Can fasting make you faster? Some studies have suggested that intermittent fasting (IF) help you gain strength, burn fat, and ultimately improve your performance.
What is Intermittent Fasting?
Here’s the key: IF isn’t about eating less, but rather eating within a specific time window. Simply limiting your calorie intake to a specific period every day can kick off a cascade of physiological adaptations that can improve your health.
Basic IF guidelines say that you should fast for at least 12 hours every day — that is, eating only within a 12-hour window, and fasting for the other 12 hours of the day. Dr. Satchin Panda, Professor at the Salk Institute for Biological Studies, recommends upping that window to a 14-16 hour daily fast in order to maximize benefits, especially when it comes to improved muscular endurance.
12 hours might sound like a long time, but consider that on average, most of us get about 7-9 hours of sleep per night. If you eat a relatively early dinner and do a fasted workout first thing in the morning, you’ll most likely find it easy to hit that fasting window with minimal adjustments to your schedule. T
INCREASE FAT OXIDATION
Exercising in the fasted state forces the body to use its energy systems more efficiently, since carbohydrate stores are nearly depleted after a 12-16 hour fast.
Fasting also activates the body’s sympathetic nervous system (SNS) which is responsible for our fight-or-flight response. When the SNS is activated, heart rate increases, digestion slows, and muscle tension increases. During fasted exercise, the activation of the SNS causes an increased breakdown of fat for energy (Varady et al. 2013).
Fat oxidation also increases for 24 hours following a fasted workout (i.e. an easy aerobic exercise session done first-thing in the morning following an 8-12 hour overnight fast). Essentially, fasting helps your body become better at metabolizing fat rather than relying on the carbohydrates that are readily available in a non-fasted state.
DECREASE INSULIN RESISTANCE
Many endurance athletes will eat little meals or snacks every couple of hours (while awake) to give the body a continuous source of energy throughout the day. However, perpetual food intake also requires a constant release of insulin to help maintain stable blood sugar, which over time can cause the body stress. Worse, if insulin is constantly present in the bloodstream, the body can develop resistance, which is a precursor to diabetes.
Much like a muscle’s response to exercise stress, your digestive system needs time to recover so it can respond efficiently to the next stimulus. Fasting allows the body’s digestive, endocrine, and inflammatory system to repair and reset (Sutton et al., 2018).
While overnight fasting generally provides the body with sufficient time to rest, it is the challenge of a fasted morning workout that puts the body’s physiological systems (and subsequent endurance benefits) into overdrive. After completing a workout in a state of glycogen depletion, the body’s growth hormone and testosterone responses are stronger compared to athletes who fuel more constantly (Greenfield 2018).
How to Incorporate IF Into Your Training
Fasted exercise doesn’t need to be hard, in fact, most of the benefits of fasted exercise can be attained by performing a light, aerobic workout in a state of glycogen depletion. It could be a 30-minute walk or hike, an easy swim, or even just a sauna session — the key is to get moving and get your heart rate up for at least 20-30 minutes (Greenfield, 2018).
High-intensity interval training (HIIT) is much more difficult to perform while fasted. HIIT (>70% Max heart rate) requires the use of glycogen as a fuel source, and attempting a HIIT workout in a fasted state will likely result in poor performance due to low energy availability. However, the ability to perform high-intensity workouts in a fasted state seems to vary greatly among individuals, so talk to your coach before attempting such workouts.
It is also important to remember that refueling is paramount after a fasted morning workout — the body readily absorbs carbohydrates, fats, proteins, and micronutrients quickly and efficiently in the 1-2 hour window following fasted exercise. My favorite post-fasted workout meal is a big bowl of oatmeal, nuts, dried fruit, and whey protein powder.
How to Fast
Traditional fasting allows you to drink only water during the fast. That means no calories, flavoring, salt, sugar, etc. Fortunately, most experts agree that you can have your morning coffee without technically breaking your fast — just skip the cream and sugar (Panda, 2018).
Your success in intermittent fasting for endurance performance depends on finding an eating window that works for you. If you are a night owl, for example, try making your eating window 12PM-9PM – followed by a 15-hour fast. If you’re a morning person like me, try a 9AM-6PM window – which still makes for a 15-hour fast.
When it comes to IF, the most important thing about maintaining your daily fast is that it is consistent and sustainable. Try different windows, meals, and timing to see what works best for you.
Greenfield, Ben. 2018. The Benefits of Fasted Exercise.
Panda, Satchin. 2019. Circadian Fasting
Sutton, Elizabeth et al. 2018. “Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with Prediabetes.“ Cell Metabolism, Volume 27, Issue 6, 5 June 2018, Pages 1212-1221.e3
Varady, Krista A. et al. 2013. “Alternate day fasting for weight loss in normal weight and overweight subjects: a randomized controlled trial.” Nutrition Journal, 2013, 12:146