Blood Sugar Trends: Defining What’s Truly “Normal”
With the rise of direct-to-consumer continuous glucose monitoring, there has been growing interest in understanding blood sugar trends. Reasons for CGM use include to improve metabolic health, prevent diabetes, enhance sports performance and recovery, or simply out of curiosity. Users can access real-time data, averages, trends, and insights at any time, day or night.
With all this data, you might find yourself wondering: What do my numbers mean? Should I be concerned? Is this normal? All valid questions. Let’s explore the evidence behind defining “normal” blood sugar trends.
Diagnosing Diabetes
To define what is considered normal, it’s best to start by examining what the medical community has identified as abnormal or diagnostic.
Diagnostic criteria are updated regularly, but the best source for consensus is the American Diabetes Association Standards of Care. The ADA Standards of Care are grounded in the latest scientific research and clinical trials and are widely recognized as the gold standard for evidence-based guidelines.
Diabetes in Non-Pregnant Adults
Screening and diagnosis of diabetes in adults can occur in various ways. When evaluating glucose levels, an individual should meet one or more of the following criteria:
- Hemoglobin A1c ≥6.5%
- Plasma fasting glucose ≥126 mg/dL, defined as no caloric intake for >8 hours
- 2-hour post-prandial ≥200 mg/dL, following a 75-gram oral glucose tolerance test
- Random glucose ≥200 mg/dL, with classic hyperglycemic symptoms
In the absence of overt hyperglycemia, a diagnosis requires confirmatory testing. It’s important to note that this diagnostic criteria does not distinguish the type of diabetes (e.g., Type 1, Type 2, MODY, LADA, etc.).
What about Prediabetes?
Prediabetes is a condition in which blood sugar levels are higher than normal but not high enough to be classified as diabetes. The criteria for diagnosing prediabetes in nonpregnant individuals include one or more of the following:
- Hemoglobin A1c 5.7%–6.4%
- Plasma fasting glucose 100–125 mg/dL
- 2-hour postprandial glucose 140–199 mg/dL (75-g OGTT)
Prediabetes is often asymptomatic, meaning many people don’t realize they have it.
Defining "Normal" Glucose Trends
Based on the diagnostic criteria above, we can assume that “normal” glucose levels mean:
- Your fasting or morning blood sugar is regularly less than 100 mg/dL
- Your post-meal blood sugar (after consuming more than 75 grams of primarily carbohydrate-based food) is less than 140 mg/dL
But what if you have that random ice cream cone on a Friday night, and your blood sugar spikes to 175 mg/dL? Does that mean you automatically have prediabetes? Should you be worried?
Probably not, and here’s why.
Factors That Influence Blood Sugar
There are many variables that influence blood sugar levels. In fact, Adam Brown, author and advocate for a healthy lifestyle with diabetes, argues that there are at least 42 factors that impact blood sugar. Some have an immediate effect, like a spike in adrenaline, while others can cause a prolonged impact for days, such as the flu—or even worse, COVID. In the absence of regular glucose monitoring, most go unnoticed.
Identifying the Cause of a Glucose “Spike”
Here are some of the top causes of elevated blood sugars I often see in clients who do not have diabetes:
- A seasonal cold or allergy flare-up
- A short course of steroids prescribed to treat inflammation or injury
- Overtraining for a major event, such as a marathon or century ride
- A highly refined carbohydrate treat (like an ice cream sundae) in someone whose diet is typically very low in total carbohydrates
- Hormonal shifts related to the menstrual cycle, aka “that time of the month”
While sustained elevations in blood sugar over time can pose a risk, a single spike above your target range typically isn’t cause for alarm or a reason to rush to your doctor with concerns about diabetes.
Getting Personal: A Peek at My Data
As someone working in the field of diabetes care and education, I regularly wear a CGM to better understand the user experience. I consider myself to be in good metabolic health—I exercise daily, prioritize healthful eating, and maintain a lean body composition. Objectively, my most recent A1c was 5.4%. However, I’ve had a few glucose readings that surprised me.
Graph #1: The Autonomic Response
In the first image above, my glucose spiked to over 210 mg/dL after witnessing a motor vehicle accident in my neighborhood. My heart was racing, adrenaline was surging, and I was visibly shaking. Thankfully, no one was hurt—but the initial shock really rattled me.
Graph #2: The Pit Falls of Caffeine
In the second image above, it seems as if my morning coffee consumption is catching up with me. As you can see, I ate breakfast with coffee just before 8 AM, followed by a small peak around 140 mg/dL, which quickly dropped back to about 80 mg/dL as my pancreas responded with insulin.
However, as the morning went on, I continued sipping—on what I hate to admit was probably close to a full pot of black coffee—until almost noon. During that time, I hovered at 140 mg/dL for close to two hours, which most direct-to-consumer CGMs would flag as “too high.”
If you’re unfamiliar with the coffee–caffeine connection, caffeine tends to mobilize free fatty acids, which can create a temporary state of insulin resistance. This allows more glucose to circulate in the body.
Graph #3: A Sleepless Night
If you weren’t already aware of all the pitfalls of a poor night’s sleep, you can go ahead and add elevated blood sugars to the list. Unfortunately, I can’t quite recall the reason for this particular night—but if I had to bet, I’d say it had something to do with my toddler.
As you can see in the image, my overnight fasting glucose was about 5 points above the upper limit for a healthy fasting range.
Key Takeaways
With the growing accessibility of continuous glucose monitoring, more people are tuning into their glucose data—and asking what it all means. While CGMs offer powerful insights into how food, stress, sleep, and movement impact our bodies, it’s important to remember that a single glucose spike doesn’t define your metabolic health.
Instead of focusing on isolated highs or lows, look at the bigger picture:
- Are your fasting levels generally within a healthy range?
- Do your post-meal values come down in a timely manner?
- Are you noticing consistent patterns tied to sleep, stress, or certain foods?
Glucose variability is normal—even in people without diabetes. So if your numbers surprise you, that’s okay. Let them start a conversation, not a crisis.
- Mann S. 42 factors that affect blood glucose: a surprising update. diaTribe. Published April 10, 2023. Accessed March 20, 2025. https://diatribe.org/diabetes-management/42-factors-affect-blood-glucose-surprising-update
- American Diabetes Association Professional Practice Committee, ElSayed NA, McCoy RG, et al. 2. Diagnosis and classification of diabetes: standards of care in diabetes—2025. Diabetes Care. 2025;48(Supplement_1):S27-S49. doi:10.2337/dc25-S002
- Wong H, Singh J, Go RM, Ahluwalia N, Guerrero-Go MA. The effects of mental stress on non-insulin-dependent diabetes: determining the relationship between catecholamine and adrenergic signals from stress, anxiety, and depression on the physiological changes in the pancreatic hormone secretion. Cureus. 11(8):e5474. doi:10.7759/cureus.5474
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- Xin Y, Wang Y, Chi J, et al. Elevated free fatty acid level is associated with insulin-resistant state in nondiabetic Chinese people. Diabetes Metab Syndr Obes. 2019;12:139-147. doi:10.2147/DMSO.S186505
- Knutson KL. Impact of sleep and sleep loss on glucose homeostasis and appetite regulation. Sleep Med Clin. 2007;2(2):187-197. doi:10.1016/j.jsmc.2007.03.004
