Non-diabetic blood glucose levels (BGLs) typically range from 4-6.0 mmol/L but can briefly rise to around 7-9 mmol/L after eating. Continuous glucose monitors (CGMs) are being marketed to help achieve an “optimal” range (generally <6.0 mmol/L) by following a low-carb diet to prevent minor physiological fluctuations.
The Evidence (or Lack Thereof)
Claims that maintaining a very narrow BGL range is beneficial for health in people without diabetes are not supported by evidence. These “evidence-based” claims are often drawn from studies of people with diabetes and then extrapolated to justify that a very narrow BGL range is “optimal.” For example, wide glucose variability in diabetes increases the risk of micro and macro-vascular complications (blood vessel damage), but this refers to fluctuations far above the physiological range (e.g., >15 or 20 mmol/L over long periods).
HBA1c Levels
Regarding HBA1c levels, most studies focus on diabetic populations. However, a UK study (EPIC Norfolk Cohort) followed several thousand men without diabetes. An HBA1c of 5.5% or higher, which is essentially pre-diabetes, was associated with negative outcomes. In contrast, an HBA1c of <5.0% versus 5.0-5.4% showed no difference in mortality outcomes over several years of follow-up, indicating that an ultra-low HBA1c is unlikely to be beneficial for health.
Understanding Blood Glucose Spikes
High BGLs from insulin resistance or type 2 diabetes are a side effect of the disease rather than the underlying cause. Small glucose spikes from eating carbohydrates do not cause diabetes. For example, the Mediterranean diet, which includes lots of carbs, fruits, and vegetables, is associated with very low rates of type 2 diabetes.
The Role of Diet
A low GI diet low in ultra-processed foods is undeniably good for long-term health. However, do we really need a CGM to know that an apple and water are usually healthier than a triple choc mint and soft drink? The main benefit of CGMs might be feeding curiosity and learning which foods are low GI.
Following advice from dietitians and dietary guidelines can achieve similar outcomes but is less expensive and won’t pathologize normal physiology and foods (e.g., a nectarine will raise BGL more than bacon). It’s important to avoid developing unhealthy restrictive relationships with food and remember that it’s okay and healthy to enjoy a piece of cake sometimes. 😎