Uploaded November 2023 | Updated September 2026, 1 hour ago
Alex McDonald is just an ordinary guy. He’s not an elite athlete, he’s not a doctor, he’s just following the science.
Alex has gone deep into the science behind ketogenic diets and has followed this way of life eating a low carb and now carnivore diet for more than a decade.
He set out to prove the power of fat adaptation by completing a challenge no one has ever done before, running 5 marathons in 5 days, all completely fasted.
Alex’s final meal was on the eve of the first marathon and he didn’t eat again till day 5 after the fifth marathon. He only drank water and consumed salt.
He tracked every data point from calories used to his glucose levels, his ketones, he completed a full blood panel before and after as well as a full body scan before and after the challenge.
This is hard data! Alex has proved that we have a huge amount of energy stored on our bodies in the form of body fat - around 100,000 calories, which is way more energy than you need for 5 marathons over 5 days. Whereas we can only store about 2,000 calories in the form of glucose.
Listen to Alex share his incredible story. Hopefully this inspires others to prioritise their health, become fat adapted and start getting more out of life.
You can follow Alex on Instagram @ketomarathons and learn more about his story on his website ketomarathons.com
Alex McDonald is just an ordinary guy. He’s not an elite athlete, he’s not a doctor, he’s just following the science.
Alex has gone deep into the science behind ketogenic diets and has followed this way of life eating a low carb and now carnivore diet for more than a decade.
He set out to prove the power of fat adaptation by completing a challenge no one has ever done before, running 5 marathons in 5 days, all completely fasted.
Alex’s final meal was on the eve of the first marathon and he didn’t eat again till day 5 after the fifth marathon. He only drank water and consumed salt.
He tracked every data point from calories used to his glucose levels, his ketones, he completed a full blood panel before and after as well as a full body scan before and after the challenge.
This is hard data! Alex has proved that we have a huge amount of energy stored on our bodies in the form of body fat - around 100,000 calories, which is way more energy than you need for 5 marathons over 5 days. Whereas we can only store about 2,000 calories in the form of glucose.
Listen to Alex share his incredible story. Hopefully this inspires others to prioritise their health, become fat adapted and start getting more out of life.
You can follow Alex on Instagram @ketomarathons and learn more about his story on his website ketomarathons.com
