# Ultra-Marathon and Carnivore Diet: Dr. Anthony Chaffee Interviews Justin Boyle, Winner Without Sweet Energy Gels
*By Laurent Glatz – for Athletic Carnivore*
**Running 160 kilometers without consuming sweet energy gels, then winning ultra-endurance competitions: is this truly compatible with a carnivore diet?** This is exactly what Justin Boyle explains in an interview with Dr. Anthony Chaffee. His experience challenges a widely held belief in sports: that to sustain prolonged effort, one must regularly consume carbohydrates.
Dr. Anthony Chaffee: Physician, Former Rugby Player, and Carnivore Approach Specialist
Dr. Anthony Chaffee is an American physician practicing in Australia, known for his work popularizing the carnivore diet and human metabolism.
After studying molecular and cellular biology, he earned his medical degree from the Royal College of Surgeons in Ireland. A former professional rugby player, he has been interested for over twenty years in the relationships between diet, metabolic health, and athletic performance.
He hosts the podcast *The Plant Free MD*, where he interviews doctors, researchers, and athletes to examine the effects of a primarily or exclusively animal-based diet.
This time, his guest is **Justin Boyle, known as Ultra Carnivore**, an American runner whose journey deserves close attention.
Justin Boyle: From Beginner to Ultra-Marathon Winner
In May 2023, Justin Boyle adopted a carnivore diet. Interestingly, he was not yet seriously running at that time.
He started modestly with 5-kilometer runs, gradually increasing his distances. Within a few years, he completed three 100-mile races, each approximately 161 kilometers.
In one of his first races at this distance, he finished 100 miles in 24 hours.
But what’s most remarkable is that he didn’t just finish these races.
On June 27, 2026, Justin Boyle won the **Toxic Trail 37** in Florida, covering nearly 60 kilometers in 6 hours, 44 minutes, and 3 seconds.
His nutritional strategy during this competition? According to his testimony, a few pieces of bacon and butter. No conventional carbohydrate refueling.
He also recounts winning a 12-hour race after accelerating in the final kilometers to catch and surpass his main rival.
These performances raise a question: how does his body sustain such efforts with such a low carbohydrate intake?
The Famous Marathon Wall: An Inevitable Barrier?
During the interview, Dr. Chaffee asks Justin Boyle about a well-known phenomenon among runners: the *marathon wall*, that sudden feeling of energy depletion after several hours of effort.
Justin’s answer is particularly insightful.
He explains that he has never truly experienced this sudden energy crash. Of course, his legs get tired, muscles ache, and the kilometers weigh on him. But he describes a relatively steady energy availability.
**He clearly distinguishes muscle fatigue from a lack of fuel.**
Dr. Chaffee connects this observation to a fundamental physiological mechanism: adaptation to fat utilization.
Our bodies store a limited amount of glycogen in the liver and muscles. In contrast, even a relatively lean person has fat reserves representing tens of thousands of kilocalories.
With a sustained low-carbohydrate diet, muscles can develop an increased capacity to oxidize fatty acids during exercise.
The liver can also produce ketone bodies and generate glucose through gluconeogenesis.
This doesn’t eliminate all glucose needs nor the potential benefits of carbohydrates for certain intense efforts. But it helps explain how an adapted athlete can sustain prolonged activity without constantly relying on sugary refueling.
Could the Real Advantage Also Lie in Digestion?
This is probably one of the most revealing parts of the interview.
Justin Boyle does not claim to be faster than all carbohydrate-consuming runners.
He rather highlights another advantage: **not having to eat continuously during a competition.**
Ultra-endurance races can cause nausea, abdominal pain, diarrhea, or difficulties absorbing refueling foods.
For Justin, being able to run for several hours with very little food, without these discomforts, represents a practical advantage.
Performance depends not only on the amount of available energy but also on digestion, food tolerance, muscle capacity, and recovery.
By drastically reducing intake during races, Justin greatly simplifies his refueling strategy.
However, this is his personal experience and not a guarantee that all carnivore athletes will enjoy the same digestive comfort.
What This Interview Brings to Athletic Carnivore
The value of this interview is not just in the victory of an athlete following a carnivore diet.
It highlights **the difference between consuming energy and being able to efficiently mobilize one’s own reserves.**
Justin Boyle does not scientifically prove that the carnivore diet is superior to all other nutritional strategies. However, his results concretely illustrate that excellent endurance performance can be achieved without significant carbohydrate consumption.
This is a crucial distinction.
For Athletic Carnivore, this experience reinforces the interest in studying metabolic flexibility, fat adaptation, and individual responses to diet.
Two athletes may have comparable energy reserves but not exploit them the same way. Their dietary history, training, sleep, and recovery also influence performance.
The carnivore diet can be an interesting approach for some athletes, but its effectiveness depends notably on metabolic adaptation and the nature of the efforts practiced.
The real question is not to copy Justin Boyle’s diet but to understand how your own body functions.
**Because having thousands of calories in reserve does not necessarily mean knowing how to use them effectively in all situations.**
At Athletic Carnivore, this individual metabolic terrain reading is precisely what we seek to deepen through our analyses and personalized reports.
[**Discover Athletic Carnivore Analyses**](https://athleticcarnivore.fr/)
**And you, does your exercise fatigue really come from a lack of energy, or from how your body uses its different fuels?**
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**Sources:** Interview of Justin Boyle by Dr. Anthony Chaffee, *The Plant Free MD*; [Official results of Toxic Trail 37, June 27, 2026](https://ultrasignup.com/m_results_event.aspx?did=134585); [Dr. Anthony Chaffee’s profile](https://dranthonychaffee.com/about).
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