Should I wear a Continuous Glucose Monitor (CGM) to track my blood sugar?

By Rohini Bajekal, Nutritionist (MSc), Co-Author of Living PCOS Free and Communications Lead at PBHP UK

Blood sugar monitoring has become a recent trend, especially among influencers and a host of new companies promoting the use of continuous glucose monitors (CGMs) to optimise health, manage body weight and improve wellbeing.  A continuous glucose monitor (CGM) is a medical device that estimates what your glucose level is every few minutes and keeps track of it over time. CGMs are currently available on the NHS for people with diabetes, usually for those with Type 1 diabetes. These medical devices can also be purchased privately over the internet. The device, once applied, usually to the arm, tracks blood sugar around the clock and shares that data with your phone (and insulin pump if you are on insulin) every few minutes. For people living with diabetes, it reduces the need for constant finger-pricking tests and is a life-enhancing, life-saving device. It may also improve maternal and neonatal outcomes in women with gestational diabetes. However, the question remains as to what role it should have in shaping nutrition and lifestyle choices for individuals without diabetes.

In recent years, CGMs have become very popular with biohackers and other individuals in the wellness space who do not have diabetes or even pre-diabetes but claim that the device can be used to guide smarter diet and exercise choices, lose weight, and improve energy levels. As a nutritionist living with monogenic diabetes (MODY), this is an area I too have become interested in over recent years. It is normal for glucose to fluctuate throughout the day, depending on activity, stress and of course food intake. Due to a lack of CGM data in healthy non-diabetics, there is actually no consensus on how high a normal  glucose “spike” is directly after a carbohydrate rich meal. However,  the normal blood glucose level at least 90 minutes after a meal (post–prandial) should ideally be under 7.8 mmol/L (140mg/dL)  for those without diabetes. For the majority of healthy individuals, normal fasting blood sugar levels are between 4.0 to 5.4 mmol/L (72 to 99 mg/dL). While this is a hot topic, there is currently no published study suggesting that CGM monitoring translates into improved health or nutrition choices for people without diabetes. A CGM costs approximately £50 and lasts for only two weeks, adding up to around £1400 per year with daily use. While this cost is out of reach for most people, the trend has still continued along with influencers promoting blood sugar “hacks,” such as eating food in a particular order, drinking vinegar-based drinks or consuming certain supplements. There is very little or no evidence behind these claims.

My concern as a nutritionist is that tracking glucose levels using a CGM can be very confusing for someone without the ability to understand the graphs displayed during monitoring. Fluctuations in blood glucose are a physiologically normal occurrence in healthy individuals, providing they come down to a healthy level within a couple of hours. Avoiding spikes does not necessarily result in more health-promoting behaviours. For example, blood sugar can rise during high intensity exercise but this might scare someone into avoiding this type of exercise if they are not able to contextualise the “spike” they see. There is also a trend among keto influencers around “flatlining” glucose. The result could be someone cutting out carbohydrates and perhaps choosing bacon over a banana because the former will not “spike” blood sugar as much, although will certainly have a more detrimental impact on insulin resistance. The only reason that blood glucose might remain high for a longer period after eating a banana is because of underlying insulin resistance – this is the issue rather than the banana itself! It is important to remember that CGMs only record blood glucose levels and do not have the ability to track other cardiometabolic risk markers such as high blood pressure, cholesterol, and triglycerides. Therefore, someone who swaps carbohydrate rich foods for low carbohydrate animal-based foods such as meat and cheese might find their glucose is more under control in the short-term but their LDL cholesterol goes up, raising their risk of heart disease and other health issues.

If you are constantly irritable, feel “hangry,” eat a lot of processed sugary foods, struggle with your sleep or concentration, it may be advisable to make dietary and lifestyle changes to tackle insulin resistance. The good news is that it is possible to reverse insulin resistance, particularly in the early stages. The aim is to make the body’s cells sensitive to the action of insulin again so that glucose gets cleared from your bloodstream and picked up by your cells more efficiently, which means your pancreas can stop producing so much. According to Diabetes UK, 13.6 million people are at increased risk of type 2 diabetes in the UK – an estimated 1 in 3 adults is living with pre-diabetes. Complications of diabetes include cardiovascular disease, kidney damage and eyesight issues among others. A CGM may be helpful for a short period for someone on the cusp of developing type 2 diabetes providing that they are working with a qualified health professional who can guide them with regards to interpretation of the data. However, as mentioned, this is a significant expense. CGMs are not provided to those with prediabetes on the NHS. Furthermore, we do not need a CGM to tell us which diet and lifestyle is healthy – either for PCOS management or type 2 diabetes prevention. Decades of research and thousands of studies have outlined the optimal dietary pattern and lifestyle practices to reduce one’s risk of diabetes.

We know that plant-based diets are healthful at every stage of life and high fibre diets in people with diabetes have been shown to reduce insulin requirements and, in some, put diabetes in remission even without weight loss. Dietary patterns that are rich in plants such as the Mediterranean diet and DASH diet can positively impact all other cardiometabolic risk markers too. People at risk of diabetes should be advised to focus on a predominantly plant-based dietary pattern, including intact whole grains, legumes, fruit, vegetables, nuts and seeds, herbs, and spices. These foods are full of fibre helping to keep blood sugars stable. Eating a fibre rich plant-based diet helps promote healthy gut bacteria and helps to reduce inflammation and oxidative stress, normalises blood sugars and lowers insulin resistance. I would also suggest eliminating or reducing processed meat, fried foods, refined grains like white bread, white rice, pastries, and ultra-processed foods including sugary cereals, pastries, cakes, sweets, and sugar-sweetened beverages. Other lifestyle changes also play a significant role in reducing our risk of diabetes, especially regular movement, restorative sleep, addressing stress triggers, avoiding alcohol and smoking. Aerobic exercise and resistance training are both recommended to help improve insulin sensitivity, with a short 20-minute post meal walk being especially beneficial.

CGMs certainly may provide helpful insights particularly for certain groups such as high performing athletes. These including understanding how blood glucose is impacted by the menstrual cycle (insulin sensitivity can be reduced in the luteal phase) which can help coaches working with female athletes. While we need more studies, CGMs may encourage positive behaviours such as seeing the impact of moderate exercise, e.g., a walk after eating a meal (known as “post-prandial” exercise) on the glucose curve. However, there is currently no concrete evidence that CGM monitoring leads to improved health outcomes in those without diabetes. In fact, CGMs may even cause harm to certain individuals. They are likely unsuitable for those with eating disorders or anyone who is prone to obsessive tracking. They may increase anxiety levels. For certain individuals, this type of monitoring could be more harmful than helpful, resulting in pathological stress.

As a nutritionist, I am concerned that this type of expensive medical device is being touted as an accountability tool. As millions of people in the UK are living with prediabetes or type 2 diabetes, the key focus should be education around a lifestyle that prevents constant surges of insulin and blood sugar, which over time can lead to chronic inflammation and disease. In other words, a high fibre plant-rich diet, with regular exercise, stress management and adequate sleep. I would urge caution when it comes to hyper-fixating on blood sugar levels alone and focus on an overall healthy diet and lifestyle that can be sustained and enjoyed in the long-term. For more details on plant-based nutrition and lifestyle, visit our website and try the Plant-Based Health Professionals 21-Day Challenge.

References

Diabetes UK, https://www.diabetes.co.uk/diabetes_care/blood-sugar-level-ranges.html Updated November 2022

Diabetes UK, https://www.diabetes.org.uk/diabetes-the-basics/types-of-diabetes/type-2/preventing Updated April 2023

 Guess, N. (2023), The growing use of continuous glucose monitors in people without diabetes: an evidence-free zone. Pract Diab, 40: 19-22a. https://doi.org/10.1002/pdi.2475

Iida, Y., Takeishi, S., Fushimi, N., Tanaka, K., Mori, A., & Sato, Y. (2020). Effect of postprandial moderate-intensity walking for 15-min on glucose homeostasis in type 2 diabetes mellitus patients. Diabetology international, 11(4), 383–387. https://doi.org/10.1007/s13340-020-00433-x

O’Malley G, et al. Assessing glycemic control using CGM for women with diabetes in pregnancy. Curr Diab Rep 2021

Panigrahi G, Goodwin SM, Staffier KL, Karlsen M. Remission of Type 2 Diabetes After Treatment With a High-Fiber, Low-Fat, Plant-Predominant Diet Intervention: A Case Series. American Journal of Lifestyle Medicine. 2023;17(6):839-846. doi:10.1177/15598276231181574

Reynolds, A. N., Mann, J. I., Williams, S., & Venn, B. J. (2016). Advice to walk after meals is more effective for lowering postprandial glycaemia in type 2 diabetes mellitus than advice that does not specify timing: a randomised crossover study. Diabetologia, 59(12), 2572–2578. https://doi.org/10.1007/s00125-016-4085-2

 Tsereteli, N., Vallat, R., Fernandez-Tajes, J., Delahanty, L. M., Ordovas, J. M., Drew, D. A., Valdes, A. M., Segata, N., Chan, A. T., Wolf, J., Berry, S. E., Walker, M. P., Spector, T. D., & Franks, P. W. (2022). Impact of insufficient sleep on dysregulated blood glucose control under standardised meal conditions. Diabetologia, 65(2), 356–365. https://doi.org/10.1007/s00125-021-05608-y