As the amount of fitness information available is getting bigger, the chances of being exposed to bad advice are also growing, creating more fitness myths than ever. Yet, one of the most debatable myths that has been out there forever is the myth of working out on an empty stomach.

It has been a prevailing thought for decades that you shouldn’t eat or drink prior to working out, and it seems that only recently the public has started questioning its accuracy.

“Fasted” versus “Fed”

The common belief of the effectiveness of the “hungry workout” isn’t unsupported; actual research backs it up. The British Journal of Nutrition^[1] and the International Journal of Sports Nutrition and Exercise Metabolism both published studies that show data in favor of “fasted” as opposed to “fed” training when it comes to the percentage of fat lost per workout.^[2]

Additionally, a study published in the European Journal of Applied Physiology shows that fasted training provides a better anabolic post workout response to weight training, meaning it provides a better environment for building lean mass.

Namely, the conclusions indicate that “prior fasting may stimulate the intramyocellular [stored fats] anabolic response to ingestion of a carbohydrate/protein/leucine mixture following a heavy resistance training session.”^[3]

Moreover, by providing better absorption of the post workout meal nutrients, fasted training has the great potential to improve insulin sensitivity, and is, therefore, an important agent in the fat loss process.

As insulin sensitivity shows how easily fat and muscle cells in our body take in glucose, regulating insulin sensitivity helps lower the blood sugar levels, which is one of the most important factors in weigh loss. The Journal of Physiology published a study^[4] that shows significantly greater insulin sensitivity improvement for the fasted training group as opposed to fed training group.

Finally, fasted training proved beneficial to endurance performance. In a study^[5] published in the Journal of Strength and Conditional Research, ten professional cyclists maintained lean mass, lowered fat mass, and maintained performance.

Why fed training is better?

However, there is another side to the story that trumps the beliefs of efficacy of fasted workouts. As sports dietetics specialist Kelly Pritchett, Ph.D., R.D. explains, while the body’s response to a high-intensity fasted workout is to burn glycogen, the stored up carbohydrates, eventually, the body starts to adjust to the new system and starts storing fat from the next meal and burning less calories in order to compensate.^[6]

Additionally, a study^[7] published in the American Journal of Clinical Nutrition shows no benefits of fasting, since longer periods of avoiding food showed a decrease in resting metabolic rates (calories burned per unit of time, a day usually.)

What’s more, fed training actually helps reduce appetite later in the day, as a study^[8] in the journal Appetite shows. Whereas both fed and fasted training participants were expanding the same amount of energy throughout the day, the fed training participants experienced lessened appetite later on, which means less snacking or overeating later in the day, which is great news for anyone who wants to lose weight.

Although it may seem (according to scientific data) that fasted exercise provides better results, later and more extensive research shows the opposite is true.

As far as the fat burning capacity of fasted training is concerned, while it is accurate to some point, on the other hand it is proven to be counterproductive.

Namely, throughout the course of a high-intensity fasted workout, having no more fat to burn, the body starts to burn muscle instead. As another study^[9] published in the European Journal of Physiology shows, during high-intensity training, without prior eating, the body relies on burning muscle proteins for energy, which is certainly an unwanted scenario for both professional athletes, and people who are just trying to shed some weight and feel better.

Another important benefit of fed training is that it gives you the ability to improve at a steady rate, which is impossible to achieve through a fasted workout regimen, as a study^[10] from the Journal of Science and Medicine in Sport shows. Being able to push yourself a little bit further each time, and outperform your previous training, isn’t feasible with fasted training since your body lacks the energy to rely on for additional strength. By eating a light meal before your workout, your body will be provided with enough energy to help you perform a little better each time.

As the study concludes, “meal ingestion prior to daily exercise can modify some of the exercise training-induced adaptations normally seen with endurance training compared to when daily exercise is undertaken in the overnight-fasted state.”

How Fed training affects fat loss

When it comes to burning fat, the results are more favorable for the fed training method. As another study^[11] in the International Journal of Sport Nutrition and Exercise Metabolism shows, physical activity after a light meal is far more effective for fat loss.

The study analyzed the effect on oxygen consumption (VO2) and substrate utilization (how our bodies burn fats and carbs), estimated by the respiratory-exchange ratio (RER) in eight young healthy men who were exposed to the same moderate-intensity workout. The results showed that breakfast increased both VO2 and RER significantly, and more importantly, the difference was still significant 24 hours after exercise. This means that fed training increases lipid utilization (the breaking down of fat cells), which is essential for weight loss.

Another study^[12] in the Journal of the International Society of Sports Nutrition has managed to completely refute the belief that fat loss is much faster throughout fasting training, as the results showed no significant difference in weight loss between women who ate a meal-replacement shake before working out and those who performed training without any meal.

Conclusions

All research considered, a fed workout actually has more scientifically proven benefits to overall health, fitness, weight loss, and workout performance, as opposed to fasted training. It may seem like fasted training aids in body fat loss, but in the long run, it actually has counterproductive effects, as the body starts to store fat and burn less calories as a precaution.

Additionally, the studies show far greater and longer effects on burning body fat with fed training than those of a fasted. Moreover, the decreased appetite shown in groups who performed fed training is another reason for people who want to shed some weight to enjoy a light meal before a workout in order to prevent later cravings.

Finally, for reaching new higher goals in fitness and training, a fed workout is again a much more productive option, since the calories provide enough energy for extra effort.

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