Dear Lyle,
I have heard varying suggestions for pre-workout meals and before bedtime. Several authorities seem to be dead set against food (especially) carbohydrate consumption will inhibit Growth Hormone release by raising insulin levels. I work out late in the evening and I am not sure whether I should be eating carbohydrates after my workout. On the one hand I want to replenish my glycogen stores, but on the other I don’t want to stop the release of growth hormone when I go to bed. I would be grateful for your thoughts on this subject.
It is true that insulin and growth hormone are antagonistic to one another. Generally, high blood glucose/insulin levels reduces growth hormone levels. By the same token, low insulin/blood glucose causes growth hormone to go up. The problem with just looking at GH levels is that GH per se is not that terribly anabolic (it is useful for fat loss).
Most likely, any anabolic effects of GH are mediated through something called IGF-1 (Insulin like Growth Factor 1, also called somatomedin). When GH is released and a host of other factors are in proper place (including adequate dietary energy, protein, etc), the liver will produce IGF-1. Also, IGF-1 can be released by muscle cells themselves (most likely due to eccentric muscle trauma).
As to effects on muscle growth, I happen to disagree on the relative importance of GH for muscle growth. Studies that injected GH into individuals weight training showed NO greater muscle growth in the GH group vs. the non-GH group. Fasting actually raises GH the highest and we all know how good fasting works for putting on muscle.
The reason is that While it’s true that high glucose/insulin will decrease GH release, especially at rest, I have to wonder how much effect it will have during exercise. Once exercise starts, insulin levels start to drop almost immediately due to the release of catecholamines so I’d guess a 5-10′ warmup would lower any high insulin levels from a high carb meal.
Thing is, I’m not convinced that the overall hormonal response to training is that critical. That is to say, the effects of overall tension, fatigue and muscle damage play a much greater role in my mind than any hormonal release. Now, it may be that maximizing/optimizing the hormonal response (GH or testosterone) to training may increase gains but I still think that the overall loading, etc is more important.
As to eating carbs before your evening workout, you have to weigh this:
Is it more important to you that you: a. get a good GH response from your training b. have adequate blood glucose (from your snack) to support your high intensity training.
Yes, it’s all wonderful to get a good GH response from training but if it means having a crummy workout because you’re running out of steam, it’s a moot point. The same thing applies to the debate over eating before morning workouts. If you work out early in the morning, yes you might get more of a GH response from training on an empty stomach but weigh that against training with low blood sugar. If your workout goes poorly because you don’t have any energy, you won’t grow no matter how perfect the hormonal response is.
As far as post-workout carbohydrates, at least one study has shown that the combination of protein and carbohydrates raised both insulin and GH after a workout. The reason is that the carbohydrates raised insulin which then caused a drop in blood glucose (which is what insulin does) which caused a GH release. Ultimately, I think replenishing muscle and liver glycogen after a workout are relatively more important than worrying *too* much about GH release during sleep, etc.
About the author
Lyle McDonald+ is the author of the Ketogenic Diet as well as the Rapid Fat Loss Handbook and the Guide to Flexible Dieting. He has been interested in all aspects of human performance physiology since becoming involved in competitive sports as a teenager. Pursuing a degree in Physiological Sciences from UCLA, he has devoted nearly 20 years of his life to studying human physiology and the science, art and practice of human performance, muscle gain, fat loss and body recomposition.