In the last parts of our series in Fueling as a T1D athlete, we talked about planning and monitoring glucose. This part addresses what inevitably happens in real races — glucose doesn’t always behave exactly as planned.
Here, Riccardo Raso explains how he adjusts fueling based on trends, not single numbers, and why avoiding overreaction is just as important as avoiding hypoglycemia.
The Full Series:
- The T1D Athlete Mindset
- Carb Loading with T1D
- Triathlon Fuel & Hydration Plan
- Glucose Monitoring during Training and Races
- Fuel Adjustments Based on Glucose Levels (this article)
When Glucose Is Trending Down Faster Than Expected
If glucose is trending down faster than expected, I anticipate my next intake slightly or use a faster-absorbing option. In the past, before using Nduranz, I sometimes carried a small emergency glucose source, such as a 15 g pure glucose vial.
However, with Nduranz, I generally don’t feel it’s necessary: Nduranz gels are fast yet “long enough.” The Nrgy Drink mixes are slower and even more sustained.
Considering Trehalose As a Carbohydrate Options
I do think Nduranz could benefit from a trehalose + maltodextrin + fructose option as an additional tool for specific contexts — keeping the overall glucose-to-fructose ratio close to ~1:0.8, but adding a “slower base” to aim for flatter curves and fewer spikes.
Mechanistically, trehalose produces lower post-ingestion glucose and insulin peaks than glucose, consistent with a slower glycemic profile.1
In endurance-relevant data, trehalose supplementation during prolonged cycling has also been associated with improved 20-min time-trial performance after a 100-min preload, supporting that it can be a viable exercise carbohydrate source in practice.2
The added maltodextrin + fructose component would still align with the broader evidence that multiple transportable carbohydrates (glucose-based + fructose) increase delivery/oxidation capacity at high intakes.3, 4, 5
Important Note on GI Tolerance
As with any “slower” CHO option, it’s worth noting that trehalose maldigestion/low trehalase activity can cause GI symptoms in some individuals, so it’s best framed as an additional tool rather than a universal default.
When Glucose Is Stable or Gently Rising
If glucose is stable or gently rising, I stick to the plan and avoid unnecessary corrections that could lead to over-fueling. I’ve learned that reacting too aggressively often creates more problems than it solves, especially in long races.
A key point — and a useful contrast — is that there’s no value in panicking mid-race when the plan has already been tested across scenarios and refined through racing.
In long endurance events, glucose dynamics are not “clean lab curves”: competition stress and high-intensity segments can push glucose upward via stress hormones, and that effect can be more pronounced in T1D — so a higher reading is not automatically a problem if trend, symptoms, and execution remain under control.6, 7, 8
Avoiding Hypoglycemia Is the Priority
It helps to remember that even in endurance athletes without diabetes, CGM data show that glucose can run high during prolonged events.
For example, in an ultramarathon study, glucose ranged roughly ~62 to ~252 mg/dL, and mean glucose increased substantially by the end of the race — evidence that values >180 mg/dL (and occasionally >200 mg/dL) can occur in real endurance settings.9
In T1D specifically, evidence syntheses suggest that acute mild-to-moderate hyperglycemia before or during exercise is unlikely to meaningfully impair aerobic performance for most people, whereas even mild hypoglycemia can have clearer negative impacts — so I treat “avoiding hypo” as the bigger immediate performance constraint.10
Glucose Level Targets during Races
My practical in-race target — defined and refined through repeated laboratory testing and race-specific simulations — is to stay:
- Above ~120 mg/dL (alarm set at 130), and
- Below ~190 mg/dL (alarm set at 190, but only if at or above 190 for more than 15 minutes; otherwise skip).
This range is based on a combination of:
- Submaximal graded exercise testing with indirect calorimetry, used to map carbohydrate versus fat oxidation and to identify the intensities at which my metabolism becomes predominantly carbohydrate-dependent
- Threshold assessments, including gas-exchange/ventilatory thresholds and respiratory compensation markers) to anchor those findings to race-relevant intensities
- Field-based race simulations using CGM data together with a fully replicable fueling protocol to validate metabolic stability under real competition stress.11, 12
If glucose approaches ~190 mg/dL and remains there for more than 15 minutes, I apply my pre-agreed ultra-rapid insulin strategy, rather than reacting impulsively to transient fluctuations.
Decision rules, simplified:
- If I’m ~130 mg/dL, stable, and the next intake is in <5 min → I wait.
- If I’m ~130 mg/dL and the next intake is in >5 min → I anticipate slightly.
- If I’m ~130 mg/dL with a rapid downward trend → I take ~½ emergency gel + bring forward the next sip/intake.
For reference, pro endurance athletes with T1D often frame race management around trend direction/rate-of-change and frequently cite a practical race goal band around 120–180 mg/dL, which aligns closely with how I think about staying “safe + effective” without over-correcting.13, 14
A Hard Lesson: When a Logistical Error Ended a Race
I had one episode where a hypoglycemia event forced me to stop the race early. In that race, I made a critical logistical mistake: I forgot to pack my insulin pen needles in the race belt/waist pack.
Because I had no needles, I then made an aggressive decision: to continue fueling normally anyway, even though I could not dose insulin in the standard way. The alternative (stopping intake) would have made finishing impossible.
Predictably, my glucose started to rise as the bike progressed, and I needed a solution. Around km 20–25 of the bike, I approached an ambulance and asked if they had insulin pen needles.
They did not.
The only option available to me seemed to be using a standard injection syringe from the medical kit.
Why This Became Dangerous
Here is the key practical issue (explained simply): pen needles deliver insulin in very small, precise “clicks/units” from the pen, while a syringe is designed to draw and inject a volume of liquid, and it is much easier to accidentally pull too much insulin when you are improvising under race stress.
In other words, I moved from a system built for precise unit dosing to a system where a small volume error becomes a large insulin error. I inserted the syringe into my insulin pen cartridge, drew insulin, and injected it — but I drew too much, which meant I inadvertently administered an excessive dose.
From that point onward, the trajectory was essentially locked: during the run my glucose kept dropping despite normal countermeasures, until it reached a level that became unsafe (~45 mg/dL).
At that point I made the correct safety call and withdrew, because continuing would have meant risking severe hypo symptoms including loss of consciousness.
No improvisation rule: I do not rely on non-pen syringe dosing during a race unless it is a true medical emergency and there is no alternative.
Redundancy is Now Non-Negotiable
It is not an episode I am proud of, but it was a single, isolated incident, and it changed how I manage risk. The prevention is now straightforward — and systematic.
I now always carry spare pen needles in at least two separate locations (primary belt + secondary backup).
Also non-negotiable: in both my T2 bag and, in the case of a full Ironman, in the bike special needs bag at km 90, I always carry:
- A backup glucometer
- Spare insulin
- Spare pen needles
This is a direct consequence of a single past race. Since then, redundancy has become a fixed part of my race execution, not an optional safeguard.
The Takeaway
This is exactly why my approach overall is built around predictability and repeatability: not because I want to be conservative, but because in long-course racing the biggest risks often come from one small logistical miss cascading into a physiological problem.