If you’d have asked me six months ago if it was humanly possible to race a 10 to 14 hour endurance race without fuel, specifically carbohydrates, only consuming water, I’d say it might be impossible.

Yet that is what I will do this November when I race the 140.6 mile Ironman Arizona. An Ironman consists of swimming 2.4 miles, followed by a 112 mile bike race and then the final leg running a 26.2 mile marathon. To be an official finisher I have to complete the total in 17 hours or less. The pros run in about 8 hours. My fastest time ever was 13:51 at this race in 2010.

I’ve discovered that I can actually race this long without the need to consume any carbohydrate while I race. At my pace intensity I’ll be burning about 650 calories per hour and I anticipate a finish at best of 12 hours and worse about 13 1/2 hours. That would mean I’ll be burning about 7,800 calories.

In February this year I discovered how to get my body into ketosis. That’s the state where my brain is being fed by about 65% ketones and 35% glucose. The ketones are created in my liver by metabolizing fat as fuel. Beginning in April I’ve completely switched to a ketogenic diet (70% fat, 20% protein and 10% carbohydrate) to allow my body to be a constant state of ketosis.

I switched to this diet for two primary reasons in the beginning;

  1. I wanted to lose the excess fat I had gained over the last few years, and
  2. As a fuel source for the body, fat metabolizes with less oxygen thus as an athlete I could go faster on the same oxygen supply than I could if my body was using carbohydrates (glucose).


Perhaps you’ve heard of bonking. It’s where an athlete has used up all their stored glucose (glycogen) and the brain shuts the body down to survive on what little glucose remains. It’s a survival mechanism.

tired-from-runningIt’s a weird feeling. I’ve bonked in at least 6 Ironman races (maybe more). The body gave me no warning either. When I raced Ironman Texas in May 2014 I was having a great race.  I was hauling on the bike at a record pace of about 21 mph. Then in a short period of time, less than a minute, my energy level tanked. That was at mile 90 of the 112 mile bike ride. The last 22 miles I may have averaged 10 mph as I sadly watched 100s of athletes pass me.

I had bonked hard. My glycogen levels were depleted. My brain shut me down. I had to walk the marathon and another slow finish for me.

That Ain’t Right

I had bonked in other races too and the outcome was always the same; I walked most if not all of the marathon finishing late at night after most everyone had gone home. As an athlete I didn’t think this should continue to happen to me. After all, I had faithfully trained for each race and did everything my coaches (race and nutrition) told me to do. In each case they offered very little reason why I had bonked.

At times I was very disappointed at these poor results. It’s a bummer to faithfully do everything asked of me and then to have major failures on race day, time and time again. I was like the Einstein quote, I was going insane doing the same thing and expecting a different result.

Insulin Resistance

The reason my coaches could not offer a plausible explanation for my bonks is they had never considered that I was insulin resistant (IR) (I describe IR here). I’m not even sure they even know what it was. Most people, including endurance coaches, have a classic carbohydrate bias. I’m convinced this has plagued many IR athletes who have been “told” to eat a lot of carbohydrates and very little fat. IR athletes don’t do well at all on carbohydrates, me included. I bonked because all the carbohydrates I consumed during the race were insufficient because my working muscles turned it’s nose away from the  insulin delivering the glucose in my blood stream to them (i.e., my muscles were resistant to my insulin, thus the name Insulin Resistance). My body and brain needed something to burn so it used up most of the stored glycogen already in my muscles. I only have about 1,600 to 2,000 glycogen stored calories there. Once glycogen levels are depleted my brain shut my body down to preserve enough glucose to provide for it’s needs. Also in those races my body was not a fat burning machine sufficient to fill in the gaps needed to take care of my body’s total needs for fuel.

Racing in Ketosis

Thankfully I now am fully FAT ADAPTED.  My low-carb diet has moved my body into a constant state of ketosis and my primary fuel source is fat as opposed to glucose. My liver is now producing a good supply of ketones for my brain. During my race I’ll rely on my own fat stores to provide my race day fuel.

My goal on race day is to weigh 180 lbs. I’ll be at about 10% body fat. That would mean I’d have about 18 pounds of fat to use as fuel during the race. That 18 pounds equates to a whooping 63,000 calories! That’s way more than I’ll need and since my brain will only need about 100-200 calories of glucose, my stored calories in glycogen will be way more than I’ll need.

It’s my anti-bonk formula!

Never Felt Better

I’ve never felt better since I started to race in 2006. Going on a ketogenic diet and lifestyle in April this year was the best thing I’ve ever done to further my career and improve my overall health. There are many world class endurance athletes who are using a low-carb ketogenic diet too. Chris Froome, the three time winner of the Tour de France, is a fat adapted low-carb athlete to name one.

Some of the side benefits of being a ketogenic athlete for me has been:

  1. I recover from hard workouts better, thus allowing me to incorporate more intensity and volume into my training schedule
  2. I sleep better and that aids in recovery
  3. I’m losing all the excess fat I’ve carried the last three years. When I raced the Hawaii Ironman, the World Championship, I weighed 198 pounds (October 2015). I’ll be 18 pounds lighter and that will mean I’ll race faster. Can you imagine riding your bike with an 18 pound weight vest on your back?
  4. I have great energy!
  5. I have no GI issues that at times have hampered me in training and racing.
  6. I do not have the massive food cravings I used to get almost every night (I’ve devoured a few bags of salt and vinegar chips as a result!)
  7. In training I don’t need to pack around a bunch of gel and gu packs or drink sugary sports drinks for my calories. I now just consume water and electrolytes in training, exactly what I’ll consume in my race.
  8. My brain is being fed ketones and it loves them! I have better cognition and I believe better brain health. There have been many studies done on brain health and ketones to support what I’ve been feeling.


My Training Update

As of May 31, 2017

My cumulative  TSS (training stress score) is 76.1.

Each time I exercise the routines are given a score based on my baseline tests (i.e., my lactate threshold pace). The harder or longer the routine the more TSS points they are rewarded. Days I rest and don’t work out I don’t receive any points. My race goal is to break 12 hours. That could possible qualify me to race in the World Championship in my age bracket of 60-64. According to stats compiled by my software coaching program (Training Peaks) I need a TSS between 80-100 to have a time of 12 hours. My goal is an injury free TSS of 120. The TSS is the daily average TSS for the prior 45 days.

The last 28 days:

Total work out time: 56:14 (hours and minutes)

Bike 24:22
Run 12:24
Swim 8:12
Strength (weights) 6:36
Walk 4:38

About the Author Michael Lantz (Big Papa)

The Wellness Warrior™; Health & Leadership/Business Coach, Speaker, Blogger, Author, Ironman Triathlete Helping others live with more health and joy, paying for their dreams and make a difference in the world! Learn more: http://HealthIsAHabit.live