211 km Without Eating: What Five Fasting Marathons Reveal About the Carnivore Diet

# 211 Kilometers Without Eating: What Five Fasting Marathons Reveal About the Carnivore Diet

*By Laurent Glatz – for Athletic Carnivore*

**Is it possible to run five marathons in five days without consuming a single calorie?** Conventional sports nutrition wisdom places carbohydrates at the center of endurance runners’ diets. Yet, in September 2023, a 42-year-old Australian named Alex McDonald undertook an experiment that challenges our understanding of human metabolism.

Who is Alex McDonald?

Alex McDonald is neither a doctor, dietitian, nor former professional athlete. He is a Chartered Accountant (CA ANZ), director of a private family office, and a board member of the Australasian Metabolic Health Society (AMHS), an Australian organization dedicated to metabolic health.

Since January 2010, he has been interested in low-carbohydrate diets. His journey gradually evolved from paleo to ketogenic, and then to a carnivore diet.

He has completed training in sports nutrition and low-carb diets through Nutrition Network, while personally deepening his knowledge over more than a decade.

In 2023, he decided to put his convictions to the test with a physically demanding challenge.

Five Marathons, Five Days of Fasting, and 211 Kilometers

From September 13 to 17, 2023, Alex McDonald ran the equivalent of five marathons—**211 kilometers—without eating any food**. His intake during the challenge was limited to water and electrolytes.

This challenge was not improvised. He prepared for seven months, completing 77 fasted training sessions covering approximately 700 kilometers, under medical supervision including sports physician Paul Mason.

Before the challenge, his diet consisted almost exclusively of beef, lamb, pork, poultry, fish, seafood, eggs, and some dairy products.

The results he presented in his conference are particularly insightful. Despite five days of fasting and several dozen hours of exertion, his blood glucose mostly remained between 4 and 6 mmol/L, while his ketone bodies rose up to 4.3 mmol/L.

He completed the five marathons without experiencing the notorious “energy wall.” However, he did suffer exercise-related injuries, joint pain, significant inflammation, and an episode of overhydration.

**His body still had energy available, but his musculoskeletal system had reached its limits.**

What This Experience Teaches Us About Fats

The core of his demonstration rests on a biological mechanism: **adaptation to using fats as fuel**, known as *fat adaptation*.

Our bodies store energy in several forms. Glycogen, stored mainly in muscles and liver, represents a relatively limited reserve. In contrast, adipose tissue contains tens of thousands of kilocalories, even in lean individuals.

Alex McDonald estimated he had about 100,000 kilocalories stored in fat reserves, while his glycogen stores represented roughly 2,000 kilocalories.

When a person reduces carbohydrates long-term, their body can increase its capacity to oxidize fatty acids. The liver also produces ketone bodies, while gluconeogenesis generates the glucose necessary for certain physiological functions.

This does not mean carbohydrates cannot enhance some performances, especially at high intensity. However, it demonstrates that **continuous carbohydrate intake is not essential to sustain all prolonged efforts**, particularly when the body is adapted and the intensity remains compatible with significant fat utilization.

What Does This Have to Do with the Carnivore Diet?

This is where the experience becomes especially relevant for Athletic Carnivore.

Alex McDonald did not merely abstain from carbohydrates for five days. He had previously built a long-term metabolic adaptation by eating primarily animal-based foods.

The carnivore diet can promote this adaptation by drastically reducing carbohydrate intake while providing proteins, fats, and micronutrients.

His experience highlights a fundamental distinction: **having energy reserves and being able to mobilize them efficiently are two different things.**

However, it does not prove that everyone should become carnivore, nor that a carnivore diet is inherently superior for every sport. This is a documented individual case, not a comparative clinical trial.

The ability to use fats also depends on training, dietary history, metabolic health, and exercise intensity.

What If the Real Challenge Is Your Metabolic Flexibility?

The question raised by this conference goes far beyond running.

Why do some people easily tolerate several hours without eating, while others quickly experience energy drops, cravings, or concentration difficulties?

Why does carbohydrate reduction bring stability to some but fatigue or decreased performance to others?

These differences cannot be explained by a single variable.

Alex McDonald’s experience reminds us that our metabolism has significant adaptive capacity, but its expression depends on individual context.

At Athletic Carnivore, this distinction is precisely what interests us: understanding how diet, physical activity, and metabolic adaptation interact in each individual.

**Before copying someone else’s diet or performance, you must understand your own physiology.**

Discover premium analyses and reports at [Athletic Carnivore](https://athleticcarnivore.fr/).

And you, does your body truly lack energy, or do you still struggle to efficiently mobilize the energy it already has?

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**Sources:** Alex McDonald’s conference, *Keto Marathons* (ketomarathons.com), official biography of the Australasian Metabolic Health Society (amhs.org.au).

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