This is a question that has been floating around the internet for, what feels like, forever. It seems like you can read an article that says "YES! Fasting is the key to SUCCESS in fat loss!" and then turn around and find one that says the polar opposite. With that in mind, I present my random research into the subject. Again, I haven't performed a study myself but I have found quite a few.
Eating carbohydrates 30 minutes before exercise, in Coyle, E and team’s 1983 study, resulted in a faster decrease in muscle glycogen and blood glucose concentration during exercise. This would in turn, result in less endurance during prolonged exercise. The team suspects that cause of the loss of endurance is from the process the body goes through following a carbohydrate meal, i.e. increase in insulin levels. Interestingly to me, their study, amongst others, found that providing carbohydrates during exercise frequently delayed the onset of fatigue.
What is muscle glycogen? (Elmhurst College)
* The storage form of glucose in the muscles. Glucose is one of the monosaccharides absorbed by the body when breaking down plant based material. The other two are fructose and galactose. In a nut shell, glucose is sugar. During intense exercise, when he energy stores in the form of fat aren’t enough, the glycogen stored in the muscle is converted back into glucose for immediate use via the bloodstream.
Carbohydrates are a key fuel source for exercise, with the major source during exercise being the muscle glycogen stores (Ivy, 1991). “The greater the muscle glycogen stores, the longer the exercise time to exhaustion.” After its depletion during exercise, assuming you eat an adequate amount of carbohydrates, muscle glycogen levels return to pre-exercise levels within 24 hours. “For the average endurance athlete, a daily carbohydrate consumption of 500 to 600g is required.”
Now, you’re probably saying “But these are all talking about endurance exercises! What about me?!” Well, I have news for you, you can choose to eat nothing or to eat something. The difference for the rest of us isn't large enough to matter, in my opinion. According to the recap of a 2010 Belgian study, by Jennifer Sygo (2013), a registered dietitian and sports nutritionist, the group that fasted before exercise had the best results in weight management at the end of the study while the people who didn't fast had gained weight but more endurance by the end. I would like to point out that the men in this study consumed a breakfast high in fat. If you’re not consuming a breakfast high in fat then...well you’re likely still fine having breakfast before the workout. If you do have a high fat breakfast, then I would suggest exercising and then eating.
Another study by Paoli and team (2011), found that people who ate before exercising burned more calories throughout the day vs those that fasted. So this is something else to keep in mind.
In my opinion, for what it’s worth since I’m not a medical professional…YET!, if you’re doing to be doing light to moderate exercise and you’re not hungry then don’t even worry about it. If you’re going to be running a marathon or doing an intense program like P90X3 or Insanity then I would suggest you eat
first and wait an hour for the insulin spike to normalize before working out and then, during the breaks, munch on some carbs (veggies or fruits, ideally) or have a well-rounded protein shake.
Personally, I have a protein shake or a smoothie with some Greek yogurt and wait at least 25 minutes before I workout. It’s not a meal high in fat and since it’s liquid, it gets into my system faster, so I don’t see a problem. I find that when I don’t have something before I start I am sluggish and don’t push as hard as I could.
Let me know if there's a topic you'd like me to cover next Monday! This topic was suggested by my friend Pam.
Belgium study recapped by Jennifer Sygo: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3002457/
References
Coyle, E., Hagberb, J., Hurley, B., Martin, W., Ehsani, A., & Holloszy, J. (February 4, 1983). Carbohydrate feeding during prolonged strenuous exercise can delay fatigue.
Elmhurst College (2003). Glycogen. Retrieved from http://www.elmhurst.edu/~chm/vchembook/547glycogen.html.
Ivy, J. (January 1991). Muscle glycogen synthesis before and after exercise. Department of Kinesiology, University of Texas, Austin.
Kravitz, L. (n.d.). Eating or fasting for fat loss: A controversy resolved. Retrieved from http://www.unm.edu/~lkravitz/Article%20folder/fasting.html.
Krssak, M., Petersen, K., Bergeron, R., Price, T., Laurent, D., Rotheman, D., Roden, M., & Shulman, G. (October 27, 1999). Intramuscular glycogen and intramyocellular lipid utilization during prolonged exercise and recovery in a man: A10C and 1H nuclear magnetic resonance spectroscopy study. Retrieved from http://press.endocrine.org/doi/abs/10.1210/jcem.85.2.6354.
Sygo, J. (February 7, 2013). Fasting and fitness: Should I eat before I exercise? It depends on your workout goals. Retrieved from http://life.nationalpost.com/2013/02/07/fasting-and-fitness-should-i-eat-before-i-exercise-it-depends-on-your-workout-goals/.
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