Intermittent Fasting and Ultra-Running — how compatible are they?
I’m a mountain ultra runner. While I don’t travel around the world doing multiple 100-mile footraces each year, I do train every year for one hard mountain ultra event — either the Wasatch Front 100 Mile Endurance Run or the Bear 100, both based near my home in the Salt Lake Valley in Utah. I train from late winter until race day in September.
For the last six years, I’ve had a very similar seasonal training block pattern. I start out with around 20 low altitude and low incline miles per week. I slowly build up to a 60–70-mile and 15,000-foot vertical gain ‘peak week’ (which will include one day going 45–50 miles during that week). After ‘peak week’, I taper for a few weeks before race day.
Once the race is over, I significantly back off on running miles to recover. I generally enjoy the holidays with food and family instead of with solo miles on remote mountain trails. Then I start it all over the next year.
I’ve been fortunate to have completed all six 100-mile mountain footraces I’ve entered. In 2016, I placed as the third fastest 50+ year old male at Wasatch with a race time of 28 hours and 48 minutes. I was 51 years old.
As I crossed the half century mark in age, I noticed my metabolism slowing down, which made it harder to reduce weight from ‘off season’ to end of ‘training season’ through running alone. Rather than combat it, I just accepted it as a fact of life — I should be slowing down in my 50s. Also, my overall running performance gradually declined from 2015 through 2017 as reflected in my same-race and same-trail segment times. I love trail running, so wasn’t too impacted or concerned by the lowered performance — I just accepted it as a factor of age.
Then the company Don Brown, MD, Jeff Swartz and I co-founded built a mobile app for intermittent fasting (IF) called LIFE Fasting Tracker. As expected, I felt obliged to test it out.
It’s been a life changer for me.
I started using IF in the first week of March 2018. I follow a 16:8 IF plan (that’s 16 straight hours of not eating each day followed by 8 hours when I do eat). The IF definition of fasting means no caloric intake, so I drink water during the timeframe when I’m not eating. Typically, I fast five days a week now, though some weeks I’ve fasted as little as two days due to vacations, backpacking trips, etc. My average since March 2018 has been four days a week with an average of five days a week during the last two months (trends I can see in the LIFE Fasting Tracker app!).
Using the LIFE Fasting Tracker mobile app, I track fasts, hours in ketosis, see others in my Fasting Circles who are fasting, and access an IF learning library. It’s become a part of my daily routine — no different than looking at email, Facebook, or my Strava results.
There was an initial adjustment period in my mountain ultra training while keeping a 16:8 IF schedule. I usually eat dinner between 6pm and 8pm, so that meant I wouldn’t be eating until 10am to noon the next day. I typically went on longer runs of 2–4 hours in the early morning at least two days a week; this meant I’d be doing these long runs after fasting for at least 10 hours. At first I felt slightly weaker on these runs, but over time I noticed I was feeling more energetic. And my performance on these training runs improved as my body adapted to burning fat instead of glycogen during these ‘late fast’ runs. By 100-mile race day, my fastest times on same-trail segments occurred during these ‘fasting runs’. Additonally, I felt more satiated after I ate and (unlike before) didn’t get the ‘munchies’ when I wasn’t eating.
I did have to adapt part of my training due to the effects of long-term IF. One outcome is that my body got used to running without any continuous fueling. I really noticed it during my ‘peak week’ 50-mile day. I was fine for about 14 miles, then my gut started rejecting what I ate. I was using similar food from previous years (Salted Nut Bars, Clif Bars, Peanut M&Ms, bananas, etc.). But they were just sitting in my gut and making me nauseous. I went the next 31 miles on three Dixie cup-sized shots of Coke, half a squeeze packet of applesauce baby food, and a few potato chips. To boot I threw up at mile 38 and noticed some food I ate from 12 hours earlier in what ended up on the ground. Obviously this wouldn’t work for going 100 miles in 36 hours or less. I needed to re-train my gut to take in nutrition while running instead of hoping I could suffer without food through 100 miles on my feet, climbing and descending 24,400 feet in the Wasatch 100.
I ended up choosing to implement a modified ‘IF taper’ program in the week leading up to the race; I went from 16 hour fasts to 14 hour fasts, then to 13 hours, then to 12 hours, and finally I stopped IF altogether two days before the race.
By race day I was six pounds lighter at the end of the 6-month training block than in past years — with no other major modification to my training routine except for my 16:8 IF regimen.
I decided to not risk fate with a ‘solid-food-heavy’ nutrition plan during the race. I put Tailwind in most of my drop bags, so I could get into these drop bags at aid stations along the course and could keep 300 calories and electrolytes in a bottle along the entire 100 miles. I also put some Red Vines and Clif Bars in a few drop bags in case my gut felt good enough to tolerate them. And I planned to eat one Clif and Power bar each during the first part of the course, which for me is a three hour power hike. After that climb, I decided to go for Swedish Fish, gummies, bananas and even pieces of baked potatoes at aid stations. I’d avoid anything with oils, added fiber, etc.
During the race I stuck with this plan. No grilled cheese, no Nutella wraps, no trail mix, etc. At one aid station about 20 miles into the race I tried a small pickle and within a few minutes felt my stomach turn. I didn’t risk any more ‘exotic’ foods after that. I took a few ginger ale shots and asked for triple-strength Gu Roctane drink at each aid station. For the trail I grabbed Swedish Fish and nibbled on a few types of potatoes (boiled, mashed and fried). That was about all I felt like risking in my gut.
I went the first 31 miles in good time. I picked up co-worker Kyle Clegg as a pacer from mile 31 to 45, and I got a huge boost from seeing some of my family, who showed up at mile 45 and mile 67 aid stations and who came to the finish line as well. And my daughter Valerie paced me on the course from mile 89 to the end, which was super supportive.
In the end, I went the 100 miles in 27 hrs 36 minutes and finished as the top male aged 50+ by over 50 minutes and in 27th place overall out of 300 starters and 187 finishers. Stupidly, I pushed too hard at the very end to beat my previous all-time finish time (on the old and faster Wasatch 100 course) by one minute. I ended up passing out from heat exhaustion, but not until after an amazing shower and massage. Due to my almost exclusive liquid nutrition plan I lost 10 pounds from Friday AM to Sunday AM. But I didn’t vomit on the course for the first time in four 100 mile races, so I think I learned some things about liquid and nutrition management.
I’m ecstatic about my finish time, which was 1 hr 12 mins faster than I’ve ever run this same course, and I attribute a lot of it to incorporating IF in my training block. With declining finish times in the last three years it was a huge boost to have seen consistently faster (and personal best times) throughout 2018. I never imagined such an outcome. Feel free to check out my UltraSignup results to see this trend.
The science supporting IF is strong and building. It promotes overall recycling of ‘junk’ in your body’s cells (scientifically called autophagy), which translates into healthy changes in nutrient signaling and efficient metabolic switching. If for no other purpose than to keep my cells healthy and to reduce risk of inflammation, cancer, auto-immune conditions, etc., I would be a strong proponent of IF. And having a daily mobile app to track my fasts gives me a great reminder and motivator.
Based on this season of dramatically improved running performance and general feelings of increased energy and wellness, I’m definitely sticking with IF. Who knows what another year will bring?
What about you? Have you tried combining IF with long-distance running? Let me know!