Advantages Of Cardio On An Empty Stomach?

 

By: Intense-Fitness Writers   

You very often hear people saying that for best fat loss results, cardio training should be performed on an empty stomach.  People everywhere are waking up first thing in the morning and hopping onto their home treadmill or making their way to the gym in hopes that doing this before their breakfast meal will speed up the fat loss process.

But, few ever think about the performance and metabolic adaptations that this practice can have.

Let’s look at one study that assessed just that.

The Research Study

J Appl Physiol. 2010 Nov 4. [Epub ahead of print]
Beneficial metabolic adaptations due to endurance exercise training in the fasted state.
Van Proeyen K, Szlufcik K, Nielens H, Ramaekers M, Hespel PJ.

1K.U.Leuven.
Abstract


Training with limited carbohydrate availability can stimulate adaptations in muscle cells to facilitate energy production via fat oxidation. Here we investigated the effect of consistent training in the fasted state, versus training in the fed state, on muscle metabolism and substrate selection during fasted exercise. Twenty young male volunteers participated in a 6 week endurance training program (1-1.5 hr cycling @~70% VO(2)max, 4d/week) while receiving isocaloric carbohydrate-rich diets. Half of the subjects trained in the fasted state (F; n=10), whilst the others ingested ample carbohydrates before (~160g) and during (1g(.)kg(-1) b.w.(.)hr(-1)) the training sessions (CHO; n=10). The training similarly increased VO(2)max (+9%) and performance in a 60 min simulated time trial (+8%) in both groups (P<0.01). Metabolic measurements were made during a 2 hr constant-load exercise bout in the fasted state @ ~65% pre-training VO(2)max. In F, exercise-induced intramyocellular lipid breakdown was enhanced in type I fibers (P<0.05), and tended to be increased in type IIa fibers (P=0.07). Training did not affect IMCL breakdown in CHO. In addition, F (+21%) increased the exercise intensity corresponding to the maximal rate of fat oxidation more than did CHO (+6%) (P<0.05). Furthermore, maximal citrate synthase (+47%) and β-hydroxyacyl coenzyme A dehydrogenase (+34%) activity was significantly upregulated in F (P<0.05) but not in CHO. Also, only F prevented the development exercise-induced drop in blood glucose concentration (P<0.05). In conclusion, F is more effective than CHO to increase muscular oxidative capacity, and at the same time enhances exercise-induced net IMCL degradation. In addition, F but not CHO prevented drop of blood glucose concentration during fasting exercise.

What This Means To You

So what the researchers in this study wanted to look at was what impact training for endurance had without eating beforehand in terms of total fuel usage during the session as well as performance values.

They divided the subjects into two groups who would cycle for 1-1.5 hours four times a week at 70% of their VO2 max.  One group was fed a dose of 160 grams of carbohydrates before the training as well as more carbohydrates during the session while the other group was forced to train without any ingested carbohydrates (or other nutrients).

After the results were back, the researchers noted that both groups improved in similar manners on their VO2 max measurement, thus performance was enhanced to the same degree.

In addition to that though, the fasted training group was able to increase the rate at which the muscle fibers utilized fats as a fuel source while also preventing a drop in blood glucose that took place throughout the session.

Those that had been fed the carbohydrates before training did notice a decrease in blood glucose levels.  This could, in some people, hinder performance significantly as declining blood glucose levels are associated with feelings of weakness and in some cases, even being dizzy as well.

The Take-Home Message

So the take home message from this study is that training for endurance in the fastest state can improve your body’s ability to utilize fat as a fuel source during extended periods of activity.

This could be beneficial information for those who are on fat loss diets utilizing a lower carb approach and who are trying to sustain weight training as well.

Since for weight training your body will rely on glucose as a fuel source, by reducing the reliance on glucose on any cardio training you’re performing, you’ll help spare those carbohydrate stores in the muscle for when you really need them – during weight lifting.

So it appears empty-stomach cardio is about more than just faster fat burning, it may prove to be beneficial in other regards as well.

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