Insulin: To Spike or Not to Spike?

To Spike or Not to Spike, That Is the Question?
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Post-exercise nutrition is critical for maximum gains. The stimulus of training triggers signaling pathways within muscle cells that allows for greatly enhanced muscle protein synthesis rates. These pathways do not stay active for
long, however. There is a window
 of opportunity immediately post-exercise in which one can significantly increase the anabolic effects of ingested nutrients. This window stays open for a couple of hours at most. After that, the impact of nutrient intake on muscle protein synthesis gradually declines. The more “trained” you are, the faster the anabolic sensitivity dissipates.

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The obvious question for most at this point is, “What nutrients will allow me to best take advantage of this anabolic window?” It has been known for many years that protein, or more specifically amino acid availability, is critical to maximize the effects of your post-workout feeding. What has also been recommended is that you ingest a high glycemic–index carbohydrate along with your protein. This would not only replace glycogen used during your workout, but also create an insulin spike that would presumably enhance protein synthesis. After all, insulin is an “anabolic” hormone.

Over the years there have been many studies performed to illustrate the importance of timing post-workout protein and carbohydrate intake. Surprisingly, there have been only two studies looking at the true influence
 of carbohydrates and/or insulin in combination with protein on the rate of muscle protein synthesis post-workout. After all, it seemed obvious that you needed an insulin spike to maximize protein synthesis. If we take a look at those two studies that did question the importance of adding high-glycemic carbs to post-workout protein drinks, what we find might surprise you.

In 2007, a group working out of Maastricht University in the Netherlands examined the impact of adding carbohydrates on post-exercise muscle protein synthesis.(1) They had 10 healthy 20-somethings work out for one hour using a traditional resistance exercise protocol. The three post-workout treatment conditions were protein only (PRO), protein with a low carbohydrate dose (PRO + LCHO), or protein with a high carbohydrate dose (PRO
+ HCHO). A total of 12 servings were given every 30 minutes for each treatment condition to ensure a continuous and ample supply of both glucose and amino acids during the six hours of recovery. Each subject returned seven days later to receive a different post-exercise treatment until all had been tested under each condition.
 Their results indicated that, given an ample amount of easily digested high-quality protein (casein hydrolysates), added carbohydrates had no effect on post-workout protein synthesis rates regardless of the amount of carbs given.

In support of these findings, another study more recently published in Medicine and Science in Sports and Exercise utilized a similar protocol (i.e., workouts followed by protein or protein + carbs) but this time they were more interested in the impact of creating a post-workout insulin spike.(2) Would it affect protein synthesis rates? Would it decrease protein breakdown? Would it trigger anabolic signaling pathways more effectively? You probably know where this is heading. The answer is 
no, it didn’t. Spiking insulin didn’t reduce protein breakdown, and it didn’t enhance anabolic signaling pathways. The insulin spike didn’t even increase muscle blood flow! What appears to have happened was, because they used a protein source (whey) that has already been shown to maximally stimulate post-exercise protein synthesis as well as increase insulin levels, no further anabolic effect was possible even from an insulin spike. The insulin level triggered by whey alone was able to maximally inhibit protein breakdown, increase blood flow, and activate anabolic signaling pathways.

The take-home message is: Just make sure you are getting some high-quality, easily digested protein into your gullet immediately after your workout. Whether you ad carbs or not will not have a significant effect either way.

Reference: 1. r. Koopman et al., Am J Physiol Endocrinol Metab., 293(3):e833–42, 2007. 2. A.W. Staples et al., Med Sci Sports Exerc., 43(7):1154–61, 2011.

 

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