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Fat Adaptation for Endurance Performance

By Andre Obradovic and Peter Defty | July 19, 2016, 11:25 a.m. (ET)


As a marathoner I struggled for six years wondering why I could never lose the belly I had around my waist. I was following the prescribed low-fat, high-carb diet, running 70 kilometers a week and, at 48, doing a 3:45 marathon. Yet I was always hungry and had to get two massages a week for sore calves.

Then, two years ago, I attended a talk given by Dr. Stephen Phinney. While what Phinney said went completely against the conventional wisdom of sports nutrition and, admittedly, my own belief system, he mentioned Dr. Timothy Noakes had made a complete 180-degree reversal of his previous stance on nutrition and successfully corrected his progression of Type-2 diabetes. This struck me, as Noakes is a legend in sports science and was willing to say, “I was wrong.”  As my carbohydrate-centric approach was not working, I decided I would give a fat-fueled approach a try. I did my research and settled on a fat-adapted approach called OFM (Optimized Fat Metabolism), which is mentioned in Dr. Phinney & Dr. Volek’s book “The Art and Science of Low Carbohydrate Performance.”

Two years after making the change, I am a lean 141 pounds and have no inflammation that requires therapy. My oxidation has shifted from 65 percent of VO2 max to 85 percent of VO2 max, and my lactate threshold is now reached at 90 percent of Max HR instead of 72 percent when I was a carbivore. More importantly, my cholesterol values have improved with my HDL almost doubling and my triglycerides plummeting to a quarter of what they were in my high carb days.  

Now as a triathlon/marathon coach, I have seen my clients with the same fat-phobic belief system become fat adapted. They lose the weight, are less injured, more mentally and emotionally balanced and less stressed.  Just as important, they perform better not only in their sport but also in every aspect of their lives.

It seems Dr. Phil Maffetone and six-time IRONMAN World Champion Mark Allen were onto something decades ago as the concept of fat adaptation has made a resurgence. This time, however, it’s here to stay. Endurance athletes are not only winning and setting records on a fat-based approach, but now there is actual published science to support the real world results. As the saying goes, “what’s new is old.”

In March 2016, the first paper to come out of the FASTER Study (Volek was published in the journal "Metabolism." While early adopters did not wait for the science, the results now provide compelling reasons for endurance athletes to consider the shift toward fat as fuel. This may come as a shock to many of you because these results challenge the conventional wisdom of the last 40 years.

So what are the take-home points from “Metabolic characteristics of keto-adapted ultra-endurance runners”?

  • Peak fatty acid oxidation, in layman’s terms fat burning capacity, was 2.3 times higher in the LCD cohort at 1.54 grams/minute mean versus the HCD cohort with was 0.67 grams/min mean.


  • The current body of science suggests the upper end, which humans are capable of burning fat, being 1.0 gram/minute. The existing science suggests most well trained athletes will metabolize around 0.5 grams /minute … half a gram! Even the faster HCD cohort mean was 0.64 grams/minute.
  • The crossover point of maximum fat oxidation shifted from 60 to 70 percent of VO2 max (LCD cohort & established body of science to date) to 70 to 80 percent of VO2 max placing it right in the sweet spot for triathlon racing.
  • Post-exercise glycogen replenishment in the LCD cohort was similar to the HCD cohort post exercise even though the LCD cohort did not ingest a significant amount of exogenous carbohydrates before, during or after the tests.


Another paper, “Rethinking the role of fat oxidation: substrate utilization during high-intensity interval training in well-trained and recreationally trained runner,” (Hetlelid published online in August 2015, suggests the role fat oxidation plays at higher intensities than previously thought. The nuggets from this study include:

  • Well-trained runners oxidized nearly three times more fat than recreationally trained athletes during HIT.
  • The findings suggest that the capacity to oxidize fat at high exercise intensities is a supremely advantageous adaptation for endurance athletes.

While Maffetone’s development of the maximum aerobic function (MAF) test represented a game-changer in its day, it never received the credit it deserved for giving Allen that critical edge in performance. The fat-adaptation strategies in use today are much more robust models, which not only emphasize aerobic base training but training in higher zones specifically to increase fat adaptation at higher intensities — both of which are well established in endurance training. However, it is the sharply carbohydrate-restricted dietary shift that induces a key physiological shift in energy substrate utilization. Coupled with physical activity commensurate for triathlon training, this dietary shift creates a synergistic adaptation to tap into fat as fuel at levels previously not thought possible.

Current observation suggests once this shift is in place, the window of carbohydrate tolerance for most athletes is much wider than for a sedentary person adhering to a strict ketogenic diet and thus some level of carbohydrates can be strategically brought back into the diet and fueling for performance. This quantity is far less than the massive amounts of carbohydrates of a conventional diet for endurance athletes. While more research is needed, empirical observation suggests most triathletes will be seeing a 30 to 80 percent reduction in the calories necessary to fuel their training and racing, obtain consistently better performance and have a faster recovery.

It is important to note the LCD cohort from the FASTER Study trains and races by following the Optimized Fat Metabolism (OFM) program and not the strict ketogenic diet they were on during the data collection for FASTER. Ketosis is the foundation of OFM. While science is a wonderful tool, well-designed scientific studies control variables while the real world is a very different and dynamic environment.

Fat adaptation presents both challenges and tremendous opportunity. It is disruptive change at its finest. If you have been following the current dietary guidelines and they are not working for you, do you own research and seek help from health professionals who understand the benefits of a low-carb lifestyle.


Andre Obradovic is a USA Triathlon Level I Certified Coach, Triathlon Australia Development Coach, ICF ACC Leadership and Personal Coach, Certified Low Carb Healthy Fat Coach and Certified Personal Trainer. He is a passionate triathlete and marathoner in the 50-54 age group. He works with his wife who is studying to become a certified Nutritional Therapy Practitioner, by helping clients optimize their life.

Peter Defty has a B.S. in biology from the Plant Science University of California. He is a Davis General Manager at VESPA Power Products, a developer of VESPA's Optimized Fat Metabolism (OFM) program.  

Doctors Stephen Phinney, M.D., Ph.D., and Jeff Volek RD, Ph.D., two of the world's leading researchers in ketogenic diets, took notice and made a point to discuss Defty's work on Optimized Fat Metabolism (OFM) in "The Art & Science of Low Carbohydrate Performance" as well as use his pool of OFM athletes for research studies.

The views expressed in this article are the opinion of the author and not necessarily the practices of USA Triathlon. Before starting any new diet or exercise program, you should check with your physician and/or coach.