This is still a much now than when the first debate of fasted vs fed cardio started. This obsession with fasted cardio started in 1999 when Bill Phillips, a bodybuilder and author, talked about how he optimized his fat loss by exercising in a fasted state. From his book, that was all people took in. Not his training regime, not his nutrition plan. But, is it actually fact?
Deighton, Zahra, & Stensel Study
In 2012, this group published a study on changes in the body and on appetite after fasted or fed (they use the term postprandial) cardio. The general results showed that those who ate a meal before running had better appetite control later in the day and that there was no difference in energy intake. Also, compared to the control group both the fasted and fed groups had lower relative energy intake but they found no additional benefits to exercising before or after breakfast.
Cambridge Study
In 2013, Cambridge University also published a study looking at energy intake after exercise and overall energy balance. This study, similar to the 2012 study above, found that there was no difference in calories (or energy) consumed after exercising. However, they group did find that ‘least positive’ energy balance at the end of the day was with the fasted exercise group. When writing this post, we were unable to find the raw data to determine what least positive energy balance entailed.
Sports Nutrition Study
In 2014, a group published an article in the Journal of the International Society of Sports Nutrition. This study, unlike the last two, was an all-female cohort group where they exercised three days a week and had a calorie deficit inducing diet. The 20 participants were them split into the fasted or fed cardio groups. Both groups showed significant lose in body weight and fat mass but there was no difference between groups.
The Science of Fat Loss
Because it seems the science is showing us that there really is no difference in when you do your cardio, let’s recap on how the body burns fat. The three primary steps are:
1. Mobilization: The body has to actively get stored fat out of the cell by using enzymes and hormones like adrenaline and glucagon.
2. Transport: Once the stored fat is mobilized, the fatty acids travel within the bloodstream.
3. Oxidation: This is the ‘burning of fat’ that people are looking for. The heart, muscle, and liver will use the fatty acids in the blood stream to produce energy.
Depending on where you are at in your body composition journey, there are common areas that people struggle with. People on the lower ends of healthy body fat percent and are trying to lower for aesthetics or to meet a weight class will have lower mobilization and transportation, especially in areas that have reduced blood flow. For these individuals, the body is also adapting to make it more difficult to mobilization stored fat.
For individuals in the middle, usually there is no issue with either stage. The key for this group is to stay in a calorie deficit and to understand the fundamentals of nutrition. Finally, for the individuals in the higher body fat percentage (above the healthy range), it is common that oxidation is impaired because of the excess fatty acids in the bloodstream.
Why Has Fasted Cardio Become The Thing of Fat Loss?
It is all anecdotal. As you’ve seen from the very few studies that we have citied, there is no science (not bro science) to show that there is a significant difference. Some people, again anecdotally, feel fasted cardio helps the people in the lower end of the body fat percentage range because it is forcing mobilization. However, there is no science at the time of posting this that we could find that shows any different. Yes, in 1986 there was a study that showed appeared to show higher fat mobilization and oxidation but the fast was 23 hours. A 23 hour fast is not manageable or recommended in any capacity when trying to lose weight so we are dismissing that study.
The Bottom Line
Do cardio when you want to. If you find you are more efficient and need to work out earlier in the morning before breakfast, so that. If you like to exercise an hour or two after lunch, awesome. The key to success is consistency and calorie deficit when looking for fat loss and depending on where you are at, there may be some struggles. However, that is when you need to stick with your plan the most.
Resources:
· Deighton K, Zahra JC, Stensel DJ. Appetite, energy intake and resting metabolic responses to 60 min treadmill running performed in a fasted versus a postprandial state. Appetite. 2012;58(3):946-54. doi:10.1016/j.appet.2012.02.041
· Gonzalez JT, Veasey RC, Rumbold PLS, Stevenson EJ. Breakfast and exercise contingently affect postprandial metabolism and energy balance in physically active males. British Journal of Nutrition. 2013;110(4):721-732. doi:10.1017/S0007114512005582
· Trabelsi K, El abed K, Stannard SR, Jammoussi K, Zeghal KM, Hakim A. Effects of fed- versus fasted-state aerobic training during Ramadan on body composition and some metabolic parameters in physically active men. Int J Sport Nutr Exerc Metab. 2012;22(1):11-8. doi:10.1123/ijsnem.22.1.11
· Trabelsi K, Stannard SR, Maughan RJ, Jammoussi K, Zeghal K, Hakim A. Effect of resistance training during Ramadan on body composition and markers of renal function, metabolism, inflammation, and immunity in recreational bodybuilders. Int J Sport Nutr Exerc Metab. 2012;22(4):267-75. doi:10.1123/ijsnem.22.4.267