Post Exercise Nutrition to Maximize the Training Effect

Introduction

All too often athletes are looking for a food or diet that will increase their performance “during competition”. This is a misguided approach. The key role for nutritional intervention is during the training period. Nutrition will have the greatest impact on “performance” if it is used as an adaptive facilitator after appropriately periodized training sessions rather than as a magic potion. This must be done on a consistent basis. When implemented properly, strategic post-exercise nutrition can greatly effect the extent to which the athlete adapts to training. From this perspective, training and diet can not be considered as separate factors. The food and supplements that you take and the work that you faithfully perform is training. On the day of competition it will not be the athlete who trained harder who wins, it will be the athlete who trained smarter.

Exercise causes acute changes in the metabolic environment of muscle tissue. These changes favor catabolism during exercise, and anabolism immediately after exercise. Because these changes are acute, some lasting only a few hours, the post exercise meal is critical to optimizing the anabolic effect of exercise. This article will discuss post exercise nutritional strategies based on current research in this area.

During exercise muscles use metabolic fuels at an accelerated rate. In order for physical work to be continuous, the body mobilizes stored fuels to make available fatty acids, glucose, and amino acids for oxidation. This is a catabolic process and cannot occur simultaneous to anabolic process’ such as glycogen formation and protein synthesis.

In order for the body to recover from exercise, the catabolic environment must be quickly changed to an anabolic environment. The food that you eat after training effects the hormonal milieu in your body in order for this to take place. With the rapid introduction of carbohydrate, protein, and fat into the system post exercise, the body is able to begin reparations on damaged tissue and replenish fuel reserves.

Carbohydrates

Carbohydrates are important for performance and perhaps more importantly for recovery. Studies have shown an increased ability of muscle tissue to take up serum glucose immediately following strenuous exercise (Goodyear 1998). This is due to what is called, “non-insulin dependant glucose uptake”. After a meal, muscle cells transport glucose across the cell membrane in response to the hormone insulin. Insulin binds with its receptors at the cell surface causing a cascade of events that ends with proteins, called glucose transporters, being translocated to the cell surface. Once at the cell surface, these glucose transporters allow glucose to pass through the membrane where they can be phosphorilated and eventually stored as glycogen.

Membrane transport of glucose will exhibit saturation kinetics similar to the effect of increasing substrate concentration on the activity of enzymes. The rate of glucose entry into your muscle cells is limited by the number of glucose transporters. Once all available glucose transporters are associated with a glucose molecule, the rate of glucose entry will go no higher.

There are at least 5 different classes of glucose transporter proteins. They are designated GLUT1, GLUT2, GLUT3, GLUT4, and GLUT5. Each class of GLUT protein differs in its kinetic parameters and are found in specific tissues. GLUT-4 is the primary isoform regulated by insulin, and sensitive to muscle contraction.

Muscle contractions, much like insulin, cause a separate set of GLUT-4 proteins to be temporarily translocated to the surface of the muscle cell (Sherman 1996). This greatly increases the rate at which muscle tissue can take in glucose from the blood after a bout of exercise. The effects of exercise on glucose uptake lasts for a few hours into the post exercise period. If the post exercise meal is lacking in carbohydrates, the replenishment of glycogen is delayed. If carbohydrates are lacking in the diet, exercise will cause a glucose deficit and glycogen stores will continue to fall without being replenished to pre exercise levels.

There has been some controversy about which type of carbohydrate is best for post exercise glycogen replenishment. Some argue that simple sugars such as dextrose are best after exercise. Others say that drinks with glucose polymers are best. Still others say that there is no need to buy fancy sports drinks and that simply eating a meal high in carbohydrates such as pasta or rice is sufficient. Studies have shown no difference between different types of carbohydrates eaten post exercise and the rate of glycogen replenishment as long as sufficient quantities of carbohydrate are consumed (Burke 1997). Even when the post exercise meal contains other macronutrients such as proteins and fats, the rate of glycogen replenishment is not hindered, given there is sufficient carbohydrate in the meal as well. These studies tell us that the rate limiting step in glycogen replenishment after exercise is not in digestion or the glycemic index of a given source of carbohydrate. Over a 24 hour period it is the total amount of carbohydrate consumed that is important.

The rate limiting step in glucose uptake during exercise is determined by the rate of phosphorylation once glucose has entered the muscle cell (Halseth 1998). Glycogen synthase activity is also a possible rate limiting step (Halseth 1998). These processes are not readily influenced by the composition of the “post exercise” meal, but rather by the extent to which glycogen was depleted during exercise as well as the amount of carbohydrate and fat consistently included in the diet.

It is recommended that at least 0.7 – 1.0 gram of carbohydrate per kilogram body weight be consumed immediately after exercise and then again 1-2 hours later. If you experience gastric upset try increasing the amount of water you consume with the carbs. Try to shoot for a total of 7-10 grams of carbohydrate per kilogram of body weight over a 24 hour period ³ for maximum glycogen storage. This may well be in excess of caloric needs but it is important to shoot for this intake if glycogen storage is your primary goal.

Protein

Protein is another critical nutrient to included in the post exercise meal. Protein is essential to post exercise anabolism. Protein provides amino acids which are used to rebuild damaged tissues as well as provide enzymes and carrier proteins necessary for adaptation to exercise. Without protein, which supplies essential amino acids for endogenous protein synthesis, the body’s ability to adapt to exercise is greatly diminished.

Studies have shown a 12 to 14 day period after the onset of an unaccustomed exercise program, in which nitrogen balance, the ratio of protein intake to protein loss, is negative (Butterfield 1987). Any study looking at protein needs and exercise must take this into account. Nitrogen balance during this period appears to be insensitive to total caloric intake, but can be improved with a high protein intake if adequate calories are supplied (Gontzea 1975). Even though additional protein intake will prevent nitrogen balance from becoming negative, it will still fall despite high protein intake during the first two weeks of exercise.

Muscle specific messenger RNA (mRNA) produced subsequent to training has a half life of only 4-5 hours. It is so short because mRNA has no “quality control” mechanism built into the coding. By keeping the half life short, any errors in the sequence won’t be able to produce enough defective proteins to do irreparable damage to the cell or organism. This also allows tight control of protein metabolism.

The timing of protein intake is important. If the anabolic stimulus from exercise is to be maximized, a steady flow of amino acids must bathe the muscle while mRNA content is high. It should be no surprise that the optimum time for protein intake after your workout is relatively brief compared to frequency of training a particular muscle. Muscle protein synthetic rate (MPS) is elevated in humans by up to 50% at about 4 hours following a bout of heavy resistance training, and by 109% at 24 hours following training. A study done by Macdougall (MacDougall et al 1995) further examined the time course for elevated muscle protein synthesis by examining its rate at 36 hrs following a bout of heavy resistance training. Six healthy young men performed 12 sets of 6- to 12-RM elbow flexion exercises with one arm while the opposite arm served as a control. MPS was calculated from the in vivo rate of incorporation of L-[1,2-13C2] leucine into biceps brachii of both arms over 11 hours. At an average time of 36 hours post-exercise, MPS in the exercised arm had returned to within 14% of the control arm value, the difference being nonsignificant. The following conclusions can be drawn from this study, following a bout of heavy resistance training, muscle protein synthetic rate increases rapidly, is more than double at 24 hours, and then declines rapidly so that at 36 hours it has almost returned to baseline.

Current recommendations for total protein intake for athletes is between 1.6-1.8 grams per kilogram body weight, depending on who you read, however, it is not uncommon for bodybuilders to consume in excess of 2 grams per kg of body weight with no ill effects. It should be remembered that the body does not have the capacity to effectively store amino acids. Protein should be eaten at least every 3-4 hours. The evening meal should contain slowly digesting protein that will allow a steady release of amino acids into your system well into the night. Dinner is a perfect time for steak or other meat dishes.

Fat

Little is known about the effects of fat in the “post-exercise” meal. Total fat intake is probably more important for a bodybuilder than just considering the post-workout meal.

Essential fatty acids in sufficient quantities have the ability to alter physiology. Fatty acids such as omega-3s’ and omega-6s’, when consumed in differing ratios in a consistent and deliberate manner, can alter the composition of cell membranes which alters the production of prostaglandins in working muscles and thereby can modify everything from glucose transport to protein synthesis (Hayashi 1999). These effects are seen after at least 5 days of consuming of these fats in moderate to high doses. Eating them immediately after training and at no other time will most likely not have any dramatic effect.

Some forms of fat may delay gastric emptying which theoretically could slow the rate at which nutrients become available to tissues. We can only speculate whether this would have any “long term” effect on gains. Most research indicates that glycogen replenishment is delayed but not reduced when gastric emptying is prolonged.

There is some indication that cholesterol may be an important nutrient immediately after high intensity resistance exercise. Total cholesterol has been shown to be significantly lowered for at least 90 hours following a single bout of resistance exercise (Smith 1994). Serum cholesterol may be needed for incorporation into damaged cell membranes after resistance exercise. I’m not implying that you should eat a high cholesterol meal right after training. Taken together, research is still lacking where the optimal levels and composition of post-exercise fats are concerned.

Fluids

I couldn’t really write an article about post exercise nutrition without at least mentioning fluid replacement. Hydration is extremely important on the cellular level. Muscle growth is inhibited by dehydration. In bodybuilding we tend not to focus on fluid replacement because unlike runners or cyclists, most bodybuilders do not become dehydrated after a single workout. The rate at which you become dehydrated from training depends on how much you sweat (Gisolfi 1990). Some people sweat a lot when lifting and others don’t sweat a drop. A good rule of thumb is to drink 1 ml for every calorie that you need. So, if you eat 3,500 calories a day, try to drink 3 ½ liters. If you exercise in hot or humid climates add 2 cups of water for every pound you lose while exercising.

It’s about synergy

As mentioned earlier, macronutrient intake modulates post-exercise protein synthesis in ways that are just beginning to be understood. Yes, protein is required to supply essential amino acids for protein synthesis, but what is the mechanism by which protein is controlling this process? Also, are carbohydrates and fats needed only for fuel replacement, or do they play an “interactive” role in post exercise protein synthesis? Recent research has shed light on these questions.

Researchers from the Division of Nutritional Sciences at the University of Illinois examined the effect of post exercise meal composition on protein synthesis. To do this, they looked specifically at the activity of specific proteins known to regulate protein synthesis at the translational level.

Initiation of translation (the binding of mRNA to the ribosomal pre-initiation complex) requires group 4 eukaryotic initiation factors (eIFs). These initiation factors interact with the mRNA in such a way that makes translation (the construction of new proteins from the mRNA strand) possible. Two eIFs, called eIF4A and eIF4B, act in concert to unwind the mRNA strand. Another one called eIF4E binds to what is called the “cap region” and is important for controlling which mRNA strands are translated and also for stabilization of the mRNA strand. Finally, eIF4G is a large polypeptide that acts as a scaffold or framework around which all of these initiation factors and the mRNA and ribosome can be kept in place and proper orientation for translation.

The researchers in this study looked at the association of the mRNA cap binding protein eukaryotic initiation factor-4-E (eIF4E) with the translational inhibitor 4E-eukaryotic initiation factor binding protein-1 (4E-BP1) in the acute modulation of skeletal muscle protein synthesis during recovery from exercise. Fasting male rats were run on a treadmill for 2 h at 26 m/min and were fed immediately after exercise with either saline, a carbohydrate-only meal, or a nutritionally complete meal using Ensure Powder (54.5% carbohydrate, 14% protein, and 31.5% fat). Exercised animals and non-exercised controls were studied 1 h post-exercise.

Muscle protein synthesis decreased 26% after exercise and was associated with a fourfold increase in the amount of eIF4E present in the inactive eIF4E.4E-BP1 complex and a concomitant 71% decrease in the association of eIF4E with eIF4G. Refeeding the complete meal, but not the carbohydrate meal, increased muscle protein synthesis equal to controls, despite similar plasma concentrations of insulin. Additionally, eIF4E.4E-BP1 association was inversely related and eIF4E.eIF4G association was positively correlated to muscle protein synthesis. This study demonstrates that recovery of muscle protein synthesis after exercise is related to the availability of eIF4E for 48S ribosomal complex formation, and post-exercise meal composition influences recovery via modulation of translation initiation.

The results of this study tell us a few things:

1. Insulin (via carbohydrate intake) alone is not enough to prevent 4E-BP1 from sequestering eIF4E. EIF4E must be free to bind to eIF4G in order for protein synthesis (i.e. recovery from training and net muscle growth) to begin. Insulin as well as amino acids must be present at the same time as indicated by the results from the group that were fed a mixed nutrient meal. So although feeding of the carbohydrate meal resulted in elevated blood glucose and elevated insulin levels, carbohydrates alone are not sufficient to allow protein synthesis to begin.

2. The only group that experienced a significant drop in cortisol levels was the mixed meal group. The carbohydrate-only group showed that neither blood glucose nor insulin had any effect on reducing cortisol levels. In contrast, the mixed meal group showed cortisol levels even below those in the control group who did no exercise and were also fed the same meal.

It would have been nice for the authors of this experiment to have explored the effect of the fat content in the “mixed meal”. From the results we saw that cortisol was lower in the mixed meal group. We can only speculate wether this was due to the protein, the fat, or some combination of protein, fat and carbs. Further research in this area should take into consideration all components of the post exercise meal. One other issue that might be addressed in humans is the time frame during which re-alimentation is critical to “long term” adaptation to exercise.

In closing…

Post-exercise nutrition is critical if one wants to maximize the anabolic effects of exercise. The post exercise meal should consist of carbohydrate, protein and fat in a form that is easily and quickly digestible. There are many meal replacement products that fit the bill. Just pick the one you like the most. Don’t worry about sugar content because right after a workout, fat storage is not a big issue. A liquid meal is the most practical method of post-exercise feeding although it is probably not essential. The ratio of macronutrients depends somewhat on the nature of the training session. An emphasis on high glycemic carbs, complete readily digestible proteins such as whey or high quality soy, and essential fats such as flax oil will meet the criteria for an effective post exercise meal.

References:

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Gontzea I, Sutzescu P, Dumitrache S. The influence of adaptation to physical effort on nitrogen balance in man. Nutr. Rept. Inturn. 11:231-236, 1975

Goodyear LJ, Kahn BB, Exercise, glucose transport, and insulin sensitivity. Annu. Rev. Med. 49:235-261, 1998

Halseth AE, Bracy DP, Wasserman DH. Limitations to exercise- and maximal insulin-stimulated muscle glucose uptake. J. Appl. Physiol. 85(6):2305-2313, 1998

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Furukawa K, Nitta H, Nakajima N, Suzuki N, Ito I Effect of intravenous omega-6 and omega-3 fat emulsions on nitrogen retention and protein kinetics in burned rats. Nutrition 1999 Feb;15(2):135-9

MacDougall JD, Gibala MJ, Tarnopolsky MA, MacDonald JR, Interisano SA,

Yarasheski KE The time course for elevated muscle protein synthesis following heavy resistance exercise. Can J Appl Physiol 1995 Dec;20(4):480-6

Sherman LA, Hirshman MF, Cormont M, Le Marchand-Brustel Y, Goodyear LJ. Different effects of insulin and exercise on Rab4 distribution in rat skeletal muscle. Endocrinology 137:266-73, 1996

Smith L.L, Fulmer M.G, Holbert D, McCammon M.R, Houmard J.A, Frazer D.D, Nsien E, and Isreal R.G. The impact of a repeated bout of eccentric exercise on muscular strength, muscle soreness and creatine kinase. Br. J. Sports Med.1994; 28 (4) 267-271.