• Is a high fat diet best for endurance athletes? Can you become a Fat Burning Machine?

    The design of the Fat Burning Machine Diet had many influences. One of the influences came from the ultra-running community. While these runners reported unbelievable training and racing fueling rates,  I lurked from the sidelines, watching and experimenting with a very high fat diet. (I consider a very high fat diet to be one where fat is some 60% to 75% of total daily calories.)

    While I did try this high-fat diet, I found that for me the Fat Burning Machine program was much more sustainable and enjoyable. I could get the athletic and health results I sought, while enjoying many foods that would not be allowed on a 70% fat program.

    Let's look at that very high fat program so you can see why high-fat adapted daily living may be something you want to consider.


    Dr. Jeff Volek, a professor in the Department of Human Sciences at Ohio State University and a Registered Dietitian, released study data on the correlation of a high fat diet and athletic performance in ultrarunners. The data released late in 2015 compares two sets of evenly matched elite male distance runners.

    The first set of 10 runners followed a traditional high carbohydrate diet where 60 percent of calories came from carbohydrates, 25 percent from fat and 15 percent from protein. The second set of runners followed a low carbohydrate diet where a mere 10 to 12 percent of calories came from carbohydrates, a whopping 70 percent come from fat and less than 20 percent of the calories came from protein.

    Fat Oxidation vs. Exercise Intensity

    One of the biggest results of Volek's study showed that the fat-adapted athletes burned more fat at a higher pace than the traditional carbohydrate diet group. For endurance athletes, this means they have a significantly lower need for supplemental carbohydrates during training and racing, because more fat is being utilized as fuel.

    The high carbohydrate diet (HCD) group had maximum fat oxidation at a pace equivalent to around 50 percent of VO2 max. This is the fastest pace the athletes could travel while burning the highest percentage of fat for fuel. Fat oxidation occurred at an average rate of roughly 0.67 grams per minute.

    The high fat or low carb diet (LCD) group oxidized fat at an average of 1.54 grams per minute—over double that of the high carbohydrate diet group. Not only was the amount of fat oxidation higher, the high fat diet group was able to travel faster at the high fat fueling rate. This group had maximum fat oxidation at a pace closer to 70 percent of VO2 max.


    Anecdotal evidence outside of this study has reported that fat-adapted, highly-trained ultra-distance runners are completing 100-mile runs in 15 to 25 hours by using only 1,300 to 2,000 supplemental calories during the race. Rough numbers say these athletes are completing 20-hour events on around 100 supplemental calories per hour.

    Submaximal run test

    Volek also found that during a steady three-hour treadmill run at 65 percent of VO2 max pace, the fat-adapted athletes (LCD) burned significantly more fat than the high carbohydrate diet athletes.

    Numbers released from the study show that if the pace is 65 percent VO2 max, and if the runner consumes the typical high-carbohydrate-diet, roughly 40 percent of the fuel is coming from carbohydrates and 60 percent from fat.

    To put some numbers on this, if a high carbohydrate diet runner is cruising along at a pace that burns 500 calories per hour, he or she is burning around 200 calories per hour of carbohydrates and 300 calories of fat during exercise.

    Comparatively, if a high-fat-diet-adapted (LCD) runner also burns 500 calories per hour, Volek's study shows that he or she will only use 10 percent carbohydrates and 90 percent fat to fuel the run.

    The high-fat diet runner is burning roughly 50 calories per hour of carbohydrates and 450 calories of fat.

    The high carbohydrate diet runner is burning through carbohydrates at a rate of 200 calories per hour and our fat-adapted diet runner is only burning through 50 carbohydrate calories per hour. This is a huge difference.

    Because we store only 1,300 to 2,000 calories of glycogen and fat stores are well in excess of 50,000 calories for most people, Volek's preliminary findings show that utilizing more fat to fuel exercise is beneficial for the endurance athlete.


    Cholesterol concerns

    People often worry that eating fat will negatively affect total cholesterol to HDL (the good ones) level. Volek’s study found that the ratio was nearly equal in both groups at around 2.5. The goal is to have this value less than 5.0.

    Also worth noting, the LDL small particles (the bad guys) were lower in the fat-adapted or LCD group than in the high carb group.


    More details

    All graphs and charts were pulled from an excellent video presentation by Dr. Jeff Volek. Though nearly 42 minutes long, it is well worth watching - Dr. Jeff Volek “Nutrition for Optimising Athletic Performance

    More questions

    The ultrarunner group is, no doubt, a special group of men. They have helped us break decades-old paradigms about fueling during exercise. By doing this, they have opened the door to many more questions.

    As I previously mentioned, I have been following the Fat Burning Machine Diet (typically 40% to 60% fat, with timing and exercise strategies.) You can find my Leadville 100 race day fueling comments at this link.

    You can count on me to dig into the research and bring you the most up to date research and anecdotal information to help you optimize endurance exercise fueling that also optimizes health.

     Stay tuned as we learn more about the shifting paradigms of optimal athletic nutrition. 

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