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Alex Allan Nutrition
By Alex Allan on 22/06/23 | Blood Sugar Balance

Blood Sugar Monitoring: What is it and how does it work?

You’ve probably seen folk online talking about continuous glucose monitors (CGMs). Perhaps you’ve seen the adverts for the Zoe programme. Or else you might well have spotted people wearing a little white disk on their upper arm and wondered, what’s that all about?  Then there are those devices you can blow into to measure your metabolic health, and let’s not forget the time-honoured finger-prick blood tests to check out your blood glucose or ketone levels. Want to know how all of this relates to you and, of course, whether you should invest in one? Read on. 

What do these devices do?

Whether you’re talking CGM, Lumen or a blood glucose monitor, the reason people are using these devices is that they want to know what their blood sugar levels are. For some, this is a medical necessity. They have been told they have diabetes, for example, and want to get back in control of their glucose levels or, for type 1 diabetes, they need real-time information to work out how much insulin they need to dose. Since very high sugars are dangerous to the body and very low sugar levels (hypos) can be life-threatening, these monitors can mean the difference between life and death. 

Over the last couple of years, more and more people who are simply interested in their health are investing in them. These might be people who have been told they have prediabetes and who want to reduce the risk of developing type 2 diabetes, or those who are looking for answers to why their energy is lacking, or they’re struggling to lose weight, or maybe even those people who love getting data on what their body is doing. 

Blood glucose monitors

These pocket devices have been around for years, and you can buy them from pretty much every pharmacy and online. They usually come in a kit with a lancing device that spikes your finger, releasing a little drop of blood and a pack of testing strips. You insert a glucose testing strip into the machine and drop the blood onto it and, within seconds, you have your reading. 

Diabetic patients would test their glucose levels at different points in the day, perhaps first thing in the morning (this a good general indicator of blood sugar management), right before a meal and then 2 hours after a meal (when levels should fall back to the baseline level). If you don’t have diabetes, but you have prediabetes or you just want to know what your body is telling you, it’s most likely you’ll measure first thing in the morning, just after you’ve got out of bed and before having a morning cuppa or anything to eat. This is your fasting glucose reading. 

Your doctor may routinely have taken a fasted reading like this if you’ve ever had blood taken. It’s considered a reasonably poor measure of your blood sugar levels but the essential thing to note is that it is just one moment in time – literally the time you pricked your finger – and it might have been different yesterday and it might be different tomorrow. This is why having your own kit can be helpful, and it is also why doctors who are genuinely interested in what your blood sugar levels have been doing over time would test your HbA1c. 

HbA1c stands for haemoglobin A1c, which is a blood test used to measure the average blood sugar levels over the past three months. Haemoglobin is a protein found in red blood cells that carries oxygen to different parts of the body, and glucose can attach to it, forming a "glycated" haemoglobin molecule.

The HbA1c test measures the percentage of glycated haemoglobin in the blood, reflecting the average blood sugar levels over few months. This is why it’s more interesting for medical professionals to know what this number looks like for their patients rather than a single measurement taken on the one day they were in the blood test centre. You can get your HbA1c done privately and relatively inexpensively. It’s a test I often recommend to my clients. 

You can also buy similar monitors to measure your ketone levels if you’re a fan of the ketogenic diet. Some machines can measure both and you would need different strips to measure ketones to the ones you use for glucose. Otherwise, the machine works in the same way. The drop of blood, in this case, indicates whether you are in ketosis or not. 


Morning fasting glucose levels should be between 4mmnol/L and 5.4mmol/L (72 to 99 mg/dL) for non-diabetics. 5.5 to 6.9 mmol/l (100 to 125 mg/dl) may be indicative of prediabetes. 7.0 mmol/l or more (126 mg/dl or more) may suggest diabetes. I

f you are measuring your fasted sugar levels and get a reading you don’t like, don’t jump to conclusions. If you have a few consecutive readings, make an appointment to see your doctor. There are a few things outside of food and drinks that have an impact on blood glucose readings, not least stress.


Nutritional ketosis begins at 1.0 and an optimal therapeutic zone is between 3.0 and 5.0. 

Continuous glucose monitors (wearable blood glucose monitors)

When you see someone wearing a little disc attached to their upper arm, chances are, it’s a continuous glucose monitor (CGM) or, more specifically, a related device called a flash glucose monitor (FGM). The two terms are used interchangeably although there are some very subtle differences in the way they fetch their readings.

Both devices are designed to monitor blood glucose levels. A CGM continuously tracks glucose levels in real-time and provides continuous updates to the user throughout the day and night. It can also talk to insulin pumps. 

In contrast, a flash glucose monitor (like those used with the Zoe programme or the popular brand FreeStyle Libre), takes some automatic readings but it also requires the user to scan a small sensor worn on the skin with a reader or a smartphone app to get the glucose readings. The readings are stored on the sensor and can be reviewed later to get a general idea of glucose trends over time. It can only store eight hours of data, so users typically have to ensure they scan before bed and shortly after they get up just to make sure readings have been taken and there are no gaps in data. 

If you are diabetic, you might be entitled to a device on prescription. If you are simply interested in your metabolic health, you will not. You can take part in the Zoe programme, which also includes a stool test, but there is often a wait of a few months before you can participate and you pay for the programme upfront, making it quite pricey. You can also buy the FreeStyle Libre device from selected pharmacies and also directly from the manufacturer Abbott. Monitors last 14 days and cost between £55-75 each. 

Or alternatively, you can come and work with me. I often use CGMs with clients with blood sugar imbalance or insulin resistance, for example, women in menopause or with PCOS, or for those who are looking to lose weight. I’ve found the information that a CGM can provide about an individual’s reaction to certain foods can really help to personalise their programme. Plus, we can also see the effect that exercise, stress, sleep and relaxation might be having on their blood sugar levels, and subsequently their metabolic health. 

If you’d like to know more about blood sugar balance and the tech you can use to help with it, why not get in touch? You can book a free 30 minute call with me here.

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