You wake up. You haven't eaten since 8:00 PM last night. You prick your finger or glance at a continuous glucose monitor (CGM) and see a number. But what does it actually tell you? Most people think a single test result is a "pass" or "fail" grade on their metabolism, but the truth is a bit messier than that.
When you ask what should your fasting glucose be, you’re usually looking for a specific target. The standard medical answer is simple: under 100 mg/dL. But "normal" and "optimal" aren't always the same thing. If you're sitting at 99 mg/dL every morning, you're technically in the clear according to most lab reference ranges, but you might be standing on the edge of a cliff.
Blood sugar is dynamic. It's a vibrating string, not a frozen statue. Your body is constantly trying to maintain homeostasis, balancing insulin and glucagon to keep your brain fueled and your vessels clean. When we talk about fasting levels, we are looking at the baseline—the floor of your metabolic house. If the floor is rising, the whole structure is under stress.
The Standard Ranges for Fasting Glucose
Let's look at the hard data used by the American Diabetes Association (ADA). These are the benchmarks your doctor uses to categorize your metabolic health.
For a standard fasting plasma glucose (FPG) test, which requires at least eight hours without food:
- Normal: 70 to 99 mg/dL (3.9 to 5.5 mmol/L)
- Prediabetes: 100 to 125 mg/dL (5.6 to 6.9 mmol/L)
- Diabetes: 126 mg/dL (7.0 mmol/L) or higher on two separate tests
It's a tight window. Just a few milligrams per deciliter can change your clinical diagnosis. Honestly, though, the jump from 99 to 100 is largely symbolic. Your body doesn't suddenly "break" at 100. It's a gradual slide of insulin resistance that often starts years before the numbers turn red on a lab report.
Why 85 Might Be the New 100
There is a growing conversation among functional medicine practitioners and longevity researchers, like Dr. Peter Attia and Dr. Casey Means, suggesting that the "normal" range is too broad. They argue that what should your fasting glucose be for optimal longevity is likely between 70 and 85 mg/dL.
🔗 Read more: Why Raw Milk Is Bad: What Enthusiasts Often Ignore About The Science
Why? Because studies have shown that as fasting glucose creeps up within the "normal" range—say from 88 to 98—the risk of future cardiovascular issues begins to climb. A study published in the journal Lancet Diabetes & Endocrinology highlighted that even within the non-diabetic range, higher fasting glucose is associated with an increased risk of chronic kidney disease and heart failure.
If you're at 95, you don't need to panic. You’re fine. But it’s a signal. It’s a nudge from your pancreas saying, "Hey, I’m working a little harder than I used to."
The Dawn Phenomenon: Why Your Morning Number Is High
You slept great. You ate a low-carb dinner. You wake up and your glucose is 108. What gives?
This is often the "Dawn Phenomenon." It’s basically your body’s natural alarm clock. Around 4:00 AM to 8:00 AM, your body releases a surge of hormones—growth hormone, cortisol, and adrenaline. Their job is to tell your liver to dump some stored sugar (glucose) into your bloodstream so you have the energy to get out of bed and hunt a woolly mammoth (or, you know, find the coffee maker).
For some people, especially those with early-stage insulin resistance, the insulin response isn't quite strong enough to counter this morning surge. This results in a higher fasting number that might actually be the highest reading of your entire day.
There is also the "Somogyi Effect," though it's less common. This happens when your blood sugar drops too low in the middle of the night (hypoglycemia), and your body overcompensates by releasing stress hormones that send your glucose skyrocketing by morning. If you’re waking up with night sweats or headaches along with high fasting numbers, this might be the culprit.
💡 You might also like: Why Poetry About Bipolar Disorder Hits Different
Beyond the Single Finger Prick
Context is everything.
A single fasting glucose test is a snapshot. It’s like looking at one frame of a two-hour movie. To get the full story, doctors usually look at Hemoglobin A1c. This measures your average blood sugar over the last three months by looking at how much glucose is "stuck" to your red blood cells.
| Test Type | What it Measures | Normal Range |
|---|---|---|
| Fasting Glucose | Current baseline | < 100 mg/dL |
| HbA1c | 3-month average | < 5.7% |
| Oral Glucose Tolerance | Response to sugar | < 140 mg/dL (at 2 hours) |
If your fasting glucose is 105 but your A1c is 5.2%, you might just have a strong Dawn Phenomenon. If both are high, you’re looking at a systemic issue with how your body processes energy.
Actually, there’s an even deeper layer: Fasting Insulin. You can have "perfect" 85 mg/dL fasting glucose but have sky-high insulin. This means your body is working overtime, pumping out massive amounts of insulin to keep that glucose number low. Eventually, the pancreas gets tired. That's when the glucose finally starts to rise. Checking fasting insulin alongside glucose—to calculate something called the HOMA-IR (Homeostatic Model Assessment for Insulin Resistance)—is often the best way to see the "check engine" light before it actually starts smoking.
Real-World Factors That Mess With Your Results
Life happens. Your blood sugar knows it.
If you had a poor night's sleep, your fasting glucose will be higher. Just one night of restricted sleep can induce temporary insulin resistance in otherwise healthy people. Stress is another big one. If you’re stressed about the blood test itself, or you had a fight with your spouse the night before, your cortisol levels stay elevated. Cortisol is a glucocorticoid—the clue is in the name. It raises glucose.
📖 Related: Why Bloodletting & Miraculous Cures Still Haunt Modern Medicine
Hydration matters too. Dehydration reduces the volume of water in your blood, making the glucose more concentrated. If you're dehydrated, your number might look artificially high.
Then there's the "Pizza Effect." If you eat a heavy, high-fat, high-carb meal late at night, your glucose can stay elevated for a very long time. The fat slows down the absorption of the carbs, leading to a "long tail" of elevated sugar that can persist well into the next morning's fast.
How to Improve Your Numbers Naturally
If you’ve checked what should your fasting glucose be and realized you’re a bit over the line, don’t despair. The metabolic system is incredibly plastic. It wants to heal.
- Move after dinner. A 15-minute walk after your last meal of the day is magic. It uses up some of the glucose in your bloodstream before you head to bed, reducing the load on your liver overnight.
- Prioritize protein and fiber. These act as a "buffer" for carbohydrates. If you're going to eat carbs, don't eat them "naked." Put a coat on them with some healthy fats or protein to slow down the glucose spike.
- Watch the liquid sugar. Soda and juice are the fastest ways to stress your liver. High fructose corn syrup is particularly nasty because the liver has to process the fructose, which can contribute to fatty liver—a primary driver of insulin resistance.
- The "Close the Kitchen" rule. Try to finish eating at least three hours before sleep. This gives your insulin levels a chance to drop before the body shifts into its nighttime repair mode.
- Strength training. Muscle is your "metabolic sink." The more muscle mass you have, the more places your body has to shove glucose without needing massive amounts of insulin.
Actionable Steps for Your Next Check-up
Don't just look at the number and shrug. Take these steps to get a clearer picture of your metabolic health:
- Test consistently: If you’re using a home monitor, test at the same time every morning. Keep a log of what you ate the night before and how you slept.
- Request an HbA1c: If your doctor only ordered a fasting glucose, ask for an A1c to see the bigger picture.
- Ask about Fasting Insulin: This isn't always part of a standard metabolic panel, but it’s the "canary in the coal mine." A fasting insulin level under 6 uIU/mL is generally considered optimal.
- Track the trend: One high reading is a fluke. Three months of rising readings is a trend that requires a change in diet or lifestyle.
Metabolic health is a spectrum. You aren't "fine" one day and "diabetic" the next. By paying attention to where you sit in the 70 to 100 mg/dL range, you can make small, painless adjustments now that prevent major medical interventions later. Stay curious about your data, but don't let a single number ruin your day. It’s just information. Use it.