Running ultras with type 1 diabetes: “Just give me some sugar. It’ll be fine.”

Jonty Brown has learned a lot about navigating his sugar levels while running ultramarathons, including The Speed Project solo a year ago

Mar 27, 2026

It doesn’t matter how many ultramarathons I know about, or how many ultrarunners, when I hear about someone running hundreds of miles on their own, I think it’s an incredible moment in their lives. When I saw that Jonty Brown, a type 1 diabetic, was running The Speed Project solo in March 2025, I knew it was a great story.

It wasn’t the first running challenge that Jonty had embarked upon, though. Having only started running in 2020 during the UK’s Covid lockdowns after being tagged in a challenge, he soon thought, “I might as well do it every day.” That kind of thinking led to Jonty becoming the first type 1 diabetic to run across the UK just 18 months later in 2021.

Learning to fuel as a diabetic ultrarunner

But, yeah, he’s got diabetes. He was diagnosed over 20 years ago, as a tween. In this new age of running, where we have the science to meticulously calculate and maintain our energy expenditure and sodium levels, so we know the exact number of gels to chug down, how do you work wildly unpredictable sugar and insulin levels into life as an extreme endurance athlete?

“Running with type 1 diabetes… there isn’t a book for it. There’ll be a cure before there’s a book.”
“When I was first diagnosed, my nurse told me to just go out and learn. There isn’t an insulin to carb ratio for everybody – it’s completely individual, because your insulin sensitivity will change throughout your life. It’s all about just getting out and trying, so trial and error is the only way.”

He tells me about his routine where he’ll “always eat something before” a run, but also that he turns his insulin delivery system off. Jonty goes on to explain why, in the context of his malfunctioning pancreas and associated insulin sensitivity.

When you run, the sugar travels faster around your bloodstream, meaning it doesn’t have time to settle. The insulin has less to react to, so blood sugar levels drop. He has to take insulin after a run to prevent any ensuing spikes from a slowing heart rate causing blood to slow down and sugar to settle more.

THUMBS UP: me and Jonty at the launch of Runlimited Baker St last summer

It’s difficult not to laugh (wryly) while listening to all the mental gymnastics that Jonty has to go through when he’s off on a run. The nutrition for my first half-marathon was sips of the on-course Gatorade and a couple of pieces of candy. That’s less about me being hard as nails and more about having better science to do our calculations with.

He talks about how hormones (like adrenaline) affect blood sugar levels, and while he struggles when he’s had a poor night’s sleep or how his insulin levels “always start playing around” before he gets sick, he laughs that can’t imagine how he’d deal with a woman’s monthly cycle. Being able to appreciate and acknowledge his privilege while discussing his own illness is the mark of a man.

Why ultras?

While Jonty has been running since 2020, he tells me about past physical activities such as skating, surfing, and weightlifting.

“Each one would change my blood sugar in different ways. When I was doing heavier weights, it would actually skyrocket because of the adrenaline kicking around my body. When I was going on the long skates, it would drop suddenly, but if I did some stairs or a rail, it would spike again.”
“I found, for me, that ultras really work well because it’s slower, I can talk, I can digest stuff, I can pick on what I’m going to eat and when I’m going to eat it. It’s in marathons where it just hits the fan. It’s the adrenaline, you’re going hard, and you need to get six to eight gels in.”

Not long before we spoke, Jonty had run 104km around Victoria Park in east London to celebrate 104 years since insulin was discovered. He does these kinds of runs in aid of diabetes awareness, raising money for Breakthrough T1D, a charity that aims to improve the lives of people with diabetes.

During that 64.6-mile run, he tells me that his mate got him a can of Coke because he saw Jonty fading slightly. It’s an easy fix in the big city, but when he’s out in the sticks on his own, he has to get creative.

“There’s a trick I’ve learned recently that if I’m coming in low, and I need to get some sugar but I’m nowhere near anywhere, if I do three 10-20-second sprints as hard as I can, it’ll boost my sugar levels, which will last me until I get home.”

Sprint repeats to get home? That sounds like the lesson Jonty learned while skating. The long sojourns saw his sugar drop, but skating down a few rails gets the adrenaline pumping enough for a temporary energy boost.

He took that knowledge into running The Speed Project solo a year ago. While running from LA to Vegas as part of the Adidas Runners team, he saw people like Mikey Kratzer running the course solo. He wondered, “Is it doable?? It was an itch I needed to scratch.”

“It was one of those experiences where I actually learned a lot. When my sugar levels are good, I’m good, but when they’re not, it hits the fan a bit. It highlighted the diabetic moments within it.”

He tells me he “got friends for life from it, which I think is the best trophy anyone could ask for.” I think finishing fourth and being the first type 1 diabetic to have completed the course solo are also great things to be able to say.

Putting diabetics first

Through his work thinking deeply about how his experiences fit with how his body reacts, the number one theme for Jonty is him trying to find ways to make it easier for (other) people with diabetes. He raises awareness and money for charity, but he puts his own body through unbelievable stress to find out what works. There isn’t a book for it, remember. When I ask him what else he’d like to say, his answer is immediate.

“I would love to be a guinea pig. I’ve put it forward to people before, but they wouldn’t be able to put me into a test because I could die, but I won’t because I know the feelings of when I’m going to go low and when I’m going to go high. Just give me some sugar, it’ll be fine.”
“Let’s work out exactly the fueling for a diabetic. I’ve done research and I’ve tried and tested. High fat foods are really good if I’m doing a half-marathon because for 90 minutes your body will use what’s already stored. Realistically, you could get away with doing a half as a diabetic, and not have to worry about working out the other sources of energy. I could go off avocados and nuts, and squirrel those things into me prior, but how do I do that with the longer stuff? The only way is to go out and test it.”

In my opinion, this is the book that Jonty said wouldn’t be written. It’s fair that he laughs when I suggest he writes it. He’s got a lot on his plate with being the co-founder of a growing number of Runlimited stores around London with Molly Bryan, and working with communities to give them a welcoming space (I hosted three panels at the St. Paul’s branch last summer), all while logging a toe-curling weekly distance

While that cure for diabetes is still being sought, listening to Jonty Brown might be the next best thing.

This is Running: t-6 days in the UK

The Speed Project features three times in my book, This is Running. Pre-order copies have already begun to be delivered in the UK. The US release is April 7th, and they’re surely not far behind. If you enjoyed reading this far, you need this book.