Fat Adaptation: The Emerging Science from FASTER

Like the Bob Dylan song, there is a “change is coming on” in sports physiology. A small but growing group of Ultrarunners & Triathletes have been actively pursuing a fat-adapted approach with success, including some of the elite athletes, most notably ultra-runners Zach Bitter, Jon Olsen, Jenny Capel and Nikki Kimball along with triathletes Triathetes Amanda Stevens, Rodrigo Gonzales, Nell Stephenson and Jess Anderson. Fat adaptation involves sharp carbohydrate restriction in conjunction with a complementing increase in fat consumption (with many of those fats being saturated fats) to induce the physiological shift necessary for the body to “switch” to burning “fat as fuel” at much higher rates. The various terms for this can be “Ketosis”, “Keto-adapted”, “fat-adapted”, “Nutritional Ketosis”. In conjunction with the dietary shift specific training, both in low and high intensity is programmed into the training blocks to push the fat burning envelope into higher intensity levels.

Observationally, athletes following this approach have been able to complete ultra-endurance races on a fraction of the caloric intake normally necessary, many athletes report completing 100 Mile runs or sub-10 hour IM Triathlon on 600-2000 calories. Unfortunately, there is scant science to support the plausibility of such a dramatic drop in consumption. That is, until now. In 2013 Dr. Jeff Volek RD/PhD, his graduate students and colleagues commenced data collection for the FASTER Study (FASTER=Fat-Adapted-Substrate oxidation in-Trained-Elite-Runners) to look at the physiological differences between elite male ultra-marathon runners with one cohort following a conventional high carbohydrate diet and the other following a low carb/fat-adapted strategy.

On November 2, 2015 the first paper from FASTER submitted for Peer-review publication in the Journal “Metabolism” was approved for publication. This ground-breaking study used two cohorts of ultrarunners (runners who regularly compete and train in events beyond the marathon distance of 26.2 miles).  From the chart below  these two cohorts, High Carb Conventional Diet & Low Carb Fat-Adapted Diet, were very well matched. 

The chart below represents the macronutrient profile of the two cohorts. As you can see from the pie charts the conventional diet follows what most athletes are advised to consume while the Low-Carb cohort has a very high fat intake. Keep in mind this is as a percentage of calories and because fats are over twice as much caloric density and very satiating when fat is consumed in a carbohydrate restricted diet an athlete simply does not eat much and tends not to overeat so the idea many people imagine of a high fat diet does not fit the reality of how it is practiced daily.

Now since virtually everyone reading this article is doing so for their athletic performance and health it is important to note virtually all of the LCD athletes follow the OFM protocol so do cycle in concentrated forms of carbohydrates “strategically” and use the supplement, VESPA, for their races and high intensity blocks of training, however, to control variables for the study, their diet was restricted to a Low-Carb/NK protocol. FASTER is a very robust study and includes muscle biopsies, a very thorough blood panel, urine and cheek cell analysis etc. At the time of this writing Dr. Volek and his team are analyzing data and writing up their papers, and some of these papers are probably already going through the peer-review process prior to submission for publication. This being said, a few basic and key markers have emerged from the data. Here are a few highlights: Fat utilization: The current science says the absolute maximum amount of fat an athlete can burn is upwards of 1.0 grams/minute with most highly trained athletes falling into the 0-45-0.75 grams/minute range (Venables et.al.; “Determinants of fat oxidation during exercise in healthy men and women: a cross-sectional study”), .41 grams/minute in moderate performance athletes and .27 grams/minute in low performance athletes (Lima-Silva et. al.; “Relationship between training status and maximal fat oxidation rate”). The chart below depicts the data taken from the Venables study.

  Above Chart from Venables et.al.;“Determinants of fat oxidation during exercise in healthy men and women: a cross-sectional study” FASTER: The chart below from FASTER shows the data points of the two cohorts. As you can see the high carb cohort fat oxidation rate data is consistent with the Venables data, thus is consistent with the existing body of science. Examining the data points between the two charts it is evident the HCD cohort of FASTER were actually on the upper level of conventional fat oxidation capability (0.67 gm/min. On the other hand the low-carb/fat-adapted cohort was on a completely different level. The mean fatty acid oxidation rate was OVER twice the rate of the high carbohydrate cohort (1.54 gm/min vs. 0.67 gm/min). The lowest rate of fat oxidation in a LCD subject was 1.1 grams/minute which is higher than what the current published literature suggests is possible with one subject actually recording a rate of 1.8 grams /minute of fatty acid oxidation!

FASTER data on fatty acid oxidation rate The Crossover Point:  The Crossover Point Hypothesis was developed and studied by George Brooks et.al. at UC Berkeley and it basically measured where an athlete would “Cross-over” from burning primarily fat to primarily carbohydrates for exercise. This investigation established that athletes, depending upon level of aerobic training, “crossover” between 35-65% of their VO2Max. In real world terms it defined that fat was only relegated to low and mid-level intensity of exercise and did not play a role at higher aerobic intensities as seen here:

FASTER not only challenges the intensity level but coupled with the increased rate of oxidation yields a completely new paradigm for re-thinking how an athlete should approach their aerobic training for energy substrate utilization:

As you can see from the graph, the high-carb cohort data falls consistently in line with the current published literature, but, with the low-carb cohort, not only does the fat utilization shift into the realm of higher aerobic intensity (the realm which is regarded as the “sweet spot” for endurance athlete performance) it does so at a much higher rate of fat utilization. The final chart depicts the mean fuel partitioning of the subjects over a 3 hour submaximal treadmill run at 65% of VO2Max. While both cohorts were burning more fat than carbohydrates by the end of the 3 hours, the low-carb subjects are burning approximately 30% more fat and, consequently 30% less carbohydrate than the high-carb subject. Some of the LCD subjects actually reported their data showed them burning 98% fat and 2% CHO at 65% effort on this portion.


These charts and graphs provide a strong visual of the significance such a shift can have for the endurance athlete, particularly for the athlete who is experiencing fueling/energy and/or gastrointestinal issues. Remember, in the real world, every athlete is different and you are your own N=1. For the athlete who is already experiencing the benefits of a “fat-adaptation” this article can serve to show your skeptical friends and family what you have been experiencing and saying is not pseudo-science, a placebo effect or anecdotal, and you really are not lying about how few calories you consume during training or competition.

The FASTER data strongly suggest a seismic shift is coming and a complete rethinking of how to perform will emerge. From my vantage point this information does not necessarily mean carbohydrates will be eliminated from an athlete’s diet but, more so, as we say here at VESPA, used “strategically” in the diet and fueling. Working with athletes of all ages, genders, ability levels and sports the observational evidence and results suggest carbohydrates do need to be a part of the program for optimal performance and health for athletes with a high volume of training especially when harder efforts like high intensity/speed training and/or competition is involved. Athletes participating in high intensity sports like martial arts and Cross-fit report similar results. It needs to be noted most, if not all, of the LCD cohort in FASTER follow the OFM protocol in real life and competition noting their best performance comes from fat-adaptation, VESPA and strategic carbohydrates. These observations are consistent with the published literature which suggests keto-adaptation yields excellent endurance but yields limited ability to tap into aerobic threshold intensity levels when compared to glycolytic pathways. Some people will do better than others in this regard but all would probably see increases in their higher intensity performance by adding some carbohydrates into their diet and/or fueling. This being said this yet to be published data suggests by incorporating a fat-adapted foundation most athletes are going to realize improved performance and recovery gains. There is a lot more esoteric scientific data that will emerge from FASTER.

Based on our real-world, athlete derived data/feedback our speculation is:

  • Mitochondria count and size will be higher and larger in the LCD cohort.
  • Another difference between the cohorts will be in hormonal levels and balance which will yield new insights into both lipolytic and glycolytic metabolic pathways.
  • Lower oxidative stress / free radical formation and significantly lower lactate load in fat adapted athletes.
  • Post exercise ketone surges will be moderate while post exercise glucose surges will be surprisingly high, yet transient, and beneficial to the athlete because this transient glucose surge will serve as an endogenous muscle glycogen storage mechanism.
  • Papers published from FASTER will support the OFM Program’s empirical hypothesis (or as some would term it our radical speculation) that performing super high volume of aerobic exercise utilizing glucose as the main energy source may having more long-term deleterious effects on an athlete than benefits, however, for the athlete who metabolizes fat for the vast majority of the aerobic spectrum  high volume aerobic exercise has marked and significant long-term health and performance benefits.

Finally a special thanks to the subjects who allowed themselves to be poked, prodded, biopsied, and, probably worst of all, subject to a 3 hour treadmill staring at a concrete wall in the name of furthering science. The feedback I have received from Dr. Volek and his staff are all the subjects were great to work with which reflects on our community. Related Links:






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