Should You Try Fasting Before Your Next Morning Swim?

Question:

I have been swimming for 30 minutes, 4 days a week, at 6AM. Is it best to not eat a sensible breakfast until after I swim? My son is a varsity state swimmer and says not to eat until mid or late morning so that my fat is burned as fuel first.

– Lorin and Diana S.

Answer:

Tristen Alleman, one of our Pro Results® Personal Training Directors, shared that it’s best to do your morning aerobic work while fasted in order to burn more fat. Theoretically, since the body has been using glycogen overnight (fasted) while insulin levels drop, it shifts toward greater fat utilization in subsequent exercise. Most research supports this notion, though it may not be the case during energy restriction. There is also a lack of evidence showing resultant changes in body composition.

I’d advise eating your breakfast just after your morning workout and not waiting until mid-morning, both for your muscle recovery as well as for convenience – it’s easier to eat your sensible meal before getting to early work.

Resources:

Beneficial metabolic adaptations due to endurance exercise training in the fasted state. K Van Proeyen , et al. Journal of Applied Physiology. 2011;110(1):236–245.
Body composition changes associated with fasted versus non-fasted aerobic exercise. BJ Schoenfeld, et al. Journal of the International Society of Sports Nutrition. 2014; 11:54.
Training in the fasted state improves glucose tolerance during fat-rich diet. K Van Proeyen K, et al. The Journal of Physiology. 2010; 588(Pt 21): 4289–4302.

– Debbie J., MS, RD

This article should not replace any exercise program or restrictions, any dietary supplements or restrictions, or any other medical recommendations from your primary care physician. Before starting any exercise program or diet, make sure it is approved by your doctor.

Some questions have been edited for length and/or clarity.