Zach Bitter: Fastest 100-Miler In US History


Late last year Zach Bitter emerged as the fastest American in the history of long distance ultrarunning, setting an American record for 100 miles on a track in 11 hours and 47 minutes (roughly a 7 minute 4 second per mile pace) at Desert Solstice last December. He also set the world record for covering the longest distance in 12 hours with 101.7 miles at that same event. But he wasn’t done: earlier this year Bitter set the American record in 16 hours and 23 minutes for 200k (125 miles) on a track at the South Carolina 24-hour event. A few weeks later Bitter won the Mad City 100k for the 100k National Championship, which will send him to the World 100k championships as a member of the US team.

Bitter’s ascension to the elite ranks was marked by a 38-minute course record at the Chicago lakefront 50-mile race in a time of 5 hours and 12 minutes (6.15 pace) back in 2011, which was the fastest US 50-mile time in over 30 years. Somehow Bitter took his extraordinary 50-mile foot-speed and extended it to 100 and then 125 miles. We tracked down the unassuming Wisconsin native and resident to learn more about “how did he do it?”

Zach Bitter Explains How He Did It

The initial driving forces that led me into the world of ultramarathon running are not unique. I think most people would agree that the challenge of pushing their limits, exploring the unknown and forming meaningful relationships with likeminded people are in part why they find so much satisfaction in ultrarunning. As my experiences grew, and I met with some success, I began to ask myself the question: What would it take to meet my full potential? What would it take to morph the talents I do have into something that could compete with the best? In a sport like ultrarunning, where so much is based on how much you are willing to sacrifice in training, nutrition and personal life, I stood a chance.

Photo: Zach Bitter

Photo: Zach Bitter

The steps I took in these departments during the past two-and-a-half years culminated in my recent performances. I am not the most talented ultrarunner, but I am beginning to maximize my potential, and with continued growth and experience I hope to reach new benchmarks. But even more exciting for me, I hope to see folks more talented than I am reach their potential and create a whole new concept of what is possible in the sport.

Intensity training at various levels from allout sprints to long tempo runs at 5:30/mile have been a huge part of why I can manage to stay consistent throughout a race that eclipses 10 hours, and also maintain the intensity required to average low six-minute miles in distances reaching 50 miles. Adapting the body to feel comfortable at a faster pace is vital to maintaining form and enduring an ultra. Mentally and physically being able to maintain a pace that might otherwise seem impossible for an entire day all of a sudden becomes manageable. Specific intensity sessions I do and why can be found through my website at

Along with training both my aerobic and anaerobic systems, I strongly believe in and incorporate strength training into my training regimen. This enhances recovery, injury prevention and overall wellness in a sport that can be crippling at times. I have always enjoyed weightlifting since high school, but I needed to adapt for specificity. Maxing out on the bench press was replaced by core strengthening circuits and both pushing and pulling exercises (both weights and body weight routines) and a series of squats, lunges and box steps. My weight training transformed me into a highly injury resistant, biomechanically efficient runner. I believe this is a primary reason why I am able to race on hard flat surfaces without any overuse injuries.

Specificity is a lesson I knew about, but didn’t really take full advantage of until this past fall. You can’t reach your full potential by training in an environment in which you aren’t racing. I live in Wisconsin, which has beauty of its own, but is lacking in terms of climbing, descending and altitude. Taking advantage of my training environment meant taking a swing at some flatter stuff. Chicago Lakefront, Desert Solstice, South Carolina 24 Hour and Mad City 100k were the beginnings of heeding to the “race on what you train” philosophy. This doesn’t mean I don’t enjoy the trails and mountains, or that I will avoid them. I just have come to accept and understand that with my current training environment, the races I will likely really nail are going to be flatter and faster courses.

Nutrition is an incredibly important aspect to my training, racing, and recovery. It may, in fact, be the most important. It has allowed me to recover faster, stabilize my energy levels, improve my sleep and even improve my biomarkers. But most importantly, by altering my diet and lifestyle, I have been able to transform my body to burn fat as the primary fuel, even at fast running paces for long periods of time – and distance. It has been approximately 2½ years since I dove into my current nutritional strategy. Developing my Optimized Fat Metabolism (OFM) has allowed me to re-train my body to do what it was designed to do. Burn fat.

Briefly and in simple terms this means getting the body to switch to burning fats as the preferred fuel and it is done by severely restricting carbohydrates to get insulin levels way down so your muscles utilize the beta-oxidation pathway and the liver makes ketones. As the insulin levels go down, the ability to burn fat goes up. As this occurs, insulin sensitivity goes way up so when carbs are “strategically” brought back (as at a race) they work like never before with minimal to no impact on fat metabolism. Other than a few sluggish days during the first couple of weeks as the body relearns to optimize fat, the benefits were apparent quickly.

During the transition time away from carbs I did run a lot but never pushed it, allowing my body to go through the growing pains of fat adaptation. At the same time I restricted my carbs I was upping the fat in my diet, including foods containing saturated fats because, when fat-adapted, the body actually prefers to burn saturated fats. Unfortunately, due to 40 years of fat phobia and bad science, most people have a deep-seated fear of fat, especially saturated fats. Inevitably, one of the first things people ask about when I tell them the amount and types of fats I consume has to do with heart disease and cholesterol levels. Consistent with the research literature, my cholesterol numbers improved on this diet over my previous diet. Nothing else changed. In fact, the amount of miles I ran, and strength training frequency, were nearly identical in my “high carb” 2011 and my “high fat” 2012. You can read about it at zachbitterrunning.blogspot. com/2012/10/high-carb-vs-high-fat.html.

This fat-adapted shift to fat as fuel allows cells to readily access the limitless calories available from fat via beta-oxidation and ketosis. If you want to know the hard science behind all of this I recommend obtaining copies of The Art & Science of Low Carbohydrate Living and The Art & Science of Low Carbohydrate Performance by Drs. Jeff Volek PhD and Stephen Phinney MD, PhD. They are the gurus on nutritional ketosis. I had the pleasure of first meeting them during the summer of 2012 when I participated in a study they were doing at Western States. This March I participated in a study they are doing at the University of Connecticut called FASTER for Fat Adapted Substrate oxidation in Trained Elite Runners. Based upon the data collected thus far, fat-adapted athletes are breaking the conventional “Crossover Concept” (Brooks et al.) and performing exercise all the way up to their VO2 max using mostly fat as fuel. The implications of tapping into fat-burn at this level for ultra-endurance sports are obvious.

For fats and oils I use a fair amount of butter, coconut oil, cream and sometimes medium chain triglyceride (MCT) oil because they are high in monounsaturated and saturated fats. I have fish oil for my Omega 3’s and olive oil on my veggies and salads.

I try to avoid the industrial oils which means pretty much anything made using high pressure, heat and chemicals for extraction because they are easily oxidized and highly inflammatory. Unfortunately, like sugar and high glycemic carbs, they are also ubiquitous in our food supply and often marketed as being “healthy.”

One of the best strategies I worked out was for bone broth; I would buy a rotisserie chicken and have it for dinner then took the remains and made broth. Broth (and liver) are key elements in the dietary concepts of OFM.

I consume plenty of fresh vegetables and fruits but do keep an eye on high glycemic fruits like bananas and pineapples. This diet is hardly depriving except that I am not having a ton of refined carbohydrates, which are nutritional wastelands relative to calves’ liver or broth or wild caught salmon. Because I am well fat-adapted and physically active, adding some carbs back into my diet doesn’t appear to have much of a negative impact.

Training On OFM

Once in an OFM state always use a long slow warmup even before a speed workout so the muscles and cardiovascular system are fully primed with oxygen and the blood vessels are dilated properly for oxygen carrying capacity because fat only burns aerobically.

Even though I am a high mileage runner I make certain I am taking plenty of time to recover, get sleep and chill. I cannot overstate the role proper recovery and downtime play in performance. I see too many endurance athletes who are constantly time-constrained and stressed, which chronically elevates cortisol levels. When elevated chronically, cortisol impedes fat metabolism and this is a self-perpetuating stress cycle. Also, hydration becomes critical when burning fat.

Racing On OFM

With a fat-adapted body, I have been able to take in many fewer carbohydrates on race day, thus, allowing my body to focus its precious blood supply on cooling and muscle contraction, rather than digesting copious amounts of gels, sports drinks and other sugary concoctions.

VESPA has been a key to my success, I use it during training and racing. It uses a naturally-occuring peptide from the Asian Mandarin Wasp. This peptide triggers the wasp to metabolize the stored fat in its thorax into energy at a high rate. The physiology of animal cells is remarkably similar across species and is why I believe the wasp extract peptide shifts metabolism toward higher rates of fat metabolism in humans too. Since I began OFM, I have been able to reduce my race day hourly carbohydrate intake by over 200 calories and feel better. Another benefit I see is because I am not trying to digest calories in the heat I can hydrate as long as I have the right balance of salt and water. S!CAPS, Salt Stick, NUUN and other commonly available products work, though the dosing tends to be much higher than what is recommended on the bottle.


On recovery days I can drop my carbohydrate intake to under the 100-150 grams I take in during high volume/intensity training, and at times even as low as 50 grams on heavy recovery days. The reason for the post-race and heavy recovery day carbohydrate restriction is to limit inflammation and oxidative stress, as well as to give the body a chance to really zone back in on exclusive fat metabolization following a race where it shared a large piece of the load with carbohydrate metabolism.


As a full time high school teacher it is not uncommon to pile 20+ hours of training a week on top of an already busy schedule. I have been blessed with a job I love, family and friends who are understanding, and an understanding girlfriend. Training can mean waking up at 4 a.m. on weekdays to get in between 10-18 miles before work, and often hitting the roads, trails or even track again after work. These all factor into why I can keep my mental stress levels low, which is crucial when putting my body through such heavy physical stressors on a regular basis. If the desire was not there, it would be easy to settle for less. Sure, I sacrifice certain activities I would otherwise partake in, but to me it’s worth it to realize my full potential and share my experiences and knowledge with others. For me ultrarunning is the greatest activity for learning and teaching.


1 Comment

  1. Rick Otani on

    You’ve affirmed what I’ve always suspected, that a low carb diet is best. I ran my best ultras when I was under 20g/day and handled the aid station foods fine.