Does Skipping Breakfast Actually Burn More Fat?

Imagine you're casually scrolling through your social media feed, a digital jungle of brightly colored images and bold claims. 'Lose 10 pounds in a week with this secret!' 'Eat like a caveman!' As you swipe, a trend you haven’t seen before catches your eye: fasted cardio. It sounds appealing: burn more fat by simply timing your workout differently. 

In a world saturated with wellness advice, how can you know if this is truly effective or just another fleeting craze?

What is Fasted Cardio?

Before we delve into whether fasted cardio actually burns more fat, we need to bring everyone up to speed on what fasted cardio is. Some might believe that fasted cardio is just running on an empty stomach, but it actually has a specific physiological definition. For cardio to qualify as fasted cardio, the following have to be true:

• Your insulin levels are low.

• You have no actively digesting food in the GI tract.

• Blood glucose is stable (not elevated from a recent meal)

• Stored fuel (fat and glycogen) has become the primary fuel source.

When you eat, your body releases insulin to store food in your cells, primarily as fat. When there’s no food in your system, your body switches from storing mode to burning storage mode by lowering insulin. So, simply put, your body has to be fully switched into “burning storage mode.”

Most studies define 'fasted' as 8 hours or more without food, as that is how long it takes to reach the state that is described above (water is allowed). This means that if you wanted to do fasted cardio, you’d have to have not eaten for at least 8 hours. 

An easy way to achieve a fasted cardio state is to work out in the morning before breakfast (your last meal having been yesterday evening). With that in mind, let’s dive in and find out if it’s worth the hype.

Fasted Cardio and Fat Burning

So, does doing cardio fasted really burn more fat compared to doing it after eating?

Yes... But there is a catch.

When you train fasted, your body uses more fat for fuel than carbohydrates. It has no other choice! Without carbs from a recent meal in the bloodstream, it turns to fat as its primary source of fuel. If you were to eat before your run, your body would choose to use the food from your meal now circulating in the bloodstream for energy. Your body actually prefers to use carbs for energy, simply because it’s more convenient.

When you train fasted, your body’s insulin levels are low, so it switches into ‘burn storage mode.’ In one meta-analysis, people actually burned up to 30% more fat when exercising in a fasted state compared to a fed state. Sounds like great news, so what’s the catch?

Burning Fat isn’t the Same as Losing Fat

Most people don’t realize how smart their body is. Turns out that when you burn more fat and fewer carbs during a workout, your body compensates throughout the rest of the day by burning less fat and more carbs. The same is true in reverse! If you eat before a workout and burn more carbs, your body will burn more fat later in the day.

So by the end of the day, the total body fat burned will be the same, whether those 100 calories come from fat during fasted cardio or from carbs during fed cardio.

If you really want to lose fat over time, it’s all about making sure you burn more calories than you store, AKA if you’re in a calorie deficit.

The Takeaway

Losing fat is largely about what you eat and how much you eat, rather than when you eat. So if you like fasted cardio, then go for it! If you prefer to fuel before you work out, that works great too. Ultimately, what matters most is finding a routine that fits your lifestyle, feels sustainable, and helps you stay consistent over the long term.