Fasted vs fed cardio: Makes no difference physiologically, studies find

For the longest time, at least the past three years, I would try my best to wake up early, 5 or 6 a.m., and hit the gym first thing in the morning before breakfast. All that to see more fat-loss results. I have to admit, I always thought it worked. However, it turns out, I could’ve happily had breakfast before pushing myself through a 30- to 45-minute cardio half still asleep.

Studies have found that whether you perform cardio exercise in the fed or fasted state makes no difference physiologically. It all comes down to what you consume throughout the day. Of course, no surprise there, as it is still 70 to 80 per cent the diet that gets and keeps you in shape, no matter what.

Doing fasted cardio, in other words, going for a jog, bike ride or hopping on the elliptical on an empty stomach for 30 to 45 minutes, has had a myth surrounding it as the magical tool to losing body fat. Many thought that because your body had been fasting for eight to 12 hours, it would reach for deeper fat stores for energy as oppose to using something recently consumed.

But why for a long time trainers and fitness lovers would and still do swear by fasted cardio?

Fat oxidation — the process of breakdown of fat cells for the use of energy — happens at a faster rate when insulin is low. Insulin is influenced by blood glucose levels. And, blood glucose levels are at their lowest when we haven’t eaten for at least eight hours, making the insulin the lowest in the morning as well. So, if you do low-intensity aerobic exercise in the morning, your body will use body fat as fuel to have energy.

At first sight, it makes sense, right? Or at least I thought it did. But technically, fasted cardio uses up the same amount of calories as fed cardio. Furthermore, with fasted, all you do is make a “hole” for the food you’re consuming right after. While with fed, you’re using up that food you just ate. You end up in the same place. Looking at it this way, I could see how it makes no difference at all.

A study published in 2014 in the Journal of the International Society of Sports Medicine, was one of the first ones that looked at the difference between fasted and fed aerobic exercise — or the lack of it. Its subjects were 20 women in their 20s, whom were divided up into two groups. One would do fasted and the other fed cardio, while consuming the same restricted number of calories a day (between 1,200 and 1,300 calories) for four weeks. Their training consisted of one hour of steady-state aerobic exercise performed three days a week.

While both groups have lost weight throughout the protocol, the study found no significant difference between the two groups’ fat loss. The findings concluded “that body composition changes associated with aerobic exercise in conjunction with a hypocaloric diet [eating fewer calories than you burn] are similar regardless whether or not an individual is fasted prior to training. Hence, those seeking to lose body fat conceivably can choose to train either before or after eating based on preference.”

It might be disappointing to many, (me certainly), that all those early morning fights with the alarm weren’t tackling those stubborn fat problems. Here is though what we can learn from it. If fasted cardio is a motivation for you to keep what you eat throughout the day in check, and helps you stay consistent, then by all means don’t stop. But all in all, it all comes down to calorie intake and diet. It doesn’t matter whether you have breakfast or don’t before your morning exercise, but what matters the most is what you’re having. As for what the right breakfast pre-workout meal may be, I’ll bring you another post next week with some tips. Until then, happy lifting and working out.