Should You Run On Empty Stomach?

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Running on an Empty Stomach

Some studies have found that running on an empty stomach helps burn fat faster. When glycogen levels are low, the body produces enzymes that break down fat into free flowing fatty acids that can be used for producing energy. On the flip side, the body may break down muscle tissue instead of fat. You may also get exhausted faster. Net net, it might be best to run with some fuel in the tank.

One of the biggest ongoing debates in running is whether one should run on an empty stomach or fully fuelled.

The case for running on an empty stomach

One of the first proponents of ‘fasted cardio’ or performing aerobic exercises like running on an empty stomach is American fitness trainer and author Bill Phillips. In his book Body For Life, he says exercising on an empty stomach maximizes fat loss. By doing so, we are starving our body of food and reducing the blood-sugar levels in it causing glycogen (stored carbohydrate) levels to fall.

Here’s what happens to the body if we run on empty stomach:

  • Due to low glycogen levels, enzymes like hormone-sensitive lipase (HSL) or adipose triglyceride lipase trigger fat breakdown into free-flowing fatty acids (FFAs)
  • FFAs become available in the plasma through this process called lipolysis
  • Through oxidation, FFAs are broken down and used to fuel the exercise session

There are studies that have proved Phillips’s point. In one such study, six healthy men were made to cycle for 60 minutes at a low to moderate intensity.1 They were split into two groups–one that fasted overnight before the bike ride and the other that performed the ride after ingesting glucose or fructose to the tune of 0.8g/kg to replenish glycogen levels one hour before the experiment. When checked half an hour and one hour after the experiment began, the rate of fat burn was found to be higher in the fasted group than the glucose group. The same was true for the quantity of free-flowing fatty acids in the two groups.

The case against running on an empty stomach

Studies have found that fasted cardio can result in faster burnout and exhaustion with the slightest increase in the intensity of the exercise. In order to increase your workout intensity, your body needs a ready source of glycogen. If the body is not able to find this, it leads to an increase in the release of amino acids and degradation of proteins.2 This means that instead of fats, the body is using up tissue proteins to provide energy for the workout.

Also, fasted running need not necessarily convert to faster calorie burn, found a 1999 study.3 Observing subjects who exercised at 50 per cent of their maximum heart rate, researchers found that regardless of whether they had eaten or not before the workout, there was no significant difference in the amount of fat burned. Only after the first 90 minutes did the fasted group show a considerable difference in fat burn capacity.


If you are running a short distance for leisure, the condition of your stomach may not make much of a difference. But if weight loss is your goal, running without fueling your body adequately may not help – there is a good chance of you getting exhausted well before the finishing line. A good diet plays as important a part in weight loss as exercise.  So, wouldn’t it be better to keep your body fueled and burn that excess fat by running an extra mile?

References   [ + ]

1. Zoladz, J., S. Konturek, K. Duda, J. Majerczak, Z. Sliwowski, M. Grandys, and W. Bielanski. “EFFECT OF MODERATE INCREMENTAL EXERCISE, PERFORMED.” Journal of Physiology and Pharmacology 56, no. 1 (2005): 63-85.
2. Blomstrand, Eva, and Bengt Saltin. “Effect of muscle glycogen on glucose, lactate and amino acid metabolism during exercise and recovery in human subjects.” The Journal of Physiology 514, no. 1 (1999): 293-302.
3. Horowitz, Jeffrey F., Ricardo Mora-Rodriguez, Lauri O. Byerley, and Edward F. Coyle. “Substrate metabolism when subjects are fed carbohydrate during exercise.” American Journal of Physiology-Endocrinology And Metabolism 276, no. 5 (1999): E828-E835.
CureJoy Editorial

The CureJoy Editorial team digs up credible information from multiple sources, both academic and experiential, to stitch a holistic health perspective on topics that pique our readers' interest.

CureJoy Editorial

The CureJoy Editorial team digs up credible information from multiple sources, both academic and experiential, to stitch a holistic health perspective on topics that pique our readers' interest.