Is Normal Fasting Blood Sugar Actually Safe? 6 Warning Signs of Prediabetes

Your lab report shows: Fasting glucose 6.1 mmol/L, reference range 3.9-6.1, normal. You breathe a sigh of relief, thinking your blood sugar is fine.

But here's something you probably don't know: Your fasting glucose may be just barely within normal range, but your body may already be in prediabetes.

Why? Because routine fasting glucose tests only capture your blood sugar after fasting for 8-10 hours. Many people with prediabetes have completely normal fasting glucose. The real problem shows up after meals—when you eat carbohydrates, blood sugar spikes, insulin works desperately but can't bring it down in time. This phenomenon is called postprandial hyperglycemia, or impaired glucose tolerance.

And routine checkups almost never check post-meal blood sugar.

Prediabetes isn't "you might get diabetes"—it's "you're already getting diabetes." It's a gray zone where blood sugar is elevated above normal but hasn't yet reached diagnostic criteria for diabetes.

The defining characteristics: fasting glucose 6.1-6.9 mmol/L (called impaired fasting glucose, or IFG), or 2-hour post-meal glucose 7.8-11.0 mmol/L (called impaired glucose tolerance, or IGT), or HbA1c 5.7-6.4%. Any one of these abnormal means prediabetes.

Most concerning is that approximately 35% of Chinese adults have prediabetes. That means one in three adults is in this gray zone. Even more concerning is that many have no idea.

Prediabetes is dangerous precisely because it has almost no symptoms. But if you pay attention, your body sends subtle distress signals.

Signal 1: Extreme post-meal sleepiness

If you're irresistibly sleepy after lunch and must nap to recover, it could be blood sugar fluctuation. Normally, blood sugar rises slightly after eating, insulin is secreted appropriately, and blood sugar returns to normal within 2 hours. But with insulin resistance, post-meal blood sugar spikes higher, insulin response is delayed, causing dramatic blood sugar swings. The brain doesn't get adequate blood supply, creating intense sleepiness.

Signal 2: Abdominal obesity

Men with waist circumference over 90cm, women over 85cm—regardless of total weight—have excess visceral fat. Visceral fat releases inflammatory cytokines that directly interfere with insulin's work, causing insulin resistance. Abdominal obesity is one of the strongest warning signs of prediabetes.

Signal 3: Skin darkening

If you notice skin becoming darker and thicker, especially around the neck, armpits, or groin—looking like it's never clean enough—it could be acanthosis nigricans, a skin manifestation of insulin resistance. Elevated insulin levels stimulate skin cell proliferation and pigment deposition. This change is subtle, and many mistake it for tanning or poor hygiene.

Signal 4: Vision that fluctuates

If your vision is sometimes blurry, sometimes clear, and these changes correlate with meal timing, it could be blood sugar fluctuations affecting your eyes. Blood sugar changes affect the shape of the eye's lens, altering refraction. Some people's vision paradoxically "improves" when blood sugar rises—this is actually an early cataract signal where the lens swells with fluid, changing its optical properties.

Signal 5: Unexplained weight changes

If you're eating more but losing weight, it could be the classic diabetes presentation—insulin resistance prevents cells from utilizing glucose, so the body breaks down fat and muscle for energy. Conversely, if you're eating little but gaining weight, especially abdominal fat, insulin resistance may have slowed your metabolism. Both situations warrant concern.

Signal 6: Frequent night urination

If you need to urinate twice or more each night, and it's not from drinking too much before bed, it could be polyuria from elevated blood sugar. When blood sugar exceeds the renal threshold, kidneys excrete excess sugar, taking large amounts of water with it, causing polyuria and thirst. This symptom is more pronounced in diabetes, but can appear in prediabetes.

Prediabetes is fundamentally about insulin resistance.

Normally, when you eat carbohydrates, blood sugar rises, the pancreas secretes insulin, and insulin acts like a key opening cell doors to let glucose enter and be used. Blood sugar falls, insulin secretion decreases, everything returns to balance.

But in insulin resistance, cells stop responding to insulin. The key doesn't open the door properly, glucose can't enter cells, and accumulates in the bloodstream. The pancreas secretes more insulin attempting to compensate, but cells become increasingly insensitive. It's a vicious cycle.

Long-term insulin resistance doesn't just cause elevated blood sugar—it brings a cascade of problems: high blood pressure (insulin causes sodium retention), dyslipidemia (insulin promotes hepatic triglyceride synthesis), polycystic ovary syndrome (insulin affects hormonal balance), fatty liver (insulin promotes hepatic fat synthesis).

If you have any of the following, consider annual fasting glucose and HbA1c testing: age over 35; BMI over 24 (for Chinese) or elevated waist circumference; family history of diabetes; history of gestational diabetes; polycystic ovary syndrome; hypertension or dyslipidemia; long-term antipsychotic medication use.

When testing, beyond fasting glucose, strongly consider adding HbA1c. Fasting glucose only reflects blood sugar at the moment of blood draw, potentially affected by previous day's diet, sleep, or stress. HbA1c reflects average blood sugar over 2-3 months and is more stable and reliable.

Here's encouraging news: Prediabetes can not only be reversed, it's the final window of opportunity to reverse diabetes.

Large studies show that without intervention, 5-10% of prediabetes converts to diabetes annually. But with active intervention, conversion rates can drop below 1%. In other words, most people who take appropriate action can prevent ever developing diabetes.

The core is lifestyle change—non-negotiable change.

Diet-wise, the most effective intervention is reducing refined carbohydrates. Rice, noodles, bread, sugar—these foods cause dramatic blood sugar swings. Replace with whole grains, beans, vegetables for more gradual blood sugar rise. Ensure adequate protein—protein increases satiety, reduces appetite, and helps preserve muscle mass.

Exercise-wise, at least 150 minutes weekly of moderate-intensity aerobic activity: brisk walking, jogging, swimming. Even more important: 2-3 strength training sessions weekly. Muscle is the largest glucose-consuming organ. Increasing muscle mass improves insulin sensitivity.

Sleep matters too. Sleep deprivation directly causes insulin resistance. One night of sleep restriction can detectably reduce insulin sensitivity the following day. Ensure 7-9 hours of quality sleep nightly—this isn't luxury, it's health necessity.

Want to know if you're at high risk for prediabetes? Use our Chronic Disease Risk Assessment tool below.

Enter your basic information, body measurements, lifestyle habits, and the system calculates your diabetes risk level and provides personalized improvement recommendations. Early detection, early intervention—prediabetes is completely reversible.

Prediabetes is like a smoke alarm—it alerts you before the actual fire. You can ignore it and regret when the house is burning, or take immediate action and nip it in the bud.

Over 300 million Chinese have prediabetes. Without intervention, a substantial portion will progress to diabetes. But if you're reading this now, you still have a chance to catch this final window.

Don't be reassured by "normal" fasting glucose. If your waist is elevated, you have family history, or you're over 35, check your HbA1c. This simple test could change your life trajectory.

Use our Chronic Disease Risk Assessment tool above to start your assessment, then take action based on recommendations. Prediabetes is your body's final warning—catch it, reverse it, don't wait until it's irreversible.