Fasted Cardio – Secret Fat Loss Weapon or Pseudo-Science?

To Fast or Not to Fast?

Like old lore etched in stone, many gym-goers looking to drop a few extra pounds adopt the routine of not eating breakfast before running off to the gym to knock out an hour of cardio.

Does fasting really make a difference? A few scientifically controlled studies are available to help us get a better idea so we’re going to discuss those studies a little more closely.

The Why and How of this Old Adage

The working theory centers upon stored fuel stores, namely carbohydrates as glycogen in your liver and muscle. After a night’s sleep, liver glycogen stores are fairly depleted and science studies for years have told us that when stored carbohydrates are reduced, our body will burn more fat and exercising in this state will ramp things up even more.

It makes sense in theory.

Like so many other topics, the science tells us it all depends on the conditions.

For example, Brad Schoenfeld and colleagues recently published a paper on the topic in the Journal of the International Society of Sports Nutrition. They required 21 healthy college-aged females to follow the exact same exercise program for a 4 week period.

Each participant exercised 3 days per week for 60 minutes while wearing a heart rate monitor to closely monitor their exercise intensity. One group was given a meal replacement protein shake immediately (250 calories, 40 grams carbohydrates, 20 grams protein, 0.5 grams fat) before each workout or immediately after each workout.

Finally, all participants had their body composition assessed before and after the four-week exercise program. Also, a very key point for this study was that all participants were prescribed to also follow a restricted-calorie diet (each woman consumed around 1,250 calories each day).

Makes sense right? If you want to lose fat, you need to restrict caloric intake.

The Results?

Fasting didn’t matter.

Nope, not one bit. Both groups lost weight, both groups reduced their body mass index (a height: weight ratio predictive of obesity and risk for disease), both groups lost fat, but the amounts lost were similar between the groups.

Say what? You mean to tell me I have been starving myself every morning feeling like utter garbage heading to the gym for a workout and I could have a little snack before heading off to the gym?

Yep, that’s what this one study says.

Some Perspective and Things to Come

However, keep in mind a few things. First, both groups were the same. Meaning…

If you like exercising in a fasted state go for it.

If you want a small snack before your cardio, go for it.

Also, another key point has to be brought up.

If getting up first thing for a workout is the difference between you feeling great and dominating your day, then I say do it and to hell with body fat changes.

We all know working out makes you feel better, look better and healthier and this is a good thing.

Full text to the article here: http://www.ncbi.nlm.nih.gov/pubmed/?term=25429252

This post was written by Chad Kerksick, an Assistant Professor of Exercise Science at Lindenwood University in St. Charles, MO. Dr. Kerksick is a nerd for exercise physiology and particularly enjoys discussing strategies to lose fat and enhance performance through diet, supplementation and exercise.

Reference:
Schoenfeld BJ, et al. Body composition changes associated with fasted versus non-fasted aerobic exercise. J Int Soc Sports Nutr 2014 Nov 18;11(1):54.

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