How To Run A Marathon With Type One Diabetes

Let me be clear about something upfront. I am not a doctor. I am not a certified diabetes educator. I am a Type 1 diabetic mom who has run 15 marathons and figured out a lot of this the hard way, so you don’t have to.

This is real world advice from someone who has been there. Take it, adapt it to your own body, and always work with your medical team. But also know that everything in this post comes from actual miles, actual lows, and actual race days.

Let’s get into it.

Before The Race — Get Your Blood Sugar Where You Want It

My target before a marathon is 150.

Not 100. Not 120. One hundred and fifty.

Here’s why. You are about to run 26.2 miles. Your blood sugar is going to move. A lot. Starting at 150 gives you a cushion without starting so high that you spend the first miles coming down.

Race day adrenaline is also real, and it is coming whether you want it or not. Your blood sugar will spike at the start line simply from excitement and nerves. I let it happen without correcting. Chasing a correction during a marathon is a problem you do not want to create for yourself. Your body will find its rhythm once you settle into your pace.

Practice this in training. Long runs are dress rehearsals for race day. Treat them that way.

Fueling Strategy — The Most Important Section In This Post

Over practice your fueling. I cannot say this enough.

Whatever you plan to eat on race day you need to have eaten on every single long run leading up to it. Your stomach, your blood sugar, and your body need to know exactly what is coming. Race day is not the time to try something new.

I alternate Clif Shot Bloks and SiS Gels during marathons. What I love about Shot Bloks specifically is that you can break them up and take one at a time instead of consuming a whole gel all at once. For a T1D runner that means more control over blood sugar — a little glucose at a time instead of a sudden spike you have to chase. SiS Gels are isotonic, so you don’t need extra water to digest them which is one less variable to manage when you’re already juggling blood sugar, pace, and hydration simultaneously.

Start fueling early. Don’t wait until you feel like you need it. By the time you feel it you’re already behind.

The Science Behind Marathon Fueling — And Why It’s Different For T1D

Here’s what the research tells us and what 15 marathons has taught me.

Most marathon runners need between 60 and 90 grams of carbohydrate per hour to maintain steady energy and avoid hitting the wall. Your body’s stored glycogen can only carry you so far — most runners need to start fueling as early as 40 to 50 minutes in, well before you feel like you need it. The number one rookie mistake is waiting until you feel tired. By then you’re already behind.

For T1D runners this isn’t just about energy. It’s about blood sugar management simultaneously. Those are two different jobs happening at the same time in your body and your fueling strategy has to account for both.

Frequent fueling wins over large infrequent doses for T1D endurance athletes — consuming smaller amounts of fast acting carbs every 30 to 45 minutes keeps blood sugar steadier than larger boluses taken less often. This is exactly why I love Clif Shot Bloks over traditional gels for blood sugar control. One blok at a time instead of a whole gel at once means I control the glucose drip instead of chasing a spike.

SiS GO Isotonic Energy Gels deliver 22 grams of carbs per gel and because they’re isotonic you don’t need water to absorb them — one less variable when you’re already managing blood sugar, pace, and hydration at the same time.

Here’s my personal marathon fueling schedule as a T1D runner:

Miles 1 to 6: Settle in. Let the adrenaline spike happen. Don’t correct it.

Mile 6: First fuel. One or two Shot Bloks. You feel fine. Take them anyway.

Every 30 to 45 minutes after: Alternate Shot Bloks and SiS Gels. Small and frequent beats large and infrequent every time.

Always: Check your CGM trend not just your number. A 150 dropping fast is a completely different situation than a 150 holding steady.

Aid stations: Know where they are. Gatorade is your emergency backup. I used it at NYC and it saved my race.

One more thing. Your gut is trainable. Practice your exact race day fueling on every single long run to increase absorption and reduce the risk of GI distress on race day. Your stomach needs to know what’s coming just as much as your legs do.

Over practice fueling. Over pack lows. Repeat until it’s automatic.

Insulin Management During a Marathon — The Part Nobody Talks About

Here’s something most T1D marathon guides skip completely.

You can’t just eat gels and hope for the best. Your body needs insulin to actually convert those carbohydrates into energy. Without it the glucose just sits in your bloodstream going nowhere useful while your muscles are begging for fuel.

This is where it gets personal and where every T1D runner has to figure out what works for their own body.

My approach is micro dosing. Small amounts of insulin timed with my fuel intake so my body can actually use what I’m eating. Not a full correction. Not a guess. A deliberate small dose matched to what I just took in, guided entirely by what my CGM trend is showing me.

I watch trends obsessively not just numbers. A steady 150 and a dropping 150 require completely different decisions. Your CGM arrow is your best friend on race day. Use it.

I also run every marathon in manual mode.

This is a personal choice, and I want to be clear; there is no single right answer here. Automated insulin delivery technology has helped many T1D athletes maintain excellent blood sugar control during marathons and that works beautifully for a lot of people. But I want to be in control on race day. Manual mode means every decision is mine. I know exactly what insulin is on board, exactly what I’ve taken, and exactly what my body is doing at every mile.

After 15 marathons that level of control is what I trust.

Research shows that reducing pre-race breakfast insulin doses and carefully managing bolus insulin during the race helps T1D runners maintain better time in range throughout the marathon. Work with your endocrinologist before race day to figure out your specific protocol. What works for me after 15 marathons took years to figure out and your body is different from mine.

The bottom line is this. Fueling and insulin management are two sides of the same coin for T1D runners. You cannot just eat gels like a non-diabetic runner. You have to actively manage both sides of the equation simultaneously while also running 26.2 miles.

Nobody said it was easy. We do it anyway.

Over Pack Your Lows. Seriously. Over Pack.

I went low during the New York City Marathon.

I ate through every single piece of fuel I was carrying. Every last fruit snack, every Shot Blok, every backup snack. Gone. I was grabbing Gatorade from aid stations just to keep moving.

I finished. But it was not the race I planned.

Pack more than you think you need. Then pack more. Low snacks are not optional extras — they are safety equipment. Fruit snacks, Nerds Gummy Clusters, glucose tablets, whatever your low treatment of choice is. Carry all of it. Your Flipbelt holds more than you think and your Camelbak pockets exist for exactly this reason.

You can always bring snacks home. You cannot undo a bad low at mile 18.

Gear You Actually Need

A few non negotiables for T1D marathon runners:

Your CGM is your best friend on race day. Check it regularly and know your trends not just your number. Use Skin Tac adhesive wipes before you apply your sensor — sweat and 26.2 miles will test every CGM adhesive you’ve ever trusted. Skin Tac keeps it in place from start line to finish line as well as skin grip for an extra sticky.

Your Flipbelt carries your low snacks, your phone, and your fuel without bouncing or shifting. I have run every marathon with one.

For anything over 10 miles your Camelbak hydration vest keeps you hydrated hands free with pockets for all your race day supplies. Dehydration affects blood sugar and on a marathon that is not a variable you want to add. *Most races don’t allow hydration vest; I only wear this for long training runs.

My Coros Apex 2 tracks everything — pace, heart rate, GPS, and battery life that actually lasts through a full marathon. Reliable data mid run helps me make better blood sugar decisions when I can’t think straight at mile 22.

Wear your medical ID on every single run and every single race. Write your emergency contact information on the back of your bib. Every race. No exceptions. If something happens out there the first responders need to know you have Type 1 diabetes and they need to be able to reach someone who loves you.

The Mental Game 

Running a marathon is hard for everyone. Running a marathon while managing a chronic condition that requires constant decisions adds a layer most runners never think about.

There will be miles where your blood sugar is doing something inconvenient and you have to make a decision in real time while also running 26.2 miles. This is normal. This is T1D marathon running.

The good news is that T1D runners are some of the most mentally tough athletes out there. You have been making life or death decisions about your body since your diagnosis. Running 26.2 miles is hard. You already know hard.

What I Wish Someone Had Told Me Before My First Marathon

Practice fueling on every long run without exception.

Over pack your lows every single time.

Let the adrenaline spike happen at the start without correcting.

Write your emergency contact on the back of your bib.

Your blood sugar will not be perfect on race day. It never is. Perfect is not the goal. Finishing is the goal.

And finally — tell someone at the start line that you have Type 1 diabetes. A fellow runner, a pace group leader, anyone. You don’t have to make a big deal of it. Just let one person near you know. Community matters out there.

You trained for this. Your pancreas doesn’t get a vote on race day.

Go run!💙