The early bird gets the six-pack, so the saying almost goes. That’s why the pre-dawn gym floor is full of men putting brave but tired faces on their pre-breakfast pump. They might not be able to lift as much; they may well give up earlier. But ask these men why they’ve set their alarms for an ungodly hour and you’ll be told that fasted training is the quick route to a lean physique.
The reasoning is logical: take away your body’s favoured fuel and it will scramble for another way to keep going. When you hit the gym without eating, you’re already running pretty low on its preferred propellant, glycogen, so fat has to fill the void. Bye-bye spare tyre. However, this theory doesn’t quite stand up under closer scrutiny.
The blubber-burning benefits of fasted training aren’t without evidence: a study from Northumbria University found that working out before breaking your fast increases fat oxidation by more than 20 per cent during exercise. But as any Men’s Health man knows, what happens on the gym floor is only a tiny piece of the puzzle.
Intense training is the pilot light that ignites your fat-burning fires. But to keep the fire going, you need fuel. Attempt Tabata starved and, as soon as your glycogen runs out, you’ll hit the wall.
That’s why endurance athletes espouse occasional fasted training – the key word here being “occasional”. Working out starved mimics that point in the race when your glycogen is gone but the finish line is still kilometres away. Over time your body learns to target fat for fuel. However, that’s just a back-up generator. Come race day, you’ll need to load up on carbs to power you as far as possible before your second-string engine kicks in, then hope it takes you to the tape. If you haven’t tried working to the point of energy depletion before, don’t expect this to happen. Instead, your pre-feed session will be curtailed when your first set of deadlifts wipes you out. Not a muscle-building protocol that athletes would recommend.
Fasted training’s short-term wins come with some long-term losses, specifically to your muscle mass. When your alarm sounds, you’re pulsing with the stress hormone cortisol, which breaks down your body mass to help provide energy. Sadly, it’s not discerning enough to separate fat from muscle. Provide something else to digest and cortisol dissipates. If you stay hungry, it gobbles up your biceps.
If you’re trying to ditch the last couple of kilos, then briefly resorting to fasted training may help, but it’s unsustainable. Fill your tank, then work until it’s empty. You’ll not just reach the finish line – you’ll build a body worthy of the podium.
Deals with the Devil
The University of Texas at Austin found that, compared with carb-fuelled athletes, fasted ones increased fat oxidation only after 90 minutes of exercise.
Pile it High
Eating one gram of carbs per kilo of body weight ups your force and endurance, says a Mississippi State University study
The Acid Test
Even if you’re fuelling up, long sessions can turn your body catabolic. Pre-workout branched-chain amino acids help limit the losses.