What is the Optimized Fat Metabolism Diet?
I was reading about ultrarunner Zach Bitter’s hundred-mile treadmill world record last month and I came across a few interviews were Zach mentioned the OFM or Optimized Fat Metabolism diet as being a key part of his nutrition strategy during his ultra runs. Bitter went on to talk about how he uses the OFM diet to “supercharge” his running by strategically using carbohydrates on top of his improved fat metabolism.
After doing a little more research on the OFM diet, I found that it is essentially an extension of low carb and/or ketogenic diets for endurance athletes. And while there’s not a lot of research on it, I do believe from a sports science standpoint there is probably some validity in the optimized fat metabolism diet, especially for endurance athletes like runners, triathletes but also possibly Crossfit or other strength athletes. The OFM diet seems to be a favorite of ultrarunners like Zach Bitter, Jeff Browning and Peter Defty.
I think the one downfall some people have with the ketogenic diet is that they make it too restrictive for themselves. They fail to take advantage of the benefits of their higher fat metabolism especially if they are athletic. They focus too much on keeping strictly low-carb and staying in the “magical” ketosis world, regardless of their activity level and fail to see the benefits of adding carbohydrates back when exercising.
These are often the same people complaining how their exercise performance has dropped on a ketogenic or low-carb diet, and many of them end up abandoning a low carb diet before they can reap the full athletic benefits.
As a sports medicine doctor, I’ve worked a lot of medical tents in both marathon and Ironman distance triathlons. One of the most common medical issues we see in our medical tents after the race is due to G.I. or gastrointestinal issues. Athletes come in with nausea, vomiting, diarrhea or stomach cramping, complaining how they just couldn’t keep up with their nutrition on the race course and ended up having a less than success race. When talking to these athletes or more are usually find that they were attempting to take in too many calories in either sports drinks or energy gels and that their stomach just can’t handle and process it. As a result, their stomachs shut down, they aren’t able to keep running at the pace they had trained for, and eventually, some of these marathon runners or triathletes end up seeing me in the race medical tent.
The stomach is a fickle thing during exercise. As the exercise intensity increases, the body shunts blood away from the stomach and intestines and increases blood flow to the exercising muscles. This decrease in blood flow diminishes the number of carbohydrates that the stomach can process and absorb during exercise. At rest, most people can absorb roughly 250 to 300 calories (60 to 70 grams) of carbohydrates per hour in their gut. If you start exercising and the intensity increases, this rate of carbohydrate drops significantly for most athletes. 1. That’s not much in the way of sports drinks or energy gels. Athletes attempting to exceed this limit end up dealing with GI issues.
Benefits of the Optimized Fat Metabolism diet for endurance athletes
So that’s where becoming fat-adapted as an endurance athlete may be a nutritional advantage over the typical “high carb” runners and triathletes.
Jeff Volek’s group demonstrated in the FASTER study2 (Fat Adapted Substrate use in Trained Elite Runners) that endurance athletes that were fat-adapted due to a low-carb diet had much higher utilization of fat (called fat oxidation) during endurance exercise than athletes that were on a regular high carb diet. Essentially, these athletes were on an Optimized Fat Metabolism diet.
The ability to use more fat during exercise also means that fewer carbohydrates are required to fuel that exercise. That’s an important take-home point. If you’re using more fat to fuel your long run as a fat-adapted athlete, you need to replace fewer carbohydrates per hour than your non-fat adapted competitors. That means not having to take in as much carbohydrate calories in sports drinks and energy gels and lowers the risk of stomach and intestinal issues.
Zach Bitter and the Volek FASTER study
Ultrarunner Zach Bitter was part of the Volek FASTER study and Zach published some of his metabolic data on his website. What I found both fascinating and amazing was Zach’s levels of fat adaptation and fat utilization while running. The researchers measured fat and carbohydrate metabolism of the athletes while running at different speeds and intensities on a treadmill. Usually, as your running speed picks up, there’s a significant shift from fat burning to carbohydrate utilization. What I found astonishing was that when Zach was running at 75% of his VO2max (roughly 7:00 minute mile pace), he was still using 98% fat and only 2% carbohydrates. Granted, this is someone that finds a 5 minute-mile pace comfortable, but for other endurance athletes that will most likely spend most of their race around the same intensity level, that 98/2 ratio of fat/carbs is impressive. That fat/carb ratio means the Zach needs to take in very little carbohydrates as he races and allows him to avoid many of the GI issues that plague other endurance athletes.
- Jeukendrup, A. E. Nutrition for endurance sports: marathon, triathlon, and road cycling.” J Sports Sci 29 Suppl 1: S91-99, 2011