Myth Busting–Fasted Cardio

Time to crack heads and bust some more myths!I need to thank Layne Norton for pointing this one out! The big take away is that doing your cardio in a fasted (no food) state is probably not the best approach, and a min is not more effective despite all the articles you read about targeted fat loss with early AM cardio. Others will argue that if they have some protein or branched chain amino acids in the AM, then do cardio it will help protect muscle and target fat more. Well, they did not look at during this study and not to split hairs but that is not technically fasted cardio now is it?

I am not the first to point this out and others like Alwyn Cosgrove have been saying this for years, but it is cool to see a study on it.

To go one step further, I would recomend some high intensity work first. Kettlebells work great for high intensity work and they are WAY cheaper than horrible treadmills. Drop me a line if you are interested.

J Appl Physiol. 2008 Apr;104(4):1045-55. Epub 2008 Feb 14.
Effect of training in the fasted state on metabolic responses during exercise with carbohydrate intake.
De Bock K, Derave W, Eijnde BO, Hesselink MK, Koninckx E, Rose AJ, Schrauwen P, Bonen A, Richter EA, Hespel P.

Research Center for Exercise and Health, F.A.B.E.R. – K.U.Leuven, Tervuursevest 101, B-3001 Leuven Heverlee, Belgium.

Skeletal muscle gene response to exercise depends on nutritional status during and after exercise, but it is unknown whether muscle adaptations to endurance training are affected by nutritional status during training sessions. Therefore, this study investigated the effect of an endurance training program (6 wk, 3 day/wk, 1-2 h, 75% of peak Vo(2)) in moderately active males. They trained in the fasted (F; n = 10) or carbohydrate-fed state (CHO; n = 10) while receiving a standardized diet [65 percent of total energy intake (En) from carbohydrates, 20%En fat, 15%En protein]. Before and after the training period, substrate use during a 2-h exercise bout was determined.

During these experimental sessions, all subjects were in a fed condition and received extra carbohydrates (1 body wt(-1) .h(-1)). Peak Vo(2) (+7%), succinate dehydrogenase activity, GLUT4, and hexokinase II content were similarly increased between F and CHO. Fatty acid binding protein (FABPm) content increased significantly in F (P = 0.007). Intramyocellular triglyceride content (IMCL) remained unchanged in both groups. After training, pre-exercise glycogen content was higher in CHO (545 +/- 19 mmol/kg dry wt; P = 0.02), but not in F (434 +/- 32 mmol/kg dry wt; P = 0.23). For a given initial glycogen content, F blunted exercise-induced glycogen breakdown when compared with CHO (P = 0.04).

Neither IMCL breakdown (P = 0.23) nor fat oxidation rates during exercise were altered by training. Thus short-term training elicits similar adaptations in peak Vo(2) whether carried out in the fasted or carbohydrate-fed state. Although there was a decrease in exercise-induced glycogen breakdown and an increase in proteins involved in fat handling after fasting training, fat oxidation during exercise with carbohydrate intake was not changed.

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