The skinny on fasted cardio

How many times have you heard your favorite fitness idols referencing fasted cardio? Whether or not there are benefits to fasted cardio has become one of the topics of debate amongst many researchers, coaches, athletes, and trainers. Each argument can sound compelling which leaves the general population in a state of confusion. So, does fasted cardio trump cardio in a fed state?

Fat loss occurs through three processes:

  1. Mobilization - Removing fatty acids from a fat cell.

  2. Transport - Moving fatty acids via the bloodstream and finally

  3. Oxidation: Where the fatty acids are burned within smooth and skeletal muscles.

As the body becomes leaner, mobilizing fat becomes more difficult. At lower body fat levels “troubled” areas are more pronounced. These are typically areas of less circulation, making mobilization and transport all the more difficult. When exercising, up to 50% of the fat being oxidized is intramuscular triglycerides which would have no impact on appearance in the areas of general concern (hips, abs, lower back, waist, etc). Some areas may never reduce in size due to the accumulation of brown adipose tissue (BAT)

The facts on Fasted cardio are a bit more clear today than 20 years ago. For individuals who have lower body fat levels (Less than 12% in men and less the 18% in women) cardio in a fasted state may have some minor benefit in the final phases of prep for bodybuilding. It is important to note that most people do not know their actual body fat percentage. Using calipers will not give you an accurate reading. However, a DEXA scan is proven more accurate than tools such as calipers, Inbody or any other bio-electrical impedance device. Our visual perception of body fat typically inaccurate. An adult male with 12% body fat is typically leaner than one would think when hearing that number. The same can be said for women when body fat for a female is roughly 13%. Visually, this number is fairly lean to the eye. For people carrying body fat levels of 15% ≥, chances are there are no issues mobilizing, transporting, and oxidizing fatty acids. Namely due to the abundance of fat cells readily available for use. From an evidence standpoint, it does not appear that individuals in this category would benefit from fasted cardio even in the presence of a moderate energy deficit. The most important aspect of cardio and its effects on fat loss is how many calories are burned. Combing a customized cardio prescription with an individualized nutritional plan that ensures a negative energy balance will result in optimal fat loss when adherence is present. We could argue that cardio, in general, is not necessary, but seldom is this the case. One thing is for certain, excessive cardio whether fasted or fed is generally unnecessary. The caveat to all of this is that this is completely based on the individual's needs.

With the current research, it is obvious fasted cardio is not needed to achieve fat loss let alone ultra-lean levels of body fat especially if the goal is to preserve muscle mass while in a hypocaloric state. Above all, use a method that you know you can realistically adhere to, but keep in mind that cardio, fasted or fed can interfere with all facets of your metabolism. From energy expenditure during the day and while you’re training. If you’re an advanced level trainee who is at a plateau in their weight loss, look deeper into your approach. There are more effective strategies than fasted cardio.


1. Body composition changes associated with fasted versus non-fasted aerobic exercise

Brad Jon Schoenfeld, Alan Albert Aragon, Colin D Wilborn, James W Krieger and Gul T Sonmez

2. Fatty acid oxidation is directly regulated by carbohydrate metabolism during exercise

E. F. Coyle, A. E. Jeukendrup, A. J. Wagenmakers, W. H. Saris

American Journal of Physiology - Endocrinology and Metabolism

3. Exercise improves fat metabolism in muscle but does not increase 24-h fat oxidation

Edward L Melanson, Ph.D.,1,2 Paul S. MacLean, Ph.D.,1,2 and James O. Hill, Ph.D.2,3

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