Who Should Track Their Blood Sugar?

Prediabetes is common in the U. S. — around 1 in 3 people have it. And many people may not know they have it. But last year, the FDA approved the first over-the-counter continuous glucose monitor. https://www.fda.gov/news-events/press-announcements/fda-clears-first-over-counter-continuous-glucose-monitor Since then, more people without diabetes have started checking their blood glucose levels. Diabetologist and University of California, San Francisco professor of medicine Dr. Sarah Kim https://medicine.ucsf.edu/people/sarah-kim shares the science behind blood glucose with host Emily Kwong https://www.npr.org/people/767284140/emily-kwong. Check out more of NPR’s coverage https://www.npr.org/2025/06/11/nx-s1-5418465-e1/should-you-track-your-blood-sugar-with-a-continuous-glucose-monitorabout continuous glucose monitors. Interested in more science of the human body? Email us your question at [email protected] mailto:[email protected]. Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave http://plus.npr.org/shortwave. See pcm.adswizz.com https://pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences. NPR Privacy Policy https://www.npr.org/about-npr/179878450/privacy-policy

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• 1:38Emily Kwong?

  'Tis the season of eating.

• 1:43Emily Kwong?

  I'm joined by health correspondent Ping Huang. Hey, Ping.

• 1:46Speaker 02

  Hey, Emily.

• 1:48Emily Kwong?

  We wanted to invite you on the show to talk about your experience with a continuous glucose monitor, a CGM. What prompted you to start wearing one?

• 1:56Speaker 02

  Yeah, so I've been prediabetic for a few years now, like on and off. And most recently, it's been mostly on. And I saw that they got approved for overly counteruse last year. So a few months ago, I decided to try one.

• 2:09Emily Kwong?

  Yeah, and I know that prediabetes is really common in the US. Around one in three adults have it. But not everybody knows they're prediabetic.

• 2:18Speaker 02

  Right, yeah. I mean, being prediabetic basically means clinically that a person's glucose levels are higher than people without diabetes, but not quite in the diabetic range. And so...

• 2:29Speaker 03

  You may see higher glucose rises after certain meals. You may see bigger changes in your glucose, whether you're sedentary versus active. So you will see more variety in the glucose levels.

• 2:41Emily Kwong?

  This is Sarah Kim. She's a diabetologist and professor of medicine at the University of California, San Francisco.

• 2:46Speaker 02

  Yeah, and a lot of what she's saying actually matches the experience that I've been having. So my levels spike after meals, especially if they're super carb-heavy, or if I'm basically just sitting around for most of the day.

• 2:56Emily Kwong?

  Which sometimes journalism is like that.

• 2:59Speaker 02

  Yep.

• 2:59Emily Kwong?

  I see you pounding away at your keyboard.

• 3:01Speaker 02

  Sitting for hours.

• 3:02Emily Kwong?

  Those glucose levels just go doot, doot, doot, doot. How does your CGM help you manage prediabetes?

• 3:09Speaker 02

  So what that continuous glucose monitor is actually doing is that it's measuring the glucose levels just under your skin in the interstitial fluid, which is basically the fluid between your cells.

• 3:19Emily Kwong?

  Oh, cool.

• 3:20Speaker 02

  And then that glucose level in that fluid is then converted to a number that shows your blood glucose.

• 3:26Emily Kwong?

  Oh, okay. So you're watching your numbers. Like, how? And how is it reading your levels?

• 3:33Speaker 02

  Yeah, so it's like this little plastic gray circle that's embedded into the side of my upper arm with a tiny needle. It lasts for about two weeks each time, and it's connected to my phone so that I can use an app to track my levels throughout the day.

• 3:46Emily Kwong?

  Yeah. I mean, in addition to revealing your current blood glucose level, Sarah told me that CGMs can also show how your blood glucose is trending.

• 3:55Speaker 02

  Yeah, for sure. I mean, you know, when I see a reading, it'll tell me that it's at a certain level, and it's either rising, or steady, or falling.

• 4:02Speaker 03

  It can tell you, we think, based on the way that your blood glucose is trending, you might have a very high glucose in the next 30 minutes.

• 4:11Emily Kwong?

  The decision to use a CGM is totally something you should talk to your doctor about. But Ping, what have you learned from using yours?

• 4:19Speaker 02

  Yeah, it's been really useful for me personally. I've learned a couple of things about how my body responds to, you know, carbs, for instance. Like, I'm really sensitive to carbs. If I eat a sandwich for lunch, it's going to really spike my blood sugar. It is also really helpful for me to take walks after meals, like, just for 10 or 15 minutes. And I can actually see the impact of that immediately on, like, the graph that's attached to my phone. And the other really critical thing that it told me was that I really just wasn't exercising enough. And so it's prompted me to exercise more. And I've also seen that that's made a big difference in my body's ability to, you know, deal with blood sugar.

• 5:00Emily Kwong?

  Ping, thanks for coming on the show. Happy eating this holiday season.

• 5:03Speaker 02

  Thank you.

• 5:04Emily Kwong?

  A short wave, or stick around, because we are going to continue riding the glucose wave. We'll talk to Sarah Kim about why your body needs glucose to function and what happens when there's too much or too little. I'm Emily Kwong, and you're listening to Short Wave, the science podcast from NPR.

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• 6:59Emily Kwong?

  Okay, short overs. To go even deeper with glucose and digestive health, I am talking to Sarah Kim, the doctor at University of California, San Francisco, who you heard from earlier. And Sarah, I just want to start with some of the basics about sugar in the body, because we ultimately need glucose to function, right?

• 7:16Speaker 03

  Absolutely.

• 7:17Emily Kwong?

  Where does it come from?

• 7:18Speaker 03

  So glucose comes from the food that we eat. It comes from carbohydrates, specifically in sugars. And glucose is the specific kind of sugar that the body uses for energy currency. So we absolutely need glucose all the time to fuel our cells.

• 7:35Emily Kwong?

  I remember having to draw from memory the Krebs cycle in freshman biology class. And it was all about how the mitochondria like convert glucose to usable energy, to ATP.

• 7:50Speaker 03

  You remember many details of that. I'm impressed. But we get our ATP from glucose. We can get ATP from fat and other things. But glucose is ultimately the main currency.

• 8:04Emily Kwong?

  Okay. Glucose is the thing we're after for energy. So how does it get stored in our bodies?

• 8:12Speaker 03

  So each cell can store some glucose, and some cells can store a lot more glucose, like your muscles, that need a lot of glucose, because they're the ones, you know, moving your body. And we store that in the form of glycogen. And then your liver is actually the organ that stores extra glucose to share later.

• 8:37Speaker 03

  And when you are not eating, like when you're sleeping at night, the liver will give out glucose to the rest of the body so that we have glucose all the time.

• 8:46Emily Kwong?

  Okay. And I know that part of what's happening with like glucose uptake, like the cells sucking in that glucose involves this hormone called insulin. What's insulin doing?

• 8:59Speaker 03

  So hormones are just chemical messengers in the body. Insulin comes from a specific cell in the pancreas and insulin goes to throughout your body and allows cells to actually take up the glucose into the cell. So imagine your cell is a house and it has a door. But in order for the glucose to go into the house, it needs the key. So you use the key to open the door. The key is insulin. So if you don't have insulin, that doesn't happen and there's a problem.

• 9:30Emily Kwong?

  And we all know how frustrating it is to get locked out of the house. You know, when you're just at the door and all you need is that dang key. Yeah, and humans, when you lock those insulin keys, it looks like diabetes. Type 1 diabetes means the body does not produce insulin. So people take insulin medication, whereas type 2 diabetes means the body has more insulin resistance. What is that?

• 9:53Speaker 03

  Yeah, great question. So type 2 diabetes is a little bit different. It is a combination of insulin resistance and some insulin deficiency. So insulin resistance means that the insulin's there, the keys are there, but you need like five keys to open the door instead of just one key. Because the one key is not strong enough. And so your body has to make extra insulin in order to do insulin's job. And then over time, one can say that the cells that make insulin get exhausted. They start to die and are non-functional. And so you have actually then a decline in insulin production.

• 10:35Speaker 03

  So you have both a resistance to insulin and also just not enough insulin.

• 10:39Emily Kwong?

  So I have two family members with type 2 diabetes and they were always talking about their blood sugar. Like I gotta watch my blood sugar. And when I was a child, I just... Thought my grandpa's blood basically was made of cookies. But um, what is blood sugar? And why is that pertinent to diabetes?

• 11:03Speaker 03

  So when we say blood sugar, it's just our casual way of saying blood glucose.

• 11:08Emily Kwong?

  Okay, so before glucose gets stored, it travels through our bloodstream?

• 11:11Speaker 03

  Yeah, because it's the sugar in the blood. Um, and blood glucose has a healthy range. So in people without diabetes, blood glucose can range anywhere from as low as maybe 60 milligrams per deciliter of blood, um, up to maybe about 140 after a meal milligrams per deciliter of blood. And having glucose concentrations above that and below that can be problematic. So we do want it in that healthy range.

• 11:43Emily Kwong?

  Can you expand more on what can happen if uh, the body spends a lot of time above and also below that?

• 11:50Speaker 03

  Yeah, so the glucose is actually not getting into the cells where they're needed. And so instead, they're still in circulation. They're still in the blood. The blood is like the highway of the body. It's trying to deliver lots of different things to all parts of your body, including glucose. And so when that happens, actually, um, the blood vessels can get damaged over time. It's like damaging the roads. And this is essentially the root of the diabetes complications. So we have some very vulnerable vessels in our eyes, in our kidneys, um, that supply the nerves and like our feet. Um, and those get damaged early and then you can get damage to bigger vessels, to our heart and to our brain.

• 12:31Speaker 03

  Um, so it's the vessel complications of diabetes that are what we want to prevent. And that can happen with prolonged high glucose levels.

• 12:40Emily Kwong?

  Uh, wow, okay. And I know uh, type 2 diabetes and type 1 have strong genetic components. Uh, there's also lifestyle that can really change how it looks for folks. So how does diet interact with glucose levels, considering that what we eat is where glucose comes from?

• 12:57Speaker 03

  Absolutely. So um, what we teach people with diabetes is that we can choose carbohydrates that are slower digesting.

• 13:07Speaker 03

  So that whatever insulin the body is making,

• 13:11Speaker 03

  you can handle a slower load of glucose rather than a big burst of glucose, say, from a glass of juice. If you have like the whole fruit, it has fiber, it's digesting more slowly, the glucose goes into the bloodstream more slowly, then the body can handle that better, even if it has an impaired insulin-making system. And then always remembering to include the other macronutrients, the proteins, and the good fats to balance out your diet. And then exercise is really important because exercise actually makes your body more sensitive to insulin. And so when you exercise, instead of five keys needed to open the door, you may only need three.

• 13:56Emily Kwong?

  And Sarah, what about time of day? Does time of day impact blood sugar? Like especially when you're eating foods that are high in glucose?

• 14:07Speaker 03

  Everyone tends to be more resistant to insulin in the morning hours. And that's because of the other hormones that are circulating in the morning that are helping you to get up and get ready for the day.

• 14:21Emily Kwong?

  Gotcha, okay.

• 14:22Speaker 03

  So when people have diabetes, they're number one, more insulin resistant in the morning naturally. And then if they eat a big carbohydrate meal in the morning, it's kind of like a double whammy for the system. And so their glucose levels may go higher than they want.

• 14:40Emily Kwong?

  Okay, for all of us, diabetic or not, what are your top tips for keeping blood sugar in a healthy range? Especially heading into the holidays.

• 14:50Speaker 03

  Okay, my big message for the holidays is don't worry about the holidays. If you really wanted to focus on your health, I would say focus on the other 350 days of the year. And, you know, don't torture yourself during the holidays.

• 15:06Emily Kwong?

  Just enjoy the delicious season.

• 15:09Speaker 03

  Indulge in the holidays and maybe try not to indulge so much when it's not the holidays. That should be the message.

• 15:18Emily Kwong?

  Sarah Kim at UCSF, thank you so much for coming on Short Wave to talk about this and happy holidays.

• 15:23Speaker 03

  It was so fun. Thank you.

• 15:30Emily Kwong?

  This episode was produced by Rachel Carlson and edited by Rebecca Ramirez. Tyler Jones checked the facts. Kwasi Lee was the audio engineer. Beth Donovan is our senior vice president of podcasting. I'm Emily Kwong. Thank you for listening to Short Wave, the science podcast from NPR.

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