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What does current research say about the effect of overnight fasting?

by TONY NUÑEZ, PHD

HOW DOES OVERNIGHT FASTING AFFECT EXERCISE INTENSITY?

People have performed fasted cardio for years, but there is minimal research on how it compares with carbohydrate-supplemented cardio in respect to exercise duration, power output and important blood markers. In particular, data has been lacking on differences in sprint-interval training performance while fasted (SITFAST) versus carbohydrate-supplemented (SITCHO).

Researchers wanted to understand the effects of SITFAST (n = 11) and SITCHO (n = 9) when performed 3 days per week for 4 weeks by well-trained cyclists (aged 18–45). Training began with four SIT bouts (30-second sprint, 4-minute recovery) and increased by one bout per week. Participants performed aerobic capacity and time-to-exhaustion tests on a bike before and after the training. SITFAST cyclists trained after a minimum 10-hour fast, while the SITCHO group consumed breakfast (2.5 grams of carbohydrate per kilogram of body weight) before the training and drank a 20-ounce Gatorade drink during the workout.

The SITCHO group exhibited higher work and peak power outputs than the SITFAST group during training. Nonetheless, the SITFAST group had longer time-to-exhaustion durations and distances than the SITCHO group following training. Researchers suggested that improved aerobic enzyme activity during SITFAST training may have led to greater improvements in aerobic endurance.

REFERENCE: Terada, T., et al. 2018. Overnight fasting compromises exercise intensity and volume during sprint interval training but improves high-intensity aerobic endurance. The Journal of Sports Medicine and Physical Fitness, doi:10.23736/S0022-4707.18.08281-6.

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AFM_Author_Nunez TONY P. NUÑEZ, PHD, is an assistant professor in exercise science at Metropolitan State University of Denver. He is an active researcher and presenter in the exercise physiology and fitness field.

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