Is It Necessary to "Spike" Insulin Post-workout?
The rationale of maximizing the insulin response is to counteract the catabolic nature of the post-trained state, switching the hormonal milieu into an anabolic one, thus speeding recovery. Although this might benefit those who train fasted or semi-fasted, many don’t realize that a pre-exercise meal (and in some cases the mid-exercise meal) is doing more than enough spiking of insulin levels for anticatabolic purposes.
It’s an important objective to not only maximize muscle protein synthesis, but also minimize protein breakdown. However, the latter doesn’t require a massive insulin spike, but rather just a touch beyond basal/resting levels. To illustrate this, Rennie & colleagues found that even during a sustained high blood level of amino acids, no further inhibition of muscle protein breakdown occurred beyond insulin elevation to approximately 15 µU/l,20 which is slightly above normal basal levels of 5-10 µU/l.
To reiterate, the pre-exercise meal can have profound effects on insulin levels that surpass the length of the training bout. Tipton’s team found that as little as 6g essential amino acids + 35g sucrose taken immediately before exercise (45-50 minutes of resistance training) was enough to keep insulin elevated to roughly 4x above fasting levels 1-hour post-exercise.21 It took 2 hours post-exercise for insulin to return to resting levels. A similar insulin response was seen with 20g whey by itself taken immediately preworkout.22 If carbs were added to the pre-training protein, there would be yet a greater insulin response.
As far as solid food goes, Capaldo’s team examined various metabolic effects during a five hour period after ingesting a meal composed of 75g carb (47%), 37g prot (26%), and 17g fat (27%).23 Although this study didn’t examine training effects, this meal would make a nice post-workout meal due to its absolute (and proportional) amounts of protein and carbohydrate. The fat-fearing camp would warn against the meal’s fat content interfering with the insulin response. However, this meal was able to raise insulin 3 times above fasting levels within 30 minutes of consumption. At the 60 minute mark, insulin was 5 times greater than fasting. At the 300 minute mark, insulin levels were still double the fasting level.
Elliot and colleagues compared the effect of fat-free milk, whole milk, and a higher dose of fat-free milk (to match the calories of the whole milk) taken 60 minutes post-resistance exercise.24 Whole milk was superior for increasing net protein balance. Interestingly, the calorie-matched dose of fat free milk containing 14.5g protein, versus 8.0g in the whole milk (an 81% advantage), but still got beaten. The investigators speculated over the possible mechanisms behind the outcome (insulin response, blood flow, subject response differences, fat content improving nitrogen retention), but end up dismissing each one in favor of concluding that further research is necessary to see if extra fat calories ingested with an amino acid source will increase muscle protein synthesis. Lingering questions notwithstanding, post-workout milkfat was the factor that clinched the victory – at least in overnight-fasted subjects.
To put another nail in the coffin of the insulin spiking objective, post-exercise glycogen resynthesis is biphasic.25 Unlike the subsequent "slow" phase which can last several hours, the initial "rapid" phase of glycogenesis lasting 30-60 minutes immediately post-exercise is not dependent upon insulin.
Maximizing post-workout hyperinsulinemia may be beneficial for athletes with more than a single exhaustive endurance-containing training bout separated by less than approximately 8 hours, but in all other cases, the benefit in "spiking" insulin is nil.
In line with this theme, interesting research has surfaced in recent years challenging the idea that highly glycemic (and thus insulinemic) carbohydrates taken post-workout are the optimal for recovery. Erith’s team found no difference between post-exercise high- and low-glycemic index (GI) carbohydrate intake on exercise performance the following day.26 In a similar study, Stevenson’s team actually saw better next-day performance in subjects who consumed low-GI post-exercise carbohydrate than those who consumed high-GI post-exercise carbohydrate.27
REFERENCES
21. Tipton KD, et al. Timing of amino acid-carbohydrate ingestion alters anabolic response of muscle to resistance exercise. Am J Physiol Endocrinol Metab. 2001 Aug;281(2):E197-206. [Medline]
22. Tipton KD, et al. Stimulation of net muscle protein synthesis by whey protein ingestion before and after exercise. Am J Physiol Endocrinol Metab. 2007 Jan;292(1):E71-6. [Medline]
23. Capaldo B, et al. Splanchnic and leg substrate exchange after ingestion of a natural mixed meal in humans. Diabetes. 1999 May;48(5):958-66. [Medline]
24. Elliot TA, et al. Milk ingestion stimulates net muscle protein synthesis following resistance exercise. Med Sci Sports Exerc. 2006 Apr;38(4):667-74. [Medline]
25. Jentjens R, Jeukendrup A. Determinants of post-exercise glycogen synthesis during short-term recovery. Sports Med. 2003;33(2):117-44. [Medline]
26. Erith S, et al. The effect of high carbohydrate meals with different glycemic indices on recovery of performance during prolonged intermittent high-intensity shuttle running. Int J Sport Nutr Exerc Metab. 2006 Aug;16(4):393-404. [Medline]
27. Stevenson E. Improved recovery from prolonged exercise following the consumption of low glycemic index carbohydrate meals. Int J Sport Nutr Exerc Metab. 2005 Aug;15(4):333-49. [Medline]
Alan Aragon’s Research Review, January, 2008 – Inaugural Issue Page 6
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