The “post workout window” has always received a lot of attention from athletes and health and fitness enthusiasts alike. Should you slam down a protein shake immediately? How much protein? What about simple sugars? Should you avoid fat? All these questions you likely have asked or been asked if you are a strength and conditioning coach. In order to get the most out of your workout and and continue to progress, nutrition is absolutely imperative. But what if I told you the best thing to eat post-work is nothing at all!

---

   The basics of nutrition is and always will be calories in vs. calories out. If you want to gain weight, consume more calories than your burn. If you want to lose weight, consume less calories than you burn. It is only when these fundamental understandings are in place that you can specify your diet to your personal needs and goals. That being said, if you wish to gain weight, it is probably necessary to consume 5-7 meals a day. On the other hand, if you you wish to lose weight you can either consume less meals or more frequent, smaller meals. However, the timing of the meals you consume is less important than the amount of food you consume. In the pyramid of nutrition, caloric content is the base! Knowing this will allow you to take full advantage of the “anabolic window” after a strenuous strength and conditioning workout.

The Post-Workout “Anabolic Window”

   If you have spent any amount of time in the gym, reading fitness magazines, or online, you’ve probably heard of the post-workout anabolic window. The period of heightened absorption, utilization, and ultimately gains is said to occur during this brief period. But when looking at the post-workout period a bit more in depth, you may be surprised. Protein synthesis has been shown to increase for approximately 48 hours post-workout, with levels nearly doubled at 24 hours. This means that your ability to increase lean muscle mass is optimized following your workout, but not just for a couple hours. During this heightened period of protein synthesis, you should be consuming the needed calories to either gain or lose weight. The amino acids that comprise protein rich foods  are directly responsible for the building blocks of skeletal muscle. Anyone wishing to put on extra lean muscle mass must increase protein intake. However, don’t forget the important roles of both carbohydrates and fats. Carbohydrates are stored as muscle glycogen and will be the fuel source for all upcoming high intensity exercises, practices, and competitions. Fats have many benefits of regulation including hormonal regulation as well as being the most calorically dense of the macronutrients at 9 calories/gram.
   Also during the post-workout period, acute rises in muscle building and repairing hormones such as testosterone, growth hormone, and IG-1 drastically increase immediately following your workout and are peaked for approximately 30 minutes (testosterone has been shown to be elevated longer).  Chronic resting increases in these hormones does not occur, actually being a greater benefit than one may initially think. Acute rises following intense resistance training allows heightened sensitivity of the receptors to these hormones, ultimately allowing greater improvements. This means you must train hard and often to get the full of benefit of these powerful hormones. What you may not know is that you could be inadvertently robbing yourself of the benefits of these hormones by the choices you make immediately following your workout!

The Benefits of Fasting

   The benefits of fasting have received a lot of attention lately. Some of the most powerful benefits of fasting include heightened cellular repair and gene expression. Preliminary research even shows that caloric restriction diets and periods of fasting, commonly termed “intermittent fasting”, have a positive impact on life expectancy. However, these benefits are outside the scope of this article. A benefit more directly related to athletes and health and fitness enthusiast is heightened hormone levels, more specifically testosterone and growth hormone.
   Whenever someone thinks of strength and muscle mass, testosterone is always in the back of the mind. Testosterone has a longstanding reputation for being the most powerful muscle and strength builder. Being able to naturally increase your testosterone levels will likely aid in recovery, continued improvement, and ultimately performance. However, when someone thinks about increasing hormone levels they likely never think of fasting. Research has shown that when you eat your testosterone levels drop. Numerous studies show eating as little as 300 calories (or more) elicits an acute decrease in testosterone. This decrease remained for as long as three hours in some cases. Interestingly, the drop occurred regardless of type of food consumed. For an athlete this means less muscle mass, strength improvements, energy and recovery!
   Testosterone is not the only hormone that has positive effects on strength, muscle mass, and recovery. Growth hormone and IGF-1 are two very powerful hormones with similar effects as testosterone. An easy way to think of growth hormone, and IGF-1 release due to growth hormone, and insulin are the two having an inverse relationship. When one is high the other is low. Insulin spikes in the presence of carbohydrates to absorb blood glucose, but by restricting food intake and choosing not to eat, insulin is not released. This lack of insulin release does not blunt the hormonal response in your body. This means you know have heightened growth hormone and IG-1 levels by choosing not to eat. Your body also does not use energy for the digestive process, which may be why people actually report higher energy levels after having fasted regularly (they also become more efficient at burning fat as fuel). By choosing to fast you can spike your muscle building hormone levels, the same hormones shown to increase as a result of intense resistance training! But beware, too much of a good thing is not a good thing. Fasting too long also causes decreases in these powerful hormones among other potential health risks. Before we dive too deep, let me stop and say. I am not promoting an athlete/fitness enthusiast fast. I am just shedding light on the potential benefits of temporarily fasting at the correct times to enhance results. This can all get confusing….so lets break this down and get the best of both worlds!

BEST OF BOTH WORLDS

   As mentioned earlier, protein synthesis is heightened for 48 hours and acute rises in muscle building hormones are peaked post-workout. But, eating is shown to surprisingly decreases these hormones. However, don’t forget that caloric amount is the most important aspect of nutrition. By manipulating these variables, you can optimize your hormone levels post-workout and still reap the benefits of proper nutrition.
   When high-intensity resistance exercise is followed by eating food and/or a post-workout shake, testosterone level were shown to decrease below resting levels! This relationship was not seen in individuals who were given a placebo (zero calories). If you think food is more powerful than hormones I would have to disagree with you. Especially considering the principles of nutrition we’ve already discussed. Provided you have the time and discipline it may be beneficial to incorporate a 30-60 minute fast post-workout fast to allow more time for the powerful anabolic hormones to have an effect on the body. Following this brief fast, a balanced meal of protein, carbohydrates, and fats is recommended. It is important to mention, that exercise itself induces increases in these hormones as well, and choosing to fast post-workout will allow you to extend the time-period of these hormones. By choosing to eat immediately post-workout, you have not eliminated all the effects of the hormonal response to exercise, you just have cut it short. Keep that in mind when choosing the best nutrition plan for you.
   The next question, how long should you wait to eat following a workout? This, like all of your nutritional decisions, depends on your goals. If your goal is to gain weight, you will likely need to eat more meals which requires more time and less time available for post-workout fasting. On the other hand, if you wish to lose weight you will consume less meals and need less time to consume these meals, allowing you to fast longer post-workout. Regardless of your goal, I believe everyone can benefit by fasting 30-60 minutes post workout.

WHEN TO AVOID PWO FASTING

   The post-workout fast may not be optimal for everyone. Post-workout nutrition should not only be viewed as recovery from a prior workout but just as importantly as preparation for the upcoming workout/event. Your body’s main fuel source for intense workouts or sport is stored glycogen as a result of carbohydrate consumption. Unless you plan on running marathons every day, you are not burning through all your glycogen. Think of muscle glycogen as a gas tank. As long as you fill it up before your next trip, you will be good to go. It is true that exercise causes additional receptors to be present on the muscle to absorb more carbohydrates following a workout, however that does not mean you will not absorb those nutrients later in the day as well. It is believed that one can store approximately 15 grams of carbohydrates per kilogram of bodyweight in skeletal muscle and an additional 60-90 grams in the liver. However, athletes performing multiple workouts a day, those who workout and practice, or have multiple games a day should avoid the post-workout fast to fully benefit from refueling for the upcoming game or event. In these cases, calories consumed following a workout or game will be necessary and vital to your performance.

Summary

   Post-workout fasting should be viewed as a tool to reap potential additional benefits from an intense strength and conditioning session. I would not recommend fasting post-workout to someone who does not have a solid foundation of diet and nutrition or who is competing or training multiple times a day. Those who are disciplined may find benefit after implementing fasting over a period of time. I would suspect the benefits will not happen immediately, but down the road it may add up. For the general health and fitness enthusiast, fasting is a great way to decrease body fat, increase energy levels if continued over a period of time, and elevate hormones. So if you are looking for a slight edge, next time you get done with an intense workout, wait 30-60 minutes prior to eating. The little gains add up over time!

References:

• Interisano, S. A., and K. E. Yarasheski. “The time course for elevated muscle protein synthesis following heavy resistance exercise.” Can J Appl Physiol 20 (1995): 480486MacIntyre.
• Kraemer, William J., and Nicholas A. Ratamess. “Hormonal responses and adaptations to resistance exercise and training.” Sports Medicine 35.4 (2005): 339-361.
• Ho, Klan Y., et al. “Fasting enhances growth hormone secretion and amplifies the complex rhythms of growth hormone secretion in man.” Journal of Clinical Investigation 81.4 (1988): 968. —> GH spikes/release were undetectable in the fed state…in control (fasting) rise were seen!
• Habito, Raymundo C., and Madeleine J. Ball. “Postprandial changes in sex hormones after meals of different composition.” Metabolism 50.5 (2001): 505-511.
• Röjdmark, S. “Influence of short-term fasting on the pituitary-testicular axis in normal men.” Hormone Research in Paediatrics 25.3 (1987): 140-146.
• Bloomer, Richard J., Gary A. Sforzo, and Betsy A. Keller. “Effects of meal form and composition on plasma testosterone, cortisol, and insulin following resistance exercise.” International journal of sport nutrition and exercise metabolism 10.4 (2000): 415-424.
• Schumm, Sean R., et al. “Original Research Hormonal Response to Carbohydrate Supplementation at Rest and After Resistance Exercise.” International journal of sport nutrition and exercise metabolism 18 (2008): 260.