I see a ton of people on social bragging about fasted cardio. You would think that the cardio kings are passing out medals of honor for these people getting up before they eat to get on a treadmill. It has become a real popular fat loss strategy.
The thinking around fasted cardio sort of looks legit when you hear it broken down from someone. But I want to tell you the truth and the science.
Most people think an overnight fast brings about a reduction in circulating blood sugar levels, reducing the amount of carbohydrates stored in the body. Your body is supposed to be forced to used fat for fuel rather than carbs to fuel your workout.
Seems like an ideal way to help with fat loss, right? Unfortunately, logic doesn’t translate into practice. There is a lot wrong with this logic. I'm going to give you 3 reasons why fasted cardio isn't what it has been glorified to be.
#1 EPOC
Fasted cardio blunts the special part of exercise that most researchers call the "afterburn". EPOC stands for excess post exercise oxygen consumption. EPOC is the amount of oxygen required to restore your body to its normal, resting level of metabolic function (called homeostasis). It also explains how your body can continue to burn calories long after you’ve finished your workout.
Eating before exercise has been shown to increase the magnitude of EPOC. And guess where majority of calories expended in the post-exercise period come from? Your fat stores. This means that more EPOC equates to more fat being burned. This clearly shows why you should eat before you do cardio.
#2 Available Energy
Doing a cardio session after not eating for 8 - 12 hours is rough. If you have never experienced it, take my word for it that you will hit a wall pretty quickly. To perform well at high exercise intensities, your body needs a ready source of glycogen. When those stores are depleted you can't sustain training intensity. And when you hit that all you can bet that fewer calories will be burned both during and after exercise, blunting total fat loss.
#3 The Big Picture
Your metabolism doesn't operate in a vacuum. It would be nice for our body to burn fat like a machine but it doesn't happen that way. This is actually the most important point of all. A huge mistake made during exercise is worrying about the number of fat calories burned during an exercise session. Because you can't assume that lost body fat as a result. The body continually adjusts its use of fat and carbohydrate for fuel depending on a variety of factors.
As a general rule, if you burn more carbohydrates during an exercise session, you’ll ultimately burn more fat in the post-workout period and vice versa.
Who cares whether you burn a few extra fat calories in the course of a workout if an hour later the ratio shifts to a greater carbohydrate oxidation? In the end, the only thing that matters is total fat loss. From a practical standpoint, fat burning should be evaluated over the course of days and weeks. Not on an hour to hour basis.
There is little reason to perform cardio on an empty stomach if your goal is to maximize fat loss. At best, the effects on body composition won’t be any better than had you trained in a fed state. The worst scenario is you’ll lose muscle and perhaps even reduce total fat loss.
So eat something before you go to the gym, go for a walk, or a jog. You will reap the benefits.