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Fat Adapted.
5 Marathons.
In 5 Days. Fasted.

Fuelled by Fat: Five Marathons in Five Days, No Carbs Needed — Showing you how you can enjoy the benefits of fat adaptation in your every day life.

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The Objective

It is a common belief that ‘carbohydrate loading’ is required for endurance activity to ensure sufficient fuel stores. This challenge is to demonstrate that the human body adapted to a ketogenic lifestyle is adequately fuelled on fat and does not require the intake of any carbohydrates (carbs) as a fuel source whatsoever.

The objective is to complete five marathons over a consecutive five day period without consuming any calories. The total distanced covered will be 211km.

A critical requirement will be that the body is functioning in a ketogenic state and is thus ‘fat adapted’. Prior to commencing the challenge it is essential to have maintained a consistent ketogenic lifestyle in order to allow for a metabolic shift from carbohydrate to fat metabolism.

This endeavour may seem extreme in today’s society however it is evolutionarily consistent with how the human body evolved to function. For millions of  years, our ancestors did not hunt on a full stomach. Hunger drove them to move and hunt.

The intention is to demonstrate that exercising in a fasted state is safe and effective provided the body is fuelled appropriately. The benefits of being fat adapted and limiting carbohydrates extend far beyond any one endurance feat and is in fact key to unlock a universal improvement in health for everyone.

This is NOT an exercise in starvation nor a demonstration that calories are not essential. The focus is entirely on highlighting the energy availability and associated physical capability of the human body when fuelled appropriately on fat and in the absence of carbohydrates.

Not a Doctor.
Not a Dietician.
Not an Elite Athlete.
Just Following the Science.

About Me

I’m Alex, 42 and have embraced a low carb high fat (LCHF) lifestyle since January 2010. Initially, I planned a one-month test of low carb and expected to return to my original diet afterward. Yet, the drastic improvements in my well-being during that first month were so compelling that returning became impossible.

For over a decade, I’ve delved deep into the research underpinning low carbohydrate and ketogenic diets, including the completion Sports Nutrition and LCHF Advisor Training through the Nutrition Network and attendance at several global LCHF conferences. The benefits extended not only to me but also to friends and family who adopted LCHF and experienced the benefits in weight loss, increased energy and much more. Although I briefly engaged in running during my late twenties and completed 3 half marathons, more than a decade has passed without participating in long-distance events. My focus shifted to calisthenics and resistance training, but now I’m poised to embark on my first marathon, marking a fresh and exhilarating challenge.

Ensuring Safe Challenge Completion

Medical support and supervision from experts in the fields of low carb nutrition, sport and exercise have played an essential role in ensuring that this challenge is achievable and will be done so safely.

Dr Paul Mason

Dr. Paul Mason is a Fellowship trained Sports and Exercise Medicine Physician, holding a Bachelor of Medicine, Bachelor of Surgery (MBBS) (Honours) (USYD)..., Bachelor of Physiotherapy (LTU) and Masters of Occupational Health (LTU). Renowned internationally, he's a leading authority in low carbohydrate diets, shaped by years of patient care and lectures. His commitment to evidence-based practice fuels his challenge of medical orthodoxy when warranted, while his holistic approach, informed by evidence rather than convention, addresses conditions from metabolic diseases to inflammatory pain. Dr. Mason's clientele include elite athletes in the AFL, NRL, A-League, and Olympic teams, all benefiting from his comprehensive approach that optimizes function and performance.

Dr Alex Petrushevski

Dr Alex Petrushevski graduated from the University of Tasmania in 2008, attaining Honours in the MBBS. He has worked in various teaching hospitals in 2 states..., including working for several years within Sydney Cancer services, and had his research published in an International journal during this time. His postgraduate qualifications include the Fellowship of the College of General Practitioners and the Diploma of Child Health from Sydney University. He currently works in general practice in addition to practising within Sydney Low Carb Specialists. He is passionate about preventative health, improving the lifestyle of his patients and treating chronic diseases without medication if possible. Having seen the immense benefits low carbohydrate nutrition has provided for many of his patients in general practice he is keen to share this exciting cutting edge medical therapy with more patients in our clinic. Alex is a foundation member of the Society of Metabolic Health Practitioners and has done further nutrition training through the Nutrition Network. He is also a member of Low Carb Down Under, and has presented several times at Low Carb Down Under conferences.

Dr Jessica Turton

Jessica is the Director of Ellipse Health and holds a PhD in nutrition awarded by the Faculty of Medicine and Health at the University of Sydney....Her thesis investigated the use and efficacy of low-carbohydrate diets for diabetes management, with a specific focus on type 1 diabetes. Dr Turton conducted a clinical trial in collaboration with the CSIRO using a fully online delivery model which enabled Australia-wide participation. The aim of the study was to assess the safety and effect(s) of a nutritionally adequate low-carbohydrate diet on type 1 diabetes management outcomes. The trial was completed successfully in 2022 and the results are expected to be published in 2023. Jessica has co-authored several research articles in leading scientific journals, including "An Evidence-based Approach to Developing Low-carbohydrate Diets in Type 2 Diabetes: A Systematic Review" in Diabetes, Obesity and Metabolism (read it here). Jessica was invited to speak at the American Diabetes Associated Conference in June 2020 to present the evidence for low-carbohydrate diets and nutritional ketosis in the treatment of diabetes and obesity. Jessica has a passion for working with individuals to identify the primary nutritional problems affecting their health and preventing them from reaching their goals.

Dr Ian Lake

Dr. Ian Lake is a General Practitioner over 37 years of experience and holds degrees in Medical Cell Biology and Biochemistry. As a type 1 diabetic... Dr Lake is a strong advocate for sharing the benefits of low carbohydrate lifestyles and their effectiveness in diabetes management. Dr Lake is a founding member of The Public Health Collaboration (PHC) and is a medical advisor for Type 1 diabetes at the European Keto Live Center in Burghausen, Germany. Dr. Lake's initiatives include leading the Zero Five 100 challenge, where a group, including Olympic athlete James Cracknell, completed a 100-mile journey over five days fuelled solely by stored body fat. This project underscores his dedication to pioneering research at the intersection of diabetes management, endurance, and innovative low carbohydrate medical approaches.

Shaun Waso

In 1997, Sean Waso entered into the Comrades Marathon, a gruelling 90km ultra-marathon in South Africa, in an attempt to lose weight....Despite 9 months of intensive training he remained overweight. Years later, inspired by Prof Tim Noakes' book ‘Challenging Beliefs’, he tackled his potential insulin resistance by cutting carbs. In four years, Sean lost 24kg, normalized his BMI to 23, and regained energy. In 2022, Sean and Sam Bell led a group of volunteers in the Fasted Fat Fuelled Freedom Run, covering 160 km over five days in a fasted state from Vredenburg to Cape Town. In recent years, Shaun has ventured into the realm of health and wellness, discovering a profound interest in helping others achieve a healthier lifestyle. In pursuit of this passion, he has developed a bespoke online therapeutic carbohydrate restriction program, which has proven to be a game-changer for individuals seeking to transform their lives through dietary changes. He writes regularly about the subject in his blog

Sean Sakinofsky

Sean Sakinofsky is a trailblazer in the world of endurance cycling. Far from the ordinary, Sean's journey has been defined by pushing boundaries and defying conventions.... What sets him apart is not just his remarkable physical feats, but his unwavering commitment to unveiling the truth about our health. Following the loss of his father to oesophageal cancer and faced with a familial history of cancer and heart ailments, Sean’s journey led him to recognize the impact of diet on our health. He recognised the unsettling role of sugar in promoting disease and realized the processed food industry's role in fostering sugar addiction. Sean's mission? To challenge the notion that carbohydrates are essential for physical performance. In 2020, he embarked on ground breaking endurance rides that defied conventional sports science. Multiple times he has achieved levels of performance beyond his Functional Threshold Power (FTP) for over 5 hours without hypoglycaemia, and relying solely on salt and water. A true advocate of the Low Carb High Fat (LCHF) lifestyle, Sean serves as a beacon of inspiration, encouraging others to think innovatively about health.

The 5 Marathons

The first marathon will commence the morning of Wednesday 13 September and an additional marathon will be completed each day until the 5th and final marathon on Sunday 17th September.

The venue for the first 4 marathons combines both the Sydney International Regatta Centre and a loop around the Nepean River in Penrith NSW Australia. One lap of this route equates to 21.1km hence this course will be completed twice each day.

The final marathon 5 will be the official Sydney Marathon to be held on 17 September 2023. Details can be found here.

Fasting will commence the evening of Tuesday 12 September and will continue until the completion of the 5th and final marathon on Sunday 17 September. Consumption during the 5 day fast will only consist of water and mineral supplementation (sodium, magnesium and potassium). As a result, the marathons will be completed in a fasted state and without any caloric intake for the 5 days. Existing body fat will be the primary source of fuel.

How much energy is required to run 5 Marathons?

At a steady pace of 7 minutes per km (8.4km/h), the caloric requirement per 42.2km marathon is approximately 3,300 Calories (calculated here) Thus the caloric requirement for 5 marathons is roughly 16,500 Calories (which is approximately 16-20 % of available energy stores). A slower pace will reduce this caloric requirement. Approximately 25,000 Calories will be expended during the 5 day fast once the baseline daily energy expenditure is included.

Strava map of marathons 1-4
Sydney Marathon Course Map

Marathon Strategy

Whilst it is tempting to simply run as fast as possible, the chosen strategy is to ignore pace and instead concentrate on heart rate for the duration of each marathon. The goal whilst running is to ensure that average heart rate is maintained at 140 bpm. This would equate to a ‘zone 2’ level of effort which is deemed to be most efficient for ‘fat burning’.

Here is an example of heart rate during a training run:


An essential requirement to be able to complete this challenge is to become ‘fat adapted’ and conditioned to burning fat as a fuel. Alex has been adhering to a low carbohydrate high fat (LCHF) / ketogenic diet for more than 13 years and has thus been fat adapted for significant period of time. Advice from both a qualified dietician and a team of medical doctors has ensured an optimised ketogenic diet was followed.

A number of periods of 3-4 day fasts have formed part of the preparation. Fasting in conjunction with a ketogenic diet comes very naturally due to the huge level of satiety obtained from the combination of nutrient dense animal sourced foods, their high fat content and a metabolism that recognises that the body is already carrying vast amounts of stored energy. The mental effort required to maintain a prolonged fast whilst ketogenic is thus minimal.

Every training run prior to this challenge has been completed in a fasted state.
It is critical that adequate hydration is maintained for the entire 5 day challenge. Hydration requires both adequate electrolyte replenishment and, of course, water. The strategy will be to drink to thirst (and not over hydrate) and to consume between 4-6tsp of mineral salt each day.

Finally, the importance of sleep is often overlooked. The goal is for 9-11 hours’ sleep per night during the challenge to maximise recovery between marathons.


Throughout the challenge, the following measurements will be taken at least twice daily.

  • Blood Glucose (via Continuous Glucose Monitor)
  • Blood Ketones
  • Urine concentrations (via Vivoo strip) of:
    Ketones, Protein, pH, Hydration, Calcium, Magnesium, Sodium & Vitamin C
  • Weight
  • Hunger
  • Mood


Blood tests and Dexa scans will be conducted to compare full body composition and metabolic markers before and after the challenge.

Frequently Asked Questions (FAQs)

How far will you be running?

The goal is to complete 5 marathons over 5 days. Each marathon is 42.2km (26.2 miles) which will equate to a total distance of 211km (131.12 miles).

The objective is to demonstrate the vast stores of energy that are accessible for a fat adapted individual adhering to a ketogenic lifestyle. By not ingesting any calories for the entire 5 days, it removes any possibility that my energy is being obtained from an external fuel source.

Yes. In fact, I have enough energy stored as body fat to complete over 22 marathons. In order to complete this challenge, I will only require 25% of my available energy.

There are 9 Calories for each gram of fat. At a weight of 75kg and a body fat percentage of 15% I am carrying approximately 11.25kg of body fat. This equates to over 100,000 Calories of stored energy!

At a steady pace of 7 minutes per km (8.4km/h), the caloric requirement per 42.2km marathon is approximately 3,300 Calories. (calculated here) Thus the caloric requirement for 5 marathons is roughly 16,500 Calories (which is approximately 16-20% of available energy stores). If we allow an additional 2,000 Calories per day for baseline daily energy expenditure it is estimated that 25,000 Calories will be expended during the 5 days.



“It has been estimated that adipose tissue stores alone could supply sufficient energy for nearly 4 days of running [96 hours], compared to less than 2 hours using only muscle glycogen stores”

Professor Tim Noakes, Nutrition Network

The body stores energy in two main forms – glucose and fat. Glucose is stored in the body in the form of glycogen and has the capacity to provide approximately 2,000 calories of energy at any given time. In contrast, energy stored in the form of fat is significantly larger.

In my case, weighing 75kg with a body fat percentage of 15% I will have more than 100,000 calories of stored energy (that is 50 times more than my glycogen store!).

Theoretically, I have enough energy stored on my body to complete over 22 marathons.

My Fat Fuel Tank is 50 Times Larger Than My Carbohydrate Fuel Tank:


Ensuring adequate recovery between each marathon will play an important role for success. Hydration and the replenishment of electrolytes are a critical component. Salt will be consumed in both tablet form and as a mixture in water. Medical advice suggests targeting 4-6 teaspoons of salt in addition to some magnesium and potassium supplementation.

Sleep will play a vital role in allowing time for my body to restore and prepare for the next marathon. At least 9 hours of sleep will be attained each evening.

The anti-inflammatory nature of the ketogenic diet and the fasting element of this challenge should assist in speeding up recovery and minimise muscle soreness. Personal experience attests to very minimal (if any) muscle soreness in all of my training for these marathons.

 “A high-fat diet is superior to a high-carb diet. One of the benefits is that it helps you recover faster”

Dave Scott – Ironman Hall of Fame inductee and 6 time Hawaii Ironman Triathlon Champion. Twitter July 20th 2016

This is NOT an exercise in starvation nor a demonstration that calories are not essential.

The focus is entirely on highlighting the energy availability and associated physical capability of the human body when fuelled appropriately on fat and in the absence of carbohydrates.

Unlock 50x More Stored Energy

Since the 1960s, we’ve been told that carbohydrates are a vital source of energy, and pre-endurance event carb loading is a necessity. Consequently, strategies were developed to optimize performance through the use of carbohydrates and supplements for refuelling. All this research is founded on the assumption of a ‘carbohydrate metabolism’. However, this presumption has overshadowed an alternative approach. For athletes who are ‘fat adapted,’ the conventional rules of carbohydrate consumption no longer hold true. So, how does one transition to a state of fat adaptation? The answer lies in adopting a ketogenic diet.

The ketogenic diet involves consuming high fat, moderate protein, and severely restricting carbohydrates for a few weeks. This shift in eating patterns prompts the body to prioritize fat metabolism, unlocking the vast energy reserves stored in adipose tissue. Unlike the limited glycogen stores of around 2,000 calories, even lean individuals possess tens of thousands of calories stored as fat.

Fat-adapted athletes can tap into this virtually boundless source of energy, bypassing the “wall” and enjoying sustained performance during endurance events. This approach not only challenges traditional thinking but also demonstrates the body’s remarkable capacity to thrive on fat-derived energy, offering a new perspective on optimizing athletic performance.

“I am looking forward to following Alex in his attempt to run 5 marathons in 5 days. There is plenty of evidence to support his theory that it is possible to do this on a low carb healthy fat nutrition program and I look forward to his success in providing further evidence.”


Running in their Footsteps: Learning from the Pros

I am very grateful for the work of those that have carved a path for me to follow and appreciate their advice in planning my own version.


Zero Five 100

In September 2020, Dr Ian Lake lead a team of 8 participants to complete 100 miles (160km) over 5 consecutive days running on nothing but water. This is the equivalent of 4 marathons over this period. All 8 participants not only successfully completed the challenge but also reported “improved mood, mental clarity and focus” and “all participants maintained high levels energy”.


Fasted Fat Fuelled Freedom Run

In April 2021 a group of runners lead by Shaun Waso and Sam Bell completed 160km in 5 days from Vredenburg to Cape Town in South Africa. All participants were running in a fasted state for the entire event and consumed only water, black tea, black coffee with some mineral supplementation (sodium, magnesium).

Learn the Keto Basics

The focus is entirely on highlighting the energy availability and associated physical capability of the human body when fuelled appropriately on fat and in the absence of carbohydrates.