Posted: October 28, 2004

Multisport: "Secrets of Post-Workout Nutrition"

For athletes, high-carbohydrate diets optimize muscle-glycogen levels, and lofty muscle-glycogen concentrations improve endurance-exercise performance (1). Achieving magnificent glycogen levels is not just a matter of eating plenty of carbs, however; the timing of carbohydrate intake is important. For example, consumption of carbohydrate immediately after either endurance or resistance exercise may enhance total daily muscle-glycogen re-synthesis, compared with consuming the same amount of carbs earlier in the day or postponing the carb consumption until a few hours after exercise (2 & 3).

Interestingly enough, taking in carbohydrate right after an exertion is over also seems to have a pronounced effect on protein metabolism. For example, post-workout carbs can decrease the rate of protein degradation in muscles (4) and increase whole-body protein synthesis (5). These twin effects are of course highly desirable for athletes, whose performances will generally fall if significant quantities of protein are lost (remember that proteins are the building blocks of muscles and that certain proteins can also serve as energy-releasing enzymes within muscle cells).

Why do carbs save - and even boost - the production of proteins? For years, exercise scientists have reckoned that the basic mechanism underlying carbohydrate's protein-helping attributes is simply that ample carbs give muscles enough energy to stimulate protein production. However, proteins are made of subunits called amino acids, and the breakdown of a very important group of amino acids called the branched-chain amino acids is regulated by the activity of an enzyme called BCOAD. As you might expect, a diet which is very rich in protein leads to an increase in BCOAD activity in the liver. On the other hand, when athletes step up their carb intakes, BCOAD activity drops (6). Thus, luxuriant carbohydrate ingestion seems to spare protein by calming down BCOAD.

Training per se also has an impact on BCOAD activity; chronic training produces a drop in BCOAD activity in the muscles (7). In general, "down-regulation" of BCOAD is considered to be a positive adaptation, since it means that muscles, which are primarily composed of protein, will be less apt to "break down" and will be more inclined toward building new structures during periods of heavy exertion.

When training increases in volume or intensity, considerations related to total carbohydrate intake, the timing of carb intake, and the impacts of diet and training load on protein metabolism become particularly crucial, because upswings in training can deplete muscle-glycogen stores and throw athletes into a state of "negative nitrogen balance," in which they are losing more protein than they are making. To see what sort of nutritional strategy might be best for athletes who are undergoing an increase in total training load and who want to max-out muscle glycogen and stay positive with protein, Mark Tarnopolsky and his colleagues at McMaster University in Hamilton, Ontario recently studied 10 active female athletes over two separate, one-week periods (8). The choice of female athletes as subjects was particularly appropriate, since many sports-active females have abnormally low protein (9) and total-calorie (10) intakes.

Prior to the onset of the study, all 10 women had participated regularly in some form of endurance activity; the average training load was three 45-minute workouts per week. All of the athletes were eumenorrheic, and they were tested only during the mid-follicular phases of their menstrual cycles (days four through 11). Average VO2max, measured during progressive cycling to fatigue, was 46.3 ml/kg-min.

The athletes completed two separate seven-day interventions - a control trial and a post-exercise-supplementation trial. During these two trials, the athletes' energy, carbohydrate-, and protein-intake patterns were exactly the same: The women consumed approximately 2160 calories per day and 1.4 grams of protein per kilogram of body weight per day (and thus 86 grams of protein each day). The overall composition of their diets was 58-% carbohydrate, 16-% protein, and 26-% fat.

On days one, three, and four of the seven-day trials, the women worked out in the mornings by cycling for one hour at an intensity of 65% of VO2max (about 76% of max heart rate). On day three, the women completed a second, additional one-hour workout at 65% VO2max in the afternoon, and on day six the athletes finished off a 90-minute exertion at the 65-% VO2max intensity. On the seventh day they didn't rest, instead cycling for as long as possible at 75% VO2max (about 85% of maximal heart rate). Thus, the volume associated with each week's training schedule was nearly 150% above the usual level (335 versus 135 minutes).

During the study, both the control and post-exercise-supplementation groups made use of a beverage produced by Mead-Johnson Canada Inc. which is called "Results." 66% of the calories in this quaffable came from carbohydrate, while 23% originated in protein, and 11% were derived from fat. The post-exercise-supplementation athletes imbibed "Results" immediately after their one-hour bike rides ended, while the control groups consumed the same amount of the Mead-Johnson product at breakfast, well before the bicycle exertions were undertaken. As mentioned, total energy, carbohydrate, and protein intakes were identical in the two groups; the only difference was in the timing of the "Results" ingestion.

And what an impact that difference had! When the beverage called "Results" was taken right after exercise instead of at breakfast, the experimental results were significantly different for a wide range of variables, including fat oxidation, carbohydrate concentrations, protein breakdown, exercise capacity, and body weight! As you might expect, carbohydrate breakdown tended to be greater during workouts when the extra carbohydrate (from "Results") was taken in the morning, before the workout, rather than after the training session. Also not surprisingly, fat oxidation was greater during exercise when "Results" intake was postponed until after a workout was over. These findings are simple to explain: When athletes take in extra carbohydrate at breakfast, their liver and muscle stores of glycogen tend to rise, and thus they have more carbohydrate fuel available for prolonged exercise later in the day. When carbohydrate intake prior to exercise is more minimal, fat is forced to supply more of the energy needed for long exertion.

The key results, though, related to nitrogen balance, body mass, and performance. When "Results" was taken in after exercise rather than at breakfast, nitrogen balance was positive, which simply means that the athletes were taking in more nitrogen than they were losing (which is another way of saying that their protein stores were increasing). When "Results" was taken at breakfast, on the other hand, nitrogen balance during the heavy training was negative (protein was being lost). In addition to saving protein, drinking "Results" right after workouts also prevented excessive losses in body weight during the heavy training. When "Results" was quaffed after training sessions, the athletes lost 1.5 pounds during the seven-day period of extended training, but when "Results" was just a breakfast potable the loss in mass totaled 3.1 pounds, a statistically significant difference. Last (but not least), use of "Results" after workouts - rather than at breakfast - allowed the athletes to exercise an average of 47-% longer (!) during the 75-% VO2max effort which took place on day seven. As you take in these results, again remember that the athletes were eating the same amount and type of food during the two different trials; the only difference was the timing of the "Results" guzzling!

Why does carb intake right after exercise produce such great results? Well, carbs control our old friend BCOAD, an action which helps muscles hang on to more of their very desirable protein. Also, post-exercise carbs drive up blood insulin levels, and insulin can have a very powerful effect on muscles. To determine insulin's specific effects, scientists in the Department of Internal Medicine at the University of Texas Medical Branch in Galveston, Texas recently infused insulin into the femoral arteries of athletes following heavy-duty resistance exercise involving the legs (11). When insulin was not supplied to the athletes' legs, the rate of leg-muscle protein degradation was about 15-% higher than the rate of leg-muscle protein synthesis following exercise; simply put, the athletes' leg muscles were losing protein. However, when insulin was supplied to the leg muscles after exercise, the rate of protein synthesis was not augmented, but the rate of protein degradation dropped by about 30%! This drop in degradation created a situation in which protein balance was positive following exercise; the athletes were immediately building up their muscles in response to the training they had performed.

One of the fascinating aspects of this University-of-Texas-Medical-Branch research was that insulin preferentially drove certain amino acids into the leg muscles. For example, insulin increased the leg-muscles' rate of absorption of an amino acid called alanine threefold after exercise but had little effect on the absorption of other amino acids such as phenylalanine, leucine, and lysine. This raises the prospect that muscles prefer to receive specific amino acids after exertion and that well-planned "cocktails" of amino acids, when ingested after exercise (or before and after exercise), might have the greatest-possible effect on intramuscular protein synthesis. In this study, only the protein-degradation rate was curbed; protein synthesis was not enhanced. However, the lack of augmentation of protein synthesis may have been due to the fact that no additional amino acids were given to the athletes, either orally or intravenously; to enact protein synthesis, they had to rely on the normal concentrations of amino acids already found in their tissues and blood plasma. The combination of a "top-shelf" amino-acid cocktail and high insulin levels might have incredibly positive effects on protein synthesis and recovery from exercise in serious athletes.

As we have been pointing out, when athletes ingest carbs right after exercise, they consequently have better nitrogen balance and - as a result of greater glycogen - better performance on the following day (as they did on day seven of the McMaster-University study). If you are a skeptic, you might be saying: Why couldn't breakfast (pre-exercise) carbs do the same thing? In theory, they should be able to, but the "catch" is that muscles are most receptive to taking carbohydrate on board during the two hours immediately after exercise. This means that muscles may be more likely to hold onto inordinate amounts of ingested carbohydrate if the ingestion occurs immediately after a workout.

What are the practical implications of this research for your training? To promote recovery and increase your chances of performing well during subsequent training sessions, take in carbohydrate and protein immediately after your workout ends. According to Tarnopolsky, you should attempt to consume a minimum of one gram of carbohydrate per kilogram of body weight within 20 minutes after exercise ceases, and two grams of carbs per kilogram of body weight would be better. For a 59-kilogram (130-pound) athlete, the latter pattern would entail the consumption of 118 grams (472 calories) of carbs right after a workout; for a 73-kilo (160-pound) athlete, 146 grams (584 calories) of carbohydrate would be required.

As Tarnopolsky points out, there is definitely a two-hour "window" following exercise during which muscles maximize their carbohydrate absorption, but this window gradually slides shut during the two-hour period. "We know that the benefits of carbohydrate intake diminish somewhat just 30 minutes after exercise, and that the 'extra edge' associated with post-exercise carb intake is totally gone after two hours," says the Canadian physiologist. Overall, the safest policy is for athletes to take in their carbs immediately after a workout or race is over.

How much protein should be taken onboard along with the carbs? "I'm guessing about 10 grams of protein," says Tarnopolsky, "although it is possible that 20 grams would be better." The McMaster-University researcher also suggests that athletes should rely at least partially on real foods, rather than special supplements, for their post-exercise nutrition. "Foods are less expensive than supplements, for one thing," notes Tarnopolsky, "and there are also evolutionary issues involved. Our bodies seem to do best at assimilating amino acids when those amino acids come from balanced proteins in real foods, not when sub-groups of amino acids are ingested in isolation. Remember, too, that actual foods tend to be richer in a variety of vitamins and minerals, compared with amino-acid supplements."

So what food source of protein and carbohydrate does Tarnopolsky recommend for post-exercise consumption? How about that humble potable called skim chocolate milk? "It appears to be almost perfect," comments the well-respected Canadian scientist. Indeed, chocolate milk contains rich veins of both protein and carbohydrate (just a cup of the chocolate beverage packs nine grams of protein and 26 grams of carbs, plus a not-too-shabby 288 mg of calcium). The stuff is almost as good as Kenyan tea!

Let's say you weigh 60 kilos (132 pounds) and thus are looking for 120 grams (480 calories) of carbohydrate shortly after exercise. Two cups of skim chocolate milk would provide the 10 to 20 grams of protein you need post-exercise (actually 18 grams), plus 52 grams of carbs. Along with a cup of Gatorade (15 grams of carbs), a banana (28 grams), and a bagel (38 grams), you would be more than home free, with a total intake of 133 grams of carbohydrate (if the Gatorade made your stomach too "sloshy," you could omit it and still rest on 118-gram carbohydrate laurels).

Milk has another feature (in addition to its generous protein and carbohydrate contents) which makes it ideal for after exercise: As Tarnopolsky points out, milk's proteins have very high biological value, and milk contains two unique kinds of protein - the "whey" proteins and the "casein" proteins. As it turns out, whey proteins tend to be absorbed by the human intestine very rapidly, while the casein proteins are taken up more slowly. "This creates a unique situation in which milk can provide amino acids to muscles very quickly after it is ingested (because of the whey proteins) and can also provide a steady flow of amino acids to the muscles over an extended period of time (because of casein). We believe that this may really bolster the protein-synthesis rate in muscles after exercise, compared with the consumption of other kinds of protein which don't provide such 'broad-spectrum' absorption," says Mark.

"The overall strategy (of taking in carbs and protein right after exercise) becomes particularly important if you train twice a day, or if you sometimes train in the afternoon or evening of one day and then during the morning of the following day," advises Tarnopolsky. "When either of those things happen, you will be attempting to exercise without enjoying 24 hours of carbohydrate recovery, and thus your muscles are very likely to be glycogen-impaired. As a result, it is critical for you to stoke up on the carbs (plus protein) right after the first workout in the closely linked training-session duet.

Tarnopolsky himself is a post-exercise chocolate-milk drinker, and he is also a highly successful elite athlete. Mark has finished first at the United-States long-and-short-course ski-orienteering championships, he was won a number of highly competitive trail runs (and set new course records while winning the 25-K Ganaraska Trail Run in Barrie, Ontario in both 1999 and 2000), and his adventure-racing team has captured the gold ring in the elite open category at a variety of rugged events, including the Raid-the-North-Ontario 36-Hour Race, the Adventure Racing Canada Enduro 6-Hour event, the Salomon Winter Adventure Race Enduro 6-Hour competition, and the Subaru Adventure Racing Series. For more details, please visit http://www.teamhammer.ca

Note that the new research on nutrient timing and the consequent upgrade of chocolate milk as a preferred sports drink mean that the actual composition of any workout that you complete consists of far more than just the exercise you perform. A workout also includes a "nutritional warm-up" consisting of pre-exercise amino acids (we'll describe the right amount for both endurance and resistance athletes in an upcoming issue of Running Research News) and a post-exercise and a post-exercise nutrient-intake period during which you ingest the right amounts of carbohydrate and protein (about 10 to 20 grams of protein and two grams of carbs per kilo of body weight, which is almost one gram of carbs per pound of weight). These pre- and post-exercise intakes should be planned just as carefully as the actual running, rowing, cycling, swimming, cross-country skiing, or strength training that you do.

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References

(1) Circ. Res. 20-21 (Suppl. 1), pp. I99-I114, 2000
(2) Journal of Applied Physiology, Vol. 83, pp. 1877-1883, 1997
(3) Journal of Applied Physiology, Vol. 84, pp. 890-896, 1998
(4) Journal of Applied Physiology, Vol. 82, pp. 1882-1888, 1997
(5) Medicine and Science in Sports and Exercise, Vol. 32, pp. 1412-1418, 2000
(6) Journal of Clinical Investigations, Vol. 79, pp. 1349-1358, 1987
(7) Am. J. Physiol. Endocrinol. Metab., Vol. 278, pp. E580-E587, 2000
(8) International Journal of Sport Nutrition and Exercise Metabolism, Vol. 12, pp. 172-188, 2002
(9) British Journal of Nutrition, Vol. 64, pp. 23-36, 1990
(10) International Journal of Sports Medicine, Vol. 10 (Suppl. 1), pp. S17-S21, 1989
(11) Diabetes, Vol. 48(5), pp. 949-957, 1999  

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