What I learned wearing a real-time blood glucose monitor

Nutrition is about to get personal
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Non-invasive blood glucose monitoring, the kind where you don’t have to draw blood to take a measurement, has long been wearable tech’s Holy Grail. “When will our watches be smart enough to tell us what and when to eat?” is a question we’ve been asking leading brands for years.

The first company that creates a smartwatch or a fitness tracker that reveals your blood sugar levels in real time, will have a game changer on their hands. It would dwarf Apple’s recent EKG innovation and see devices flying off the shelves.

Why am I so confident such a device would sell? Because the applications for this technology would be huge. From helping diabetics manage their blood sugar to making it easier for people to lose weight, it could even tell endurance athletes when it’s time to top up on carbs.

We’d be able to stop obsessing about calories alone and start seeing how the foods we consume affect us on a personal level. You need only look at the 150 million users on MyFitnessPal to see how obsessed we all are with what we eat. This tech would put previously invisible information about our own unique response to foods, sleep and even stress, into the hands of everyone.

Read this: Need to know on wearables and blood glucose monitoring

What would that mean in practice? Well, imagine being able to choose what you ate for lunch based on how that food actually affects your body. Not what the latest science says about the average person, your unique response. That’s a pretty powerful concept.

Now what if we told you this tech is already here. Ok, it’s not built into a watch yet, and getting this tech into a wrist-worn device might be a way off, but real-time blood glucose monitors such as the Freestyle Libre already exist. Right now they’re aimed at helping diabetics all over the world manage their blood sugar levels but clever entrepreneurs have already started to piggyback the hardware and harness the insights for non-diabetics too.

What I learned wearing a real-time blood glucose monitor

These new NFC-powered sensors insert tiny sensor filaments just 0.4mm thick, 5 millimetres under the skin to accurately measure glucose. Combined with a pod that sits on the outside of the skin – about the size of a 50p coin across and a coin deep – these track your glucose levels. With the tap of a smartphone on the sensor, up to eight hours of blood sugar readings, including an up-to-the minute readout, are sent to a partner app where you can dissect the information, spot patterns and even get warnings when levels are out of whack. It’s impressive stuff.

As an ultra and marathon runner I’ve spent the past five years following a training plan with a nutritional approach that puts stable blood sugar levels at the core. Why? Because balanced blood sugar levels come with huge benefits that include better weight management, improved sleep and more consistent energy.

The diet you need to follow to maintain stable blood sugar levels also tends to mean less sugar and fewer fast-burning high glycaemic index carbs, and that can help your body learn to burn fat as a fuel source. Something that’s useful for endurance.

So when I got the chance to try out myLevels, a company leading the way in harnessing real-time blood glucose tech for health and fitness, I was intrigued to see what I would find.

The myLevels app uses the Freestyle Libre sensor technology to let users link their real-time sugar spikes to the food they eat. There’s a food log and each food you eat gets a timestamp along with a "spike score" so you can find out what foods are best for you personally. For example, my response to a cookie might not be the same as your response.

The app is still in beta and undergoing initial tests with a small cohort. I was lucky enough to get into the early testing group and I’ve been living with the myLevels app and the FreeStyle Libre sensor for two months. Here’s what I’ve discovered so far.

Augmenting yourself: Easier than you think

What I learned wearing a real-time blood glucose monitor

The Freestyle Libre sensor is applied with a stamp-like device that clicks the white pod into place on your arm. On the underside of the applicator there’s a fearsome looking spike that looks like it should hurt. Remarkably you don’t feel a thing as it’s only the fibres that go into your arm.

Mine did draw a little blood, but no more than a pin prick and once the sensor’s on and you’ve been wearing it a few days, while you don’t forget about it – because you’re obsessing about taking readings – you barely notice it.

What you do notice is people’s reaction when you demonstrate what it does. It blows their mind. And so it should, because for most people this will be the first time they’ve seen a bio-hack in real life. You become acutely aware that you’ve augmented yourself with a sensor, made your body smarter. With one pain-free click you have become a cyborg.

Taking readings is slightly addictive

If you’ve ever used MyFitnessPal or another food logging app, you’ll probably have spent the first week or obsessing about your new toy, meticulously scanning and logging everything you stick in your face. But that early excitement can wear off as the chore of diarising every meal hits home.

There’s none of that with myLevels because the app doesn’t need all of the nutritional information, just a photo of the food you ate, snapped and saved along with the time you ate it, and blood sugar readings are done with a single tap.

You find yourself tapping frequently throughout the day. Just woke up. Tap. Had your first coffee. Tap. Went for a walk at lunch. Tap. The same curiosity and desire to understand what’s going on with your own body is there, it’s just far easier to see the cause and effect.

You get a sense for when you’re low

My guess is there’s not a single person reading this who hasn’t had an afternoon slump. The brain goes fuzzy, lethargy strikes and you start to eye up the vending machine or the nearest sugary snack. In all likelihood that’s low blood sugar, a response to the lunch you ate a few hours ago. With this technology you can actually see if that’s the case, or you’re just knackered from lack of sleep, working too hard or both.

Suddenly feelings you’ve been having all your life can be mapped to an objective number that could show what’s really happening. What’s even more fascinating is that you can actually roll backwards and see if changing what you eat for lunch prevents the same pattern recurring the following day.

Stress can spike your blood sugar

What I learned wearing a real-time blood glucose monitor

While it may be obvious that what you eat affects your blood sugar levels, I hadn’t expected to find there are other things that can spike your blood glucose and one of them is stress.

Occasionally during my two-month trial of myLevels I spotted a spike in my blood sugar chart even though I hadn’t eaten for a decent period of time. What I also realised was that these sudden upswings came around times when I had moments of high stress.

That’s because when we’re stressed our bodies can go into fight or flight mode. Sensing we might need energy to escape imminent danger, the liver frees up glycogen which turns to glucose, thus sending blood sugar levels up.

This is why stress therefore can hamper our best efforts to lose weight.

The blood sugar of an ultra runner

What I learned wearing a real-time blood glucose monitor

As part of my test with myLevels I ran a four-day ultra marathon, covering 120km and running for between 3 and 15 hours a day. To fuel these runs I tend to turn to practical and portable sources of carbohydrates, including sports drinks, energy gels and bars.

I expected to see big spikes in blood sugar from this but I hadn’t realised just how high my glucose levels might go. At times I hit close to 12 mmol/l.

According to the NHS, a normal blood sugar level before eating is 4-7mmol/l and under 8.5-9mmol/l two hours after a meal.

The World Health Organisation defines hyperglycaemia, aka high blood sugar, as “Blood glucose levels greater than 7.0 mmol/L (126 mg/dl) when fasting and blood glucose levels greater than 11.0 mmol/L (200 mg/dl) 2 hours after meals.”

Diabetes.co.uk also adds: “Although blood sugar levels exceeding 7 mmol/L for extended periods of time can start to cause damage to internal organs, symptoms may not develop until blood glucose levels exceed 11 mmol/L.”

Now I wasn’t at high levels for long enough for this to necessarily be a problem, but it is interesting to see just how high the glycaemic index of my race nutrition must have been to pump me that high – even while I’m running hard and my muscles are pulling sugar from my blood as fuel.

And also to see how long the sugar from the fuel I consumed stayed in the system. Over time it’s feasible that I could test different energy products and find a fuel source that works best for me.

My blood sugar can get low at night

This isn’t something I necessarily wanted to share with the world but I occasionally suffer from terrible night sweats. This isn’t just a little perspiration, it’s more like a torrential outpouring where I can wake up and wonder if I’ve done the unthinkable and wet the bed.

The reason I’m sharing this is that before I used my glucose sensor I wasn’t sure why this was happening. My GP didn’t really have an answer and because it came and went I decided to largely ignore it.

But what the FreeStyle Libre revealed was that each time I had a big sweat, it coincided with a low blood glucose ‘event’. This is a marker where your sugar levels fall low enough that the FreeStyle app feels it necessary to raise a flag.

What I also realised was that these ‘events’ often happen after I’ve done a big training session earlier in the day. While I definitely need to do more testing to find out if it’s the workouts or the way I’m eating afterwards that’s causing this, the fascinating thing here is that the technology has helped me add context to something I’ve been wrestling with for a while. Something even my doctors haven’t gotten to grips with.

Personalised nutrition is coming

This is why myLevels and FreeStyle Libre are just the starting point of a journey I think will lead us to ever more personalised nutrition. We will increasingly be able to understand what foods serve our bodies best, when we should eat them and in what quantities.

We’ll be able to do that in context of the activities we engage in and in a way that supports the goals we want to achieve, be it more energy for an important meeting, something to help us sleep a little better or the perfect way to fuel a four day ultra marathon.

The truth behind the saying “you are what you eat” is only going to become more apparent.

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Kieran Alger


Kieran is a world record-setting runner and one of the UK's most experienced running journalists.

A constant tester of the latest fitness technology, he's always hunting for innovations that can make him run faster, further and generally be in better shape.

Kieran is often found wearing four GPS running watches at once. And to date he's tracked more than 50 marathons, 13 ultras and countless half marathons - including the Marathon Des Sables.

In 2022, he became the first person to run the river Danube from sea to source, a measly 1,830 miles in 66 days. And still had time to test running gear.

Kieran regularly takes running tech to the extremes for Wareable and the likes of Runner's World, Mens Health and Wired.

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