One of the most widespread beliefs in the fitness world is that fasted cardio (or training) is more effective at fat loss than fed cardio.
This belief is based on the logic that, on an empty stomach, the body is forced to use fat as a source of energy for the physical activity, but is it really like that?
There are at least 2 situations that can contradict this belief:
1. Various studies have shown that workouts performed after a meal have a better performance and work capacity than fasted workouts, and therefore, over the long term would be more effective for fat loss.
2. The body can use other energy sources, including the muscles, so an intense fasting cardio workout could, under certain conditions, be counterproductive.
Until 2014, there has been no study to directly compare the effect of fasted or fed cardio on fat loss with effective weight loss.
In 2014, has been published in the “Journal of the International Society of Sports Nutrition” the first study comparing the effects of fasted vs fed cardio on body composition changes entitled “Body composition changes with fasted versus non-fasted”, authors “Brad Jon Schoenfeld, Alan Albert Aragon, Colin D Wilborn, James W Krieger and Gul T Sonmez”
The result of the study is shown in the next image
The authors of the study concluded:
” In conclusion, our 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. Hence, those seeking to lose body fat conceivably can choose to train either before or after eating based on preference. It should be noted that given the small sample size and short study duration, we cannot rule out the possibility that either condition might confer a small benefit over the other with respect to fat loss.”
Conclusions and practical advice
From the current scientific evidence there is no difference between fasted cardio and fed cardio with regard to fat loss. So, the best time of day to perform cardio is of personal preference, whether it is in the morning, afternoon or evening.
More than focusing on cardio to lose weight, it is recommended to focus on creating the right calorie deficit to allow a gradual weight loss.