Research Review: Fasted Cardio vs. Fed Cardio

A few weeks ago, a study was published titled “Effects of fed- versus fasted-state aerobic training during Ramadan on body composition and some metabolic parameters in physically active men.”

This was intriguing to me as the topic of fasted versus fed-state cardio has been an interest of mine for many years.  There has long been a belief, as seen by many folks pedaling away at the gym in the morning, that fasted cardio was somehow superior to fed-state cardio for fat loss; however the science I’ve reviewed on the topic just never supported that belief except in specific instances which I’ll likely talk more about in future posts.  For this reason, I’ve always recommended to my clients that they simply do what works for them.  Long-term success of any designed program is the most important thing; in other words, if they are finding it difficult to train in a fasted state then don’t feel this is the most vital aspect to their fat-loss goals.

In reading the abstract of the study, I was immediately startled by the researchers stated conclusion:

Body weight decreased in FAST and FED by 1.9% (p<.001) and 2.6% (p=.046), respectively. Body fat percentage decreased only in FAST by 6.2% (p=.016).

The authors conclude that aerobic training in a fasted state lowers body weight and body fat percentage. In contrast, fed aerobic training decreases only body weight. In addition, Ramadan fasting induced change in some metabolic parameters in FAST, but these changes were absent in FED.

Essentially, they are concluding that training in a fasted state was the only way to decrease fat percentage which was a plain odd statement considering that any type of hypocaloric diet should produce fat loss as has been proven in controlled study after study after study.  So the question I asked myself was “why would this research conclude any differently”?

Potential Confounder?

If you read the entire study you quickly find the answer as they provide more specific details on the diets for the various groups.  Here you can see the “energy intake”, measured in kilocalories per day.  If you pay attention to the numbers you will quickly see a problem.  The FED group was consuming nearly 600kCal/day more than the FAST group for the majority of the study!  I’m going to go out on a limb here and say that this puts the researcher’s conclusions into doubt, what do you think?