Jun 10, 2025
How Blood Glucose Affects Your Body and Brain
Why tracking your blood sugar matters for your body, brain, and long-term health.
Cognitive Performance
Written by
Mito Team
When you hear “blood sugar,” you might think of diabetes. But here’s the truth: your fasting blood glucose level can reveal a lot about your health—even if you’ve never had a blood sugar issue in your life.
It’s one of the simplest, most important numbers to track. And with just a small tweak in your daily routine, you can improve it, sometimes before problems even show.
Let’s take a closer look at fasting blood glucose levels, what they mean, why they matter, and how they affect your body and brain.
Understanding Fasting Blood Glucose
Your body runs on glucose, a type of sugar that comes from the food you eat. After you eat, your blood sugar rises. Your body then releases insulin to help move that sugar into your cells for energy.
But your body also needs a way to keep blood sugar steady between meals, especially overnight when you’re not eating. That’s where fasting blood glucose comes in.
Your fasting glucose level is the amount of sugar in your blood after not eating for at least 8 hours, usually first thing in the morning before breakfast. It’s one of the easiest and most affordable tests you can do, and it’s packed with useful information.
What Is a Good Fasting Glucose Level?
The fasting glucose range that most labs consider “normal” is:
70 to 99 mg/dL for healthy adults
100 to 125 mg/dL may signal prediabetes
126 mg/dL or higher suggests possible diabetes (needs confirmation)
But here’s the thing: “normal” doesn’t always mean “ideal.”
More and more research shows that the ideal fasting glucose for most people is right around 85 mg/dL glucose. People who consistently fall in this range tend to have better insulin sensitivity and a lower risk for long-term metabolic issues like type 2 diabetes, heart disease, and even cognitive decline.
So, if you’re wondering what a good fasting glucose level to aim for, shoot for 80 to 89 mg/dL. It's a tighter range, but a more protective one.
How Blood Glucose Levels Affect the Body
Your blood sugar level affects almost every system in your body. When it’s well-balanced, you feel energized, clear-headed, and satisfied after meals. But if it’s too high or swings up and down all day, it can trigger all kinds of problems, like:
Fatigue: Even if you sleep well, blood sugar swings can leave you feeling wiped out.
Weight gain: High insulin levels from high glucose make it easier to store fat.
Hunger and cravings: Spikes and crashes in glucose can make you reach for more snacks.
Poor skin health: Chronically high glucose can damage collagen and speed up skin aging.
Increased inflammation: High glucose triggers inflammation that can harm blood vessels and organs.
Long-term, high fasting glucose levels can lead to insulin resistance, a condition where your cells stop responding properly to insulin. This makes it harder to control your blood sugar and increases your risk for prediabetes, type 2 diabetes, and heart disease.
How Blood Glucose Affects the Brain
Your brain depends on glucose for energy. In fact, it uses about 20% of your total daily glucose supply—more than any other organ.
That’s why stable blood glucose levels are essential for clear thinking, good mood, and mental focus.
If your glucose is too high, too low, or constantly spiking, you might notice these symptoms:
Brain fog
Trouble concentrating
Mood swings or irritability
Poor memory
Headaches
Over time, high glucose levels have been linked to a higher risk of Alzheimer’s disease and cognitive decline. Some researchers even call Alzheimer’s “type 3 diabetes” because of how much blood sugar and insulin affect brain health.
How Does the Brain Get Glucose When Fasting?
Even when you haven’t eaten in 8, 12, or even 24 hours, your brain still gets the glucose it needs. But how?
When you're fasting, your body relies on glycogen, a stored form of sugar in your liver. Once glycogen runs low, your liver starts making new glucose through a process called gluconeogenesis. It turns protein, lactate, and even fat into glucose, just enough to keep your blood sugar stable.
In longer fasts (over 24 hours), your brain can also start using ketones, an alternative fuel made from fat, which helps spare muscle and maintain steady mental function.
What Can Affect Your Fasting Glucose?
Fasting glucose is a useful number, but it can be influenced by a lot of different things, like:
Sleep: One bad night of sleep can raise fasting glucose the next morning.
Stress: When stress is high, blood sugar also rises.
Late-night eating: Especially meals high in carbs or alcohol.
Exercise habits: Daily movement helps improve insulin sensitivity.
Hormones: Menstrual cycles, menopause, thyroid issues, and more can shift glucose.
Even if your diet is clean, these other factors might explain why your number creeps up.
Track Your Blood Glucose—Even If You Feel Fine
Here’s the thing: you don’t need to have diabetes to benefit from knowing your fasting blood glucose level. Many people with “normal” lab results are already heading toward insulin resistance and don’t know it.
Tracking this one number over time gives you early insight into your metabolic health, before more serious issues show up.
At Mito Health, we don’t stop at giving you your numbers. Our comprehensive blood panel includes fasting blood glucose tests to identify your baseline and whether it fits the ideal fasting glucose range or not. We’ll also look at other key markers like insulin, HbA1c, and inflammation so you get the full picture.