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Bulletin #58 – Carbohydrates — The Optimal Fuel For Success, Part II

In the last article we began ourdiscussion of carbohydrates as the pre-ferred fuel for athletic performance. It iswell known that the ability to sustain mod-erate to heavy exercise for prolonged pe-riods of time is related to initial muscleglycogen concentration (1). The moreglycogen you have stored in yourmuscles, the longer you can exercise at agiven work load. One experiment showedthat when muscle glycogen levels were0.63 grams of glycogen per 100 gramsof muscle, a standard exercise load couldbe maintained for 57 minutes before fa-tigue. When glycogen levels were in-creased to 1.75 grams per 100 grams ofmuscle, the same exercise could be per-formed for 114 minutes. And if the initialglycogen level was 3.31 grams per100 grams of muscle the exercisecould be continued for 167 minutes(1,2). The close correlation betweenmuscle glycogen levels and time toexhaustion is a good reason to fol-low a high carbohydrate diet. It hasbeen suggested that glucose andfatty acids cannot cross the cellmembrane (that is, enter the cell)fast enough to provide adequate fuelfor intense exercise (1). This is whymuscle glycogen (glycogen alreadystored inside muscle cells) is themost important fuel for exercise.Now let’s talk about somespecific dietary strategies to maxi-mize endurance performance. It isvery important to fill glycogenstores completely before participating inan exhaustive endurance event.  

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Endur-ance athletes who train on successive daysare likely to require 65-75% of their calo-ries from carbohydrates to optimize per-formance (1). It may be that feelings oftiredness which are attributed to overtrain-ing are in fact due to low glycogen stores(1). Some cases of “overtraining” mayreally just be under-nutrition. Foods richin complex carbohydrates are preferableto refined sugars because they are morenutrient dense and result in lower bloodglucose and insulin levels. This makes itmore likely that the carbohydrate will bestored as glycogen rather than being con-verted to fat. It is recommended that thelast meal consumed before an enduranceevent be relatively light and contain a mix-ture of easily digested complex carbohy-drate and protein (1). This meal shouldbe eaten about two to three hours prior toexercise to allow time for the stomach toempty. Improvements in exercise perfor-mance from pre-exercise carbohydrateingestion is probably due to a delay in thenormal decline of blood glucose duringexercise (1). Most likely, this works bysupplementing hepatic (liver) glycogenreserves. A recent study has shown thatingestion of one to two grams of carbo-hydrate per kilogram of body weight onehour before exercise can improve perfor-mance (1). In this experiment the carbo-hydrate was given in liquid form, whichis what we would generally recommendif you’re going to eat something withinan hour of exercise. This allows for morerapid digestion and absorption than is pos-sible with solid food.

Pro-Carb Powder™(original Vanilla or the new Chocolate fla-vor) is ideal for this, supplying 22 gramsof medium-chain carbohydrate(maltodextrin) along with four grams ofprotein per scoop. That means a 180pound athlete would need about fourscoops taken 30-60 minutes before com-peting.Consuming carbohydrates duringexercise can also improve performance.This works by helping to maintain bloodglucose levels and preventing hypoglyce-mia, rather than by sparing muscle gly-cogen (1). Keep in mind I’m talking aboutmaximizing exercise performance here,not fat burning. If you’re doing aerobicssimply to burn fat then you don’t wantto eat anything during exercise be-cause this will decrease the utiliza-tion of body fat as fuel. Competitiveendurance athletes may however im-prove performance by consuming acarbohydrate drink during exercise.This will help replace fluids as wellas maintain blood glucose.

The rateof gastric (stomach) emptying is keyhere, as this ultimately controls theavailability of the ingested carbohy-drate. The stomach empties faster thefuller it is, so it is advised to keep thestomach volume relatively high bytaking frequent small drinks.Maltodextrin theoretically should exitthe stomach faster than glucose so-lutions due to its lower osmolality (theconcentration of particles in a solution).A rate of about 45 grams of supplementalcarbohydrate per hour seems adequate tomaintain blood glucose levels during mod-erate exercise (1). This would be onescoop of Pro-Carb Powder™ every 30minutes.Whatever you do, stay awayfrom fructose as an exercise fuel. Fruc-tose is the sugar found naturally in fruit and, ironically, in most sports bars (theParrillo Bar uses rice dextrin, not fruc-tose). Some people recommend fructosefor athletes because it has a low glycemicindex and results in a low insulin response.This line of reasoning however fails toconsider the big picture of fructose me-tabolism. Fructose is a bad choice for ath-letes for two reasons. First, a significantproportion of it is converted to fat by theliver. This is probably the reason it has alow glycemic index and a low insulin re-sponse. Second, it does not work well forrestoring muscle glycogen. Fructose ismetabolized by the liver, not by muscle.

Trials with fructose supplementation dur-ing exercise have failed to demonstrate animprovement in performance (1) and us-ing fructose as a carbohydrate source toreplenish muscle glycogen stores follow-ing exercise does not work as well as glu-cose or glucose polymers (1,2).Restoration of muscle and liverglycogen reserves after exercise is criti-cal for recovery and subsequent exerciseperformance (1). I feel it is also very im-portant in order to derive the maximaltraining effect from exercise, so that youcan go out and have improved perfor-mance next time. Now we will discussthe type, timing, and amount of carbohy-drate needed to maximize recovery of gly-cogen stores after exercise.Research shows that glycogenlevels can be restored within 24 hours fol-lowing exhaustive exercise if 600 gramsof carbohydrate are consumed (1). Thismakes good theoretical sense, becausemost people can store around 400 gramsof carbohydrate as glycogen (and maybetwice that much using carb loading tech-niques). So 600 grams provides enoughto replenish glycogen stores plus a littleleft over to use as fuel during your recov-ery day. (It is assumed that you will notbe exercising during this 24 hour period.)The rate of glycogen synthesis is mostrapid immediately following exercise.

This is due to several factors, includingincreased activity of the enzyme thatmanufactures glycogen, increased perme-ability of the muscle cell membrane to glu-cose, and increased sensitivity of muscleto insulin following exercise (1). Youshould try to consume one to one-and-a-half  grams of carbohydrate per kilogramof body weight every two hours for thefirst six hours after exhaustive exerciseand a total of 600 grams during the first24 hours.The type of carbohydrate usedalso affects the degree of glycogen reple-tion. This effect is most likely due to theglycemic and insulinemic responses ofvarious carbohydrates. Fructose causesa much lower blood sugar level and insu-lin level than glucose-based carbohydrates.It is well known that fructose is not nearlyas effective as glucose at restoring muscleglycogen (1,2). This is probably becausefructose metabolism is essentially confinedto the liver. Several studies have comparedsimple sugars versus complex carbohy-drates, with various results. Some stud-ies have found no difference, and somehave suggested that simple sugars resultin better glycogen recovery during the first24 hours.

One study found that complexcarbohydrates resulted in higher rates ofglycogen synthesis after 48 hours (1,2).Apparently complex carbs work betterover the long term and higher levels ofglycogen can ultimately be achieved us-ing complex carbs. My recommendationis to avoid sugar but to use a relativelyshort chain glucose polymer such asfound in Pro-Carb Powder™ or theParrillo Bar for the first six hours afterexercise and then rely on complex carbsfor the remainder of glycogen repletion.This should result in optimal glycogenrecovery. Simple sugars are more easilyconverted to fat than complex carbohy-drates, and this may be the reason thathigher glycogen levels are seen after 48hours with complex carbs. The complexcarbs are more prone to be stored as gly-cogen while simple sugars more readilyspill over into fat stores. The best carbchoices for glycogen repletion are com-plex starches such as rice, potatoes, sweetpotatoes, beans, oatmeal, and so on. Con-trary to what some proponents of the highfat diet say, current research proves thatcomplex carbohydrates have very little ten-dency to be converted to body fat (3,4,5).Several studies have directlycompared the effects of carbs versus faton endurance. One compared a high carb- low fat diet (83% carbs, 3% fat) to ahigh fat – low carb diet (94% fat – 4%carbs).

They found that the group con-suming high carbs burned more carbo-hydrate during exercise and had an en-durance time of 210 minutes comparedto 88 minutes for the high fat group (2).A high carbohydrate diet results in greatermuscle and liver glycogen stores plushelps maintain blood glucose levels longer,resulting in greater endurance. Hard train-ing athletes need extra carbohydrate tosupport their exercise activity. When agroup of athletes was fed a diet contain-ing 40% carbohydrate, their muscle gly-cogen levels steadily declined over a fewdays of training. When they wereswitched to another diet containing thesame number of calories but 70% carbs,their glycogen stores were maintained (2).This is very important. It means that notonly do athletes need extra calories to fueltheir exercise activity, but it also matterswhere the calories come from. A high fatdiet cannot maintain glycogen stores evenif it is adequate in calories. This is be-cause fat cannot be converted to glycogen. Also keep in mind that athletes needmore protein than sedentary people. Thishas been proven in many studies usingnitrogen balance techniques.We recommend a diet providingone to one-and-a-half grams of protein perpound of body weight each day with therest of the calories provided by complexcarbohydrates.

Try to limit fat to 5-10%of calories. Use high quality, low fat pro-teins such as chicken breast, turkey breast,egg whites, and fish. Good starchy carbsare things like potatoes, rice, beans, andoatmeal. At each meal you should alsoinclude a fibrous carb, such as broccoli,asparagus, salad greens, or other veg-etable. Each meal should be balanced,containing one complete protein source,a starch, and a fibrous vegetable. Try todivide your daily grams of protein and yourtotal calories evenly among six smallmeals. The Parrillo Performance NutritionManual contains exact instructions onwhich foods to eat, which foods to avoid,and how to structure your diet. It alsocontains a detailed food composition guideand comes with a food scale, so you candetermine how many calories and howmany grams of protein, carbs, and fatyou’re consuming. It contains precise di-rections on how to modify your diet tooptimize gaining lean mass or losing bodyfat.Regarding supplementation,Parrillo Performance Hi-Protein Powder™is a high efficiency protein mixture pro-viding a high level of glutamine, branchedchain aminos, and essential aminos. Thisis an excellent way to get your proteinintake up where it needs to be. It’s nowavailable in chocolate, which is delicious.Endurance athletes and bodybuilders try-ing to gain weight will do well with Pro-Carb Powder™, a maltodextrin-based car-bohydrate supplement. This is an idealsupplement for glycogen repletion andcarb loading.

We have had great successusing it alone or in combination withCapTri® before and during enduranceevents.Another product that we’ve justintroduced called 50/50 Plus™ fits thisneed for additional carbs and proteinnicely. With 20 grams of protein and 17grams of complex carbohydrate in eachtwo scoop serving, 50/50 Plus™ providesyour body with the protein necessary tostave off muscle catabolism for energyas well the extra carbs to supply energywhen you need it and help replenish gly-cogen stores when you’re finished withyour activity. 50/50 Plus™ comes in fourdelicious flavors — Vanilla, Chocolate,Orange Cream, and Milk — and can bemixed with water or stirred into your foodto boost your nutrient levels.Endurance athletes should also considerLiver-Amino Formula™. This supplementis the ultimate source of heme iron, whichis a superior iron source for building bloodcells. Creatine is another supplement thatcan help extend your energy base. And allserious athletes should be using EssentialVitamin Formula™ and Mineral-Electro-lyte Formula™.Even if you’re a bodybuilder andnot an endurance athlete, vigorous aero-bic exercise will help you get bigger andleaner. Aerobics helps build capillary den-sity in muscle tissue, allowing for betternutrient delivery and more growth. Aero-bic conditioning also trains your musclesto rely more on fat as a fuel source butincreasing mitochondria and the level offat burning enzymes (6,7). This helps youCarbohydrates—The Optimal Fuel For Success, Part IIget leaner plus spares muscle glycogenfor a better pump. Until next time, goodtraining.


1. Liebman M and Wilkinson JG. Carbo-hydrate metabolism and exercise. Chap-ter 2 from Nutrition in Exercise and Sport,edited by Wolinsky I and Hickson JF, CRCPress, Boca Raton, 1994.

2. Miller GD. Carbohydrates in ultra-en-durance exercise and athletic perfor-mance. Chapter 3 from Nutrition in Exer-cise and Sport, edited by Wolinsky I andHickson JF, CRC Press, Boca Raton,1994.

3. Flatt JP. Dietary fat, carbohydrate bal-ance, and weight maintenance: effects ofexercise. Am. J. Clin. Nutr. 45: 296-306,1987.

4. Flatt JP. Use and storage of carbohy-drate and fat. Am. J. Clin. Nutr. 61: 952s-959s, 1995.

5. Acheson KJ, Flatt JP, and Jequier E.Glycogen synthesis versus lipogenesisafter a 500 gram carbohydrate meal inman. Metabolism 31: 1234-1240, 1982.

6. Hargreaves M. Skeletal muscle carbo-hydrate metabolism during exercise.Chapter 2 from Exercise Metabolism, ed-ited by Hargreaves M, Human KineticsPublishers, Champaign, IL, 1995.

7. Coggan AR and Williams BD. Meta-bolic adaptations to endurance training:substrate metabolism during exercise.Chapter 6 from Exercise Metabolism, ed-ited by Hargreaves M, Human KineticsPublishers, Champaign, IL, 1995.

2018-03-13T11:10:33-04:00 June 3rd, 2009|Technical Supplement Bulletins|

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