By Dayne Hudson

 

To fast or not fast before cardio?

It has been the question on the lips of many for decades.

Some swear that fasted cardio is the best while others will tell you there's no difference at all.

So who's right?

Well the good news is, research has looked into exactly this!

FAT LOSS - FED OR FASTED CARDIO?

In a recent study (1), 20 young non-obese women were split into 2 groups: the fasted cardio group or the fed cardio group.

The fasted group obviously consumed nothing at the end of an overnight fast, whilst the fed group consumed a protein shake with 20 g protein, 40 g carbohydrate and 0.5 g fat - for 250 calories it total.

Their cardio was performed 3 days per week for an 1 hour on a treadmill, with a 5 minute warm-up followed by 50 minutes of jogging/walking at 70% of their maximum heart rate. They finished with a 5 minute cool down.

This went on for 4 weeks before their results were evaluated. 

From all the homework I've done around the study and from what the researchers have said, it certainly seemed well controlled.

All participants were provided with customised meal plans which aimed at a 500 calorie deficit. Nutritional counseling was given to the subjects to help them stick to it. 

After 4 weeks the subjects were retested on all body composition measures. 

And what did they find?

Both groups lost a statisitically significant amount of weight - with the fasted group losing 1.6kg and the fed group losing 1.0kg.

And in terms of fat mass, the fasted group lost 1.1kg and the fed group lost 0.7 kg.

Yet, no significant differences were recorded between the fasted or fed groups.

The authors point out that the fasted group had a higher (non-significant) baseline body fat percentage, which meant they may have been able to lose more (the fatter you are, the fat you lose).

WHAT ABOUT MUSCLE LOSS?

The authors say there was no difference significant differences here.

Now it's important that we do not sit here and rule out fasted cardio forever, as this is just one study that shows no significant difference.

This study only went for 4 weeks as I mentioned above and there could potentially be a greater advantage from one of the groups over the long term.

However, other research has contradicted this latest piece in the literature (2).

In a study examining 8 healthy young men, cardio in a fed state was found to be superior, as they were able to put more power into their workouts.

This certainly makes sense.

To quote from the paper:

"...fasting before exercise does not enhance lipid utilization; rather, physical activity after a light meal is advisable."

Other research into this has found the same results (3). 
 
This study investigated the thermogenic effects of cardio in a fasted state, or after a glucose/milk drink.
 
10 college students participated in the study, and did 4 different workouts: low intensity, long duration exercise with the milk drink, low intensity, long duration exercise without the milk drink, high intensity, short duration exercise with the milk drink and high intensity, short duration exercise without the milk.
 
The findings showed the milk drink increased excess post-exercise oxygen consumption to a significantly greater extent, than the exercise while fasted in both high and low intensity conditions. 
 
This leads the authors of the latest study (1), the focal point of this article, to suggest:
 
"Any potential increases in fat oxidation from fasted exercise might be neutralized by an increase in the thermic effect of exercise from eating pre-exercise."
 
Essentially what they're saying is - whilst you MIGHT burn more fat whilst training fasted, it's all even in the end if you train while fed, as you burn more calories from the exercise in the fed state.
 
So whether or not you do cardio in a fed state or not is completely up to you.
 
My recommendations would be simply - just to make sure you do your cardio!
 
Any benefits you would get don't seem to be significant enough to warrant you worrying. 
 
Just focus on a good macronutrient intake and a quality calorie deficit, and you'll be on track to losing all that unwanted body fat!
 

"Stay Fit, Stay Flexed!"

 

FURTHER READING: THE FASTEST POSSIBLE WAY TO LOSE FAT KNOWN TO MAN - WITHOUT LOSING MUSCLE

 

REFERENCES

(1) Schoenfeld BJ, Aragon AA, Wilborn CD, Krieger JW, Sonmez GT. Body composition changes associated with fasted versus non-fasted aerobic exercise. J Int Soc Sports Nutr. 2014 Nov 18;11(1):54. doi: 10.1186/s12970-014-0054-7. eCollection 2014.

(2) Paoli A, Marcolin G, Zonin F, Neri M, Sivieri A, Pacelli QF. 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. Int J Sport Nutr Exerc Metab. 2011 Feb;21(1):48-54.

(3) Lee YS, Ha MS, Lee YJ: The effects of various intensities and durations of exercise with and without glucose in milk ingestion on postexercise oxygen consumption. J Sports Med Phys Fitness 1999,  39(4):341-347.

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