Does the idea of a 6am jog or a before-dawn bike ride make you roll over and hug the pillow? What if a pre-brekkie cardio session could burn more fat than your normal workout? Cardio fasting – aerobic exercise first thing on an empty stomach – is gathering pace among fitness fans as a way to burn fat faster. Internet forums are abuzz about how hitting the treadmill or bike before a morsel passes your lips can blast the fat - and the trend could be growing.
But is there any truth to the idea? Enthusiasts claim that the body is primed for optimal fat burning when you first wake up. The theory is that glycogen levels are reduced after a night’s sleep, especially if you are on a low carbohydrate diet, which encourages your body to burn its fat stores. Carbohydrates also release insulin, which blunts the body’s ability to burn fat. Insulin levels are at their lowest when you first wake up, making your body more capable of burning fat.
Not only does your metabolism fire up during a workout but it stays elevated for hours afterwards too. So, by doing your cardio first thing you can also take advantage of the ‘after burn’ effect.
Studying the sunrise
And there is some research to support the theory. One study, carried out at Kansas State University several years ago, suggests that exercising before breakfast oxidizes a kilo of fat more quickly than doing the same workout in the afternoon. Measuring respiratory gas exchange, caloric expenditure and carbohydrate and fatty acid metabolism, the researchers found that 67% of the energy burned came from fat when exercising in the morning after a 12-hour fast, compared to 50% when the same exercise was done later that day or after eating.
A more recent study, conducted by the Oasis of Hope Hospital in Tijuana, Mexico, recorded positive results when exercising after a “mini-fast” of 12-14 hours. Participants worked out three to five times a week for 45 minutes and, after 12 weeks, lost an average 9% body weight. Furthermore, fasting insulin levels had reduced by 25%, suggesting an improvement in insulin sensitivity, which can reduce the risk of diabetes.
Even so, the academic community in Australia remains to be convinced. Professor Stephen Bird, Head of Exercise Sciences at RMIT, said that while the theory behind cardio fasting “makes sense” it has only a “negligible” application to real life.
He told The Biggest Loser Club that there’s no harm in practising cardio fasting, providing you’re hydrated and not diabetic.
“However, the best time of day to exercise is the one that suits your lifestyle,” he said. “All these little things are relatively minor fine tuning but the main thing is to do the exercise at a time that you can commit to.”
Jeff Coombes, a Professor in Exercise Science at the University of Queensland, said that while it’s more likely that fat will be burned if there is less insulin present in the body, “[any improvement] would be so minimal as to be inconsequential”.
Exercising in the morning gives your body the chance to benefit from the enhanced metabolism during the day but even the earliest of risers would see no more than a 1% improvement, Coombes said. “People would be much better off focusing on putting a little less food in their mouths and exercising a bit more,” he said.
He recommends increasing incidental exercise and reducing sedentary time. “You’ll be surprised at how much extra energy you burn.”
Beyond the burn
Whether you’re a sunrise sprinter or an evening ambler, the experts agree that the best thing you can do for fat burning is to build more exercise – both incidental and planned – into your day. “Doing more is the number one factor in how much fat you burn,” Bird said.
But, ditch the duvet for your runners and you can be sure of a few extra benefits – fasted or not. The mood-enhancing endorphins will make you feel great all day. You’ll be energised and alert. And your metabolic rate will be firing on full power for hours after the session is over. There’s nothing to lose but sleep ...