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Benefits of Fasted Cardio: Is it the Best Cardio for Weight Loss?

by Elliot Reimers, M.S.(C), CNC | Reviewed by Advisory Board

Benefits of Fasted Cardio: Is it the Best Cardio for Weight Loss?

Debates over the best cardio for weight loss continue to pervade fitness subculture. Some “health gurus” are unwavering in their stance about the benefits of fasted cardio, arguing that fasting “primes” the body for fat loss during a cardio session. 

But does the evidence justify the claims? Is fasted cardio really the best cardio for weight loss? 

To answer these questions and (hopefully) provide some closure about the best form of cardio for fat burning, this article will take a deeper look at what science has to say about the benefits of fasted cardio and if it’s necessary for optimal fat loss. 

What is Fasted Cardio?

Quite simply, fasted cardio is cardiovascular exercise performed in a fasting state, such as shortly after waking up in the morning. Conventional wisdom tells us that stored fats are the body’s ideal energy source during times of nutrient/energy deprivation. Thus, many “fitness experts” contend that doing fasted cardio is the best way to lose weight.  

The benefit of fasted cardio for weight loss is pretty simple, on a theoretical level: Your body needs energy during cardio; so, if you’re fasting, it will just burn more body fat as you glide away on the elliptical, right? 

Well, yes and no. The notion that fasted cardio leads to more fat loss is a bit misguided as it fails to take into account the bigger picture. Notably, fasted cardio has been shown to lead to greater losses in lean body mass (i.e., everything but body fat) when compared to cardio done in the fed state (1). 

In addition, a recent literature review suggests that non-fasted cardio leads to better outcomes in body composition (2). In other words, eating a small protein-rich meal or snack before cardio will help you maintain more muscle tissue while achieving the same magnitude of fat loss. 

Ultimately, the timing of cardio is not as important as many people are led to believe. Rather, the focal point should be the type of cardio you perform.

What Are the Best Forms of Cardio for Fat Loss?

HIIT cardio

If you’re looking for the best cardio for weight loss, look no further than high-intensity interval training (HIIT). HIIT is any form of exercise where you alternate between short bursts of “all-out” effort and “active recovery.” 

For example, sprinting to the top of a 50-meter hill (the “high-intensity” phase) and then slowly jogging back down to the bottom (the “active recovery” phase) would be a form of HIIT cardio. (You would repeat the process multiple times to complete a full HIIT workout.) As such, heavy weightlifting and circuit training also classify as HIIT. 

Moving forward, we will focus specifically on HIIT as a form of cardio for fat loss. Traditional dogma would have us believe that low-intensity, steady-state (LISS) cardio and moderate-intensity cardio are the best forms of cardio for fat burning, but this isn’t necessarily true. The supposition that lower-intensity cardio translates to greater fat burning is based on the premise that aerobic (oxygen-rich) metabolism increases fatty acid oxidation (“burning”) more than high-intensity exercise does. 

While that is true, it also leaves out an important part of the story — aerobic metabolism doesn’t elicit the same physiologic adaptations as anaerobic (oxygen-deprived) metabolism (3). Over time, HIIT — which utilizes glucose (sugar) as a preferential source of energy — can actually lead to more efficient fat burning than low-to-moderate intensity cardio.

According to numerous studies, the benefits of HIIT may include (4, 5):

  • Increasing excess post-exercise oxygen consumption (EPOC)
  • Enhancing mitochondrial biogenesis, leading to greater calorie burning at rest
  • Improving blood lipid profiles and heart health
  • Boosting VO2max output and recruitment of type-II (fast-twitch) muscle fibers
  • Improving insulin sensitivity and blood sugar balance
  • More time-efficient than LISS cardio
Best cardio for weight loss

On the contrary, LISS cardio doesn’t create a significant rise in post-exercise oxygen consumption, nor metabolic rate (6). LISS cardio is also not very effective for increasing VO2 max and type-II (fast-twitch) muscle fiber switching (7). Done in excess, LISS cardio can actually eat away at skeletal muscle tissue and reduce maximal strength (obviously, not a desirable ramification for most gym-goers). 

In layman’s terms, LISS cardio is largely a means to an end —  burning extra calories throughout the day; beyond that, it doesn’t do a whole lot in the context of fat burning.

Now, this doesn’t mean low-intensity and moderate-intensity forms of cardio are pointless. There’s plenty of data backing the merit of cardiovascular exercise, regardless if it’s a leisurely walk or a grueling interval workout on the StairMaster (8). Frankly, anything that gets your body moving is going to contribute to weight loss if your diet/calorie intake is controlled.

In fact, a mix of HIIT and low-to-moderate intensity cardio exercises is probably ideal for fat burning.

Is HIIT the Best Cardio for Weight Loss?

While LISS may seem like the best cardio for weight loss in the short-term, research suggests that HIIT is prudent for sustained, long-term improvements in body composition (9). So, HIIT is ostensibly the best cardio to burn fat and keep it off (10). 

Contrary to lower-intensity cardio, HIIT stimulates a process in cells called mitochondrial biogenesis. In non-nerd lingo, this process means your cells create new mitochondria — which translates to greater calorie burning over time. LISS won’t produce the same physiologic and metabolic adaptations as HIIT cardio, regardless if you do fasted cardio or cardio after eating. 

Moreover, HIIT also augments muscle hypertrophy in active individuals, whereas extensive bouts of LISS cardio can actually be detrimental to lean body mass and hard-earned muscle tissue (11).

To reiterate, this does not mean you should avoid low-to-moderate intensity cardio at all costs. A balance of HIIT and lower-intensity forms of cardio is likely the ideal strategy for optimizing fat loss, especially for those who are trying to get extremely lean

Lower-intensity forms of cardio have the advantage of being less taxing on the neuromuscular system and facilitating blood flow to skeletal muscle, both of which can help with recovery between more intense workouts. 

swimming cardio

Another thing to consider is that you should make LISS cardio something you enjoy. Go for a walk around the neighborhood if it’s a nice day outside, or take a bike ride on a nearby scenic trail. Lower-intensity cardio should be fun whenever possible — you don’t have to walk mindlessly on a treadmill for hours just to lose weight. 

Benefits of Fasted Cardio: Are They Worth It?

As far as the benefits of fasted cardio go, there simply isn’t much compelling empirical evidence to substantiate the claims. Unless you just so happen to work out in a fasting state regularly, there is little reason to do fasted cardio. If anything, you’re probably better off eating at least drinking a protein shake or an essential amino acid supplement beforehand to stave off muscle catabolism.  

Now, you’re probably wondering how much cardio you should do

When fat loss is your fitness goal, start with at least two HIIT sessions plus three or four 30-minute cardio workouts at low-to-moderate intensity weekly. If you hit a weight-loss plateau, add a few minutes to your LISS cardio workouts.

The key is to keep your lower-intensity cardio sessions as brief and infrequent as possible while maintaining consistent fat loss. The less you need to depend on cardio to reach a calorie deficit, the better. 

And it goes without saying that you should be doing a combination of both resistance training and cardio for optimal fat loss. (You read that right, ladies! Don’t be afraid to lift, even if you just want to “tone” and “trim” your body.) The notion that females will (unwittingly) get bulky if they lift weights is nonsensical on so many levels.

Hopefully, you now have better insight into what the best cardio is for weight loss and how to incorporate different cardio exercises in a strategic manner to optimize fat burning. Remember, consistency is the name of the game — hit the gym regularly, stick to your weight-loss diet, and watch the fat melt off!

Fat burner supplement

If you want an extra boost, consider supplementing with an evidence-based fat burner supplement, such as the Transparent Labs Stim-Free Fat Burner, about 30 minutes prior to your workouts. This can help accelerate weight loss by mobilizing body fat and encouraging more fatty acid oxidation during and after cardio.




Elliot Reimers, M.S.(C), CNC
Elliot Reimers, M.S.(C), CNC

Author

Elliot is a NASM Certified Nutrition Coach (CNC) and M.S. candidate in the Molecular Pharmacology and Toxicology program at Michigan State University. After obtaining his B.S. in Biological Sciences from the University of Minnesota in 2013, Elliot began freelance writing and has since written 100s of articles pertaining to nutritional science, dietary supplements, exercise physiology, and health/wellness. As an inveterate “science nerd,” he loves helping people understand how nutrients, supplements, and exercise work on a cellular and molecular level so they can be smarter about what they put in - and do to - their bodies. When he's not busy writing or studying, you can find Elliot pumping iron, hiking the mountains of beautiful Colorado, or playing the piano.



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