Drs. Jeff Volek and Steve Phinney are currently working on a study through the University of Connecticut Department of Kinesiology (dubbed the FASTER Study), which is comparing the rate of fat and carbohydrate metabolization at various paces in ultramarathon runners. One of my coaching clients, Kevin Grabowski, just returned from the study. Kevin is incredibly fat-adapted. The man consumes 3+ quarts of heavy whipping cream a week! I won't spill the beans on his results, but it's safe to say he burns pure fat at his "easy pace," which is often the same as race pace on longer distance ultras. This knowledge has a lot of implications for racing something like a 24-hour event.
I am up to participate in the FASTER Study in March, so until then I can only speculate. However, this doesn't mean I can't experiment.
My theory is that I metabolize fat exclusively beginning around 7:10-7:40/mi (on flat terrain, that is). If this is true, it means I could deplete my carbs and still expect to maintain 7:20/mi pace without trouble. I set out on a run Saturday morning to test this out. My goal was to try to deplete my glycogen stores with an aggressive, fasted workout so that I could then, during the cool-down, identify what pace I could still maintain comfortably without the help of glycogen. Here's the protocol I followed:
- Overnight fast
- Pre-workout nutrition (coffee, Vespa Ultra Concentrate)
- 11 miles at 6:40-6:50/mi
- 5 mile progression (5:51, 5:46, 5:42, 5:29, 5:35)
- 4 miles at what felt comfortable (average about 7:30/mi)
Anecdotally I am pretty certain that the workout depleted my carbohydrate stores: When I finished the progression run, I was drained. I went into the 4 mile cool-down without a break. I quickly noticed that I could push my pace down close to 7:00/mi with a bit of effort, but if I just ran to comfort—my "run forever" speed—it was closer to 7:30/mi. Assuming I was successful at depleting my carbohydrate stores, I believe this was a good indicator of what pace I can currently maintain, while burning fat as my sole fuel source. (Again, terrain and other conditions play a role.)
My performance at my past few ultra races seems to support this. In my recent 50 milers (Tussey Mountainback and the Chicago Lakefront 50), my pace was well under 7:00/mi. According to my little experiment, I would have required some carbohydrate intake to maintain those speeds; my fueling of roughly 1,000 calories during each of those events makes sense.
One might argue, however, that I should still have had enough glycogen stored up to adequately meet the demand placed on me even at the quicker pace. With that thought in mind, I would argue that I did not do a "carb load" in any traditional sense leading into each of those efforts. Maybe this is something to play around with in the future. Ultimately, I think it will come down to whether I would rather take in a few more carbs during the race, or would it be easier to stock up a bit the 1-2 days prior to racing.
My performance at my past few ultra races seems to support this. In my recent 50 milers (Tussey Mountainback and the Chicago Lakefront 50), my pace was well under 7:00/mi. According to my little experiment, I would have required some carbohydrate intake to maintain those speeds; my fueling of roughly 1,000 calories during each of those events makes sense.
One might argue, however, that I should still have had enough glycogen stored up to adequately meet the demand placed on me even at the quicker pace. With that thought in mind, I would argue that I did not do a "carb load" in any traditional sense leading into each of those efforts. Maybe this is something to play around with in the future. Ultimately, I think it will come down to whether I would rather take in a few more carbs during the race, or would it be easier to stock up a bit the 1-2 days prior to racing.
Cool.
ReplyDeleteBen Greenfield was just up there: I presume for the same study.
I'm hoping to finally get an answer to a question I've had for a long time: what's the minimum amount of carbs you need? Guys like Krupicka make me think the answer's 100 calories and hour max, if you're trained. I suspect the right answer is zero.
I think it depends on your goals, and your ability to keep your heart rate in check. If my goal was to get from point A to point B with no time constraints; I could do so on zero carbs, within reason of course. But if I want to get from point A to point B as fast as my body is physically capable, it is my theory that I would be best served being very fat adapted, and using carbs strategically. An example would be right before a big hill climb. I can anticipate if I'm going to "attack" the hill, my heart rate is going to rise above what it can handle on just fat, and dip into my carb stores.
DeleteI agree, given what we know now, using carbs strategically is the most conservative strategy. Be silly to train for a race and then bonk because you're missing a few M&Ms. ;)
DeleteI'm curious about what we're capable of...
Looking forward to seeing the results.
ReplyDeleteI may need to look into the 3+ qts/whipping cream/week diet...sure are a lot of tasty things to make with that much cream! I'll let you know how my fueling plan goes for Translantau 50km Mar. 15; never run over 3 hrs....5.5 hrs at 10:10/mile has won it, so that seems an 'easy' enough pace ;) But here's a question--if I've never fat-optimized my metabolism, am I burning carbs at a certain HR level regardless of pace, do you feel (aka super hard terrain, slow pace, but high HR and thus needing carbs for me, anyway)?
ReplyDeleteThis is a good question. The distance of the race comes into play here. If it's a long enough race where you would benefit by pacing yourself anyway, then keeping the heart rate below a certain level might be ideal for fat metabolism as well as keeping a sustainable pace. If it is a short enough race where you can afford to "burn some matches" or go fast from time to time, then having carbs on board and ingested might help you get from start to finish faster. For someone who is not fat adapted, I would strongly recommend fueling up with carbs for any immediate races, and experiment with the higher fat stuff in training. The big thing here is someone who is fat adapted, like my client Kevin, is going to be able to avoid burning carbs at a higher heart rate than say someone who is eating a high carb diet.
DeleteI seem to remember from Volek and Phinney's book that some carb intake is recommended to keep the brain functioning, avoiding "central fatigue." Can the fat we metabolize be used by the brain? If so, maybe the carb needs on an ultra run are zero?
ReplyDeleteYes - this is why Phinney and Volek advocate for the "50g/day". It is a very small amount, but that's is all the brain needs. The interesting thing about fat, carb, and protein is what the body can do with it. If I'm not mistaken, protein for example, can be converted into glucose at a rate of up to 50% (meaning half the protein you consume can be processed by the body into storage carbohydrate (gluconeogenesis). Fat on the other hand, can also have some conversion, but it's much closer to 10%. This is why someone who is doing huge loads of training with two-a-days, struggles to replenish glycogen stores on the really low end of carb consumption (50g), and precisely why I follow OFM.
DeleteAs always an insightful post Zach! Love working with you. I do think that once summer hits your fat only burn pace can be ratcheted down to 7:00-7:15 or potentially even better on a cool day . . . . Let's catch up sometime soon.
ReplyDeleteTo add to the discussion....when "fat-adapted" using the OFM protocol (which includes VESPA) what we are seeing is that during exercise the liver's ability to spit out ketones at a high rate to provide brain and nervous system energy goes way up. I think this is because compare to glucose which is very tightly regulated ketones in circulation can go much higher before "bad" things happen...you don't see ketoacidosis effects until you are above 15 mmol/dl whereas the negative impacts of high blood glucose begin to take their toll with only a small rise....I suspect this is why the liver is limited in its output of glucose via gluconeogenesis and why it has the capacity to produce a lot of ketones when "fat-adapted. Because we see improve gains in lean body mass (via DEXA Scans) in OFM athletes when gluconeogenesis kicks in it is fatty acids that provide the substrate for conversion to glucose....many health professionals will say this cannot be done but actually can (http://blog.cholesterol-and-health.com/2012/01/we-really-can-make-glucose-from-fatty.html)....
ReplyDeleteNow readers should consider context & perspective.....Virtually everything written about glucose and ketones in terms of human physiology is contexted in a way that says glucose is necessary for brain and nervous system function and that ketones are a secondary fuel source in times of scarcity....(read starvation)....scarcity of what?: Sugar......now stick with me here...what if there was not scarcity just no sugar? My speculation based upon the science is ketones were actually the main brain and nervous system energy source for the majority of human exisitence and evolution with glucose playing the supporting role NOT as currently contexted in a world where most diets are laden with carbohydrates. Consider sugar/glucose/glycogen a "fight or flight" fuel.
ReplyDeleteThe 50gm/day recommendation by Volek & Phinney (some people who are really challenged need to get below 30gm/day) is the gold standard for inducing ketosis and you see this in many different peer-reviewed pubs and low-carb / Atkins style diet books....this number is based upon people who are relatively sedentary. What we are seeing is athletes with any level of training/exercise volume can easily remain "fat-adapted" in a range of 75-150 gm/day on normal days and well above that on big training days without losing their fat adaptation and using mostly fat as fuel. On race day, like an IM or longer Ultra the athlete very well may be getting most of their calories from carbs but still be "fat-adapted" . This is observational evidence but it is pretty consistent. Exercise combined with "fat-adaptation" is a powerful tool for most anyone not just endurance athletes.
ReplyDeleteZach, you wrote: "This is why someone who is doing huge loads of training with two-a-days, struggles to replenish glycogen stores on the really low end of carb consumption (50g), and precisely why I follow OFM." Can you point me to some of your writing the really describes OFM in practice? I had a swift ramp up of training after recovering from an injury, and feel like I'm not replenishing enough glycogen fast enough, so that the first three workouts of the week are great but the last couple, including long run, are slogs.
ReplyDeleteHey Ernesto,
DeleteThanks for checking out the blog post. Here is a fairly in-depth write up I did late last year. Let me know if this doesn't answer your questions.
http://zachbitterrunning.blogspot.com/2013/11/recovery-protocol.html
Zach, I find your blog very interesting because I have been low-carb (normally less than 50g per day) since 1/1/14. The first two weeks were hell, but I have now started really feeling the benefits in that I no longer need to eat in training at all (so far I have managed up to 35miles after a fatty breakfast, but without food during the run). I think it has improved my health too.
ReplyDeleteI am now getting to the stage where I feel I should start to reintroduce carbs for performance reasons, but I am wary of insulin spikes and their effect on fat burning. I have seen some literature indicating that the effect of glucose ingestion during exercise (but not immediately on starting) is less than at rest, so I plan to take in gels on that basis.
However, I see that you eat carbs before exercise (immediately before and also carbo-loading). Do you find this inhibits fat-burning, or am I being over-cautious?
Hey James,
DeleteI do eat some carbs before workouts, but it is very low and typically a form that won't generate high insulin spikes (raw honey). In fact, mornings before races I avoid carbs for the very reason you mentioned. I want to be in prime fat burning mode when I'm starting out. If I ran less miles I wouldn't eat before or during runs either. When I hit peak training, I'm hitting upwards to 20+ hours of running, speed work, and resistance training. In order to meet my calorie needs without eating, sometimes I have to sneak a few extra in here and there.
Thanks for the reply Zach. Fortunately (unfortunately?), I don't cover anywhere near your mileage each week, so I guess I'll not be eating immediately pre-workout. I am going to try carb-loading the day before my next test race though by sneaking some sweet potato into a fatty meal - it is so much fun experimenting!
DeleteI also have to steal your banana chip idea. I heard you mention on endurance planet that they were cooked in coconut oil - well spotted!
Zach, when you set initially set out on this quest to become fat-adapted. Did you focus mainly on eating the OFM diet, or did you take into account training in certain heart rate zones as well, such as using the Maffetone method or something similar?
ReplyDeleteI'm curious because I am starting on the same quest, and I just do not enjoy my runs as much using the heart rate monitor and tracking all that data. I feel like I'm pretty tuned into my level of Perceived Exertion, and I can tell when I'm going easy, medium, or hard. Am I going to lose some potential benefits of becoming metabolically efficient if I ignore HR but stay tuned into my diet and pre/post workout nutrition? Thanks for any thoughts you can share!
Billy
Hey Billy,
DeleteI've never monitored heart rate in my training. The reason is because it seems like just an extra thing to stress about that I don't need to stress about. I love running by feel. That's how I gauge recovery and effort for all my training. I wear a gps watch to get splits and mile paces, but don't mess with heart rate. I think the Maffetone method is definitely a valid approach. It has worked for many. I probably do Maffetone training during certain blocks of the year without actually monitoring. One of the perks of running a lot is you can feel the different paces pretty effectively.
That is good to know your thoughts, thanks for the insight! And best of luck with the 24-hour and other races coming up.
ReplyDeleteNo problem, and thanks!
DeleteHow does a "normal" everyday runner figure out at what pace they metabolize fat exclusively at?
ReplyDeleteHi Russ,
DeleteThe best way is to just get a test done to find the exact numbers and ratios. Even my example above is at best a theory, and I won't know andy specifics until I get tested from the Volek study at UConn. You could try to do similar scenario I did to get an idea. Basically you just want to deplete your glycogen stores and see what pace is comfortable (I don't think this method would work so well in a high carb athlete, as it is tougher for their body to go back to fat burning once they've hit high levels of carb to fat ratiio).
Hi Zach,
ReplyDeleteThank you for your post and for sharing your experience. Have you ever tried using UCAN Generation, for races/recovery ?