a continuous glucose monitor or CGM is a small device you can put on your arm or on your belly
and it measures your glucose levels continuously so you can see the change in real time,
after a meal for example. there's been a lot of questions about CGMs lately so I discussed this
with Dr Nicola guess. Dr guess received her PhD from Imperial College London for work in
diabetes prevention and she is currently research program manager at Oxford University where she
studies approaches for diabetes remission. so yeah, the main question is about CGM use,
and particularly in healthy people who don't even have diabetes or pre-diabetes even,
where do you think it makes sense, or where is it reasonable to use a CGM? okay so in type 2
diabetes I've had patients that do really well on them, it makes them feel empowered,
they like almost the reward that they get from when you give them dietary advice that they
follow, they can see it, rather than waiting three months down the line to get an A1C and being like,
oh has it come down has it not? the immediate, almost like a reward of, oh look I had the meal
that I was supposed to eat (however you want to term it) and my glucose is under control, great.
it kind of gives them the impetus to continue, but it's worth saying I'm happy with this because I
know I give them good dietary advice, that I know that the meals I'm recommending are low saturated
fats, cardiovascularly healthy, they just happen to be higher in protein and lower in carbs.
I do think there is a concern that when you make a diet glucose-centric, in other words
you are solely focused on what that diet does to glucose, that can be harmful for anyone,
including in people with type 2, because let's say you had, and this is going to upset people,
a couple of slices of bacon, some eggs and maybe like a tomato grilled. is that going
to flatten your glucose? yeah. would I want to recommend that over time for cardiovascular risk,
for the gut microbiome, for vascular function? I would worry about that. if a patient wanted to eat
like that I'd work with them to tweak it however I could, but I wouldn't recommend that approach,
and so my concern about glucocentric is you ignore what the diet might be doing to blood pressure,
you ignore what it might be doing to deeper issues of the vascular function, cardiac function and so
forth, and I think, like I said before, we care about type 2 just in terms of its glucose because
that's how it's always been diagnosed but we know that the real risk is cardiovascular disease,
yes of course neuropathy and other things but it has to be holistic and glucose-centric alone
worries me, so I wouldn't even say a CGM on its own without any good dietary support is
necessarily great, even if you had type 2, because a patient might, like I said, just
stay laser-focused on the glucose and be like, oh great. there's a really good example, like we know
with physical activity, after an intensive workout your blood glucose goes up a bit afterwards and
you wouldn't want a patient to avoid exercise because their glucose went up afterwards,
so it's just about making sure they know the principles of a healthy diet, I don't want to
be patronizing, most patients do, but in type 2 I think there's a role for it. in pre-diabetes
there's there's no evidence to my knowledge. I find it useful for identifying where glucose
is high. so very often they'll only have had an A1C, they won't know where their glucose is high,
and we touched on the different pathophysiology of fasting glucose versus postprandial and we touched
on the different diabetes risk of fasting vs postprandial, so in that sense a CGM can
be empowering for a patient with pre-diabetes because it could either put their mind at ease,
if someone just has elevated fasting and it's not that high but postprandial looks normal, I've had
patients like that with a CGM, that's nice for them, because they are probably the lowest risk,
and incidentally for those patients, it's not great data that I'm basing this
on and I acknowledge this to the patient, but there's some evidence that vigorous activity,
physical activity, can help lower fasting glucose, it looks like high fiber diets might be able to do
that too, so there would be two things that I would recommend to that patient specifically,
and if it's elevated postprandial we would often do high protein low carbohydrate and think about
other dietary factors, so that can be empowering. I am super worried about the use of CGM in people
without diabetes, and not because it's people using it and experimenting, it's because there
is so much rubbish spoken by people who should know better and "experts" about, oh avoid glucose
spikes, and they have no idea what they're talking about, and I see so many patients in my practice,
I had one who had an A1C of 5.1% and she was using a CGM and for about 20 minutes after she'd eaten,
her blood glucose went up to 7.9 or 8 millimoles per liter, so that's just around the pre-diabetic
range, except for of course pre-diabetes is when two hours after you eat it´s 7.8. it's
absolutely normal for your blood glucose to go up immediately after you eat as long as it
comes straight back down again. she was avoiding everything with carbohydrate in it because that's
what this stupid app told her to do, because she was worried about glucose spikes. her A1c was 5.1.
she was miserable, her cholesterol had gone up, she was not socializing with people,
she had an Italian background, one of the things she loved to do with her sons and grandsons
was all bake a Pizza together on a Sunday, she'd stopped doing that because of this app,
it's just craziness to me, so it's not necessarily just cgms per se it's the utter
rubbish that you have people talking about glucose spikes, which is normal physiology,
and it's not only not making patients healthier, it's making them anxious, and it's making them
choose foods because they're just focused on having a flat glucose line after they eat,
and since when is it a desirable thing to have a flat glucose, we don't even
know that this is the case, it's never been the case, so why would you worry about it.
and whenever people say, well obviously you want to keep glucose under control,
it's worth reminding people that pulsatile insulin secretion, so the same volume of insulin
infused in a pulsatile fashion, lowers insulin resistance compared to the same volume flat,
so in physiological terms this pulsatility, this up and down, is actually physiologically useful.
now, do I know this is the case for glucose? no, but based on what we know humans have eaten for
millennia, glucose would go up slightly after a meal, as long as it comes back down again,
don't worry. and my favorite part of my job is when I see these patients with an A1C that low go
back to what you're eating. this lady was eating a Mediterranean diet, it was healthier than mine,
and she had no health concerns, and she bought this app, was worried about her glucose spikes,
she was told she's doesn't tolerate carbohydrates, all based on a CGM, so I think there should be
Health warnings on CGMs for healthy people. I guess it's how you use the information you get,
right? anytime we're too focused on one pixel and we lose track of the big picture
by the way I think a lot of the use of these CGMs came about
in the kind of biohacker dudes who are really into physical activity, often endurance athletes,
and anecdotally over the past six, seven years I have seen so many
non-classical risk factor people coming in to see me who've got elevated fasting glucose,
perfectly normal post prandial, elevated fasting and they're all these crazy endurance athletes
so they're cycling 80 miles a day and stuff, and I wondered whether there was some kind
of athletic phenotype that had elevated fasting glucose. And I spoke with some of my colleagues
and they looked at their data, this is Javi Gonzalez who is an amazing researcher at Bath,
and they see a correlation between VO2 max and fasting glucose such that it looks like there
is a relationship there, and I recall some of these people, and some of them are doctors,
talking and saying, well CGMs are great, that's how I discovered I got pre-diabetes,
and this goes back to the terminology of pre-diabetes and what it actually means,
and do we need to be concerned about slightly elevated fasting glucose in isolation, I think
absolutely not, especially in someone who's doing that much physical activity, and so this almost
catastrophic misunderstanding of physiology, the lack of curiosity to really look at this and say,
what's going on with this fasting glucose, the use of CGMs has just exploded into this
thing where young healthy males think they're pre-diabetic and think they need to cut carbs,
and cutting carbs by the way I don't even think affects your fasting glucose that much,
and none of it is based on evidence so, like I said, health warnings on CGMs for healthy people.
so physiological glucose excursions, no problem, but if it's supra-physiological,
then it might be something to worry? yeah and if you want to nail me down for what becomes
something to worry about, I don't know what that is, I mean I often look with individual patients,
we´ll go through their CGMs and if someone's had a couple of slices of bread or a small meal and
their glucose goes up to 7.8, stays high, stays high for like 45 minutes, that's worrying because
that looks like either their beta cells aren't working so well or they've got insulin resistance,
but if you've got this glucose up, comes back down, that's the glucose homeostasis
working as it normally should, and the reason why we have glucose tolerance test cutoffs,
that 7.8, I'm sorry it's very late and I'm tired so I cannot translate it into
milligrams per deciliter. I'll put it in the subtitles. that's perfect, but you know,
if they get close to that 7.8 at two hours after a glucose tolerance test, that's when you worry,
we have these cutoffs because they've been looked at and standardized in tens of thousands if not
hundreds of thousands of people, and we have some confidence over what a glucose two hours after a
glucose tolerance test, or a random glucose of 11.1 looks like, that's where you worry.
I mean I consider myself pretty healthy, I've got no family history of type 2, I once ate a pizza
in the middle of the night, like a whole pizza, and I was wearing a CGM at the time because we
were testing them for a study we were doing, and I think my glucose went to 11.5 for a bit and then
came back down again, I wasn't remotely concerned. okay, quick one minute summary of all that. in
people with type 2 diabetes, there is a role for CGMs. they can give immediate feedback and they
can provide some motivation, but always coupled with healthy diet, so be wary of an exclusive
focus on glucose levels. just because a food flattens your glucose curve doesn't necessarily
mean it's health-promoting. so shoot for a holistic approach. next, people with pre-diabetes.
in this population, CGMs can help distinguish when glucose is high, fasting versus post-prandial.
for those people with fasting glucose that's a bit high but post-prandial is completely fine,
Dr guess mentioned vigorous physical activity and high fiber diets as two possible approaches. on
the other hand, for people whose postprandial glucose levels is a bit high, so after meals,
emphasizing dietary protein and moderating carbohydrate is one approach Dr Guess uses
routinely. check our previous video with Dr Guess for more details, but the bottom line is
that amino acids stimulate the pancreas to produce more insulin which can help control postprandial
glucose. on the other hand, for people who don't have pre-diabetes or diabetes, the concern with
everybody using a CGM is the excessive focus on glucose and the common misunderstanding that
physiological glucose excursions are a bad thing. it's completely normal for glucose to rise after
a meal as long as it comes back down again, what's unnatural is for it to stay high for a
long period of time, that suggests that the body is struggling to process carbohydrates normally.
so it's less about whether the CGM device is good or evil and more about how we use that
information. I hope that helps, let me know your questions below, I'll catch you guys next week