What is Insulin? Insulin Function and Insulin Resistance Explained

Written by Phil Rossi

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What is Insulin?

If you know somebody living with diabetes, chances are you have heard of insulin.

But what is it exactly and how does it work?

Simply put, insulin is a hormone created by your body that regulates blood sugar levels. It helps move sugar, or glucose, from the blood into cells for use as energy.

Without it, an excess of glucose (sugar) can build up in our blood, which can lead to some serious issues.

Where is Insulin Produced?

Insulin is produced in the pancreas or more specifically the beta cells of the pancreatic islets.

When blood sugar levels start to rise these beta cells are stimulated.

As a result, they begin to produce insulin to restore blood glucose concentrations to appropriate levels.

What Does Insulin Do?

Insulin plays a central role in keeping our glucose levels within appropriate boundaries.

When our blood sugar levels rise too high, it signals liver, fat, and skeletal muscle cells to take in glucose from the blood and use it for energy.

When the body has sufficient energy, it then signals the liver to store glucose as glycogen.

That way, when blood sugar levels get low the glycogen can be converted back into glucose for use.

How Does Insulin Work?

Insulin works in two main ways to keep blood glucose levels within appropriate boundaries.

When blood sugar levels rise (e.g., after a meal), it is produced by beta cells in the pancreas and released into your blood to tell the body’s cells to open up and let glucose in.

This in turn, reduces the amount of glucose in your blood and keeps blood sugar levels within an appropriate range. From there, the cells can then convert glucose into energy.

During this time, it also signals to the liver to absorb glucose and convert it into glycogen.

This is just a bundled up and stored version of glucose. In that respect, you can think of the liver as sort of a warehouse for holding excess glucose.

The liver can store around 5% of its mass as glycogen.

When blood sugar levels drop (e.g., before or in between meals), insulin production falls as well signaling to the liver that it needs to now raise blood sugar levels.

This causes the liver to breakdown some of its glycogen storage and release glucose in your blood which raises blood sugar levels to the appropriate level.

The liver cannot directly measure blood glucose levels. Instead, it relies on insulin to tell it.

Types of Insulin

Overall, there are several types of insulin that can be grouped into three main categories: Fast acting, intermediate acting, and long acting.

The difference between these different types include things like how quickly they act, how long they last, the peak or maximum impact, the concentration, and the route of delivery.

Here’s a quick overview of each.

Fast Acting Insulin

Fast acting insulins begin to work within 30 minutes of injection. They generally work over a shorter span of time and have a maximum impact between 30 minutes to 3 hours.

These insulins are generally used before meals and snacks to keep your blood sugar from spiking too high.

Fast acting insulins can be further broken down into similar but different subgroups of rapid acting and short acting.

Rapid Acting Insulin

Rapid acting insulin acts most like what we produce naturally in our pancreas.

Generally, it begins to work about 15 minutes after injection to drop our blood sugar and works over a short, more predictable time range.

Rapid acting insulin peaks in about one or two hours and will wear off within 5 hours.

The most common types of rapid acting are:

  • Apidra (glulisine)
  • Humalog (lispro)
  • Novolog (aspart)

Regular Insulin

Regular insulin usually starts to work within 30 minutes to an hour after injection.

These are slightly delayed compared to rapid acting insulin, but they will last longer as well with a duration of up to 8 hours.

The peak is typically anywhere from two to three hours after injection.

The most common types of regular insulins are:

  • Humulin R
  • Novolin R

Intermediate Acting Insulin

Unsurprisingly, intermediate acting insulin reaches the bloodstream slower than regular or rapid acting, generally in about 2-4 hours.

However, it lasts longer as well.

Intermediate acting insulin will last up to 18 hours and generally peaks around 4-12 hours after injection.

It is less commonly prescribed and often used alongside fast acting insulin.

The most common intermediate acting insulins are:

  • Humulin N
  • Novolin N

Long Acting Insulin

Long acting insulin will cover your needs for about one full day.

You will only need to inject it first thing in the morning or before bed and it will control your blood sugar levels for about 24 hours. When needed, long acting insulin is combined with rapid or short acting to control blood sugar.

Long acting insulins take several hours after injection to reach the blood stream and they generally have no peak.

The most common long acting insulins are:

  • Tresiba (degludec)
  • Levemir (detemir)
  • Lantus & Basaglar (glargine)

What is Insulin Resistance?

When your body is functioning properly, insulin keeps blood sugar within an acceptable range.

However, in some cases your body’s cells do not respond like they should.

Insulin resistance is one such case where your body’s cells develop a diminished sensitivity.

This means your pancreas needs to produce extra to maintain healthy blood sugar levels.

However, over time the pancreas will not be able to keep up and blood sugar levels will rise which increases your risk for developing Prediabetes and Type 2 Diabetes.

It is not quite clear what causes resistance but some risk factors include: family history, being overweight, and being inactive.

How to Reverse Insulin Resistance?

There are several ways to improve your body’s sensitivity to insulin and help reverse or slow resistance. 

Dietary changes can have a dramatic impact. Eliminating things like processed foods or sugary snacks and drinks is key. Look to replace these with healthier options like whole grains and foods that are high in fiber as research suggests that these options can reduce your risk.

Increasing your physical activity is another great option. All activity is good but try to aim for 30 minutes of moderate activity 5x or more per week. If you are unable to do that, start with whatever you can do and work your way up.

The important thing is to start and just continue to progress.

These changes are critical, not only for tackling resistance, but for living a healthier overall lifestyle.

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