Energy Drinks Increase Resting Metabolic Rate, But Do Not Influence Energy Expenditure During Exercise

Ever wondered, whether the drink that was once rumored to contain "taurine from bull sperm" and similar fashionable "energy drinks" are of any use? Well, a recent study (Nienhuesser. 2011) coming from an international team of scientists showed that the consumption of each and every of the three energy drinks used in this study lead to a statistically significant increase in resting metabolic rate (RMR).

[...] in a randomly assigned cross-over design, the subjects consumed 473 ml of one of three commercially available energy drinks or a placebo and then RMR and RER [respiratory exchange ratio; i.e. a measure of the relative amount of fat/carbs that is used as fuel] were measured 1 hour later.  The subjects then engaged in 15 minutes of treadmill exercise at 50% of V02max, during which RER and oxygen consumption (VO2) were measured. RMR was not changed by placebo, but increased (P<0.05, means ± se) above baseline by 10 ± 2.5%, 15.0 ± 2.9%, and 15.3 ± 2.9%, following Energy Drink One, Energy Drink Two, and Energy Drink Three (respectively) [...]

In view of the stimulating effect, some of the ingredients (cf. Table 1) of these chemical containing beverages exhibit, these results do not come as a surprise.

Table 1: Listing of ingredients according to Nienhuesser. 2011

What may be surprising, however, is that the study results suggest that - at least from a "calorie expenditure" point of view - the consumption of an energy drink before exercise appears to be less effective than drinking it after exercise or at your desk at the office...

L-Carnitine Works! At Least if it's L-Carnitine L-Tartrate.

Initially, carnitine was considered the super-supplement for both, the athlete seeking the ergogenic edge, as well as for the obese trying to shed unhealthy body fat. Surprisingly, however, study after study showed no to little effect on exercise performance and/or fat loss. Ultimately, it became clear that, even at very high doses, only very little of the orally delivered l-carnitine actually makes it to the muscle. Consequently, its effects on performance and body composition where negligible. Now, a very recent study by Wall et. al. (Wall. 2011) found that adding a transporter, in this case l-tartrate, to the molecule does not only help to increase muscle carnitine levels, it eventually produces exactly those effects on exercise performance and substrate metabolism one would have expected from l-carnitine supplementation in the first place.

The scientists had their 14 healthy male volunteers ingest either 80 g of CHO (Control) or 2 g of L-carnitine L-tartrate and 80 g of CHO (Carnitine) twice daily for 24 weeks in a randomised, double blind manner. Other than in previous studies with plain l-carnitine (minus the l-tartrate) there was a significant increase of muscle carnitine content with all the downstream metabolic benefits on exercise performance one would expect:

Muscle TC increased from basal by 21% in Carnitine (P<0.05), and was unchanged in Control. At 50% VO2max, the Carnitine group utilised 55% less muscle glycogen compared to Control (P<0.05) and 31% less pyruvate dehydrogenase complex activation (PDCa) compared to before supplementation (P<0.05). Conversely, at 80% VO2max, muscle PDCa was 38% higher (P<0.05), acetylcarnitine content showed a trend to be 16% greater (P<0.10), muscle lactate content was 44% lower (P<0.05) and the muscle PCr/ATP ratio was better maintained (P<0.05) in Carnitine compared to Control. The Carnitine group increased work output 11% from baseline in the performance trial, while Control showed no change.

So, after all, it was not the wrong the substance previous investigations used, but rather the wrong form - l-carnitine l-tartrate - though expensive - is the way to go to burn fat and increase athletic performance. If you do not want to buy it in bulk, I suggest you at least buy a product like MAN Sports Body Octane, where you actually know how much (here 1g) of the carnitine you're getting per serving.