For many endurance athletes, nutrition can be the make-or-break factor in performance. Too often, runners and ultra-endurance competitors are sidelined by gut distress, bonking, or the sheer stress of managing calorie intake during an event.

In this candid conversation with hosts Peter Defty and Tony Konvalin, athlete John Rutherford shares his personal journey from vegetarian/high carb, starting down OFM only to be distracted by the ‘science’ of keto into strict keto and eventually settling into the OFM Lifestyle — OFM not only transformed his racing, but his life.

When John and Peter first met in person at the 2010 Angeles Crest 100, John was a mostly vegetarian, high-carb athlete. He had started to use VESPA which solved most of his bonking and GI issues but Peter told him there was a lot more he could do to tap into his own onboard energy. After Angeles Crest and under Peter’s guidance, John started his OFM journey and the results were nothing short of amazing. This led to John being recruited to participate in the groundbreaking FASTER Study (Volek et. al.) which showed athletes who were well adapted to burning fat could burn significantly more fat than the previous ‘science’ suggested was possible and at intensities appropriate for elite level competition. John recorded the highest level of fat oxidation in the study at 1.78 grams per minute. 

The Limits of Strict Keto

But the problem with the FASTER Study was that it was touted as a keto-adapted study insinuating the athletes were following a low carb, high fat diet and fueling in alignment with the modern keto diet macros. With his exposure to Dr. Volek and the ‘science’ of keto John began following the keto diet. He describes those years as a dedicated keto athlete, meticulously counting carbs and keeping intake below 50 grams a day. While this reset helped him build a fat-adapted foundation, it came at a cost. The rigidity of the diet strained his family and social life and left him locked into a performance ceiling — he could go long, but lacked the ability to tap into higher intensities when needed. “I felt like I was running on diesel with no turbocharger,” John recalls.

Finding Freedom with OFM

Working with Peter and experimenting with the OFM concept of “Strategic Carbohydrates”, John found the performance he lacked on keto but also how OFM’s intuitive approach made eating and fueling intuitive. By combining fasted training, strategic use of carbs, Vespa, and micro-dosing ketone esters, he gained the metabolic capacity thus metabolic flexibility to race with confidence. He no longer needed to obsess over calories or fear gut issues. Instead, he could trust his body’s ability to burn fat as a primary fuel while knowing exactly when and how to introduce carbs for performance.

Racing Smarter, Not Harder

In his most recent races, John reports taking in far fewer calories than conventional guidelines suggest — and experiencing none of the bonking, bloating, or GI distress that plague many endurance athletes. A few gels at key moments, some real food like empanadas, and a steady supply of electrolytes and Vespa were all he needed to stay strong. “It was intuitive,” John explains. “Fueling wasn’t a stressor anymore — it just worked.”

The Science Behind the Shift

Peter emphasizes the importance of maintaining carbohydrate metabolic pathways alongside fat adaptation. Staying too strict with keto for too long can downregulate pyruvate dehydrogenase (PDH), the enzyme critical for effectively burning glucose when performance demands spike. In contrast, OFM’s approach uses carbs strategically to maintain the PDH pathway to yield that “turbo boost” in performance to complement fat metabolism, driving both metabolic capacity and performance.

A Sustainable Path Forward

John’s story is more than just a personal experiment — it’s a roadmap for athletes seeking freedom from rigid diets and unreliable fueling strategies. His evolution shows how OFM integrates metabolic health, performance, and sustainability. The result? Greater confidence, less stress, and a body primed to perform across all intensities.

Most of all John’s 15 year history of using VESPA and burning fat as the principle energy substrate show how sustainable OFM is while slowing the aging process to a crawl.

📌 Conclusion

 John Rutherford’s journey underscores the essence of OFM: building a fat-adapted foundation, then building metabolic capacity to maintain the metabolic flexibility to push performance when it matters most. By moving beyond strict keto, he unlocked a more sustainable, enjoyable, and effective way to race and live. Like so many of the athletes we’ve helped, John’s experience is proof that OFM works.

🎥 Watch the full conversation HERE and learn how you can apply these principles to your own training and racing.