What Is Glucose? An In-Depth Guide

The most common questions about glucose, answered.
what is glucose

If you have diabetes, prediabetes, or are concerned about developing diabetes, glucose is one term you should know. So, what is glucose?

Odds are, you’ve heard about glucose before, but do you really get what it is and why it matters? When it comes to managing blood sugar levels, whether you’re living with diabetes or not, glucose is a key player that you must understand if you want to have an active role in your own care. When doctors talk about blood sugar levels, glucose is the “sugar” in that equation. Too much glucose can lead to blood sugar spikes, which bring on those telltale sugar highs.

What is glucose?

Glucose is the primary source of energy for our bodies and brains. When we eat, the carbohydrates we consume get broken down into glucose, which enters into our bloodstream. Naturally, this causes our blood glucose levels to go up. This rise sends a signal to the pancreatic β-cells that they needs to start producing insulin, whose job it is to get that glucose out of the blood and into our cells (so it can be used for energy) or stored for future use in our muscles or liver as glycogen (long chains of sugar). Any excess glucose is converted to fat.

Is glucose a carbohydrate?

The short answer: Yes, glucose is a carbohydrate. All sugars are carbs, so glucose is a carb, too.

Is glucose a sugar?

Glucose is a type of sugar. You may have heard of glucose, fructose and sucrose — the three common sugars naturally found in foods that you eat. Fruits, vegetables, cookies, cakes, and ice cream all contain sugars that ultimately become glucose in your bloodstream.

Is glucose a monosaccharide?

Yes, glucose is a monosaccharide, also known as a simple sugar, because it’s a carbohydrate in its simplest form: it can’t be broken down any further. Fructose is also a monosaccharide that’s most often found in fruits, root vegetables, and honey. By comparison, sucrose — aka table sugar — is a disaccharide made up of one glucose molecule and one fructose molecule (that has to be broken down before your body can use it for fuel). Thus, foods that are high in sucrose are also going to be high in glucose.

What is the risk of high blood glucose levels?

When glucose enters your bloodstream, it triggers the production of insulin to get the glucose out of the blood and into your cells. However, when there isn’t enough insulin produced to move glucose out of the blood or the insulin that is produced can’t work effectively (aka insulin resistance), blood glucose levels can stay chronically high. This is exactly what you don’t want to have happen. When fasting blood glucose levels are above 125 mg/dL, it’s known as hyperglycemia. Chronically high blood glucose levels can lead to a host of serious health issues, including:

Much less commonly, blood sugar levels can drop below normal, a condition called hypoglycemia, which is caused by the presence of too much insulin or by other hormone disorders or liver disease.

What are normal blood glucose levels?

Blood glucose levels can be measured a few different ways, including a finger prick test at home, a blood draw at your doctor’s office, or with a continuous glucose monitor (CGM). With a finger prick test (measuring blood glucose) or CGM (measuring interstitial fluid, where your glucose moves after it has been through your blood vessels and capillaries), you’re measuring your levels throughout the day at different intervals from the time you wake to the time you go to bed. This way, you can track fluctuations in glucose levels as you go about your day and get more real-time, in-the-moment data on how your blood glucose levels change in response to the things you do and what you eat.

When you get your blood drawn at the doctor’s office, you’re more likely to get an A1C Test, as well as an assessment of fasted blood glucose concentration and fasted insulin concentration. The A1C test measures your average blood glucose levels over the last two to three months — a broader snapshot of your overall health and how your body is regulating glucose. Your A1C test results will fall into one of these three categories:

  • Normal: Below 5.7%
  • Prediabetes: 5.7% – 6.4%
  • Diabetes: 6.5% or above 

This information below will give you an idea of the ranges used to determine if you’re on the diabetes spectrum. 

Blood glucose levels:

Normal range – 70-99 mg/dl

Prediabetes – 100-125 mg/dl

Diabetes – 126 mg/dl or higher

Source: American Diabetes Association

If you’re already living with prediabetes or diabetes and monitoring your interstitial glucose levels daily with a CGM, what’s “normal” will vary. You will have targets for where you want your glucose levels to be in the morning and at night, plus after you eat. Doctors refer to this as time in range (TIR) — and it’s a range for a reason. Fluctuations in glucose will happen. It’s not realistic to think you can keep your glucose levels 100% stable at all times. Once glucose enters your system after a meal (even if that’s from a banana or oatmeal, instead of say, a bowl of ice cream), that rise will impact your numbers. Exercise affects glucose levels, too, as does stress

The key is to prevent your glucose levels from rising too high or dipping too low, which is why there will be a range for you to aim for. The goal is to have manageable, little peaks and valleys rather than out-of-control, sharp spikes and dips.

Your daily targets will vary depending on your specific situation.

  •  For those without diabetes, the general recommendation is to stay within a range of 70 to 140 mg/dL for the majority of the day. 
  • For those with diabetes, the general recommendation is to aim for a high percentage of the day in a range of 70 to 180 mg/dL. 

Consult with your doctor before setting a range for yourself, and read more about what is a high glucose level in our in-depth guide.

Key takeaways

While we need glucose for fuel, energy, and proper brain function, too much of it can cause serious, chronic health problems. Your goal: Find a happy medium by aiming to get your glucose from complex carbs and foods that don’t cause major spikes in your blood glucose levels. Using a CGM (check out our CGM at January AI for more info) to track your interstitial glucose levels can help you figure out a more personalized approach to managing your nutrition and lifestyle for optimal health.

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