Episode 150 – Can Blood Glucose Monitors Improve Athletic Performance?

Key Topics Covered

Person wearing continuous blood glucose monitor.

Background

  • A Continuous Glucose Monitor is a wearable device that tracks your blood glucose levels throughout the day.
  • It involves a small sensor inserted under the skin, usually on the arm or abdomen, that measures glucose levels in the interstitial fluid. The sensor transmits this information to a mobile app, allowing users to see their blood glucose meter trends in real-time. 

Assumptions We Will Make for This Podcast

  • We are focusing on athletes with good insulin sensitivity and not those at risk of diabetes, with the simple intention of trying to improve performance.
  • We will likely mostly be talking about endurance sports since that is mostly where they are being used. But in saying that, these same concepts apply in other areas.
Athlete running with a gel.

Pros

  • Although we are listing out some advantages, this likely isn’t going to be representative of our actual thoughts.
  • While there are a lot of claims around how CGMs could help you optimize fuelling strategies, I would be cautious on those claims. But there are still some potential benefits.

The main three areas of relevance are:

  1. What if you consistently have reactive hypoglycaemia. For example, some people experience low blood sugars directly when starting exercise, following pre-workout carbs. CGMs could help identify that so you could adjust your approach.
  2. What if you were to be consistently having low BGLs at certain times in exercise? I’m less concerned about this being a big factor, but it’s still something to consider.
  3. It could help as an additional screening tool for LEA. Fasting BGLs can drop a bit in response to LEA. Once again, this wouldn’t be a big factor I’d focus on, but it’s still one more piece of data.

Cons

Bread rolls with caution sign over it.

  • We will preface this with: Having increases in BGLs is normal. There is nothing inherently dangerous or bad about this.
  • When we eat food, that is broken down and converted to glucose which is released into the bloodstream. This is particularly relevant to carbohydrates 
  • Keep in mind that protein can also raise blood glucose levels.

The 3 biggest cons we see coming from wearing this type of device are:

  1. Many athletes, particularly endurance athletes, should be consuming a lot of carbs. And Wearing a GM can make them unnecessarily concerned about BGLs increasing when this is a non-issue 
  2. There is a 5-10 minute delay measuring interstitial glucose rather than blood glucose – so the reading may not always be entirely accurate to that specific point in time
  3. Of the most common machines available in Australia, one takes samples every minute, while others take samples as infrequently as every 15 minutes. As you can imagine, if something only took samples every 5+ minutes, combined with the delay, the relevance starts getting quite low for athletes in training or competition. So that is something to consider as well from a data point of view.

Neutral Thoughts

  • While the reactive hypoglycemia aspect is relevant the other two pros really aren’t.
  • The LEA aspect is something that we should be focused on trying to avoid anyway + there are many other signs. Fasting BGL’s can be measured with a single measure too, it doesn’t need to be a CGM.
  • For endurance athletes at high intensities, during competition, I’m typically aiming to give them as many carbs as they can tolerate. If they randomly had a low 1 hour in, I don’t think it would change that I’m still trying to give them as many carbs as they can tolerate.

Nuanced Perspective & Challenges

Athlete with heart rate monitor.

  • What if there was zero chance that this would negatively affect an athlete? What if it was just another piece of data?
  • Asker Jeukendrop used a great analogy when he equated BGM to HR monitors: when heart rate monitoring first became popular in exercise science, people had similar arguments about how these devices had little practical value. But now it is something that is widely used as a data point for endurance athletes.
  • We have so many tools for gathering data. And when you look at them individually, they aren’t going to solve a significant amount of problems.
    • But that example is interesting because if CGMs were simply viewed through that light, you could see that they might have potential benefits down the line.

Mindset Challenges

  • But if you then factor in the impact on athletes, it is a different issue.
  • Many practitioners have tried doing all they can to brief their athletes on how they want the CGMs to be used, and then out of nowhere the athletes have started focusing on the wrong foods.
  • Real example: An athlete using a CGM under the guidance of a practitioner just to get data stopped drinking orange juice because they didn’t realize it spiked their BGL’s so much and was so “bad.” This type of scenario is common.
  • Especially with so much misinformation online around this topic, we should be cautious about giving athletes this data.

Summary:

  • The current consensus is that CGMs for athletes without diabetes comes with risks and doesn’t really improve performance.
  • I’m personally interested in the reactive hypoglycemia aspect, but I wouldn’t even explore that unless you had identified symptoms.
  • I’d wager many people would technically get low BGLs but not get symptoms, so you don’t want to make yourself concerned about something that isn’t even an issue. 

Relevant Blogs / Resources

Relevant Studies: