By Rob Clarke Driven Sports
Yesterday’s article on dieting testosterone mentioned a couple of metabolic hormones involved with detecting energy changes, including the master metabolic regulator, leptin. A new study coming out of Spain seems to be getting some press online recently as it is suggesting that sprint exercise can “mimic” leptin when performed in the fasted state.
Ultimately I think the excitement surrounding this is the slight misreading of the phrase mimetic. To mimic something does not mean to increase it, and I think that has caught a few too many people off guard. Of those that do understand the study summary I think that they are looking too far into it, like sprints offer advantages that weight lifting won’t. And the pro-sprints group will no doubt add this to their collection of “why you should sprint” studies. But still, studies like this and the connection of leptin to body fat and fat loss will be there for a long time to come.
I should point out here that I am not anti-sprints in the slightest. Sprints are fine. They are anaerobic, and I am a fan of anaerobic exercise – particularly when the resistance can be progressively increased over time (oh, hi weight lifting!) But is there any special about them with regards to leptin?
When looking at leptin we need to remember that it is regulated in the short-term by energy balance and in the long-term by body fat levels. If you go a day without eating, the energy balance swings into deficit and leptin falls. It shoots back up fairly quickly when you do eat, however. As you diet down over the longer term, you lose fat leading to a fall in leptin signalling. To get levels back up you need to either overfeed or add the body fat back. This should all be very straightforward stuff.
When it comes to activity, a sudden burst like a set of squats – or, of course, a sprint – quickly depletes ATP stores, thereby activating the low-energy sensors including AMPk. AMPk kicks fatty acid oxidation into gear, as well as promoting glucose uptake in muscle. When leptin concentrations are normal (I should say “adequate” really) it can utilize AMPk as a tool for energy regulation by switching it on. In other words, if leptin wants to increase fat burning it can turn on AMPk to do so. And this is where I think the confusion from the study arises.
In the study the participants do not increase leptin levels. In fact, there is a slight decline. This fits in somewhat with previous study models of resistance training showing either no effect or a delayed lowering several hours after exercising. There has also been shown a long-term (three-month) lowering, but that is accounted for by the loss of body fat during the study.
What the investigation found was that fasted sprinting activates the same cellular sensors – AMPk included – in muscle that leptin does when it is in adequate supply. In other words, there is nothing magic about sprints. They are an activity, and you should be performing activity regularly – especially weight lifting – if you want to look the best you can naked. But don’t feel compelled to make them part of your next cutting regimen. Your diet takes take of that.
A line in the study suggests that the study “opens the possibility of using sprint exercise to circumvent leptin resistance in obese humans and may lead to increased leptin sensitivity.” I think getting most obese humans to do any exercise would be a start. While some have legitimate genetic issues, it is usually the lack of activity that got a lot of these people to the point of obesity in the first place.
Source: Guerra B, Olmedillas H, Guadalupe-Grau A, Ponce-González JG, Morales-Alamo D, Fuentes T, Chapinal E, Fernández-Pérez L, De Pablos-Velasco P, Santana A, Calbet JA. Is sprint exercise a leptin signaling mimetic in human skeletal muscle? J Appl Physiol. 2011 Sep;111(3):715-25.