Well, both groups … and neither of them.
The truth is that fasted cardio can’t help you lose fat faster, but it can help you lose stubborn fat faster if you do it right. If you do it wrong, though, then all you’re likely to get from it over traditional “fed” cardio is smaller and weaker muscles.
Case in point: I’ve used fasted cardio successfully to cut down to ~7% body fat while losing little to no muscle and strength:
I didn’t simply go for a jog before breakfast to get there, though.
I followed a very specific fasted cardio regimen to make it work, and I’m going to break down exactly what I did in this article. And by the end, you’re going to understand:
- What really counts as fasted cardio (and what doesn’t).
- Why people think fasted cardio helps you lose fat faster.
- The best kind of fasted cardio to lose fat without losing muscle.
- The pros and cons of fasted weightlifting.
- The best supplements to get the most out of fasted cardio.
- What to eat after fasted cardio.
- And more …
What Is Fasted Cardio?
Many people think fasted cardio is simply training on an “empty stomach,” which they usually think is simply a stomach that “feels empty.”
Fasted cardio is cardio done while in a “fasted” state, wherein your stomach is empty, but it’s a bit more than that. It has to do with how your body processes and absorbs the food you eat.
When you eat food, it gets broken down into various molecules that your cells can use, and these molecules are released into your blood. The hormone insulin is released as well, and its job is to shuttle these molecules into cells.
When your body is digesting and absorbing what you’ve eaten, and insulin levels are still high, your body is in a “fed” or “postprandial” state (prandial means “having to do with a meal”).
Once your body is finished processing and absorbing the nutrients, insulin levels drop to a “minimum” low (or “baseline” level), and your body enters a “fasted” or “postabsorptive” state.
How long it takes for insulin levels to fall back to baseline depends on the size and composition of your meal. Larger meals that include a mix of protein, carbs, fat, and fiber digest slower than smaller meals that are mostly composed of one or two macronutrients (like an apple, which is mostly carbs).
For example, research shows if you eat about 600 calories of pizza (providing about 37 grams of protein, 17 grams of fat, and 75 grams of carbs), your insulin levels will remain at double their baseline level for at least five hours.
On the other hand, if you eat a smaller, simpler meal like a single scoop of whey protein isolate, which only contains about 100 calories, 20 grams of protein, and only trace amounts of fat and carbs, your insulin levels will fall back to baseline levels in a few hours.
Your body moves in and out of these fed and fasted states several times a day, so timing your exercise correctly is the key to doing fasted cardio.
So, to recap:
- Exercise done during periods where insulin levels are elevated and food is still being processed and absorbed is “fed” training.
- Exercise done during periods where insulin is at a low, baseline level and food is no longer being processed and absorbed is “fasted” training.
Alright, now we know what fasted cardio is. Let’s now look at what science says about whether or not it can help you lose fat faster.