Quick Question: Is it true that working out on an empty stomach will make my body burn more fat?

Shorter Endurance Workouts

For those individuals trying to lose weight, it might make sense to exercise on an empty stomach when feasible. This is the case if your workout will be 60 minutes or less and is steady-state cardio such as biking, running, or using an elliptical machine. Most people have enough energy stored to exercise at a moderate pace for about 45 minutes first thing in the morning. Most research does not show a difference in performance among people who eat before aerobic exercise lasting less than an hour compared to those who are fasting. 

In healthy young men, it appears that low intensities of endurance-based aerobic exercise on an empty stomach increase the use of stored fat. This exercise in a fasting state also helps the body utilize insulin better, which might reduce the risk of diabetes development. Furthermore, protein degradation is mainly downregulated in the fasting state during endurance-based exercise, meaning that muscle is preserved rather than used for energy. 

Weight Lifting Workouts

Some experts point out that fasted workouts aren’t ideal for individuals trying to gain muscle mass or improve their anaerobic capacity. Weight training while fasting increases the chance that your body will use muscle protein as fuel. 

High-Intensity Workouts

It is not as important whether or not athletes eat before performing high-intensity exercise. During high-intensity exercise (near 80-90% VO2MAX in athletes), fat oxidation is lower, and carbohydrate utilization is higher. Therefore, it is proposed that the rate of fat oxidation rates is similar in fed and fasting states. Examples of foods that are good to eat before working out include apple slices, oatmeal, or whole-grain toast with peanut butter. 

Longer Workouts, Regardless of Exercise Type

People exercising for at least an hour are encouraged to eat between 30 and 80 grams of carbohydrate before beginning their workout. 

Regardless of whether you eat before exercising, most experts recommend consuming 16-25 grams of protein, and three times as many grams of carbohydrate, within two hours of the end of a workout to refuel the muscles and prevent protein breakdown. 

Exercising But Not Losing Weight

Generally speaking, most people become hungry 45-60 minutes after exercise, and many eat enough to balance the calories burnt during exercise, so that little weight is lost. The combination of intermittent fasting and exercise improves weight loss, body composition, and cholesterol levels more than either practice done alone. Keep in mind that a 155-pound person will burn 300 calories in a 30-minute session of circuit training and 112 calories in 30 minutes of general weightlifting. 

Bhutani S, Klempel MC, Kroeger CM, Trepanowski JF, Varady KA. Alternate day fasting and endurance exercise combine to reduce body weight and favorably alter plasma lipids in obese humans. Obesity (Silver Spring). 2013;21(7):1370-1379. doi:10.1002/oby.20353

Chen YC, Travers RL, Walhin JP, et al. Feeding influences adipose tissue responses to exercise in overweight menAm J Physiol Endocrinol Metab. 2017;313(1):E84-E93. doi:10.1152/ajpendo.00006.2017

Greatist. Is it better to eat before or after a workout? Updated July 10, 2017. 

Harvard Health Publishing. Are there any benefits to exercising on an empty stomach? Updated July 2017. 

Harvard Health Publishing. Calories burned in 30 minutes for people of three different weights. Updated August 13, 2018. 

Healthline. Should you eat before or after working out? Updated May 27, 2018. 

Huffington Post. How fasted workouts can help you achieve fitness goals. Updated September 6, 2017. 

Van Proeyen K, Szlufcik K, Nielens H, Ramaekers M, Hespel P. Beneficial metabolic adaptations due to endurance exercise training in the fasted stateJ Appl Physiol (1985). 2011;110(1):236-245. doi:10.1152/japplphysiol.00907.2010

Vicente-Salar N, Urdampilleta Otegui A, Roche Collado E. Endurance training in fasting conditions: biological adaptations and body weight managementNutr Hosp. 2015;32(6):2409-2420. Published 2015 Dec 1. doi:10.3305/nh.2015.32.6.9488