Endurance sport - to bolus or not to bolus?

I'm a true couch potato on MDI, so no suggestions at all, but I'll tag @In Response for you, I believe she has quite some experience with exercise on a pump.

Have you made any progress @bluepotter81 ?

I have a similar conundrum with cycling, though I'm on MDI. This is my experience, it's certainly not a recommendation as you'll see, I'm keen to hear how other people deal with things.

For short-ish rides (<4h) I often leave my basal alone (usually because these are unplanned), make sure I don't have any bolus on board when I leave and cram perhaps 40g of carbs, which sends me a little bit high but then I come back down and need to start eating from perhaps 1h30 onwards. For less than 2h I don't really care about residual bolus on board as long as I eat something uncovered before I leave and take enough carbs with me just in case.

For longer rides (say 6h+) this isn't a good thing as I need to eat so much in the second half of the ride that I either feel nauseous or can't easily carry enough with me, so after a few unhappy learning experiences like that, I now tend to halve my basal (I split equally pre-bed and pre-breakfast) by either completely skipping the morning dose or more usually slightly reducing pre-bed and taking very little pre-breakfast/ride.

This is where my conundrum begins, the behaviour I had last year was fine, this year it's different.

I used to get up, drink some coffee, eat breakfast (porridge) and try to get out the door fairly quickly, to prevent a blood sugar spike. This tended to work ok, I'd go a bit high, but would gradually drop back down and then start eating after perhaps 1h30 - 2h, and not need vast amounts of food (say 50g/hr).

This year I find I go really really high first thing, even if I take some bolus with breakfast I still go really high. I have noticed that on normal (non-cycling) days I'm tending to trend up in the morning, and caffeine seems to have an effect that I never previously noticed.

The previous behaviour was ok, though I obviously had more basal onboard than was necessary purely to stabilise blood sugar, though it did depend on the ride as sometimes it would not be quite enough - occasionally I'd do a 5h+ ride and not need to eat at all during the ride, which was doable, but I would be feeling pretty knackered at the end as you mention too. In cases such as this I was always reluctant to take any bolus for fear of going low immediately - occasionally I'd ride somewhere for lunch or cake and start heading upwards fairly soon after stopping (which sometimes happens, I think because of delayed digestion so the things you've eat thus far suddenly catch up!) and then further up once eating, so I'd take some bolus (1/3 to 1/2 of the normal amount) and then regret it for the rest of the day as I'd need to eat so much to avoid going low once I started riding again.

But now I'm at the point where I am actually going to need to look at planning to bolus properly - even if I take 1/2 of the cover for my pre-ride breakfast + coffee (say 2 or 2.5 units), I still go very high, so end up taking another ~1.5 units to bring myself down, and then I'm back to needing to eat once it hits the floor, and judging the point at which to start eating after the rollercoaster and while cycling isn't much fun, I imagine the big swing is probably not great for performance/how you feel either.

I plan to do some experimentation over the coming months doing some longish rides that I can bail out of reasonably quickly and head home if my initial bolus strategy is too aggressive and I'm needing to eat too much. I also plan to reduce basal further and try some "micro-bolus" doses later on during the rides (where "micro" for me is 0.5 units as it's the smallest my pen will do) to see how that affects things.

All part of the fun, this is probably not a very useful post for you, but I just thought I'd say you're not alone in these problems and it would be interesting to hear how other people deal with things/how it changes over time

SimonP78 said:

Have you made any progress @bluepotter81 ?

I have a similar conundrum with cycling, though I'm on MDI. This is my experience, it's certainly not a recommendation as you'll see, I'm keen to hear how other people deal with things.

For short-ish rides (
For longer rides (say 6h+) this isn't a good thing as I need to eat so much in the second half of the ride that I either feel nauseous or can't easily carry enough with me, so after a few unhappy learning experiences like that, I now tend to halve my basal (I split equally pre-bed and pre-breakfast) by either completely skipping the morning dose or more usually slightly reducing pre-bed and taking very little pre-breakfast/ride.

This is where my conundrum begins, the behaviour I had last year was fine, this year it's different.

I used to get up, drink some coffee, eat breakfast (porridge) and try to get out the door fairly quickly, to prevent a blood sugar spike. This tended to work ok, I'd go a bit high, but would gradually drop back down and then start eating after perhaps 1h30 - 2h, and not need vast amounts of food (say 50g/hr).

This year I find I go really really high first thing, even if I take some bolus with breakfast I still go really high. I have noticed that on normal (non-cycling) days I'm tending to trend up in the morning, and caffeine seems to have an effect that I never previously noticed.

The previous behaviour was ok, though I obviously had more basal onboard than was necessary purely to stabilise blood sugar, though it did depend on the ride as sometimes it would not be quite enough - occasionally I'd do a 5h+ ride and not need to eat at all during the ride, which was doable, but I would be feeling pretty knackered at the end as you mention too. In cases such as this I was always reluctant to take any bolus for fear of going low immediately - occasionally I'd ride somewhere for lunch or cake and start heading upwards fairly soon after stopping (which sometimes happens, I think because of delayed digestion so the things you've eat thus far suddenly catch up!) and then further up once eating, so I'd take some bolus (1/3 to 1/2 of the normal amount) and then regret it for the rest of the day as I'd need to eat so much to avoid going low once I started riding again.

But now I'm at the point where I am actually going to need to look at planning to bolus properly - even if I take 1/2 of the cover for my pre-ride breakfast + coffee (say 2 or 2.5 units), I still go very high, so end up taking another ~1.5 units to bring myself down, and then I'm back to needing to eat once it hits the floor, and judging the point at which to start eating after the rollercoaster and while cycling isn't much fun, I imagine the big swing is probably not great for performance/how you feel either.

I plan to do some experimentation over the coming months doing some longish rides that I can bail out of reasonably quickly and head home if my initial bolus strategy is too aggressive and I'm needing to eat too much. I also plan to reduce basal further and try some "micro-bolus" doses later on during the rides (where "micro" for me is 0.5 units as it's the smallest my pen will do) to see how that affects things.

All part of the fun, this is probably not a very useful post for you, but I just thought I'd say you're not alone in these problems and it would be interesting to hear how other people deal with things/how it changes over time

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I am 59 and have DM1 since 2004. The way I respond to insulin and meals and endurance exercise has changed during the years. It trial and error, and you are aiming at moving targets...

The real game changer has been continuous glucose monitoring on my Garmin watch. I found a hack based on xDrip three weeks ago.

See my other post from today how this works. I carry 1 or 2 750 ml bottles with High 5 sports drink (without protein). By observing my glucose level under exercise I can fine tune my blood glucose while exercising. I am training for Olympic triathlon, so I exercise for up to 4 hours on end.

My response has also changed - my exercise sensitivity to insulin seems to be somewhat less pronounced now to my basal (i.e. if I don't alter it pre-exercise), which may be because I'm more efficient and can produce more power for longer, so I'm not exhausting my muscle and consequently liver glycogen stores so quickly, but I've not really thought about it too much. It is what it is, and as it changes fairly slowly one adapts.

I also use XDrip+ and a Garmin Fenix watch and a Garmin headunit, both of which display blood glucose as you know. I agree this is really useful, and what would also be useful is being able to see IoB (or time till none) and CoB (with a different absorption rate for "during exercise") on the watch/headunit and a trend prediction (again taking into account exercise). These are all on my todo list, though as it works reasonably well at the moment, motivation isn't all that high, and there's always something else that takes priority (often going for a ride, especially when the weather was actually sunny over here! )

What do you do about the swimming leg of your triathlon? I'd quite like to not have my phone in the loop and instead use a Google Wear OS watch as the collector, which would mean I could be completely waterproof - I don't recall the last time I went swimming (it was abroad, though I should start going with my children in this country) but I do lurk around boats from time to time and it would be easier to not need to have my phone close by (in a plastic bag).

I saw in a different thread you said you might start your triathlon with a blood glucose of >15mmol/l, which I can sympathise with. Has this now changed, what do you try to maintain it at during the races? Edit: I see a graph from your Garmin here: https://www.diabetes.co.uk/forum/threads/spikes-when-exercising.193684/page-2#post-2632307

I have considered sports drink, but as it usually takes quite a while before my blood glucose starts dropping, I prefer to stick with water/electrolytes to avoid being too high to drink what I've brought with me. What I should probably do, having now run low on water on my last could of long rides, is stop half way around and refill one bottle with something like diluted orange juice from a supermarket. It's a shame there aren't dissolvable tablets for sport drink mix (in the same way as one buys electrolyte tablets). I could always take a container/plastic bag of course.

Just to add an update based on my most recent long ride, hopefully of interest, and at least this way I won't forget It may be much too much detail, sorry. I should also try to pull this into a graph, rather than lots of words. Something for later perhaps!

On Sunday I did a long ride (but certainly not long in comparison to the PBP which also started then!): total duration ~12h20 riding time ~10h20.

I took usual basal the night before (9U Abasaglar) and reduced morning bolus to 3U. I took a small bolus of 3.5U Novorapid when I got up (0715) though in hindsight I should have taken more. I had a cup of white coffee (~5g CHO) around 0730, blood sugar had started its morning rise (~12mmol/l), faffed around getting food ready and working out what to wear, did another blood test (~14mmol/l) and eventually had another cup of coffee + small bowl of porridge (5+30g CHO) at 0745 and then was rolling down the road at ~0810.

After an hour of Z1/Z2 exercise, my BG was >22mmol/l, not ideal, but I've been there before. I rode for another 30min ever hopeful it would start coming down on its own, but it sort of oscillated around but didn't drop below 22 mmol/l (I note this was all via XDrip+ talking to a libre2, so it's likely it wasn't quite this high). After 1h30 I decided enough was enough and I should drag it down, not least because I really needed to start eating at some point as otherwise I'd not have any appetite later on when it became more important. I took 1U Novorapid @ ~10am and continued on my way.

At ~1125 my libre was reading 10mmol/l, so I started eating - 20g of carbs (Bourneville brunch bar).

At this point the calibrated curve I was following diverged from what I think my blood glucose actually was, based on some finger prick measurements I did later in the day. At about 1215 my calibrated numbers said 7mmol/l, but I think it was probably around 9mmo/l. I ate another 10g of carbs (2x Nice biscuits, they were good), and then set about munching on some granola from a bag, which was another 30g CHO over the next 30min or so.

I arrived for lunch at ~1320 with BG of 8 (tho probably 10) mmol/l, had a cup of coffee (5g CHO), and a single slice bacon sandwich (~20g CHO) then another cup of coffee (5g CHO). Stopping is troublesome as the carbs are no longer being used so what you eat raises your blood sugar, but if you take bolus as I would have done in the past for slightly shorter rides, I end up going really low on the way back home, which isn't much fun as you need to keep eating constantly.

So this time I accepted I'd probably run high afterwards and planned to keep the stop short. In the end it was ~1h15 (I was chatting), but I eventually restarted on the homeward leg around 1435 with BG of 12 (15) mmol/l. It continued to rise for another 15min (peak of 15 (17) mmol/l), then started coming back down. Shortly before 1500 I started eating with BG 9 (10) mmol/l. I had 3 batches of 2 Nice biscuits over the next 30min with BG hitting a low of 7 (9) mmol/l around 1630 and then starting back up to a high of 10 (12) mmol/l at 1700 then starting back down.

The next cycle was similar (lasted ~an hour, with 30g CHO, min BG of 6(7) mmol/l @ ~1745 rising to 10 (12) mmol/l @ ~1810.

The cycle following that was also similar, however I'd upped the pace a bit now as I could see home was vaguely close, which may have resulted in a downward trend. I ate 30g CHO at ~1855 hit a low of 4 (6) mmol/l @ ~1915 then a peak of 7 (9) mmol/l at ~1950.

Had I been riding further I'd have eaten some more, but as I felt fine I accepted the downward trend from then on and arrived home @ ~2030 with a BG of 4 (4) mmol/l.

I had a glass of milk when I got back and my blood sugar started going up about 30min later. I wasn't sure whether I'd go low or high post-exercise, so had my bolus at the same time as food, I didn't need to bother, there was no difference to normal in my response to bolus insulin, so I ended up running a bit high after supper and then coming down to around 10 mmol/l at bed time. I took 0.5U Novorapid to fix that (I'd normally have taken more but was concerned I might go low), took my normal basal (9U) and went to bed.

I then dropped to ~3.5mmol/l and sat there solidly all night. I must have been just above the alarm threshold as I don't think it went off. My dawn phenomenon the following day was very small/almost non-existent and I had slightly higher insulin sensitivity than normal for my boluses - I'd take the normal amount and need to eat more than expected (this is as far as my analysis has gone), but by that evening everything was back to normal, including dawn phenomenon the following morning.

That was very long, sorry.

To summarise: 30g/h while riding seems reasonable with a morning basal reduction to ~1/3 of normal. I can eat that quite happily and felt fine riding - there is a net energy deficit but it's only a single day and it's easy to make it up in the evening/by eating more for lunch (but faster). I should take more bolus in the morning to cover dawn phenomenon, this will probably be fairly easy to handle as there's no issue with forcing food down so early in the day if I get it wrong. It may also be a case of nerves as this was my longest ride to date. Practice makes perfect, ideally not being so high tho!

While I have previously commented that I don't need to reduce basal the night after exercise, it appears to depend on what you're used to. For really long rides it looks like I should indeed do this as the reduced morning dose is not enough of a reduction.

I think lunch stops should be shorter. To fix the BG rise I'd need a reasonable amount of bolus (2U+), but then that would clobber me later in the day. I could see myself taking 0.5U, but that won't help the rise after lunch and will just result in me going (a bit or a lot, hard to know) lower later on. I should probably try to eat a bit more too.

In terms of eating later on in the ride (when you don't really feel like it), I will have to try setting myself an alarm to remind me to eat something every 30min, rather than every hour, as this might make for less pronounced oscillations (tho they weren't bad) and also make it easier to keep eating).

I can't find the data now nor remember quite when, but while riding up a rather steep hill, I did note that my BG had gone up more than I'd expected, which made me think that my liver must be recharging its glycogen and now releasing it for me (this was well into the ride). I can't for the life of me recall when this was though, so take it with a pinch of salt. Perhaps it will become clearer when I finally get around to plotting a graph of BG vs pedal power, OTOH I may just have been day-dreaming

Just to add one more data point, I did a 6h10 122km ride yesterday (quite hard work - hilly, lots of traffic, was trying to get somewhere for a certain time - I failed on that front!)

I reduced basal in the morning to 5U (vs normal 9U). I didn't leave until 1330, so was able to sort out my dawn phenomenon, however I ate too much uncovered immediately before I left (2 slices of bread and butter, a couple of chocolates, and then munched an apple while I was riding out of the village - my blood sugar was dropping rather than rising and I felt hungry) so I did run high immediately after I started riding. When I looked it was 19mmol/l @ 1500 (failed again, doh), so I took 0.5U @ 1515, and was back down at 10mmol/l @1615 and dropping fast.

I ate 30g of carbs (part bake roll with butter and ham - good volumetric carb bang for buck imo plus it's normal food) @1620 and had another 15g carbs (3x Nice biscuits) @1655 as blood sugar was still going down (though very gradually) and I was hungry. BG bumped along around 10mmol/l for the next 2h (which I wasn't too pleased about at the time, but TBH isn't too bad, no way I wanted to take another 0.5U bolus as I didn't plan to stop for proper food), before starting to drop again, so I ate a Bourneville brunch bar (20g CHO) @1920 with my BG at ~6.5mmol/l which kept it around 6 for the next 45min. I then had a few pre-emptive sour jelly sweets (knowing I had some climbs to do on the final leg home) ~6g CHO @ 2000.

When I got home, BG was fine, I ate a carby supper (~80g CHO) with normal split dose (didn't have anything before starting to eat, and I injected at the same time). I did have much higher insulin sensitivity again (though thinking about it this is probably muscle glycogen replenishment), so had to eat much more than I would normally for the insulin I injected over the course of the evening, which was fine as I'd split dose so could see what was happening (and I was hungry!), however, once my boluses had run out, and I was wanting to head for bed, I had a small snack as I didn't want to run low overnight and it instead made me run high overnight.

It may be that my higher insulin sensitivity ran out at that point or more likely muscle glycogen replenishment was complete. I did reduce my overnight basal slightly to 8U (vs 9U), but I needn't have bothered. This morning I've had the usual dawn phenomenon, so it appears that a short ride isn't enough to raise my insulin sensitivity overnight these days (though it certain did when I started out). YMMV, hopefully of some vague interest.

Addendum: having gone out for a properly short ride today (the day after the above), I did note that I needed to eat when I hadn't expected to - I had no IoB or at most the very tail end (4h after injecting), and had 25g of uncovered carbs before I left, I needed to eat another ~50g of carbs in the middle of a very gentle 2h ride and came back with about the same BG I left with. I don't know the cause, muscles more sensitive to insulin when exercising, something for me to do some Googling for.

Hi @bluepotter81 chapeau, that's a really big day out (~186km as well as the climbing, I believe, for those who don't know), I hope you had fun

I lol'd when I read your comment, it is all a grand experiment, which always keeps life interesting. I joined the forum to see what other people do with long distance endurance events, so I thought I should detail my ongoing experiments, hopefully someone will find it of use.

Out of interest what did you eat in terms of carbs per hour (and just out of curiosity, very person specific, what type of food - I'm always interested to hear what others eat.)

Sounds like you find 50% basal rate on the pump works for you, presumably so that you can eat during the event (up from the 10% you mentioned in your first post), for comparison I'm running something like 65% basal with MDI, so a similar approach and for the same reason - too little and I'd be stable but unable to eat.

Did you try doing small boluses with your lower basal rate? I was considering this approach but given how rapidly I drop/how much I have to eat with even a very small bolus injection and the additional faff required, I've settled on letting the basal do the work, for the time being at least.

Do you think your initial spike was adrenaline/nerves for the big event, do you tend to a get a spike for other rides?

Would also be interesting to hear your comments on post-ride insulin sensitivity, overnight requirements, etc.

Thanks

SimonP78 said:

I can't find the data now nor remember quite when, but while riding up a rather steep hill, I did note that my BG had gone up more than I'd expected, which made me think that my liver must be recharging its glycogen and now releasing it for me (this was well into the ride). I can't for the life of me recall when this was though, so take it with a pinch of salt. Perhaps it will become clearer when I finally get around to plotting a graph of BG vs pedal power, OTOH I may just have been day-dreaming

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Very interesting read!
Since you use xDrip: Garmin iQ connect has an xDrip data field for BG. When you have a Garmin watch with a colour display (e.g. Forerunner 945 and above) you can have a watch face showing your glucose even if you don't exercise (not supported on an Instinct 2). When you exercise you can display the xDrip field. And you get plots in the end. I found this out 5 weeks ago and this was quite a game changer. Now I can exercise with more normal BG values.

Yes, I do this and have BG on my watch and headunit, however it's not possible to view e.g. power and BG with the same time axis zoom using the app or website as far as I can tell. Also the data recorded while riding sometimes doesn't update immediately - it seems to be an occasional problem with the Garmin Connect app not sending data over to the devices, as if I fish my phone out while riding I can see it has read the sensor successfully (I used to wonder if it was the larger number of things broadcasting in the 2.4GHz range - Bluetooth and ANT+.) It's not terrible, but makes it trickier to analyse the data (so my preference is to take the data from XDrip+ via the SQL database backups) and plot my own graphs (MATLAB).

Thanks for the detailed response @bluepotter81

bluepotter81 said:

Hi @SimonP78, as I mentioned, at the start I had porridge and toast & banana. I would then say across hours 2 to 11 I was consuming at least 120g per hour. Typically at least one gel; almost a full clif block and then eating at every station (e.g. handfuls of biscuits and jelly babies and salted snacks). I gradually move over to gels only towards the end. If I lined up everything I ate on the day, it would probably make you feel physically sick just looking at it!

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It does sound like I should probably look to eat more, probably by stopping a bit more often to buy something - stopping (and my bike leaving my sight while I go into a shop) is a problem, I must eventually cross this mental hurdle so I don't need to take everything with me!

bluepotter81 said:

Btw, I use to run at 10% basal but then bonk because I didn’t eat enough since my bloods seemed at a good level.

I’ve learned how to do small boluses too. Nothing more than say 0.5 to perhaps 1.5 (only if my bloods are sky rocketing). During the event, as the hours progress. I become very sensitive to insulin.

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I was planning to look at these, but with my massive initial spikes, I've been taking a bit more to (try to) cover these, I must experiment with some micro-doses pre-lunch stop to ensure I'm trending down, and then eat a bit more on the go afterwards once I recover from the spike. How much extra do you find you need to eat with a 0.5U bolus? Or are these just for days when your BG is too stable and you want to be able to eat something? I find 1.5U generates a massive downwards trend, as you say, which works for my initial spike (which I need to try to fix earlier/with more pre-ride bolus.)

bluepotter81 said:

Post-ride, especially after a big event, I’m usually ok through the night. I certainly have to eat more at bed. But, I get stung the next day. It’s as if all the dormant unused carbs get released the next day and I have to compensate with more and more insulin.

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That's interesting, I wonder how quickly muscle glycogen storage declines (from carb-loaded state back to normal) and whether this is having an effect, though whether that would cause you to run high I don't know - depends on how insulin sensitive the muscles are I guess. Interesting though as other people comment on needing more food/less insulin the day after exercise (and I also needed to eat a bit extra having taken standard insulin the day after my 200.)

bluepotter81 said:

I use a Dexcom G7 CGM and I love it. It’s the best thing that over had in terms of diabetes control. I’ve tried Libre but Dexcom G7 is the one for me. Unfortunately though Dexcom do not allow data fields on Wahoo bike computers yet.

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The whole thing with needing non-standard ways of getting CGM data onto bike headunits is annoying. There is a draft Bluetooth LE CGM specification available and I understand there's also a draft ANT+ spec (though only available if you pay money), it's annoying that the CGM manufacturers don't get on with it and provide a way to broadcast the data either directly from the devices (there are some hurdles, re internal calibration) or via their apps.

I did drop Wahoo a line to ask about their support for the Supersapiens ecosystem (for someone I know with a Wahoo), but they completely ignored me. I had hoped for a bit of information about how one might supply other data as the Supersapiens display widget is already there. Maybe a job for a cold and rainy day and a decompiled version of the Supersapiens app.

bluepotter81 said:

I’m keen to know what you’ve got planned next?

I’m doing Ironman Nice in June so a whole new world of experimentation awaits me.

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That sounds interesting and challenging, good luck and let us know how you get on with your prep work

I don't have anything concrete planned - re diabetes I need to fix my dawn phenomenon spikes when riding or at least reduce them, so there's going to be more experimentation with pre-ride boluses, also as I mentioned above looking at effects of micro-boluses and how they help with stopping and eating.

Regarding riding, just doing more. The 200 was fine, I felt like my legs were on good form and I could have happily gone further had I stopped for some more food at ~200km (and not sped up once home was in sight), so I think just doing some more long days out and exploring. I've been ticking off veloviewer tiles since I started as a motivator to make me ride further and ride different routes - I enjoy planning the rides. So probably a mix of making my square bigger and wandering off to visit more places directly, plus probably going and doing some organised Audax rides rather than all solo riding.

I had planned to do King Alfred's Way this year (over 3 days including riding to and from the start of the route, then staying with friends and family located vaguely close to the route), but the weather hasn't ever been particularly appealing when I've had the time, and vice versa, so I must try to get that done early next year once it's dried out (while I like a challenge, I do also want it to be mainly type 1 fun and to actually enjoy being there!)

I'm also thinking about wandering over to the continent to visit Germany, France and Switzerland (though not all in one go, as work and children!) for some credit card camping though it's only a vague thought at the moment for something to do next spring/summer as I used to work in Germany and Switzerland (and spent a fair bit of time in France along the way) and haven't been back for ages, so what better way to do it than by bike.

Last but not least (though somewhat neglected right now as I've been out riding), I've got some bike-related tech projects underway - I'm in the process of writing a replacement for the software that came with my TwoNav Cross (Linux-based bike computer) so there's some experimentation to do with that along the way (the plan being to have a standard map/metric UI along with features I'd like such as knowing which tiles I've ticked in real time, detour suggestions for POI an extra tiles along with the "cost" of doing the detour, real-time rain forecast, quick carbs input from a custom list on headunit and comms/logging in XDrip+ along with display of CoB/IoB and BG predictions from XDrip+ on headunit).

Great thread by @SimonP78 and @bluepotter81. What you’re doing is exactly what I want to get to - Audax, bikepacking, general adventure. I need to get the basics right first re bolus, basal and food and then build it up from there. There is hope!!!