So I bike for exercise, and I bike commute weather permitting. Used to run until I started getting arthritis in my hips in my 50s so I shifted to a lower-impact routine. All aerobic stuff—steady intensity w/heart rate around ~120. Effect varies by time of day, but barring extraordinary circumstances this has always always always exerted a downward pressure on my BG. For some reason I don’t see as much of that effect in the morning, but it increases throughout the day and late afternoons my homeward ride can drop me 30 points or so. I’ve been T1 since 1983 and as long as I’ve had it, this has been my pattern.
Until now!!!
For example, this a.m.'s ride to work. Starting bg 127 with a couple units of IOB on board. Arrive at work: 165, trending up. Wut??? Recent midday rides have had a similar upward rather than downward effect. Started noticing this over the last few weeks. Like going for an early afternoon ride on a Saturday is actually making my BG increase 20 pts. All of a sudden I’m having to do a correction after exercise, which for me is nuts. I mean, I know some people experience this when they do intense strength training routines, but that’s an adrenaline thing, which I don’t think this is, unless I’m suddenly going all adrenal at exercise I’ve been doing for years that always had the opposite effect. Really confusing and really annoying. I’ve noticed it happening in the past when I ride in really cold temps, <30° F, and I think the adrenaline effect IS kicking in then, but this doesn’t fit any of the patterns I’ve gotten used to over decades.
Makes me wonder if there’s something weird going on metabolically but I don’t know what it could be. Just aging? Anyone else experience a change like this?
Not sure if this has anything to do with it but I have same issues twice a year for a period of about 4 days. In the Spring/Summer when weather goes from cold to hot and in the Fall/Winter when weather goes from hot to cold it takes my body from 4-7 days to adjust and I get similar results to yours with an uptick of 20pts.
At other times in different situations which the body is not used to I also get this effect. For example, I like to take quite hot showers in the morning. After shower I find myself up 20 pts. 30-40 minutes later back to normal.
Also when I get off a climate controlled airplane after a 15-17 hour or so flight to China or India and get off airplane in 90 degree - 105 degree hot and humid conditions, just an aerobic walk to immigration/Customs/baggage claim can drop my bg 40 pts and take up to 1 1/2 hours to re-adjust to normal.
So a change in temperature with light activity can affect me in either direction and both temperature and humidity play a role.
In addition to the reason posed by CJ114 above, you could also be dropping into hypo territory which activates your liver to release glucose. Kind of like the Somogyi rebound effect that I’ve been told does not exist…
I often go high after a long run and have to bolus immediately. Sometimes up as much as 100 mg/dL. Now I automatically take 1U on run end, and monitor with carbs available on the off chance that I don’t go high. Could it be that your biking is more intensive these days enough to release adrenaline, esp with the hotter weather? Both @CJ114 and @Willow4 gave some other very likely reasons.
Well, except that I’ve been riding pretty much all seasons for years now and my pattern of going down except in really cold weather has been consistent for all that time. It’s the fact that it seems to represent a metabolic change of some kind that has me concerned.
One thing that IS different from previous years is that I started taking 20mg of Jardiance earlier this year, which has been great for lowering my basal requirement. But it’s all about dumping glucose from the blood stream, so I can’t think why that could cause this. Mostly the side-effect warnings are about running too low. But exercise does have all kinds of effects and maybe there’s some interaction there. It’s the one difference in my routine that I can pinpoint. Maybe a question for my endo…
And you are getting older. I find that my need for insulin seems to be less as I get older. I am now 78 years old and find myself quite often in hypo territory, especially with even low level exertion. Maybe an alternate lower basal for those bike rides?
For me, I usually but NOT always, drop during a run, and then a couple minutes after I end, BG starts to go straight up per Dexcom. I say NOT always because yesterday I started my run at 90 and within an hour I was at 166 and had to do a bolus mid-run! I typically do a zero basal during the run.
Maybe you could increase your basal slightly during your bike ride, at least until you figure out what is going on and whether Jardiance does in fact effect your exercise. If it is lowering your basal, then it does seem like it could have some effect during exercise.
I’ve always found I get a “bounce back” after exercise, so unless I’m in the 50s-60s I try not to treat and just wait it out. Usually it will settle in at maybe 20 pts below where it was when I started, 80-90 or so. Not abrupt as you describe, but it’s definitely a thing.
Light exercise LOWS have suddenly become a thing, for me. I have no idea. I am definitely more out of shape than last year. Maybe you are more in-shape and using more muscle all of a sudden.
Another factor is that weather patterns around the world have been very different this year from past years. In the Northeast US usually gets lots of rain in April and then outdoor exercise starts in earnest in late April to early May. This year it was still steady rain in May, delaying outdoor exercises for most by at least 1 month. Not to mention a couple of feet of snow in Montana and Colorado on the first day of Summer and hurricanes, typhoons and other nasty weather in greater abundance worldwide during normally pleasant seasons.
Diabetic bodies like climate consistency and we have not had that recently.
Hi DrBB,
Nothing unusual is going on – your metabolism is normal for a diabetic. The key is in the hepatic homeostatic state. I am helping a non-diabetic friend with Parkinson’s to perform self-therapy right now and the problem is the same.
One needs to prevent the liver from upregulating HGP (hepatic glucose production) adequately to respond to the stress-hormone secretion from the mild aerobic exercise. Elliot Joslin used to say that a diabetic should never run a short distance to catch a bus, but rather should run at least a mile. Otherwise the diabetic will become hyperglycemic. The longer aerobic demand will draw down hepatic glycogen stores sufficiently to substitute ketogenesis for HGP. Joslin could not have known the underlying physiology at the time, but he knew the phenomenon by observation.
You should adopt a maximally ketogenic diet, avoiding all carb’s. This will preserve hepatic glycogen stores at << 100%. If you do just this you will likely see the hyperglycemia disappear, I would predict.
If that is not quite adequate, or if you already eat no plant foods at all, then I would recommend insulin potentiation – a small insulin injection of Regular – just before starting the ride. You will need to experiment with the dose to optimize it. But it should be adjusted so that BG drops by ~20mg/dL below normal (~80mg/dL) to ~60mg/dL. This will induce sufficiently higher portal glucagon secretion to substitute hepatic ketogenesis in place of HGP for a few hours, while the insulin Regular flux into peripheral tissues diverts BG into muscle tissues. The effect is indirect – the increase in islets glucagon secretion will be induced by the lowered BG. There will be NO significant direct effect (i.e. in portal vein) from the peripheral insulin.
If you are not already on a maximally ketogenic diet you should do this first. The insulin potentiation may not be necessary, and moreover will not work well until the liver is in << 100% fed state (i.e. is in mild ketosis).
P.S. The key to regulating the balance between HGP and HKP (hepatic ketone production) is to control hepatic glycogen store. When the liver is fully topped up on glycogen HKP will be shut down. This is not a good thing for a diabetic (or almost anyone in the long term, for best health). When the liver is maximally depleted of glycogen HKP will be maximized, but this only occurs during a prolonged fast (or briefly, for up to one or two days, after a multiple-hour heavy aerobic demand such as a 10…20-mile run, which I do about once weekly). On a ketogenic diet there is some significant HKP and also HGP simultaneously.
Hepatic gluconeogenic rate (which is already higher for a diabetic vs. a non-diabetic, to make up for the increased HGP induced by diabetic insulin deficiency and consequent hyperglucagonemia generated by the islets paracrinology) will adjust to hepatic glycogen stores, but only with slow changes over the course of days or weeks. So only the continuous dietary practice can maintain a relatively lower rate of gluconeogenesis commensurate with a lower level of hepatic glycogen. With the liver in a state capable of higher rates of gluconeogenesis it will be able to respond to moderate exercise ATP demands more with HGP rather than HKP. This is the problem.
Acute changes can be induced with peripheral (i.e. injected insulin), heavy sustained aerobic exercise, and so forth. But diet is the predominant factor for long-term management and optimization of diabetic blood sugar.
Why your BG dropped at a younger age, and now is increasing, would have had to do with hepatic homeostatic state, and could be a function of change in age and diet and other factors. It does not really matter.
Also, as you probably already know, stress (e.g. exercise) earlier in the day is more likely to induce hyperglycemia. But if you are commuting you can’t change the timing, I guess.
P.S. Dietary carb’s will immediately replenish hepatic glycogen stores, although to a more limited extent in a diabetic than in a non-diabetic due to the diabetic’s relative portal hypoinsulinemia. Nevertheless, for maintaining partially depleted hepatic glycogen it is really necessary to avoid ALL carb’s.
Given this, ONLY de novo hepatic gluconeogenesis (from certain amino acids as substrate) can replenish hepatic glycogen. And the maximum rate of gluconeogenesis is very limited – this is a complex, energy/substrate-intensive pathway, and rate-limited. IMO this is the normal state of modern hominids – there was no significant plant food in the diet, especially on a continuous basis.
In a non-diabetic (and even in T2DM that is not quite advanced, as well) there is no hyperglycemic response to dietary protein. But in all forms of diabetes there is an inverse response (of glucagon, and hence glycemia) to carb’s.
However, even in a young non-diabetic there is a hyperglycemic response to dietary carb’s (i.e. prandial portal glucose absorbed via small intestine). Modern man is not evolved, to any significant degree, for carb’s in the diet. There would not be a hyperglycemic response otherwise. And man’s gut is, of course, that of a pure carnivore. The hard science similarly evidences man as a hypercarnivore, and indeed as the only supercarnivore on earth (meaning that a significant part of the paleolithic diet was composed of other carnivores – probably these would have been killed and eaten mainly because of starvation and resulting attempts to steal rotting megafauna kills of modern hominids groups).
As either a non-diabetic or diabetic, one can maintain mild ketosis continuously only by avoiding direct hepatic glycogen replenishment prandially. That means … no carb’s.
Thanks Mac, you’re always really good on the biochemical details of this stuff.
Actually I didn’t know that but it is certainly borne out in my experience, and not just in exercise stress. I regularly run high on Sunday mornings because of performance stress—singing in a choir, where I’m frequently leading a section or soloing.
I think another factor in the OP is that it turns out I was incubating a cold, though the symptoms didn’t appear until a day or so later. The unaccustomed BGs might have been signaling that, had I known.
