Lets compare continuous glucose monitor (CGM) results

An article by Dr Edward Leatham, Consultant Cardiologist. The opinions expressed in this article are entirely mine and not those of SCVC or the consensus view.

First published April 2024, updated Sept 2024, with the addition of Current Glucose Profile (CGP) and some clarification on how we assess ‘Glucotype’.

In today’s data-driven world, especially in the realm of healthcare, the more data patients receive and understand, the better their health outcomes tend to be. For individuals conscious about their health, having access to various health metrics such as blood pressure, heart rate, body weight, body fat percentage, and notably, continuous glucose monitor (CGM) results, empowers them to make informed decisions toward healthy living and diet choices.

The Rising Popularity of CGMs

Continuous glucose monitors have seen a sharp increase in usage, with devices now available even in supermarkets. This accessibility underscores the importance for both physicians and patients to grasp the patterns these devices reveal, which can differentiate between healthy and potentially unhealthy conditions.

CGMs and Car Management: A Useful Analogy

Just as a car’s tachometer displays varying revolutions per minute (RPMs) based on the incline and the desired speed, a glucose monitor provides detailed data on blood sugar levels in real time.  It may be completely normal for glucose to bounce around, within certain limits.  These data, while they may be within a normal range most of the time probably requires interpretation to identify when it may indicate a health issue. This point is crucial for non diabetic patients who use CGMs — especially as these individuals typically represent the largest group of CGM users.

Variability in Glucose Levels

Emerging research suggests that high variability in glucose levels, marked by rapid increases or decreases, could indicate an unhealthy metabolism. This variability may signal attenuated insulin regulation and uptake, which could lead to insulin resistance and increase the risk of developing diabetes. Though high glucose variability has been associated with a greater risk of cardiovascular events, there are currently no long-term studies specifically using CGMs to confirm this in non-diabetic patients.

Glucotype and current glucose profiles (CGP)

Between 2011 and 2018, researchers at Stanford University observed that more than half of non-diabetics who consumed standard breakfast cereal experienced significant variations in blood glucose levels when monitored by continuous glucose monitors (CGMs) [1,2]. This discovery led to the introduction of the term *glucotype*, used to describe subtypes of blood glucose patterns based on variability rather than focusing solely on spikes outside the normal range. While the term has gained traction, no universally accepted definition of *glucotype* exists yet. This makes it important to define various glucose profiles, providing both patients and healthcare providers with a better understanding of how an individual’s glucose response compares to others.

At SCVC, based on our initial six months of metabolic function tests, we observed a wide range of glucose profiles among patients. During a 1-2 week metabolic health assessment, we monitored food intake, sleep, and physical activity through diaries, along with laboratory tests, such as HbA1c, fasting blood glucose, and glucose tolerance tests. Each patient was placed into one of three groups, referred to as ‘glucotype’, based on their glucose curve . These profiles helped us classify patients into one of three innate glucotypes , with each patient’s position on the glucose response spectrum determined by their response to dietary carbohydrates.

The primary factor we observed was the frequency and duration of glucose spikes outside the widely accepted range of 3.9-7.8 mmol/L (140 mg/dL). We designate each individual’s  CGP based on their CGM results at the time of testing, while glucotype was determined by the extent and duration of glucose excursions (spikes) in response to carbohydrates. To further assess potential impact of dysregulated glucose, we calculated a new, unpublished metric called the oxidative stress index. This index is similar to the well-established time out of range metric but instead measures the average percentage of time an individual’s blood glucose exceeds 7.8  (medium) and 10 mmol/L (high).

While an individual’s glucotype seems to be largely influenced by genetic factors and gut biome, the CGM is  modifiable through lifestyle changes and dietary choices. Using CGM results, we  describe the glucose patterns of a person’s everyday life with the term current glucose profile (CGP). However, ‘glucotype’ is typically determined after observing how an individual responds to high-glycaemic foods, a method also used in tools like the Zoe Health App, where responses to a standardised high-carb food (e.g., a muffin) are monitored. This approach is especially relevant for patients who are pre-diabetic or have dysregulated glucose levels (ie are glucotype 2 or 3) and have already adjusted their diet and lifestyle. A patient with GT2   would typically have large glucose spikes than GT1 after consuming high-glycaemic foods like white bread, however could show an intermediate or even healthy CGP during testing if they were following a low-carbohydrate diet.

It remains unclear whether glucotype is truly an innate, genetically determined trait that is difficult to change through lifestyle alone. Evidence suggests that certain individuals are genetically predisposed to high glucose responses when consuming carbohydrates, while others have genes that allow them to better manage glucose levels, avoiding spikes above 7.8 mmol/L regardless of what they eat. This genetic predisposition can influence a person’s ability to maintain healthy glucose levels, and understanding these differences could help tailor individual dietary recommendations more effectively.

In summary, while glucotype may reflect an individual’s genetically determined response to carbohydrates, their current glucose profile is a dynamic measure that can change with lifestyle modifications, such as diet and physical activity. By differentiating between the two, medical teams can offer more personalised advice and treatment, helping patients manage their blood sugar more effectively based on both inherent factors and modifiable behaviours.

Glucose type weight and adipose status

While glucotype seems to be largely ‘innate’, current glucose profile and BMI are modifiable.  We found it helpful for referring physicians to therefore sub-classify each CGP according to BMI and extent /distribution of body fat, measured by hip: waist, height to waist ratios, waist dimension, neck circumference and UK collar size (in men). Our objective was to ensure we did not overlook the negative health impact of high adipose levels that can be present in those patients with healthy looking glucose profiles.

BMI and adipose distribution subtypes

We assess adipose distribution and extent using standard anthropology measures such as BMI, Hip and height to waist Ratio (WHR, WTHR), neck circumference.

NHS BMI calculator

Interpreting CGM Data

While awaiting more definitive trials, it’s valuable to observe and analyse the range of CGM results seen in various patient groups. In some individuals, a relatively narrow glucose range—typically between 3.9 and 7.8 mmol/L (72 to 140 mg/dL)—is seen. This range seems to indicate healthy responses to foods, including those high in glycaemic index.  We observed  non diabetic patients with either early or advanced coronary heart disease often have glucose spikes exceeding 7.8 mmol/L, potentially presenting a different metabolic health profile that requires closer medical attention. For those patients with coronary artery disease or raised coronary fat attenuation index, it raises the intriguing possibility that these glucose spikes and/ or high glucose variability may be contributing to their coronary inflammation. Due to widespread use of CGMs in lifestyle apps such as Zoe and Veri there are many reports that people with glucose spikes on CGM in response to food intake can lose significant amounts of body fat, by altering their food intake to minimise glucose spikes. However the long term effectiveness of CGM-guided food choices has yet to be confirmed.

What profile is healthiest?

Until we see long term trials to justify more definite answers to this question, we simply cannot know for sure, however it is known that there is an optimum BMI range – below and above which health issues are more likely to arise, and we also have evolving data suggesting that glucose variability and glycaemic responses exceeding 7.8 mmol / lit are unhealthy, so it seems reasonable to assume that the healthiest glycotype/ subtype is GT1 (ie flat glucose curve ) and the best CGP to shoot for is CGPI-B or CGPII-B  – where the BMI and THR are within a healthy range and CGM measurements show glucose excursions between 3.9 and 7.8 mmol/L, with infrequent glucose values exceeding 7.8 mmol/L per day and none over 10 mmol/L.

The Need for Controlled Trials

Currently, the absence of rigorous, controlled trials limits the ability of physicians to recommend specific interventions for patients with “unhealthy” CGM profiles. Until more is known, it’s advisable for patients to adjust their lifestyles and dietary habits to help manage and potentially reduce high glucose levels.

Examples of CGP I-V

To aid patients in navigating their CGM results, it’s helpful to see examples of different glucose patterns. To act as a guide here are 5 examples of glucose monitor results presented in a standardised graphical format- where the glucose levels that are believed to be important are shown as coloured lines, the implication being that the ideal profile and CGP might be where glucose values excursions  fall below the green line (7.8 mmol/L) with values over 7.8 mmol/L shown in red and values over 10 mmol/L shown in amber. In these time/glucose plots, individual glucose measurements are shown as coloured dots- healthy values depicted by green dots and high values in red or amber.

Balancing Glucose Levels

It’s important to note that occasional glucose spikes are not necessarily harmful. Moderation remains key, and for those with frequent spikes—particularly those with early signs of heart disease—avoiding high glycaemic foods and mitigating spikes through dietary strategies like consuming high-fiber, water-rich, or acidic foods before meals, may be beneficial.

Conclusion

Continuous glucose monitors are a powerful tool for managing health, offering real-time insights into glucose levels that can help guide dietary and lifestyle decisions. As technology advances and more research becomes available, the potential of CGMs to support disease prevention and management will likely become even more significant. Until then, a balanced approach to diet and health, informed by CGM data, appears to be a prudent strategy for those seeking to optimize their well-being.

1. Glucotypes reveal new patterns of glucose dysregulation 2018
2. Towards precision medicine in diabetes? A critical review of glucotypes 2011
3. BHF Waist measurement tool 
4. BHF How to measure body fat