So About Those Carbs Or, A Stupid Experiment Or, You're Always Learning

Disclaimer: What you are about to read is not a medical study, but rather a case study of one diabetic athlete. Your mileage may vary. In addition, I talk about treatments that are relatively uncommon at this time. Don't do any of this stuff without consulting people far smarter than I.

Over the past couple of years, I've become quite adept at consuming a lot of carbs on my runs. Typically speaking, 50-60g per hour, which is on the higher end of what most athletes can handle.

To accomplish this, I've kept my basal rates at 100%. The combination of insulin plus exercise has lead to outstanding diabetes control and has also helped me to accomplish many of my ultra running goals.

Despite that, I decided to mix things up a month ago.

I'd read some articles about ultra runners using low-carb diets. In doing so, the theory, goes, you program your body to burn fat rather than carbs. The potential benefits here - according to theory - are two-fold: 1. By consuming fewer carbs, you can keep your stomach from getting upset (something all ultra runners have to deal with) and 2. Because you're burning fat, you can drop some weight.

Both of these ideas appealed to me. Currently, I'm 9 lbs. heavier than where I like to compete at, despite all the miles I run and a diet that could be considered good. (Not amazing, but good.)

At Diabetes Training Camp, Dr. Matt said something I hadn't considered before - that lowering basal rates was a trigger to our body to burn more fat. So in other words, in some respects by keeping my basal rates normal, my body didn't know I was exercising (I don't know if Matt would put it that way - but that's how I took it).

So for the past month, I've made some changes. Most of them are fairly simple... simply adding more protein into my diet and ratcheting down the carbs. Not dramatically. Not Atkins like. But measurable.

And - and this is the important part - I've cut my insulin in half during exercise while cutting my carbs by 50-70%.

For the most part, the experiment has been a dismal failure.

On the plus side, adding protein to my breakfast has been a big win. I'm staying full until lunch. I'm going to keep doing that.

My weight has barely moved down. I could make the argument I appear to be carrying it a bit better, but I've never done anything with my weight for cover model purposes, so I don't really care.

My blood sugar control has been fine, too.

But when it comes to long runs and competing, my results have been horrible. I first noticed it on my long runs two weeks ago... Typically, I will do my brutal mid-summer runs around 8:40 per mile, but two weeks ago a comparable effort came in at 9:02.

And then yesterday, I entered a 30k trail race which - fortunately - allowed athletes the opportunity to drop down to 15k. I came through the 15k thirteen minutes SLOWER than I did last year, and didn't hesitate to stop. I shut things down.

In seeing the race results, some of what happened yesterday was likely the heat.. all of the results were slower than last year. But 13 minutes is a HUGE time fall, and I'm confident that while my overall fitness isn't where it was last year, a good chunk of it could be attributed to my carb strategy. Last year in this race, I consumed 60g/per hour. This year, I did 20g/hr.

My reduced insulin strategy worked, as I finished the 15k at 119mg. But still, it was a slow, plodding effort.

I've read enough articles to know that I could be going through a phase of training my body to burn fat. One could even argue that by not reducing my insulin for the past two years I've trained it NOT to burn fat and what I really need to do is be patient. But in thinking it through more and more, it doesn't seem to be the best strategy for me.

My coach and mentor Missy Foy trained me to be an athlete who used his diabetes to an advantage. Understand, I have the ability to take MORE insulin during a race and consume more carbs. It's like being able to run a car on super unleaded while non-diabetics have to run on regular. In the past month, I've learned how much of an advantage that is.

Of course, that also means I need to figure out a different way to cut those 9 lbs., which means I'm going back on Victoza.

Victoza is a drug primarily used by Type 2 diabetics. Taken by a Type 1 diabetic, it can help control but also - in this study - was shown to help the diabetic drop weight. I know this works because I used Victoza once before to cut weight before my 100 mile race. At the time, I stopped taking it because I thought - incorrectly - that the weight would stay off. I also felt that it was affecting my CGM accuracy. Since then, I've learned that staying on the Victoza is likely necessary to keep the weight off. I've also learned that my CGM shouldn't be affected, so I'm now taking it in my arm, rather than abdomen so see if that helps.

In other words, I'm going back to using diabetes to create a competitive advantage for me, rather than trying to limit the disadvantages its created for me. How that will shake out in the following weeks of training remains to be seen.


  1. Anonymous9:21 AM

    Great post Marcus. I've had similar results, which is frustrating because I have a hard time taking in enough carbs when I run (for a run of less than 2 hours keeping my basal at 100% only allows about 16-20 grams per hour).

  2. Super interesting stuff. I love that you talk about using diabetes as an advantage - we don't hear enough about that angle!

    Thanks for sharing!

  3. The other side of the coin is that 60+g CHO per hour can be a lot. For me, if I don't drop my basal to 25% 1.5-2hrs prior, I will drop 10mmol/L(180dg/mL) in 20min. That's a min of 180g CHO/hr.

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  5. I just discovered your blog. My son (age 5) was recently diagnosed Type I. As an ultrarunner myself, I really appreciate your insight on how a runner manages running with diabetes and all it entails. Thanks and keep it up!


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