Friday, October 5, 2018
To fast, or not to fast? That is the question
Is exercising in a fasted state detrimental on muscle growth? Does it increase fat loss? This is a controversial topic to the average gym goer, and I always here wildly different opinions on the matter. The general consensus I hear is that training while fasted will deplete muscle glycogen, decrease performance, but will increase fast loss. While training after a meal will increase performance but not maximize fat loss. I decided to look at some of the data to get the facts on these claims. This 2011 study showed that when moderate endurance exercise is done to lose body fat, fasting before exercise does not enhance lipid utilization and that physical activity after a light meal is advisable (Paoli et al.) So training while fasted is not as effective for loss, but what about muscle performance? Neufer et al. showed in 1987 that total work produced was increased in subjects fed carbohydrates before training vs. fasted subjects, also confirming what I usually hear among gym goers. So it seems it's obvious that eating before training is optimal, right? Not so fast, this 1980 study compared liver and muscle glycogen levels in carbohydrate fed and fasted rats after exercise and found that the fasted rats showed depletion of liver glycogen with an increase in muscle glycogen, while the carbohydrate fed rats showed about the same increase in muscle glycogen but with also a large increase in liver glycogen (Fell at al.). Nieman et al. confirmed this preservation of muscle glycogen after exercising in a fasted state, and also contradict the Paoli et al. study showing that lipid oxidation in fact is increased in fasted subjects vs. fed subjects. The data I presented is just the tip of the ice berg. There is plenty of literature that will contradict these studies I presented, and literature that will contradict those studies. Thus, the debates in the gym continues. One potential benefit of fasting may be on its affects on behavior, rather than the quantified data of muscle glycogen and work output measured in the other studies. Bhutani et al. showed that regular fasting contributed to positive behavioral changes such as decreased uncontrolled eating, decreased likeliness to cheat on diet, and increased satisfaction after eating. The behavioral impacts from fasting could certainly impact weight loss completely separate from the glycogen levels and work produced observed in the other studies. So with all the conflicting data on whether to fast or feed before training, I think one should focus on personal preference and trial and error until the literature can finally reach a definite conclusion. Personally, I prefer to train fasted because I do not see any decrease in performance, it takes an extra step out of my morning routine, and I do see an improvement in my appearance. What are your opinions on the topic and personal preferences when it comes to eating before training and why? Is breakfast really the most important meal of the day?
Bhutani, S., Klempel, M. C., Kroeger, C. M., Aggour, E., Calvo, Y., Trepanowski, J. F., . . . Varady, K. A. (2013). Effect of exercising while fasting on eating behaviors and food intake. Journal of the International Society of Sports Nutrition,10(1), 50. doi:10.1186/1550-2783-10-50
Fell, R. D., Mclane, J. A., Winder, W. W., & Holloszy, J. O. (1980). Preferential resynthesis of muscle glycogen in fasting rats after exhausting exercise. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology,238(5). doi:10.1152/ajpregu.1980.238.5.r328
Neufer, P. D., Costill, D. L., Flynn, M. G., Kirwan, J. P., Mitchell, J. B., & Houmard, J. (1987). Improvements in exercise performance: Effects of carbohydrate feedings and diet. Journal of Applied Physiology,62(3), 983-988. doi:10.1152/jappl.1987.62.3.983
Nieman, D. (2009). Effect of training in the fasted state on metabolic responses during exercise with carbohydrate intake. Yearbook of Sports Medicine,2009, 140-141. doi:10.1016/s0162-0908(08)79366-8
Paoli, A., Marcolin, G., Zonin, F., Neri, M., Sivieri, A., & Pacelli, Q. F. (2011). Exercising Fasting or Fed to Enhance Fat Loss? Influence of Food Intake on Respiratory Ratio and Excess Postexercise Oxygen Consumption after a Bout of Endurance Training. International Journal of Sport Nutrition and Exercise Metabolism,21(1), 48-54. doi:10.1123/ijsnem.21.1.48
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I found a meta-analysis that looked at the effect of fasted and fed states on carbohydrate and fat metabolism in adults when they performed aerobic exercise. This study looked at the glucose, and insulin concentrations after exercise. The study concluded that there was a difference in both glucose and insulin concentration from the fasting and fed states. They determined that when aerobic exercise is performed in the fasting stated, then there is a higher fat oxidation. Therefore, this study suggests that performing exercise on an empty stomach does actually reduce fat and increase weight loss. This would make sense because when exercising fat is being burned up for fuel. However, if you eat right before working out then the glucose from the food you just ate would be burned up. But, if you workout on an empty stomach, then another source of fat would need to be metabolized, which would be adipose tissue. Therefore, I think that it is actually beneficial to workout on an empty stomach or right when you wake up in the morning. It is important to keep in mind that eating breakfast after the workout is important since your brain will need lots of glucose (100-150g) to function throughout the day.
ReplyDeleteThe meta-analysis can be found here: https://www.ncbi.nlm.nih.gov/pubmed/27609363
I can definitely see the benefits of doing aerobic exercise while in a fasted state would be beneficial for fat metabolism. I found an interesting article that shows intermittent fasting causes a multitude of beneficial dietary effects. The first is that it causes and increase in insulin sensitivity. This is due to the lack of insulin being present in the bloodstream due to the fasting state. Another interesting effect of intermittent fasting in the increase release of GH. Research has shown that men show an increase of 2000% and women 1500% after 24 hours without food (Intermountain Medical Center, 2011). That's a crazy increase in GH. This research and studies are probably the reason that more people are using intermittent fasting within their diets.
ReplyDeleteIntermountain Medical Center. (2011, May 20). Routine periodic fasting is good for your health, and your heart, study suggests. ScienceDaily. Retrieved October 7, 2018 from www.sciencedaily.com/releases/2011/04/110403090259.htm
I found this post really interesting because for me personally, I know that I tend to prefer working out after consuming some sort of caloric input and that when I skip breakfast, I tend to consume more calories throughout the rest of the day. One thought that came to mind while reading your post was the effects of cortisol levels on power output and how the normal fluctuations of this hormone throughout one's day may affect a person's ability to use lipid vs. glycogen storages. This begs this question, is there an optimal time of the day to do certain type of exercise in order to promote weight-loss or better muscle gain?
ReplyDeleteWhat I really appreciate about your post is that you highlight the fact that there is so much conflicting evidence regarding intermittent fasting. Interestingly, while working at the cardiology clinic, I also listened to conflicting thoughts/ideas from physicians as well on the subject. After reading your post, I wondered what the longterm effects of intermittent fasting are? From an article I found, it seems there is still not sufficient evidence to show that intermittent fasting would be beneficial as a lifestyle as opposed to just a diet for humans (Tinsley & Horne, 2017). Given the ongoing obesity epidemic, I am sure ongoing research regarding this will be pursued and will certainly be interesting to follow.
ReplyDeleteTinsley, G. M. & Horne, B. D. (2017). Intermittent fasting and cardiovascular disease: current evidence and unresolved questions. Future Cardiology, 14(1), 47-54. doi: 10.2217/fca-2017-0038