reestenified, only the pool of to reach form in appearance To by the The se- in the to remain milky by lipoprotein abundantly escaping deposition out lumen, are solubilized consumed. of the carried taken fraction for triglycerides of and mesentery them its been the cells, droplets plasma has capillaries. from the lipid help by pancreatic intestinal allowing the meal a function promptly small give a fatty consumed in 1 d, and within a desirable range oxidation tiny the glucose draining of lipoproteins, They into the vessels, of chylomicrons. a thin with absorbed by the lymphatic by are triglycerides hydrolyzed, carbohydrate These and survival (4). intestine acids and to allow deprivation in the to fatty to accumulate enough of food emulsified The than circulating the because to four in adults is then animals fatty acids fatty a albumin-bound are acids made are avail- thus targeted tissue. 100 mg/mm) to replace the glucose removed by the nervous system. Because the influx of nutrients from the intestine occurs through tunity to replenish the carbohydrates. carbohydrates glucose relative reach roles vary glycogen carbohydrate that after depending the consumed a typical meal is converted to oxidized during in Conversion the the of of depletion meal, and the in the muscle, liver whereas postpnandial type the one-third oils and fats containing energy three precursors solubility maining large in fat a small during that not aqueous can make active whether be stored up of capillary meates the This allows adults ingestion of 500 quotient (RQ) the unusually Thus, primarily The body’s 33.5 blood influence present their and nerve or of conversion Two water. can of of ex- terminals reduces per- ‘‘85% of which is fat. to be stored per gram fat glycogen maximal as the cost of on from wt. into then a fuel remains temporary to accu- rates of total their (as close car- glycogen usual 4-6 g/kg This requires deliberate of large amounts of carbo- need will frequently that to use be are lipogenesis fat factor be can stores high-carbohydrate is an important consumed as RQ body’s conditions readily however, the are stores substantial the usual capacity, are as well overlooked, intake body 1) loads glucose glucose such induce conclusions their metabolic their number (9). A delicate the raised, under carbohydrates dissipation of that fat, (Figure d (13). 1) below missed To g/kg important to food, that use reducing into 2-3 observations: far most layer fact absorbed 1.0, at a rate oxidation the the above carbohydrate of the glycogen ovenconsumption for fat after consumed rise expansion be considerably sustained to 02 not synthesized occasional in time 8-10 being of Even respiratory converting glycogen. to > are exclusive 1 by hours), must acids rate by bohydrate and fatty In an insignifi- (1 1). does fat. a hepatic nonprotein metabolism) large, mulations cess triglycerides adipocytes many me- in small bound 1.0 wt of CO2 to build little plays diets produced nearly in Figure hydrates substrate by itself than by a thin but once formed, only their size vessels in- tissue, These adipose tissue, kJ (8 kcal) energy (on of to the conversion mixed ratio fat animals very is primarily the niassive shown stores this concomitant glycogen. body lipogenesis the that handled allows contains g carbohydrate, and (12). fat feed consuming exceeding amount de novo (ie, indicates for their Quantitatively, in is starvation without adipose cytoplasm. pand or shrink considerably, cannot be reduced by fasting, network (5). role which are compartments, form a central fat droplet (much larger the body’s other cells) that is surrounded metabolically of fat into when such to esteni- critical even by carbohydrate accounts for (or 5% of Because do body’s fats but (4). unnoticed and cells animals molecules periods triglycerides the metabolically amounts, the acids and into of carbohydrate humans process of remainder The glycerol triglycerides deprivation) in water, plants fatty providing carbohydrate concentrations by of glycerol. of long-chain content), glucogenic severe adult cant hours. accumulated fied to one molecule 10% of the weight their Conversion up fat reserves of to envision of the carbo- and of carbohydrate of leads triglycerides In of degree (6-8). It seems reasonable one-quarter to one-third glycogen oppon- storage The of a prime consumption only a fraction of substantial amounts on the size has after are stored in muscle. The in the disposition of a car- to glycogen the liver this demands by a meal and stores, one-half Fat the reserve the periphery and of liver and muscle load hydrate system, its glycogen Usually, provided bohydrate the portal retained. deduced from these of unrestricted spontaneously and ac- maintained 2) the turned into made argument common fat belief can be dis- that the high is a cause for greater energy diets. It should not consumption as a fuel, in determining of so be carbohydrates that how carbohydrate much of the Downloaded from ajcn.nutrition.org by guest on August 29, 2014 the usually amounts the three stones adjustment intake. glycogen weight, of food intake is in effect not of carbohydrate of glycogen requires body g, depending consumed, as a function reserve loading However, is generally estimated to be “200-500 the amount of carbohydrate during body’s 2% (5). of total in muscle liver. carbohydrate are for substantial periods fats Because an adult’s liver storage capacity is limited are of fuel extended Dietary 953S it possible a reserve during meals FAT 954S FLATT gluconeogenesis which in the meal 1#{149}1 C e glucose uptake also a signal to restrain provides glucose phorylase 0 09 0. in muscle during muscle permit rapid To 0 a C is activated ATP the to provide a 5) 05 0 body’s major under Maintenance 30L ad .J 0 E E OS the in because of carbohydrates. foods to al- often As after carbohydrate intake. glucosunia is effec- and nutritional these and mechanisms of glucose maintaining storage, effec- mobilization, glycogen glycogen metabolic operate amounts amounts when in there an is free facilitated if adjustment intake were complemented of to diminish or enhance food intake when and/or glycogen reserves rise on decline 16), of regulation intake from but attempts appears to operate day to day in mice to demonstrate in fed a similar in humans have so far been unsuccessful (1). What for humans is that hypoglycemia induces an ex- tremely free-living powerful urge to find food, that individuals is such that glycogen (on 03 rates reserves concentraevolution fuel occurs would be greatly to carbohydrate (15, glycogen glucose through behavior is known well tamed 04 to as well form differing that (14). This type changes in food libitum glycolysis after carbohydrate ingestion by glucose to the fuel mix rapidly of stable to food oxidation excessively modulating 0#{149} 7 in the widely by signals working glucose concentnations SO locally whenever food intake fails Yet glucose must also be rarely it is evident access glucose Phos- primarily available to maintain metabolic energy increases and oxidation and appropriate mange. C . the in adjusting tively 120 anaerobic oxidation reserve. of their avoided conditions, E by ability hypoglycemia tively 150 by catecholamines, glucose when (4). below decreases) decreases their in (or the increases) maximal diet’s food stores capacity, and carbohydrate in energy intake in are main- that increases content intake lead to (17-19). 02 0#{149}1 hours Fat oxidation Fat FIGURE glucose, 1. Changes and in six young men carbohydrate with in plasma in response (white permission in the insulin bread, nonprotein and free respiratory fatty to a breakfast jam, and fruit acid quotient, concentrations providing juice). 8372 i ± in blood observed kJ (2000 SEM. kcal) Reproduced total oxidation energy the form Because critical, effectively concentrations erates the phosphorylase glucose regulatory prevent thus rate and regulation can economy intake, is constantly mechanisms hypoglycemia. elicit the release of glucose to degrade rates of the release glycogen, used and evolved its availability that are able Declining of glucagon, by blood glucose which accel- the liver by activating as well as by enhancing is to primarily and of carbohydrate oxidation themselves oxidation balance is determined expenditure that activity, Carbohydrate carbohydrate fat balance the and protein, the is determined amino acid to the amounts readily selected and of the fat between ingested than by the amount body size oxidation and that unrelated because the body’s fat reserves on the other hand, is a function foods gap in This may seem surprising of the facts that overall by be set by indexes the of energy rather and glucose consumed, amounts and it is not likely to be influenced losses of fat (21), which are trivial large by amount of fat consumed on a given day (20). at first, but it is the consequence substrate (12). and and physical mates adjust fat oxidation to the body’s are very of the fat large. content of foods consumed, by short-term compared with fat Fat of gains or the body’s stores. The lack of direct tion and fat intake regulatory interactions is demonstrated by the between fat oxidachanges in fuel Downloaded from ajcn.nutrition.org by guest on August 29, 2014 4 high sustain adequate blood mechanisms developed indeed Because ii sufficiently by a rapid rise in the RQ 1), the contribution made oxidized 0) -J be most shown (Figure E glycogen, release of glucose. ensure lowed 0 into glucose to make nesynthesis that restrict glucose replenish the glycogen -J (6, 7). Insulin, hyperglycemia its conversion hepatic are contraction that can sufficiently tions at all times, 0.7 and concentrations as by oxidation ..C amino acid and lactate state acts to prevent by promoting blood 10 from postpnandial USE utilization induced sumed by together stimulating drate, iment secretion but a decrease described in and a breakfast affected by postpmandial the use addition of of metabolic of the RQ as a function (22). The effect ever, because with such attenuates (but does and postprandial fat of rise and concentrations 75 g carbohydrate is essentially fat a dose fat are not prevent) RQ, a decrease by 0 and the evolution 20 fact slow that dietary deposition in other although of fat how- markedly delays -j 0 adipocytes, cells in oxidation the form only of free intake has oxidation, the gut and chylomicrons allowing carbohydrate carbohydrate from into fatty ingestion fraction to (10). effect of fat to the for acids a powerful E 75 C 0 targeted a small 200 _) of 10 g in g in glucose absorption fat is converted a) (U 150 a) 0 C 0 0 (I) 0 0 Downloaded from ajcn.nutrition.org by guest on August 29, 2014 reach rate 0. U) as well is manifest, in an increase of 0 0 0 the carbohydrate-induced resulting 955S 0 hardly unaffected ingestion FAT C induced supplement AND in in canbohy- As shown by the expeminsulin response and the acid CARBOHYDRATE con- influence the 6 h after the meal (10). That fat ingestion has so little on postpmandial substrate oxidation is imputable to the relatively ing of time OF usually 40 g fat as margarine, fuels described by the an 80-g in the oxidations, during effect fatty are latter’s to an increase oxidation. 2, the providing STORAGE Fats The leads in fat, Figure in glucose eating ingestion. carbohydrates. insulin changes food with AND Thus, in promot- promotes fat oxi. dation fat only marginally, meals leads following On days 16). balance (23)-and high more balance If fat (24). balance hydrate (and accurately protein) though they tend to maintain food occur, at least in the the fan less how glycogen 100 fat gains stable of long fat run)? regulated accurately than most body c 60 I canbo- 2: fat contents, composition to fat 80 C individuals, different oxidation Some balance to be poorly with 120 . ....- which energy expected is it that mixtures a relatively adjustment excessive 50 0 the during compounding of the overall cannot be balances, that intake, to limit than eat food implies during because carbohydrate and protein zero, errors made in maintaining fat is maintained even of high- oxidation is curtailed, are the main determinant the energy balance regulated consumption fat is increased Furthermore, hover around the of with fat oxidation balances even inhibition oxidation accumulation, (15, to hours. carbohydrate so that fat (which intake does increase in fat oxidation postpnandial inhibition 800 0 with high-fat diets fat oxidation is a consequence intestinal foods is due when fat-containing of the fact that absorption (10). consumed also fat-containing release meals and hydrate less rates These effects insulin and rather than therefore, Whereas results the are mainly fat be expected short-term acid indirect, serve because they substantial of the number between changes between are These in the fat mass, whether of fat cells and/or size and phenomena can of the adipose as the result an enlargement 0 but 200 UCU E -1 by 0 1 2 3 6 5 7 6 9 (hours) cannot, in time tissue. 4 TIME FIGURE small to acid concentrations, effect of repeated oxidation 400 C 0 metabolism to produce an exact compensation. errors in the fat balance are too fat intake 0 meals. controlled carbohydrate 600 C C.) carbo- concentrations affect the size of the body’s fat stores, fatty fat oxidation on food intake, the cumulative imbalances lower E -., a) insulin to be maintained oxidation to regulate metabolism. With insulin and in the of carbohydrates, are likely in lower release of fat postpmandial of fat oxidation. resulting of fatty intake by lower amounts of are consumed, which gastric emptying and presence in a lessen are followed glycogen range, higher meals fat delays Because inhibition intakes, in a lower to a reduced lead and in seven young and dried to Expansion of an increase in the of the adipocytes, 2. Changes glucose, after meat in plasma men glucose, permission. in response the same (41 mg/dL nonprotein and 0.05551 respiratory fatty acid = E- mmol/L. - day with - E). Adapted in blood observed of white 30 g protein, on another fat, quotient, concentrations breakfast 6 g fat, and breakfast g additional X free to a low-fat (73 g carbohydrate, consuming g margarine in the insulin i ± from bread, jam, #{149}#{149}), and a supplement SEM. reference of 50 For plasma 22 with 9565 FLATF causes an increase free fatty resistance promotes and fat mix related of the to recent particular proached) fuel diet’s oxidation only the body’s its fat content, Changes made (29). mass Through noticeably, to alter the oxidized can of weight body but the How on average, regulation fat does fatty body can, one Thus, be . needed is Q mix 10 problem focused on as much fat r 5 the 0 as 0 10 FIGURE fat content body 20 30 fat content It is well the models, although that incidence diets with of obesity the extent high fat contents in most of this as the proportion from 15% unrestricted, not enough response cient to prevent to fat high-fat diets eties, there increments in accumulation. becomes dietary obesity in the in affluent dose-response to the active animals. rate Note in fatness fat from also becomes (lower (31). 40 that individual differences in the size adipose and explanation panel the range diets 3). This lead mass, and, mass have a rather a well puzzling tolerated. aspect of fat soci- aberration low is due in small in highly weak and lower 70 80 half by carcass the fraction 18% 90 as sucrose). panel: female analysis of as protein, 100 in mice total and Upper C3H even diversity energy the balance panel: mice. male Reproduced intake (0) with in provided animals insulin and acid by comparing consumed with fed raises fatty encoun- for the content are fact and relatively concentrations to solid food, although consumption (38). Increased fat accumulation fat intake, because the increased shown hydrate are fatness also account dietary fat documented in humans studies (34-37). glycogen energy in body It may between addition reduced lesser sugar glycogen oxidation ad libitum or polycose increases solutions concentrations, and in of solid food occurs despite influx of canbohy- inducing Figures 1 and 2, the and its effect on raising As amount of carbothe body’s gly- stores influences postprandial and postabsomptive The degree of replenishment of the glycogen stores thus made an important by glucose, When a greater intake. upper provides a mice at the to factor in and hence glycogen expansion make fat reserves of the oxidation Multiple-regression panel that time of Figure had relatively of sacrifice, determining by fat, high ie: the the to are kept adipose that liver of the body in an tissue glycogen elevated mass with data fat is contribution fuel mixture commensurate analysis 3 shows is a thereby lipogenesis. cogen RQs. on obesity great they necessary that the when effect the of fat, populations. correlations of habitual oxidized. range, variability as a corollary, of Effect curtailing that as starch the degree of adiposity weak in epidemiological drate variations This namely tened in affluent that the positive fat suggests tissue problem, the even to substantial (32). with induce diets, permission containing in the form (half 60 Energy es Fat determined diets (LI) CD1 mice; or female carcass of interindividual high-fat adi- fat content of mixed the high incidence of such of Figure can of is consistent fat content libitum on the abscissa Total with the range in affluent between This from degrees that over consumed that with are for content (3, 31-33). The apparent when dietary fat is very tissue hence fat higher relatively high in explaining wider minor of the ad 50 Dietery In fat increases maintenance relationship of lipogenesis mice in adipose diet’s for content. societies curve inbred metabolism varies weight established widely held view that the diets is an important factor simple the Thus, is a dose-response and changes animal of diets containing the weight mainhigher degrees of energy (15, 30). Figure 3 shows typical of the mixed diets content to to 60% (Figure 3) (15, 16). When access to food is spontaneous reductions in glycogen amounts are to allow an increase in fat oxidation that is suffi- leading posity contents of dietary tend experimental mice given free access to one of a series different proportions of fat and carbohydrate, tenance plateau is reached at increasingly adiposity on as carbohydrate established increase 3. Body maintained shown Dietary . c2O % affecting -. . degs #{243}Td)I 25 body eats? Factors ..... 35 also fuel the to be to oxidize -.--. I3o to the weight. -.. LFem&e C3H Mice (144-228 40 not affect fat content acids in effect, have not Sc 45 with but es Fet a where protein poots, (15, 30). in body by affect C Energy Dietery than effect, reached do changes made markedly chronic is then concentrations contribution about rather in time be reached (or apof fat makes a contribution state 0 B is fat shown in the is higher in the concentrations Downloaded from ajcn.nutrition.org by guest on August 29, 2014 weight glycogen 8 80!01:: to the brought is commensurate, A steady 0 of pe- by glucose this a) carbohydrate is chronic, glycogen reserves and tend to remain constant in that in fat oxidation tissue that than 0 U- the concentna- delis old)] (160-210 C stores that EPI! Mice 45 40 to acid whereas contribution adipose fat content. fatty However, fat intake glycogen it is evident is greater increase insulin relative of the fat masses on body composition will for which the oxidation to total issue: the the to higher of oxidation as well-filled accumulation (28). leads a type Enlargement metabolism alters by expansion one fat oxidized, to Furthermore, deposition promptly fuel which and fat just oxidation. intermediary ripheral intake 26, 27). fat oxidation, of abdominal tions the (15, glucose effect release, (25) to enhancing oxidation promote acid concentrations susceptible glucose thus in fatty acid USE % Body X 5.7 + % dietary indicates Effect SE; offood n overeat diets) markedly unrestricted weight gain or (31, not concentrations, be can palatability, R2 and 0.33; = wide availability, satiety high diversity of and in humans appealing mechanisms This not also variety dishes running daily great the postexercise state of RQ, increases main- degree of commonly only me- endows allows items. activity indicating that in substrate (41). meal greater of the is part of maintenance day the (44, oxida- 45). daily In mebut When routine, is reached tissue with the a lesser mass. by the diet. without the need for (46). This mass goal is to achieve goal the body’s metabolism and amino acids this expansion is more as are steady of the readily state adipose achieved when a diet with a high carbohydrate content is consumed because it is obviously easier to burn as much fat as one eats when one does not eat a lot of fat. Exercise provides additional leverage it causes a greater the specific increase in the oxidation the body will spontaneously and carbohydrate balances, sense to direct voluntary Furthermore, concentrating restrict that acids, an undesirable regulate because control fatty The to influ- to weight requires glucose, supplied tissue and maintenance A varied size, intensity selection as much of glucose. Because tam protein Food be expected enhances weight Macronutrient because them for a remark- food can periods activity of the adipose Weight in of weight as in animals reach elicits physical oxidize differences are appetizing as well must after which in glycogen at a higher societies but spontaneous average to of they provide macnonutnient fats, and protein all contrib- highly palatability, intake for state but fat content, of changes the steady them conditions spontaneously tissue mass, compensate of energy. libitum, the (superman- causes under by in affluent ad in fat balance goal than nearly of fat than and effectively mainbut does not (or cannot) as accurately (14-24), it makes efforts at this relatively soft target. on the fat balance provides a more one based on overall energy exchanges. further food intake than when faced with unappealing foods (42). This tends to raise the upper limit of the range within which glycogen concentrations are habitually maintained. In addition, the ubiquitous availability of foods, by inducing eating between meals, can have the effect of keeping glycogen concentrations high. Given the ensuing curtailment of fat oxidation, fat will accumulate until expansion of the adipose tissue mass is sufficient to bring about a rate of fat oxidation com- Awareness mensurate with maintenance this effect to become established. if one considers that the lowering blood cholesterol concentrations and in minimizing the development of arteriosclerosis (48, 49). To these reasons for restricting fat intake one can add the further argument that gen is maintained reserves fat intake, permitting is not precisely are maintained the steady of weight There is much room for range within which glyco- determined far below state their because level glycogen of saturation under conditions of unrestricted access to food (12, influence of the palatability, variety, and accessibility teristics tions, of the and hence sideration when affluent facilitate Effect The food supply on on fat oxidation, accounting habit generally weight, is generally need for the high societies, as well weight control. ofphysical habitual as when glycogen setting into up conditions of engaging not well of steady adipose that low-fat have diets because limiting fat saturated fats) appears state balance tissue to nary stores a particularly provide about the to satisfy the possible carbohydrates. decline the of foods intake more high bulk, led glucose the a key can diet’s be hunger, with disadvantage is low. on of caution inherent known for smaller of relying a word that concentrations in expected, fat content advantages con- measure to be achieved It is now in blood (particularly to be maintenance reasons, when consideration be included absorbed of weight fuel In the in high- should to rapidly a slight tempo- is a physiological event that can lead to initiation of food intake (50, 51). In animals consuming a feed of fixed composition, the time elapsed when this event occurs is proportional to the size of the activity quite effective or in inducing sumption carbohydrate con- and associations, metabolic 13). The charac- of obesity density, foods dietitians long ago to recommend low-fat diets for weight control (47). Recommendations to reduce fat intake have indeed been increasingly promulgated in dietary guidelines published by government agencies and medical on health-related the even concentra- to be taken incidence energy of the fact that fatty in substantial in limiting loss of excess understood why physical the accumulation adipose tissue increments activities is of excess (43). Yet it in food intake elicited by exercise are sometimes sufficient to ensure weight maintenance (ie, in a physically active individual), but sometimes not (ie, when someone initiates a physical training pro- preceding meal (50). It may carbohydrate influx from from a glucose-removing Rapidly absorbed this signal carbohydrates to occur view of the high elicit and not only degree the rapid rates well be linked to the the gut, when the liver has state to a glucose-releasing would earlier, of postpnandial of peripheral be expected but also more insulinization glucose end of to shift state. to cause sharply, that utilization in they in- Downloaded from ajcn.nutrition.org by guest on August 29, 2014 a relatively ably selection animals reestablished, amounts with food foods even femned to as mixed diets because mixtures in which carbohydrates, substantial during expansion palatable complemented fed exercise substantial steady However, therefore because also 0.0001). P < to experimental consumed a decrease tion in muscle, which uses fatty acids as well as glucose. addition, the exercise-induced depletion of the glycogen serves can lead to lower RQs not only during the exercise ± 0.20) of highly 39). In mice causes 957S FAT physical activity promotes fat oxidation to a greater extent than it does carbohydrate oxidation (15, 16, 44). This is not sumpris- palatability permitting to become adiposity. The diets ence ± 0.02) access, food intake diminishes (40). Expansion of the adipose may tenance ( 0.95 of a selection ket on cafeteria ( 0.24 AND gram). ing, 400; = variety Provision ute CARBOHYDRATE % liven glycogen X food OF fat + may STORAGE fat = (± AND 958S FLA’VF duced by high insulin anticipate that products in which undercooked slowly, (52), would One is still and associated vegetables), a low glycemic be less likely which index, and to trigger Dietary carbohydrates inhibit tions of glycogen that the to avoid dation the hepatic glycogen on their example, glucose pable stores. the build-up arguments if substantial, of reducing in achieving steady to of comparable of dieting of dietary into fatty but to eat uals aiming ductive in impact of effective because difficulty those that of fat oxi- most reduction, complemented by efforts increasing) carbohydrate select foods high can be not entirely; based in (8). that a reduction a long-term adipose ca- tissue weight control a reduction foods occurs in fat intake to limit (at least intake, to reduce to the extent sugar intake, intake P, Sj#{246}strdm L. Carbohydrate and quantitative ethanol reduces fat but It is of course feasible to reduce energy intake. Selecting foods not Sargent and D RA, in humans. obesity. Carbohydrate in humans. I Clin Am Kuwajima liver Nutr deter- 1985;41:1132-45. Diabetes 1971;20:785-99. in man: Metabolism Rev speculations 1978;27:1853-65. of hepatic glucose metabolism 1987;3:415-59. M, Newgard CB, the circle glycogen: nongenetic 1993;14:72-93. storage E. Regulation Metab and Rev in man. considerations. Ferrannini JD, to Am of insulin Diabetes glucose AM. intake full Foster DW. round. From Annu dietary Rev Nutr in man after 1987;7:51-73. 8. Nilsson LH, glucose and 9. Hirsch E. Metab Al, Immediate Humphreys tissue SM, I Clin hepatic ML, Invest 1974;33:5-10. in human Fielding of dietary Nutr obesity. fat BA, Frayn KN. in combination with 1994;59:53-9. MK, Christiansen de novo glycogen Lab cellularity Clark availability Am muscle I Clin 1976;5:299-311. metabolic 11. Hellerstein and Scand B. Adipose Endocrinol Griffiths Liver infusion. L, Batchelor Clin 10. Hultman fructose M, Kaempfer lipogenesis in humans 5, et a!. Measurement using stable isotopes. of I Clin Invest 1991;87:1841-52. 12. Acheson 10, a 500 after Flatt IP, lequier gram E. Glycogen carbohydrate synthesis meal in man. versus lipogenesis Metabolism 1982;31: 1234-40. 13. 14. Acheson Schutz Y, Bessard E. Glycogen KJ, storage capacity carbohydrate overfeeding Mayer I, Thomas T, Anantharaman and de novo in man. DW. Am Regulation K, Flatt lipogenesis I Clin of food Nutr intake JP, J#{233}quier during massive 1988;48:240-7. and obesity. Science 1967;156:328-37. could carbohydrate alter oxidation fat to 25% or even with some 6. DeFronzo be of not and to and Endocr Bjorntorp carbohydrate. dietary habits in obese subjects, who often have a predilection for fatty foods (33). Note that in calculating the relative proportions of carbohydrate and fat in the diet, energy consumed in the form of alcohol should be included with that provided by fat, because E Jr. Diet GF Jr. Physiology 7. McGarry Prentice food Mauri#{232}ge P. Genetic fat distribution. 5. storage should of regional Cahill 18. fat KS 1993;57:897-903. Danforth of typical by GR, 4. some on of of day-to-day 3. carbohydrates. a cap collaboration PR, Goldberg regulation C, Despr#{233}sI-P, minants mass mainte- the Nutr 2. Bouchard in fat measure and I Clin 15. because the RI, Murgatroyd balance There is not enough information to judge to what extent fat intake has to be reduced to prevent obesity and this limit is in fact likely to vary for different individuals. It seems unlikely that meeting the 30% target proposed by current guidelines (48, 49) will by itself be sufficient to prevent excess weight in individuals prone to obesity. However, this measure may have effect U acknowledge 1. Stubbs for and does not raise raises the RQ (54, 55) accumulation in complex that References raise fatty acids, rather than by conversion of carbohydrate acids (1 1-13). The admonition to restrict fat intake carbohydrate freely may be reasonable for individto maintain weight, but it is probably counterpropromoting weight loss because it will attenuate the a reduction in fat intake on the energy balance. For weight being foods advanta- inhibit of spontaneous fat is perhaps of low-fat propor- fat contents, was offered ad libitum (17, 18), and subjects who were coached in avoiding fatty foods while eating to satiety (56). Restricting fat intake also appears to be a crucial dietary measure in helping to limit and delay weight regain after periods advantage in the number Recognizing most suggest with another to which the seem glycogen palatability This increase have namely to facilitate of the food assortment available. I gratefully nance. This expectation is supported by the weight loss expenienced by subjects to whom a line of low-fat foods, designed to be one can partake. by the rapid are now a more extent is the for an expanded state which eroded lead exert although represent the need the may affect a selection (53), here may that it would perhaps of liven reviewed from insulinogenic or muscle. control Such more the that index fiber, less and eats, carbohydrates glycemic natural this could a lower fat, 16. 17. complex carbohydrate content does not so much entail the discomfort of hunger, as it does require the avoidance of a whole range of desirable foods. If done consistently, this practice has the effect of limiting the range of permissible foods. In addition to the metabolic leverage and to the reduction in the IP. of nutrient Metab 1988;4:571-81. Flatt IP. Dietary Ann N Y Acad Lissner Rev fat, carbohydrate Sci in body balance, and weight regulation. weight maintenance. 1993;683:122-40. 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