A CGM, or continuous glucose monitor, is a device commonly used for Type 1 and Type 2 diabetics. They use it to manage their blood glucose in real time.
CGM provides a continuous readout of how blood glucose changes over time. The best part is you use it without the hassle of drawing blood with a lancet multiple times. Available options include the Dexcom G6 and Libre Freestyle.
But what about their use in healthy individuals? Is there benefit to this data for those looking to fine tune their lifestyle?
Those interested in the biohacking and longevity space have already co-opted their use. As a result, you can find many blogs, podcasts, and videos singing their praises. Additionally, companies have jumped at the chance to provide devices, consulting services, and apps to use continuous glucose monitor data.
But are they putting the cart before the horse? Furthermore, does the data support their use in this population? In today’s blog we’ll discuss the controversy over their use and identify where they may provide useful information.
Controversies surrounding the use of CGM in healthy users
Low carb confirmation bias
The use of continuous glucose monitors in healthy individuals has sparked quite the discussion on social media. On the one side you have the evidence-based medicine crowd saying they aren’t useful at all.
On the other side, you have proponents, particularly low carb twitter, singing their praises as the true way to individualize your diet. As a result, both groups are shouting past each other
It’s certainly true that there really is no strong evidence that a metabolically healthy individual needs to worry about postprandial(After meal) glucose excursions. The primary controversy is that the data in Type 2 diabetics applies to healthy individuals(It doesn’t).
A clear case of confirmation bias has low carb Twitter pushing the use of these devices. In the mind of low carb Twitter, the worst thing you can have is any sort of glucose excursion. This goes back to the whole “Type 2 diabetes is bad for you” idea, which it is.
The problem with this notion is that it is an extremely myopic version of what happens in Type 2 diabetes. Yes, Type 2 diabetics have poorly controlled blood glucose. But they also have poorly controlled triglycerides. Ultimately, they simply have too much energy going through their system.
If you drop the number of carbs you eat, your CGM will clearly show this with a reduced glucose excursion. But what it won’t show is that, assuming you replaced carbs with fat, your triglycerides will go up.
A low carb diet doesn’t cure Type 2 diabetes any more than avoiding exercise cures exercise intolerance. As far as we know, only weight loss can cure Type 2 diabetes.
Creating a negative energy balance does this, and restricting carbs is simply one way of doing that. But simply swapping out carbs for triglycerides probably isn’t going to do you any favors unless gets you to maintain a healthy calorie intake.
Assumption that blood glucose response is the most important factor of a meal
While blood glucose is certainly an important marker of how we respond to a meal, there’s no data showing it’s the most important. Assuming the goal is to reduce postprandial inflammation, a recent paper shows that postprandial triglycerides were more important.
The PREDICT trial is a series of papers looking at an individual’s response to different meal types. They found that postprandial triglycerides correlated more strongly to inflammation than postprandial glucose(0.83 vs 0.24).
While this is new data and requires replication, it shows that those managing glucose by dropping carbs low and upping considerably may be increasing inflammation rather than lowering it. Another paper found that those with Type 2 diabetes had an 8-fold increase in CVD risk when triglycerides AND inflammatory markers were high vs elevated inflammatory markers alone.
This is how solely focusing on blood glucose and ignoring postprandial triglycerides can cause more problems than it solves. Ultimately, the same solution applies as above. Create a negative energy balance and both should drop.
But simply swapping out carbs for fat is not the solution. And an argument could be made that it’s actually worse.
Validity & reliability of CGM for healthy users
It’s clear that a person’s glucose response to a meal is an important variable. But is it the most important? We really don’t know. Furthermore, what is the ideal response?
Do we want the peak to stay low or the period of elevated blood glucose to be short? Or perhaps a smaller area under the curve. One major problem is that many people use the criteria for failing an oral glucose tolerance test(OGTT) as the best response. The problem is, this criteria is dictated by the parameters of the test.
The OGTT is 75g of glucose alone in fluid form. You can’t expect someone who eats a meal with a higher carb load to remain within those parameters. Consequently, you can’t say that someone who eats 100g of carbs from rice who fails an OGTT is having a pathogenic glucose response.
There is an additional concern with the accuracy of readings of CGM devices. A recent paper had individuals with Type 1 diabetes wear 2 CGM devices and cross-checked them with spot readings. They found that glucose readings were off by over 12% between devices.
Are there benefits from using a CGM?
It’s clear that a good number of people are going to come to erroneous conclusions based on data from a CGM. Additionally, companies putting the cart before the horse will offer diet optimization programs even though they’re not really optimizing diet for anything other than the glucose response. And yes, this can actually lead to harm.
But does this mean that data from a CGM is useless? Or, are there some benefits we can pull from this type of data?
There are several areas where I can see the data from a CGM being useful. First, it may be useful to see how you tolerate different higher carb foods.
You may be perfectly fine consuming 75g of carbs from a potato, but 75g of carbs from oatmeal may be problematic. Robb Wolf discussed this in his book Wired to Eat.
Second, people can use the data to fine tune the serving size of something they want to keep in their diet. For example, if you like ice cream but are concerned about your glucose response, you can always find out a serving amount that leads to a healthier glucose response.
Finally, a CGM may be useful for fine tuning non-dietary aspects of your diet to improve your glucose response to meals. Diet isn’t the only lever you can pull.
Maybe you like to eat pizza on Saturday nights and seeing your CGM data after hitting a hard workout shows you that your glucose response is much better if you do so. In the end, if this gets you to exercise more and sit on your keyster less that day, this is a win.
Keep in mind that in each of these situations, you won’t be jacking up your triglycerides to pass the glucose test. As such, there really are no drawbacks here. And there are likely a number of other beneficial ways to use this data not mentioned.
And sure, you could do all of these with a regular blood glucose meter, which I have done. But some people like the ease of use of a CGM.
A CGM can be a useful tool for a healthy individual to help them make better choices with their diet and lifestyle. It is clear that some companies and individuals will jump the gun and offer services using the data from a CGM to optimize your diet. However, the data simply isn’t there to support this idea.
Until we can collect more data, particularly on triglycerides, a CGM will simply not give you enough information to optimize your diet. The corollary here is the microbiome tests from companies such as Thryve or the former Ubiome. They were interesting, but they didn;t help people optimize their microbiome. We don’t even know what that would look like on an individual basis.
Some practitioners did become proficient at reading them and likely benefited their clients. But at the end of the day, $500 for something that may or may not provide you with useful information is a hefty price to pay for some people. I looked into CGMs last year and just couldn’t find a benefit you can’t get with A1c testing and regular OGTTs.
But, for those who want to pay for it and are aware of the drawbacks, what’s the harm? Some people simply aren’t going to sit through multiple skin pricks for OGTTs, so why not a CGM?
Furthermore, it can provide useful information when coupled with other data. I detailed how we used it with one client who was having issues sleeping in a blog you can check out here.