Goodbye CGM

After wearing a Continuous Glucose Monitor for 6 months, I'm done for now.

I started wearing a Continuous Glucose Monitor about 6 months ago, and I wrote about it at the 3 month mark. Since then, not much has changed: I could predict the glucose reaction to pretty much any foods I commonly eat. The short-term fluctuation became pretty uninteresting.

More interesting was the longer-term average. There were times when my glucose kept dropping and dropping, until I was averaging below 70mg/dL for several days in a row. Below 70 is considered hypoglycemic, and my CGM would wake me up at night, beeping furiously, when I dropped below 60.

The official threshold for prediabetes is a fasted glucose of 100, but I always thought being above 90 wasn’t great. Maybe irrational on my part, but I like to have some buffer. Call it preprediabetes.

Between 70-90mg/dL was my happy place, generally speaking, what I’d consider the “green zone.”

Not that I actually felt different: it was more of a mental/psychological thing. Pretty much the only time during the entire 6 month period when I felt my blood glucose was when ingesting a singular Starbucks frappuccino containing about 80g of sugar, sending my glucose to 190mg/dL, the single highest value measured in the entire 6 months.

Entirety of CGM data, 300 point rolling average, with diet trials & tribulations.

It wasn’t always easy to determine what caused my average blood glucose to go up or down. In the beginning, it seemed that just staying on ex150 kept slowly but surely lowering my average, until I averaged below 70mg/dL.

A subsequent re-feed between diet periods brought the average up a whopping 30 points, only for it to drop rapidly again.

But then, my average glucose actually started rising on ex150deli - was there something in the deli meats that was different from the beef I was usually eating? The small amounts of sugar they put in deli meats? Maybe the PUFA in the ham and chicken?

Eating tons of chocolate truffle every day predictably kept my average glucose higher than before, and that was not surprising. Both because I was adding sugar from the dark (mostly 85%) chocolate, and because the chocolate was significantly delaying digestion. Whereas the whipped cream would seemingly be gone within minutes, I could feel the chocolate truffle sit in my stomach like plutonium for hours. That would significantly delay absorption, and probably increase the average glucose level.

Interestingly, while I didn’t lose any weight on ex225lean, it did bring down my glucose again.

After starting a vitamin C supplement, my glucose kept climbing and climbing. It took me almost 2 weeks to realize the connection. It seems that the vitamin C slowly started building up in my system. Vitamin C apparently sets off CGMs because it’s structurally similar to glucose. The CGM even warns you about vitamin C supplements whenever you put a new sensor on. Interestingly, the blood prick meter does not get confused by vitamin C at all. I ended up with some 50mg/dL differences between CGM and blood prick for a while.

Then there’s a period where I don’t have a better explanation than stress. I certainly can’t think of anything else that would have raised my average glucose to 110mg/dL. And, just a few days after my life settled down a bit, the glucose dropped rapidly.

Unfortunately it’s hard to measure or quantify stress. I’m pretty bad at noticing I’m stressed, usually it takes me quite a while (days or even weeks) and then suddenly I realize I’ve been very stressed the whole time. So I’m not quite sure when this one began. Conversely, when the stress stops, it’s like a wave of serenity washing over me. It seems much easier to notice the sudden absence of stress.

Interesting in that last one: the average glucose correlates pretty well with the weight loss on ex150-6. The first 10 days or so, I didn’t drop ANY weight. That’s very unusual for ex150, where I normally see a big water weight drop right in the beginning. After about 10 days, my average glucose dropped from 110 to sometimes below 90. This is also the period when I started losing weight again.

Did the CGM help me lose weight?

In short, I don’t think so. I was already 30lbs down in 3 months when I got the CGM.

I think it’s an interesting gadget, and if you have any diabetes in your family, I recommend you get one for a few months. It’ll teach you exactly what certain foods do to your blood glucose. Depending on where you get it, it’s only about $70-200/mo. Shop around and ask your prescribing doctor for a coupon. Try getting the Libre 3 instead of the Libre 2. The bluetooth sync makes it 10x easier to use. I literally forgot I had one most of the time.

But for weight loss, I’m not convinced it adds value. Even with extremely strict diets (30 days of the same meal in a row) and logging every single meal & beverage over 6 months, I often have a hard time connecting the dots.

Anecdotally, I had great fasting glucose even when I was around 300lbs. It just doesn’t necessarily correlate. My theory is that something causes nutrient partitioning to store too much of our food substrates (fatty acids, glucose) as fat instead of making it available to tissues, effectively starving us on a biochemical level. That increases our fat mass, and also causes us to eat more, to make up for it. If that extra intake contains carbs, this cycle can lead to diabetes. If not, you can be 300lbs on a keto diet with great glucose control, like me.

Will I get a CGM again in the future?

Very possible. I can imagine a lot of experiments where a CGM would give interesting data, for example if I got more into ice baths or sauna, or tried fasting again.

The upcoming Libre 4 is supposed to have continuous ketone monitoring, which would be super interesting. I could see myself trying that for a couple of months.