[nahsra]

I think the "no meal announcement" features are really valuable for traditionally underserved demographics who, for whatever reason, can't "get good" at managing their disease.

The difference between how quickly food and insulin hit your bloodstream make it seem like there is no way to "algorithm your way out of" meal announcements. Food hits almost immediately, and with variable strength depending on macronutrients in it, and insulin takes ~15 minutes to start working, and peaks at 1 hour, with no concern about BG levels. Can you square these 2 for me and make it make sense?

[haldujai]

I think what you're missing for this to make sense is what is the desired outcome. For type 1 diabetics there are three important ones:

1. Time in severe hypoglycemia - ideally 0%

2. Time in severe hyperglycemia/diabetic ketoacidosis - ideally 0%

3. Time in euglycemia (also called time in target) - clinical target is >70% and for reference the median healthy non-diabetic is in target ~90-95% of the time.

Closed loop systems are very good at #1 and #2 as it takes a while for levels to get to the severe state and insulin can be administered (or withheld) based on CGM.

When we talk about algorithming out of meal announcements it's whether historical patient-specific blood glucose levels and insulin administrations (i.e. a prediction of what you eat and when) combined with CGM can keep #3 acceptable, not necessarily optimal. Medtronic is using this approach and their newest model more or less eliminates the need for accurate carb-counting but they still require meal announcements. The hope/idea is that this can potentially be eliminated in further iterations.

Another important thing to keep in mind which is sometimes lost in these discussions is that we don't treat numbers we treat patients (i.e. what are the clinical outcomes). Generally speaking, we assume the closer to normal the better but we don't have actual data about how much an extra X% outside of target ranges matters in terms of clinical outcomes and complication rates. We only really started getting this data with CGM and complications in these mild states would require very large cohorts and long (10-20 year) follow-ups to detect differences as they're likely to also be mild.

So while you're absolutely correct regarding the limitations and that an algorithm cannot outperform accurate carb-counting and meal announcements the missing piece is that it may be sufficient. Particularly if said algorithms result in improved time-in-target for patients who aren't good at managing their diabetes and find meal announcements cumbersome.

[nahsra]

First of all, clearly you have a ton of knowledge in this space, and I'm feeling very lucky I get to learn from your experience here. I have one more last question/challenge:

I totally get that we "treat the patient" -- that's sort of what I'm hinting at with the demographics. But, in my opinion this thing you said:

> we don't have actual data about how much an extra X% outside of target ranges matters in terms of clinical outcomes and complication rates. We only really started getting this data with CGM and complications in these mild states would require very large cohorts and long (10-20 year) follow-ups to detect differences as they're likely to also be mild.

... is not the same as saying "we know that 70% TIR is safe to live with no complications". I don't think any of the guidelines are that confident, because there's not enough evidence yet. Consider this study (discussed at [1]):

> Overall, increasing time spent with glucose levels in the target range of 70–180 mg/dL (3.9–9.9 mmol/L) was associated with decreasing risk for microvascular complications. For instance, 50.0% of the 10 individuals in the lowest category for TIR (<40%) had at least one microvascular complication, compared with just 27.3% of the 99 people in the highest category for TIR (≥70%).

> Moreover, El Malahi said that the 180 people with microvascular complications had significantly lower average TIR than the 324 individuals without, at 60.4% versus 63.9%.

This suggests to me that a difference of 4% of TIR can seriously affect long-term outcomes. And, by the way, even those with the highest TIR still had microvascular complications higher than the normal population. On top of that, we know that genetic and environmental factors may be at play.

Therefore, my monkey math is that 75%+ as a TIR goal may mean that even if the patient is an order of magnitude more vulnerable to complications, microvascular or otherwise, they have a much better shot.

And, unfortunately, the typical western diet with 3 meals a day and snacks, you have to be "good at managing diabetes" to get to 75%+ TIR. Thanks for reading my ramble.

[1] https://diabetes.medicinematters.com/easd-2020/glycemic-cont...