The importance of nutrition to health and fitness can not be understated. That is why the adage, "You are what you eat," is still prevalent today. But while what you eat is important, how your body reacts is even more so. And if you are looking to optimize your fitness, it is an aspect you can not ignore.

The blood glucose level measures food's effect on the body. In other words, what you eat manifests as glucose in your blood which is a crucial nutrient that every essential organ (in particular your brain) uses for energy.

In healthy individuals without diabetes, the body regulates blood sugar within a very narrow 'normal' range. But while there are normal glucose levels for general health, an optimal level can enable you to take your fitness to the next level.

In this article, we explore this further.

What Are Normal Glucose Levels?

Normal blood glucose level refers to the blood sugar quantity in the majority (95%) of healthy individuals. For context, doctors use these cut off values to determine if an individual has diabetes. For instance, fasting blood glucose (FBG) is a routinely tested parameter. It refers to blood glucose levels when you have not consumed any calories for at least 8 hours. 

Normal levels are essential because they serve as reference points for diagnosing diseases such as diabetes. For example, healthcare practitioners can classify individuals as normal, prediabetes, or diabetic based on fasting glucose levels. An FBG level of over 5.6 mmol/L (100 mg/dL) of blood is abnormal.

Post-meal sugar levels are also vital. Glucose levels should not rise too steeply following meals in normal healthy individuals. If they do, this can predispose you to various health complications such as cardiovascular disease, impaired cognitive function, and obesity. Furthermore, some studies show that drastic increases in post-meal levels can cause inflammation and even cancer. The International Diabetes Federation considers post-meal sugar levels below 7.8 mmol/L (140 mg/dL) — that return to baselines levels within 2-3 hours — to be normal.

Table 1: Reference ranges for fasting and post-meal blood glucose levels

What’s an “Optimal” Glucose level, and Why Does it Matter?

It's vital to understand that 'normal' does not necessarily mean optimal. The glucose cut-offs we have discussed earlier were used as cut-offs for diagnosis of diabetes. Studies in healthy populations (i.e. individuals without diabetes) show that the average glucose levels are lower than the targets set by most guidelines, and that increases in fasting blood glucose levels — even within normal limits — can increase the risk of diabetes and heart disease complications. Hence, we propose a more stringent glucose target, the “Optimal” Glucose level, for healthy individuals who are striving for better metabolic health. The “Optimal” Glucose levels are based on studies in healthy populations, and we detail our reasoning below. 

Fasting Glucose Goal of 3.5 to 5 mmol/L (63 to 90 mg/dL) 

Studies in healthy adults without diabetes with a normal BMI showed that the average fasting glucose was in the range of 3.9 to 4.9 mmol/L (72 to 90 mg/dL). Increases in fasting blood glucose levels — even within normal limits — have been shown to increase the risk of diabetes and heart disease complications. Hence, an upper limit of 4.9 mmol/L (90 mg/dL) for fasting glucose is proposed as optimal, as opposed to the traditional 5.6 mmol/L (100 mg/dL) cut-off. We have lowered the lower limit for fasting glucose from 3.9 mmol/L (72 mg/dL) to 3.5 mmol/L (63 mg/dL) as well, because of studies that show that some healthy individuals can spend approximately 2.8 hours per 24 hours, in the 3.3 to 3.9 mmol/L (60 to 70 mg/dL) range (with some even going below 3.39 mmol/L (60 mg/dL) for an hour).

Post Meal Glucose Goal of <6.1 mmol/L (<110 mg/dL)

Similarly, according to multiple studies, post-meal sugar levels in healthy non-diabetic adults was 5.5 ± 0.6 mmol/L (99 ± 10.5 mg/dL) or below 6.1 mmol/L (110 mg/dL) after a balanced meal. The average post-meal sugar levels rose to an average of 7.4 ± 0.8 mmol/L (133 ± 14 mg/dL) after a meal with less fibre and more refined carbohydrates. So, a post-meal level of less than 6.1 mmol/L (110 mg/dL) is a good target to strive towards.

Table 2: Proposed optimal glucose ranges for most individuals

How To Go From Normal to Optimal Glucose Levels?

Now that we've established the importance of optimal glucose levels, the next step is to determine your ideal range. This requires a different approach to what is standard practice.

Routine sugar testing such as the FBG or the three-month average (HbA1c) is a snapshot into your blood sugar profile. It does not — and cannot — track the continuous variations in your sugar levels throughout the day. Naturally, without this data, identifying your optimal levels is difficult.

Luckily, the solution is straightforward: Continuous glucose monitoring (CGM).

What is CGM, and How Can it Help?

CGMs enable individuals to track their glucose levels throughout the day. This provides more significant insights into important trends associated with health, such as glycemic variability.

Glycemic variability refers to the spikes and dips in your blood glucose levels over 24 hours. Sugar levels fluctuate with the time of day or eating or exercising. These are important because studies link large variations in sugar levels with many health complications. Other research shows that keeping sugar levels within a narrow range may be more important than avoiding high glucose levels.

By identifying trends in your glycemic variation, CGM enables you to control it within a very narrow range. This, in turn, reduces the risk of complications and improves well-being. On top of that, maintaining stable blood glucose levels can also provide you with some fantastic benefits. These include:

• Higher energy levels

• Improved focus

• Better brain function and cognition

• Improved athletic performance

• Smoother skin that is less prone to acne breakouts

Furthermore, CGMs provide the essential data (up to 1440 data points) to optimize your fitness. Your healthcare provider can use this information to recommend changes to your exercise and dietary regimens that fit your specific needs and genetic profile.

CGMs also enable healthcare providers to identify people with diabetes that would otherwise remain undiagnosed because of the inefficiencies of routine spot testing. Studies reveal that up to 73% of normal individuals have blood sugar levels above the normal limits during the day. Similarly, in another study where researchers selected participants based on very low FBGs, 10 % of them reported abnormally high glucose levels on CGMs.