Fueling Strategies to Reduce Suffering in Endurance Sports

In my career, I usually managed to finish Ironman races with solid performances, but I never ran to my potential according to testing and what my coaches thought was possible. There are always multiple variables involved in achieving a top performance, but keeping the fueling going on the run was always a challenge.

Over the last decade – and especially in the past few years – the sport has undergone a fueling revolution. Athletes are going faster and faster and posting times that didn’t seem possible 20 years ago. Several factors contribute: better aerodynamics and access to testing, running shoes with carbon plates, more accessible training information, more young talent entering the sport, and denser pro fields with larger bike packs.

After researching this post and speaking with my former coach and sport scientist Susanne Buckenlei, it became clear that improvements in fueling products are on another level. The carbohydrates available today can supply energy much faster with less chance of stomach issues than in the past. As a result, elite athletes who can sustain higher intensities in races manage to ingest enough carbs to fuel those efforts effectively. Susanne believes this is one of the biggest reasons for the recent jump in performance.

I found another argument that supports the high‑carb fueling theory that isn’t brought up very often. This one turned out to be the most convincing to me because, based on the information in my previous blog, I was skeptical about whether athletes burn a higher carbohydrate‑to‑fat ratio simply because more carbs are being consumed. I was confident that the traditional 70–75 g per hour fueling rate would stave off a bonk during an entire Ironman.

One of my close friends, sports doctor Christoph Simsch from Crailsheim in Germany, performed a study over 20 years ago that sheds a lot of light on this argument. The study was designed like this:

He conducted a double‑blind test with two similarly well‑trained groups of cyclists, each riding for two hours at a very high intensity (just below threshold). Group one received 60 g of carbohydrates per hour in a lemon‑flavored sport drink, while the other group received a placebo drink with the same lemon flavor but no carbs. The test was done twice (double blind) so both groups were tested with carbs and without and, of course, didn’t know which drink they were given. Blood samples were taken regularly and analyzed for several markers, and participants also reported their perceived stress levels verbally. I hope I have described this correctly, but Dr Simsch can correct anything I’ve missed.

The results were very clear. The carb‑free group reported much higher levels of stress and discomfort, and the blood analysis confirmed this by showing much higher levels of stress hormones in the carb‑free group. Given that it is very unlikely athletes would burn through their glycogen reserves in two hours and that stress levels were higher throughout the test, this suggests there is more to fueling than just avoiding the bonk (depleting the body’s carb stores). It would be interesting to replicate this study with three groups: a zero‑carb group, a 50‑60 g/hr group and a high‑carb group (100+ g/hr). As far as we know, no such study has yet been published—sounds like a great project for student sport physiologists.

For me, this study—along with the information in my previous blog—has convinced me that the 100+ g/hr fueling strategy can maximize race‑day performance. It’s not necessarily about minimizing the chance of glycogen depletion; it’s about minimizing stress hormones that increase suffering and pain during the race—more carbs, less suffering! I still have a few concerns and questions worth pondering.

You need to test this level of fueling in your longer training sessions at different intensities. Do not attempt a 100+ g/hr fueling strategy if you haven’t tested it thoroughly and found the product that works best for you. Keep in mind these are highly processed sugars (mainly glucose and fructose), and we know they are not great for our systems—insulin response, etc. Although a well‑trained athlete generally has a good insulin response and muscles that can metabolize carbs efficiently, this is still not a natural process by evolutionary standards. I think it’s key that athletes focus on a well‑balanced diet and eat nutrient‑rich foods and good carbs when they are not training. The downside to this energy revolution might not be known for another decade or more. So fuel up, but stay informed of the risks and always take training trends with a grain of salt.

In summary, my initial belief about fueling was to ‘avoid the bonk,’ and in general, the traditional 70 g of carbs per hour is sufficient to keep energy stores above zero. With all the knowledge I’ve gathered while writing this blog, I’ve changed my mind. It seems that the science says ‘more carbs – less suffering,’ which logically means you can sustain your intensity with less discomfort, and this should translate to an increase in performance. Athletes often aren’t able to follow a nutrition plan exactly, so getting more energy on the bike will help you start the run with more carbs in the tank when it’s even more difficult to fuel. Go for the high carbs, but test in training and see if it works for you.