In Certain Situations, 'Fasted Cardio' Could Be Beneficial
Fasted workouts are all the rage these days - wake up early and get your cardio in before breakfast. The idea is that your body will be forced to burn fat since there's no food in your stomach to use for energy. But does this actually help with weight loss or overall health? Let's explore the science behind fasted cardio.
What is fasted cardio?
Fasted cardio simply means exercising without eating recently. It's most commonly done by doing cardio in the morning before breakfast, as you've been fasting all night. After all, "breakfast" comes from "breaking your fast."
Cardio refers to any exercise that involves repeated movement for an extended period, like jogging, cycling, swimming, or using gym equipment like a stepper or elliptical. If you've ever gone for a morning run without snacking first, you've already done fasted cardio.
Does fasted cardio help burn fat?
Technically, it does - but not in a way that helps with weight loss or overall health. We all burn fat continuously just by living. Our bodies use fat stores to stay alive overnight while we sleep, knowing that we'll eat more food later in the day and can replace those fat stores.
It's essential to differentiate between burning fat and losing fat. Burning fat means using it for energy but doesn't result in weight loss unless we don't take in enough calories to replace the fat burned.
Moreover, our bodies have carb stores (called glycogen) as well, and when we do fasted cardio, we burn these stored carbs instead of fat. So, the energy used isn't entirely coming from fat.
The science behind fasted cardio
Scientists have researched whether fasted cardio can lead to increased fat burning, which could lead to weight loss. Unfortunately, the research doesn't support any weight loss benefits from fasted cardio.
In a 2014 study, 20 women were put on a calorie-restricted diet and did an hour of cardio three mornings per week. Half of the women had a shake before their workout, and half had it afterward. Despite consuming the same total number of calories, both groups lost the same amount of weight, suggesting that fasted cardio provided no advantage.
Additionally, it's unclear whether fasted cardio even increases fat burning. A 2018 review of studies found that 38% of them showed higher levels of free fatty acids in the bloodstream compared to fed cardio, suggesting fat was being burned. However, one 2011 study revealed that fat burning was greater among people who ate before exercising. Based on these results, fasted cardio probably won't help you burn more fat, let alone lose it.
The drawbacks of fasted cardio
The primary downside of fasted cardio is that you'll typically perform better during a workout when you're fed. You'll be able to push harder, last longer, and feel less tired while doing it. If you find exercise tiring, a pre-workout meal, snack, or even a sports drink might change your experience.
For longer workouts, you should definitely eat beforehand. Endurance athletes know that they need a generous supply of calories, primarily carbs, to complete marathons, all-day bike rides, or extended hikes. If you're exercising for more than an hour at a time (about 90 minutes), you should not only eat before but also carry snacks to consume during your workout.
In more severe cases, not eating before working out can cause dizziness, lightheadedness (especially for pregnant women or those with medical issues affecting blood sugar levels), and hitting a wall after a few hours - that point where your body can't keep up the desired intensity due to a lack of stored carbs. (This is more common for marathoners than for casual runners, so don't be discouraged if you're new to fueling for longer runs.)
When fasted cardio makes sense
I'm a vocal advocate for pre-workout carbs, but I personally do several fasted cardio sessions a week. I don't do it for fat-burning benefits; I simply jog in the morning and don't want to bother finding the time to eat beforehand.
Fasted cardio could be beneficial if:
- You're jogging or running short distances.
- You don't have strict timing limitations for your workout.
- You're not trying to optimize for weight loss or health benefits.
- You're comfortable with the potential challenges of exercising on an empty stomach.
If you have a tummy that's easily bothered, you may feel queasy when you eat before exercising.
You might be in a rush and your training will be brief or not too intense.
Perhaps you're working with a tight daily calorie budget, wanting to save those carbs for another weightlifting session later on.
In any of these instances, only skip the pre-workout snack if the cardio session is going to be fairly short or not so taxing. Longer sessions still call for some fuel.
If discomfort in your stomach is the concern, not fasting is better than waiting till just before a long morning run to chow down. Could you, instead, enjoy a hearty late-night treat?
It may also help to think about smaller snacks that could provide energy while having less impact on your stomach, like a banana or a sip of a sports drink.
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Although the research does not support any significant weight loss benefits from fasted cardio, some people might still choose to do it for convenience or if they're comfortable with the potential challenges. Fasted cardio could potentially increase the risks when it comes to performance and energy levels, especially during longer or more intense workouts. Therefore, individuals should carefully consider whether the potential benefits outweigh the risks, andif fasted cardio is appropriate for their own individual circumstances and fitness goals.
