Fasting before a run may seem like a strategy to enhance fat burning and improve performance, but recent medical research suggests that fasting may also have detrimental effects on metabolism and performance. Fasting before a run can significantly decrease resting metabolic rate (RMR) by up to 10%. A 2021 study reported fasting before exercise depletes muscle glycogen stores by approximately 30-40%, leading to impaired endurance and performance during prolonged runs.
Drawing upon findings from recent medical journals, let's explore other impacts fasting can have on metabolism and performance.
Fasting has been shown to reduce resting metabolic rate (RMR), the number of calories your body burns at rest. A slowed metabolic rate can reduce overall energy expenditure across the day and potentially hinder weight management efforts.
Fasting shifts the body's fuel source from carbohydrates to fat, a process known as metabolic inflexibility. While this may seem beneficial for fat burning, it can impair the ability to utilise carbohydrates, which is essential for high-intensity exercise performance efficiently.
Fasting can disrupt hormone levels involved in metabolism, appetite regulation, and energy balance. For example, prolonged fasting may lead to increased production of cortisol, a stress hormone that can promote muscle breakdown and increase fat storage.
Fasting before exercise can deplete muscle glycogen stores, the primary fuel source for high-intensity exercise. Reduced glycogen supply can impair endurance, power, and overall performance during a run.
Fasting can delay recovery by limiting the availability of nutrients needed for muscle repair and glycogen replenishment. Lack of critical nutrients can prolong muscle soreness and fatigue and impair subsequent training sessions. This further impacts your motivation to train consistently and burn calories.
A slow metabolism is not good news for runners keen on losing weight. Our blog, Weight Loss for Athletes, may be helpful.
In conclusion, fasting before a run can slow metabolism, impair substrate utilisation, alter hormone levels, deplete muscle glycogen stores, and delay recovery, ultimately compromising athletic performance.
To optimise metabolism and performance, it's essential to fuel your body with a balanced meal or snack before exercise. In a previous post, we discussed some of our go-to recommendations for pre-run snacks.
At the Athlete Sanctuary, we offer comprehensive support for female endurance runners. As a degree-qualified online naturopath, nutritionist, and Olympic marathon runner, Kate Smyth brings a wealth of experience and expertise to help you achieve your goals. For personalised support and tailored meal plans, visit www.athletesanctuary.com.au.
Kate Smyth is a sports naturopath, nutritionist and female-centric running coach. She is the founder of the Athlete Sanctuary - a holistic healthcare clinic for athletes of all levels and sporting codes.
Kate has a thirst for knowledge, with two bachelor's and a master’s degree under her belt. She has been involved in sports for many decades and competed for Australia in the Commonwealth Games and Olympic Games marathons with a personal best time of 2 hours 28 minutes.
Kate certainly knows what it’s like to face challenges when pursuing a dream.
Kate faced many challenges and obstacles during her eight year journey from fun runner to Commonwealth and Olympic marathoner (2006, Commonwealth Games and 2008 Beijing Olympics). She obtained her personal best time of 2:28 for the marathon in Nagano, Japan at 35 years of age.
Kate believes there isn’t just one way to better health and performance. Her mission is to educate female athletes on how to make the most out of being a female athlete through a holistic and balanced approach.
On the back of her deep desire to help other athletes overcome many of the same health issues she now dedicates her time to improving female athletic performance and health.
Kate has completed three university degrees including a Masters and a Bachelor of Health Science (Naturopathic medicine). She has also undertaken additional training in thyroid health, sports nutrition, digestive health and female athlete hormones…. just in case you are wondering.
She coaches, mentors and facilitates training camps for aspiring runners including some of Australia’s best distance athletes.
Kate is also a celebrant supporting families through holding meaningful ceremonies for loved ones. She has a special interest in baby/ infant naming days and memorial services for infants, babies, stillborn babies and loss through miscarriages.
As an athlete, coach and business owner she understands what it can be like to juggle many priorities. She is described by her patients as compassionate, warm, grounded, realistic, practical, and knowledgeable.
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