Fasted Cardio: A Waste Of Time?

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If there’s one topic that is highly contested when it comes to cardiovascular training, it’s whether or not fasted cardio is worth the effort.

For several years, the debate has divided the opinions of trainers, coaches, and trainees alike on the efficacy of the practice of fasted cardio. Yet despite all of this, many continue to do it.

Well, guess what, we’ve finally gotten our answer, and better yet, an answer from a recent scientific study.


Fasted Cardio – What the Science Says

Brad Schoenfeld and Alan Aragon, along with a few other industry leaders, took to the lab to test the hypothesis on whether or not fasted cardio had any effect on accelerating fat loss in the body vs cardio in a fed state. They looked at whether performing cardio after an overnight fast led to any significant change in body composition over a 4 week period in 20 female participants. Here is the abstract from the study itself:

It has been hypothesized that performing aerobic exercise after an overnight fast accelerates the loss of body fat. The purpose of this study was to investigate changes in fat mass and fat-free mass following four weeks of volume-equated fasted versus fed aerobic exercise in young women adhering to a hypocaloric diet.

Twenty healthy young female volunteers were randomly assigned to 1 of 2 experimental groups: a fasted training (FASTED) group that performed exercise after an overnight fast (n =10) or a post-prandial training (FED) group that consumed a meal prior to exercise (n =10).

Training consisted of 1 hour of steady-state aerobic exercise performed 3 days per week.

Subjects were provided with customized dietary plans designed to induce a caloric deficit.

Nutritional counseling was provided throughout the study period to help ensure dietary adherence and self-reported food intake was monitored on a regular basis.

A meal replacement shake was provided either immediately prior to exercise for the FED group or immediately following exercise for the FASTED group, with this nutritional provision carried out under the supervision of a research assistant.

Both groups showed a significant loss of weight (P =0.0005) and fat mass (P =0.02) from baseline, but no significant between-group differences were noted in any outcome measure.

These findings indicate that body composition changes associated with aerobic exercise in conjunction with a hypocaloric diet are similar regardless whether or not an individual is fasted prior to training.(1)


Ok Here’s the Breakdown in Plain English

The group of twenty women were split between 10 that performed cardio after an overnight fast, and 10 that performed cardio following haven eaten a meal.

Each group did 1 hour of steady state cardio performed 3 days a week.

Both groups followed a nutritional program that kept them in a caloric deficit to elicit fat loss. For the fasted group, they were given a shake post cardio, and in the fed group, they were given that shake before performing cardio.

The research found that BOTH groups saw significant decreases in fat mass, HOWEVER no difference were seen in a significant loss of fat mass between the groups. Meaning, fasted cardio does NOT accelerate fat loss in the way that it’s touted to.

Go back and read that last line again.


What Does This Mean For You…

So where does that leave you as a now well informed trainee?

Well, the truth of the matter is that at the end of the day, it doesn’t matter.

You can make the choice to perform your cardio in the morning, before eating, simply because you like to and mentally it makes you feel better. Perhaps it’s easier for you to get it out of the way. This stuff HAS TO fit into your complete LIFESTYLE.

So if the choice to perform cardio before you eat works for you, then you can do it.

However, do not believe the hype that you are getting something more out of it, or that it’s better than if you did it after having eaten. For those that feel that empty stomach cardio makes them feel a bit lightheaded and ill, then guess what, you can eat something before performing cardio, and still come out on top when it comes to your fat loss goals.


My Exception to the Rule – When You MUST Do Fasted Cardio

There is ONE caveat that I will say when it comes to this debate. The ONE time it has been proven that fasted cardio is INDEED preferred and necessary…

And that is when yohimbine is brought into the equation (2).

The efficacy of yohimbine is blunted when insulin is present in the blood, so it’s important to perform cardiovascular activity either before eating, or hours well after.

I usually recommend that clients wait for about 1 1/2 to 2 hours before taking yohimbine after a meal and performing cardio.

And this is typically the ONLY time I personally recommend a client to perform fasted cardio.

To conclude, as you can see, the research is now out there for you to decide what’s right for you. This game is about making it a lifestyle, and it’s important to do so intelligently and well informed.

There’s no direct harm in fasted cardio; to protect against muscle loss in the face of dieting, it’s probably a good idea to possibly ingest some BCAA powder prior to performing fasted cardio.

But even in the grand scheme of things, muscle loss isn’t a huge concern unless you are abusing the practice and concurrently not eating enough in general (even if you are in a caloric deficit).

However, don’t make the mistake of thinking that fasted cardio is better, or that your fat loss results will be greater, as clearly, the research has shown quite simply, it’s not.


What are YOUR thoughts? Leave comments below and let’s discuss.


1.Body composition changes associated with fasted versus non-fasted aerobic exercise. Brad J Schoenfeld, Alan A Aragon, Colin D Wilborn, James W Krieger Journal of the International Society of Sports Nutrition 2014, 11:54 (18 November 2014)

2.Galitzky J, Taouis M, Berlan M, Riviere D, et al. a 2-Antagonist compounds and lipid mobilization: evidence for a lipid mobilizing effect oral yohimbine in healthy male volunteers. Eur J Clin Invest 1988; 18:587-594.

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