What is Glucose? A Comprehensive Guide

What is glucose, and how does it impact your wellness? This guide explains why you should care about stabilizing glucose levels.

Caitlin Beale, MS, RDN
— Signos
Health & Nutrition Writer
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Updated by

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Science-based and reviewed

April 23, 2024
September 13, 2023
— Updated:

Table of Contents

Glucose is the primary source of energy for your body. It's the fuel that keeps everything running smoothly, powering your muscles, brain, and other vital organs. Ideally, the body keeps close tabs on glucose levels, never allowing blood sugar to stay too high or too low, but sometimes—thanks to genetics, lifestyle, or environmental factors—this system breaks down. 

If unchecked, blood sugar dysregulation is a serious health problem, so understanding the science behind glucose (aka blood sugar) is essential for optimizing your health. By learning about glucose and its relationship to the food you eat and the lifestyle choices you make every day, you can empower yourself to make positive, lasting changes.

This guide will cover what glucose is, how it's regulated in your body, what happens when it’s out of balance, and steps you can take to support your metabolic health.

What Is Glucose and How Does it Function in the Body?

Glucose is a single sugar (monosaccharide) that your body uses for energy. It's a primary energy source for your cells, including muscles and brain tissues.

The body carefully regulates glucose levels with the help of hormones and enzymes that raise or lower your blood sugar as needed. 

When your blood sugar rises, the body senses levels are too high, and the pancreas releases the hormone insulin. Your cells can't just take glucose out of the blood without help—they need insulin to unlock the door and shuttle it in. Glucose can then enter your cells for immediate energy or stored in the liver, muscles, or fat tissue. 1

Once inside the cell, glucose is broken down into the energy molecule ATP (adenosine triphosphate) through a metabolic process called glycolysis. ATP is used to power nearly every function in the body that requires energy. 1

If blood sugar drops too low, or you need more glucose for energy, the pancreas releases another hormone called glucagon. Glucagon is essentially the opposite of insulin, stimulating the breakdown of glycogen (a storage form of glucose) from the liver to raise blood sugar levels again.

There's a lot of focus on the adverse effects of blood sugar—and it's absolutely true that high blood sugar is problematic. But glucose itself isn't the problem. The body's inability to properly manage blood sugar levels can lead to complications.


Where Does Glucose Come From?

Glucose is so essential for energy production that the body has multiple ways to produce it.

Your diet is the primary source of glucose, and the major sources are carbohydrates such as rice, potatoes, pasta, bread, fruits, vegetables, and dairy products. All these foods contain various combinations of molecules broken down into smaller pieces—like glucose and fructose—by enzymes in saliva and the stomach during digestion.

The other way your body can get glucose is by breaking down stored glucose (glycogen), as mentioned above, or it can also be produced in small amounts from non-carbohydrate sources (proteins and fats) in a process called gluconeogenesis.

Carbohydrates and Blood Glucose

The rate at which glucose enters the bloodstream after eating is partly determined by the type of carbohydrates consumed (although factors such as other foods in the meal can also impact the speed of digestion).

Carbohydrates are generally classified into two main types, simple and complex carbs, and each has a different effect on blood glucose: 3

  • Simple carbohydrates, or simple sugars, are found in foods such as white flour and sugar-sweetened drinks or treats. These carbs are quick and easy for the body to break down and absorb. This rapid absorption can cause blood sugar levels to spike swiftly.
  • Complex carbohydrates—found in foods like whole grains, beans, peas, and starchy vegetables—comprise long chains of sugar molecules. The body takes longer to break down these chains, leading to a more gradual increase in blood sugar levels. 

Complex carbs are a good source of fiber. Fiber plays a crucial role in blood sugar control. It slows the absorption of sugar into your bloodstream, minimizing rapid spikes in blood sugar. Fiber-rich foods include whole grains, fruits, vegetables, legumes like lentils and chickpeas, and nuts and seeds.

The Significance of Glucose Homeostasis

In the body, homeostasis means balance or a state of equilibrium. Glucose homeostasis means the body can regulate blood sugar levels within a balanced healthy range, preventing levels from going too low or too high. 

High blood sugar, or hyperglycemia, means blood glucose levels are higher than they should be. Long-term elevated blood sugar, as seen in people with poorly controlled diabetes, can cause damage to nerves and blood vessels and lead to oxidative stress and inflammation. It can happen if the body doesn't make enough insulin to regulate blood sugar levels or when the cells aren't responding to insulin. 

Low blood glucose, or hypoglycemia, means blood sugar is below the healthy range. It can happen due to drugs designed to lower blood sugar for people with diabetes or due to certain health conditions. Symptoms of hypoglycemia include dizziness, fatigue, blurred vision, and confusion. If left unchecked, hypoglycemia can lead to coma or even death. 

Why Does Glucose Homeostasis Matter for People Without Diabetes?

Even for those without diabetes, maintaining glucose homeostasis is critical for health. It's normal for blood sugar to rise and fall, but controlling how long glucose stays elevated before normalizing and how high and low it drops also matters. Glycemic variability, a term used to describe these big swings in blood sugar levels, has been linked with adverse health outcomes. 

For those without diabetes, maintaining stable blood sugar levels may not seem like a priority. However, studies have shown that excessive fluctuations in blood sugar levels can increase inflammation and oxidative stress and increase the risk of developing metabolic disorders, cardiovascular disease, and even cognitive decline. 8

Insulin Resistance, Prediabetes, and Diabetes 

Insulin resistance means the body's cells don't respond to insulin as well as they should. It's estimated that 96 million American adults have insulin resistance, and 8 out of 10 of those people don't know it. With insulin resistance, more insulin is needed to regulate blood sugar. Eventually, the pancreas can't keep up with the demand and may even stop producing, so blood glucose remains high. 

Insulin resistance is linked to metabolic syndrome, heart disease, hypertension, infertility, and stroke. It can also make it more challenging to maintain a healthy weight—and at the same time, extra fat tissue (adipose) can secrete metabolites that influence insulin resistance. Over time, insulin resistance can lead to prediabetes or type 2 diabetes. 

Diabetes is a chronic disease that affects blood sugar levels. If not managed carefully, it can lead to serious complications, including heart disease, stroke, vision loss, nerve damage, and kidney failure.

But here's the good news: insulin resistance is usually reversible with the right lifestyle support. Knowing your blood sugar levels is so important so you can make positive changes to reduce the risk of further health problems.

What's a Normal Blood Glucose Level and How Do We Measure It?

According to the American Diabetes Association, normal blood glucose levels for people without diabetes are less than 100 mg/dL fasting or less than 140 mg/dL after a meal. 

It's also worth considering that there is a difference between "normal" and "optimal" blood sugar levels. Optimal levels are slightly lower, and some healthcare professionals suggest fasting blood sugar levels should be between 70 and 90 mg/dL, as someone with a fasting blood sugar of 99 is very close to prediabetes.

Since you can't necessarily feel high blood sugar (although some people do feel wired or anxious with higher levels), testing is the only way to know your levels. At a minimum, regular screening at annual physicals can provide a baseline to work with. 

The following tests are used to measure blood sugar:12

  • Fasting Blood Glucose: Measures the amount of glucose in your blood after an 8-hour fast. Fasting levels between 100 and 125 are considered prediabetes, and any higher than 125 mg/dL indicates diabetes.
  • Postprandial Blood Glucose: Measures the amount of glucose in your blood two hours after eating. Postprandial glucose levels should be below 140 mg/dL.  
  • Hemoglobin A1c (A1c): Measures your average blood sugar levels over the past three months. Normal is anything under 5.7% (although some experts believe optimal levels are 5.4% and below). Levels above 6.5% are considered diabetes, and prediabetes is 5.7 to 6.4%.

What About Measuring Glycemic Variability?

The above tests are important to track your blood sugar levels, but they only give you a snapshot at a specific time. Continuous glucose monitors (CGMs) can be a tool to help you understand daily trends and variability in glucose levels and provide real-time feedback about lifestyle choices.

For example, a CGM may show that while your fasting blood sugar is "normal," you have large spikes in glucose levels after eating certain types of food. This information can guide your diet or lifestyle changes for optimal blood sugar.

Tips for Controlling Blood Glucose Naturally

These evidence-based strategies can help you keep your blood sugar levels under control:

  • Incorporate Physical Activity: Regular exercise, such as walking, jogging, or cycling, can improve insulin sensitivity and help regulate blood sugar levels.
  • Increase Fiber Intake: Consuming high-fiber foods like fruits, vegetables, whole grains, and legumes can slow down glucose absorption, preventing rapid spikes in blood sugar. Aim for at least 25-30 grams of fiber per day.
  • Optimize Micronutrients: Studies suggest that deficiencies in specific micronutrients like vitamin D and magnesium may contribute to impaired blood sugar control. Ensure adequate intake of these nutrients through sunlight exposure, food, and supplementation if needed.
  • Reduce Simple Carbohydrates: Limit your consumption of refined carbohydrates, sugary drinks, and processed foods. Instead, choose complex carbohydrates like whole grains, which have a lower glycemic index and promote stable blood sugar levels.
  • Prioritize Sleep: Poor sleep can disrupt hormonal balance and contribute to insulin resistance and metabolic dysfunction. Aim for seven to nine hours of quality sleep per night to support optimal blood sugar control.
  • Manage Stress: Chronic stress can elevate blood sugar levels by releasing stress hormones like cortisol. Incorporate stress management techniques such as mindfulness, deep breathing exercises, and engaging in activities you enjoy.
  • Pair carbohydrates with protein: Pairing protein with carbs (or eating protein before carbs) helps slow digestion and reduce the glycemic response, minimizing glucose spikes. Protein-rich foods include meat, poultry, fish, eggs, dairy, tofu, beans, and lentils.

Glucose: Key Takeaways

Glucose is an essential energy source for the body, powering the brain, muscles, and vital organs. Your body closely regulates glucose levels in your blood, but when the system breaks down, it can lead to high blood glucose and high insulin levels.

You can minimize the risk of elevated blood sugar levels by addressing nutrition and lifestyle habits. Knowing your baseline blood glucose levels and tracking glucose variability with a CGM paired with the Signos app can give you real-time feedback about how your food choices, activities, and other lifestyle habits impact your glucose. With this information, you can make powerful, long-lasting changes to optimize your health.

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Topics discussed in this article:


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About the author

Caitlin Beale is a registered dietitian and nutrition writer with a master’s degree in nutrition. She has a background in acute care, integrative wellness, and clinical nutrition.

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