Debunked!
A very intriguing topic, often discussed in a wide range of
magazines, from
Men's Health,
to
Bicycling Magazine, to
Runner's World.
As athletes we are constantly looking
for methods to best refuel and rebuild our muscles after a difficult workout,
and because caffeine has the ability to exert unique effects on metabolic machinery,
it has constantly been a target for research. One thing is fairly consistent throughout the
literature, caffeine can improve exercise performance. However, a quick google search revealed the
above mainstream magazines touting the recovery-enhancing effects of caffeine,
few of them addressed the fact that this is highly debated in the scientific
literature (
on a side note, the Bicycling magazine suggests incorporating 3.6
grams of caffeine per pound of body weight DO NOT DO THIS it is potentially lethal,
I believe it is a type and they intended
milligrams).
So, because
I… dislike overly simplistic one sided
reporting of nutritional science, I have taken it upon myself to summarize recent
scientific findings are available on the effects of caffeine on exercise
recovery. For the purpose of this
summary is I will define recovery as increased glycogen synthesis, or increased
activity of intracellular pathways associated with recovery, and finally altered
secretion of hormones associated with the recovery process (insulin, IGF-1,
testosterone, leptin, cortisol).
Carbohydrates
alone are not entirely sufficient to drive massive recovery when a person is
near total glycogen depletion. A
plethora of data suggest that there is a platue on the efficiency of
carbohydrates to fully drive recovery (1.2 grams of carbohydrates per kilogram
of body weight per hour) as insulin levels will no longer increase, thus once
carbohydrates are available in sufficient quantities, insulin levels tend not increase further (1).
Similarly, and related, is the fact that
once carbohydrates are available in sufficient quantities, muscle glycogen synthesis
also plateaus. Therefore, scientists have
sought other nutritional strategies to further enhance muscle glycogen synthesis
and/or muscle protein synthesis.
Although
not universally supported (1),
the addition of amino acids or protein to a carbohydrate rich recovery meal has
been found to enhance insulin secretion, muscle protein synthesis, and in some
cases also enhance muscle glycogen synthesis compared to carbohydrates alone (2-5). Thus, this is the “Gold Standard” when it
comes to recovery nutrition. But I
digress.
Interestingly, at rest, caffeine is
known to have negative effects on glycemic control exerted by muscles (6, 7).
That is to say, caffeine diminishes the
ability of muscles to respond to insulin signals to store glucose
(carbohydrate). However, this is at
least partially abolished during and after exercise (6, 8, 9). So then, does caffeine have a role in
recovery? In 2008, Pedersen and colleagues
(10)
said yes, and cited the fact that in their study they observed blood glucose levels
to be elevated for a longer period of time in the group receiving carbohydrates
+ caffeine than compared to a group receiving only carbohydrates during the
recovery phase. This was further
supported by their observation that glycogen synthesis rates were
significantly higher in the carbohydrate + caffeine group 4 hours post
exercise. While the authors are unable
to identify a mechanism for this observation, they speculate that this is
achieved through increased intestinal glucose transport. Based on this one result, indeed, there is
some evidence to suggest caffeine may enhance recovery, if consumed with
carbohydrates for 4 hours post exercise.
However, this one study is somewhat
of an outlier when looking at the entire breadth of work done on this topic. In a more recent study performed based on the article
published by Pedersen et al. using identical quantities of caffeine and
carbohydrate, there was no difference in post-exercise blood glucose or insulin
levels when comparing the group that received carbohydrates to the group that received
carbohydrates + caffeine (11).
Furthermore, a study published in 2012 (perhaps
the most complete study to date) which compared carbohydrates + caffeine,
carbohydrates + protein, and carbohydrates alone, found that caffeine had no
effect on muscle glycogen synthesis rates (12). Furthermore, this study also investigated
whether caffeine ingestion post-exercise increases intestinal sugar transport,
and found that there was no change in the capacity of the intestines of their
subjects (elite cyclists) to transport sugar (12).
Indeed, these results are quite contradictory,
and the positive results received much more attention from the media than did
the negative/no effect results. Perhaps
one of the most overlooked differences between the 2012 study done by Beelen et
al. and the 2008 Pedersen study, was the amount of carbohydrate supplied during
the post-exercise window. Study
participants in Pedersen’s study received 1 gram of carbohydrates per kilogram
of body weight per hour, while participants in the 2012 Beelen study received 1.2
grams of carbohydrates per kilogram body weight per hour. This would indicate that athletes in the
Pedersen study received a lower dosage of carbohydrate than those in the Beelen
study. Therefore, I believe this may be
an explanation for the differences between these results.
Further interpretation of these
results can be that caffeine may enhance recovery when glucose (carbohydrates)
are available in insufficient quantities. I think that rarely do I consume the truly adequate
amount of carbohydrates within the appropriate time frame to fully maximize
glycogen synthesis (1.2 grams of carbohydrates per kilogram body weight per
hour). For me that would be approximately
80 grams of carbohydrates per hour. Usually
I grab a chocolate milk or Gatoraide that may contain roughly 60 grams of
carbohydrates. In this case,
carbohydrates alone may be insufficient to fully maximize recovery, and
coingestion of caffeine could have a beneficial effect. However, if carbohydrates are available in
sufficient quantities, I believe (IMHO) caffeine ingestion will NOT enhance
recovery, and because of the known ways in which caffeine diminishes insulin
action, there is too much risk it may hamper recovery.
Overall, the rate at which glycogen
is synthesized after a hard workout depends on a huge number of factors. For example, length and duration of the
workout, total hydration status (which can effect gastric emptying), the level
of glycogen depletion, insulin sensitivity, as well as hormones, can all significantly
effect rates of glycogen synthesis.
Works Cited
1. Howarth KR,
Moreau NA, Phillips SM, Gibala MJ. Coingestion of protein with carbohydrate
during recovery from endurance exercise stimulates skeletal muscle protein
synthesis in humans. J Appl Physiol. 2009 Apr;106:1394-402.
2. van Loon LJ,
Saris WH, Kruijshoop M, Wagenmakers AJ. Maximizing postexercise muscle glycogen
synthesis: carbohydrate supplementation and the application of amino acid or
protein hydrolysate mixtures. Am J Clin Nutr. 2000 Jul;72:106-11.
3. van Loon LJ,
Saris WH, Verhagen H, Wagenmakers AJ. Plasma insulin responses after ingestion
of different amino acid or protein mixtures with carbohydrate. Am J Clin Nutr.
2000 Jul;72:96-105.
4. Berardi JM,
Price TB, Noreen EE, Lemon PW. Postexercise muscle glycogen recovery enhanced
with a carbohydrate-protein supplement. Med Sci Sports Exerc. 2006 Jun;38:1106-13.
5. Ivy JL,
Goforth HW, Jr., Damon BM, McCauley TR, Parsons EC, Price TB. Early
postexercise muscle glycogen recovery is enhanced with a carbohydrate-protein
supplement. J Appl Physiol. 2002 Oct;93:1337-44.
6. Thong FS,
Derave W, Kiens B, Graham TE, Urso B, Wojtaszewski JF, Hansen BF, Richter EA.
Caffeine-induced impairment of insulin action but not insulin signaling in
human skeletal muscle is reduced by exercise. Diabetes. 2002 Mar;51:583-90.
7. Robinson LE, Savani S, Battram DS,
McLaren DH, Sathasivam P, Graham TE. Caffeine ingestion before an oral
glucose tolerance test impairs blood glucose management in men with type 2
diabetes. J Nutr. 2004 Oct;134:2528-33.
8. Yeo SE,
Jentjens RL, Wallis GA, Jeukendrup AE. Caffeine increases exogenous
carbohydrate oxidation during exercise. J Appl Physiol. 2005 Sep;99:844-50.
9. Battram DS,
Shearer J, Robinson D, Graham TE. Caffeine ingestion does not impede the
resynthesis of proglycogen and macroglycogen after prolonged exercise and
carbohydrate supplementation in humans. J Appl Physiol. 2004 Mar;96:943-50.
10. Pedersen DJ,
Lessard SJ, Coffey VG, Churchley EG, Wootton AM, Ng T, Watt MJ, Hawley JA. High
rates of muscle glycogen resynthesis after exhaustive exercise when
carbohydrate is coingested with caffeine. J Appl Physiol. 2008 Jul;105:7-13.
11. Taylor C,
Higham D, Close GL, Morton JP. The effect of adding caffeine to postexercise
carbohydrate feeding on subsequent high-intensity interval-running capacity
compared with carbohydrate alone. Int J Sport Nutr Exerc Metab. Oct;21:410-6.
12. Beelen M,
Kranenburg J, Senden JM, Kuipers H, Loon LJ. Impact of caffeine and protein on
postexercise muscle glycogen synthesis. Med Sci Sports Exerc. Apr;44:692-700.
