Being a performance exercise supervisor I’m not only looking to maximize the physical performance of my clients but also to direct their nutritional efforts to help maximize said performance. Since more closely aligning myself with the paleo/evolutionary style of eating, it has come to my attention that certain experts recommend forgoing what is referred to in the athletic world as post-workout nutrition. The reasoning goes that post workout insulin elevation, from the carbohydrates recommended for post workout nutrition, blunts growth hormone (GH) response, reducing the amount of nutrients that get to lean tissue, thus limiting growth, which is what we’re all after. Recent research into both GH and post-workout nutrition tell a slightly different tale.
I’m certainly not the first individual to take on the Post-workout GH puzzle. Dr. John Berardi wrote an article six years ago that showed through research that:
- While the GH increase from training is pretty big in untrained subjects (10 fold increase), it’s not quite as big in trained guys (4-5 fold increase) (1,2,3,4).
- Either way, the GH increase is very brief. It’s at its peak immediately after exercise, is double about 15 minutes after exercise, and is back down to baseline at 30-60 minutes after exercise (2,3).
- The GH release you get during the first few hours of sleep time is about a 20-fold increase in GH, while the normal GH pulses that occur during the day are between 10 and 15 fold (5). Not only are these pulses larger than the post-exercise pulse, but they last longer, too (1-3 hours).
- Carbs DO NOT decrease the normal GH pulse after exercise. Actually, according to 2 studies, a post-workout meal of carbs and protein INCREASED the post-workout GH release when compared to fasting after the workout (2, 8). Maybe the myth exists because a few endurance studies showed that infusing or drinking carbs DURING endurance exercise increased blood insulin and decreased blood GH (6, 7). But how relevant is that to weight trainers and to the post-workout period?
So GH release post-exercise isn’t as substantial as the GH release one gets during a good night of sleep and insulin increases the GH pulse post-workout above compared to fasting. While this all sounds good, recent research indicates that GH is rubbish for increasing athletic performance (9). This meta-study reviewing all of the scientific literature on GH from 1966 to 2007 concluded:
Claims that growth hormone enhances physical performance are not supported by the scientific literature. Although the limited available evidence suggests that growth hormone increases lean body mass, it may not improve strength; in addition, it may worsen exercise capacity and increase adverse events. More research is needed to conclusively determine the effects of growth hormone on athletic performance.
41 years of research and we’re still not sure if extra GH above the normal physiological range assists in any training endeavors. With this in mind, I’d like to point out a recent study that compares protein synthesis response in training individuals versus untrained individuals. As it turns out, trained muscles reach peak protein synthesis 4 hours post workout and return to resting levels of protein synthesis within 28 hours (10). This was compared this to protein synthesis in untraining muscles, which was still elevated above baseline 28 hours later but never reached the same peak rate of synthesis that the trained limb did. This further indicates the idea of the “Window of Opportunity” for getting amino acids into the body through a drink that includes fast acting carbs and branch chain amino acids (11, 12)
So what’s the take home message? First, GH response post-workout isn’t the largest we have during a normal day and may even increase with proper post-workout nutrition, but the science is still lacking as to if this is going to help us in any way. We do know that, in order to maximize protein synthesis and stimulate growth, a post-workout meal of fast acting carbs and protein is essential. This is the ONLY time to rapidly spike insulin, as your body is primed and ready to make use of the hormone. There’s a reason that Dr. Loren Cordain, arguably the father of paleo eating, wrote a book recommending this: it just works.
1. Journal of Applied Physiology; 88 (3), 982-992, 1999.
2. Journal of Applied Physiology; 85 (4), 1544-1555, 1998.
3. European Journal of Endocrinology; 141 (1), 22-26, 1999.
4. European Journal of Applied Physiology; 78 (1), 69-76, 1998.
5. Science; 177, 1205, 1972.
6. Journal of Applied Physiology; 87 (1), 124-131, 1999.
7. European Journal of Applied Physiology; 80 (2), 92-99, 1999.
8. Journal of Applied Physiology; 76 (2), 839-845, 1994.
9. Ann Intern Med. 2008 Mar 17
10. Am J Physiol Regul Integr Comp Physiol 294: R172-R178, 2008.
11. Journal of Nutrition. 2000;130:139-145.
12. J Appl Physiol 88: 386-392, 2000
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