Anyone who’s been for a run in the middle of summer, or who has been pounding the treadmill when the gym forgot to switch on the air conditioning, can tell you that workout out when it’s hot just feels so much harder than when it’s cool. But does this perceived increase in exertion actually have an effect on the way your body burns energy, and if so can it be used to help shed extra body fat?
How the body is fuelled
To get an answer to this question we first need to look at the way your body is fuelled during exercise. When you work out you will generally burn a mixture of fat and carbs for energy, and this carb to fat ratio changes based on your level of intensity. Exercising at a slower pace in a cool environment will cause your body to burn more fatty acids, while higher intensity workouts in warm conditions will move this ratio more towards burning more carbs.
But what about a lower intensity workout in warm conditions? A 2010 Spanish study showed that performing the same workout in 40C heat increased whole body fat oxidation and muscle glycogen oxidation more than at 20C. So based on this we can say that the same workout in higher temperatures has a higher card to fat ratio than it would in cooler conditions.
Can we use temperature to burn more fat?
If temperature can, directly or indirectly, have an influence on the way your body burns fuel, is there a way this can be manipulated to help people working out to lose weight? The first thing to look at is the oft-mentioned ‘fat burning zone’ your body enters when you’re doing very low intensity exercise.
While it’s true that this kind of workout will burn mostly fat, the overall amount burned will be much lower than if you train at a level of intensity with a higher carb to fat ratio. Increasing your fitness level through more intense exercise will also improve your body’s ability to burn fat, so training at a higher intensity has long term benefits as well. Rather than trying to train at a low intensity to maximise your fat burning ratio you should be looking to get fitter so your overall fat burning rate increases!
With this aim in mind, increasing the intensity of your workouts by training in warmer conditions may help to increase your overall fitness level and, as a consequence, your ability to burn fat effectively.
Freeze yourself thin
There have been a few studies into the effect that a colder environment can have on the body’s ability to burn fat. Most of the recent research has been around ‘brown fat’, an area of fat at the top of your back that uses fat as energy to help keep you warm. It works in a similar way to the shivering process, except you’re entirely unaware of the fat going to work.
A study in the Netherlands found that fairly small amounts of exposure to cold caused the brown fat activity to increase, meaning that the subjects were not only more resistant to the cold but actually burned more calories throughout the experiment. The exposure to cold involved sitting in a 15-16C room for 2 hours the first day, 4 the second and 6 the third, all while wearing shorts and t-shirt.
A similar study involved subjects sitting in a 17C room for 2 hours a day for 6 weeks. The group ended the study with a 5.2% decrease in body fat mass, while the control group (exposed to a 27C room) did not show any fat loss.
Putting it all together
It appears that temperature can have a strong influence on our body’s ability to burn fat, and while it’s only one of a number on contributing factors it may be something to consider when you’re planning your workouts. Not everyone will have the inclination to workout in a sauna and follow it up with 2 hours in an ice bath, but smaller changes may have a positive impact. Maybe go for a run when it’s hot out rather than waiting for it to cool down (hydrate properly, don’t over exert yourself etc), or try turning the thermostat down on the days where it’s a little colder. As always with fitness, it’s the small changes that make the biggest difference.