Is Oatmeal Fast Or Slow Digesting? (A Dietitian Answers)

A nice warm cup of oatmeal can be a great way to increase your carb intake. However, you might wonder whether it is a fast- or slow-digesting carb, which can affect when you include it throughout the day. 

So, is oatmeal fast or slow digesting? Oatmeal is generally slow digesting, but it depends on the type and its glycemic index (GI), which determines how quickly a food affects sugar levels. The higher the GI, the higher the impact. For example, steel-cut oats have a GI of 42, and quick oats have a GI of 66. This means steel-cut oats are slower digesting. 

Knowing how fast oatmeal digests is important because it can help you understand why you may want to choose it over other carb sources at certain times of the day.

In this article, I will discuss:

  • How long it takes for oatmeal to digest
  • Types of oatmeal ranking from fastest to slowest digesting
  • Benefits & drawbacks of eating a slow-digesting carb like oatmeal
  • When you should eat oatmeal
  • Other factors that affect the digestion of oatmeal 

Using the Glycemic Index To Determine How Quickly Oatmeal Will Digest

Before getting into how long it takes oatmeal to digest, it’s important to understand what the glycemic index is since I’ll reference it throughout this article.

The glycemic index measures how fast food can raise blood sugar levels. The lower in fiber, protein, and fat, the easier it is to absorb, which means the quicker it spikes sugar levels. As such, the higher the number in the glycemic index, the faster food is absorbed. 

It uses a scale of one to a hundred, and it classifies food into low, medium, and high categories. 

  • Low: 1-55
  • Medium: 56-69
  • High: >70

How Long Does It Take Oatmeal To Digest?

Oatmeal can take between 30 minutes to four hours to digest.

However, this depends on the type of oatmeal you use.

Steel-cut oats have slower digestion. They can take around 2-3 hours to digest fully.

On the other hand, quick oats have faster digestion, meaning it might take less than an hour or up to only two hours to digest.

Is Oatmeal a Complex or Simple Carb?

Carbs are classified into two groups: simple and complex.

Simple carbs are lower in fiber and higher in sugars. This means your body doesn’t need to do much digesting, leading to fast absorption. 

On the other hand, complex carbs are higher in fiber and starches. The body requires more processing to digest them, so they have a slower absorption rate. Thanks to this trait, they tend to be more filling than simple carbs. 

Oatmeal is high in fiber and starch. No matter which type you consume, all of them are within the complex carb category.

Types of Oatmeal: Ranking From Fastest To Slowest Digesting

There are four main types of oatmeal: steel-cut oats, rolled oats, instant oatmeal, and quick oats. Since they all have different processing, they have different fiber content, which leads to a different glycemic index.

For example, quick oats have been previously cooked and rolled out thin. This makes them break down easier. Smaller molecules mean the body can have faster digestion compared to larger molecules.

The following table compares the carb content, fiber, protein (in 100 g), and glycemic index of the four main types of oatmeal.

Type of OatmealCarbs (g)Fiber (g)Protein (g)Glycemic Index
Quick oats68.29.413.766
Rolled oats67.59.412.555
Plain instant oats69.51011.950
Steel cut oats67.51012.542

As you can see from the table above, quick oats have the highest glycemic index. This makes them the fastest digesting from the oatmeal family. On the other hand, steel-cut oats have a lower glycemic index, which makes them the slowest digesting.

Also, the table above shows the glycemic index for plain instant oats. Flavored instant oats that contain a lot of sugar have an even higher GI of 79, meaning they’ll digest quickly and won’t keep you full for long.

Glycemic Index of Oatmeal and Other Carbs

How does oatmeal compare to other types of carbs?

The following table shows the glycemic index of different types of carbs.

FoodGlycemic Index
Barley28
Spaghetti49
Corn52
Couscous65
Brown rice68
White bread75
White Potato87

While steel-cut oats are the slowest-digesting type of oatmeal (with a GI of 42), they are faster digesting than some other carb sources like barley. 

The same with quick oats. While quick oats (with a GI of 66) have faster absorption than steel-cut oats, they have slower digestion than white bread or potatoes. 

Benefits of Eating a Slow-Digesting Carb Like Oatmeal

1. Provide Long-Lasting Energy

One of the benefits of slow-digesting carbs is that they provide long-lasting energy. Since they take longer to digest, they release glucose (sugar) slowly.

This means that instead of getting a sugar rush and crash (like you would with refined grains like white bread), you get a more stable energy release. 

Having more stable glucose levels can give you more energy throughout the day and help you avoid fatigue. 

For these reasons, slow-digesting carbs like oatmeal are better for people with diabetes or those who aren’t physically active and don’t need quick energy sources.

2. Better for Weight Loss

Thanks to its high fiber content, oatmeal stays longer in the stomach. This increases your fullness levels. If you are less hungry throughout the day, it is easier to be on a caloric deficit (eating fewer calories than you need to maintain weight), leading to weight loss. 

Also, the fuller you feel, the less likely you are to snack throughout the day and have smaller portions in your meals. Indirectly, this leads to a caloric deficit without you noticing.

Drawbacks of Eating a Slow-Digesting Carb Like Oatmeal

1. It Won’t Give You Fast Energy

If you are looking to add a carb before your workout to provide you with energy, slow-digesting carbs are not the way to go. Since they take longer to digest, they won’t give you the energy you need before a workout. 

In this case, a fast-digesting carb like white rice can be a better option right before a workout since it will provide immediate energy for your training session. 

2. It Might Cause Stomach Problems

Due to the high fiber content of most slow-digesting carbs like oatmeal, you might get stomach problems like stomach cramps, bloating, and gas. 

If this is the case, add these foods in smaller quantities to allow your stomach to adjust to the high fiber content. Also, with increased fiber, drink plenty of water (at least 8 oz along with your oatmeal). Otherwise, it might cause constipation. 

When Should You Eat Oatmeal?

oatmeal

Since oatmeal is a slow-digesting food, it’s better to consume it 2 hours before training if you do want to have it before a workout. Otherwise, it might increase the risk of stomach cramps or bloat before an exercise session. I also recommend choosing quick oats over other types of oatmeal before working out since they are faster digesting.

Also, it might be a good food to add if you have long fasting hours, such as when you have meetings all day long that prevent you from eating. A slower-digesting food allows you to feel fuller for longer and avoid thinking about food during meetings. 

Another excellent option to add slow-digesting foods is before going to bed. If you are prone to getting up in the middle of the night because you are hungry, adding oatmeal can help prevent that. 

Factors That Affect the Digestion of Oatmeal

1. Cooking 

Cooking can change the food’s digestion speed. Heat can break some of the fiber, making it easier to absorb.

In fact, studies have shown that cooking can affect the glycemic index of a food. 

2. Processing 

In most cases, some of the fiber is removed during a food’s manufacturing process to make it more pleasing to eat. Removing the fiber can increase the absorption rate of the food.

That is why quick oats have a higher glycemic index compared to steel-cut oats. 

3. Added Foods

Finally, certain foods you eat with oatmeal can make it digest slower. Proteins like eggs, cheese, and chicken take longer to digest and can reduce oatmeal’s absorption rate. The same applies to fats like nuts, seeds, and avocado. 

If you want to decrease the absorption rate of quick oats and stay full for longer, you can eat it with nuts, eggs, or other protein and fat sources.


About The Author

Brenda Peralta

Brenda Peralta is a Registered Dietitian and certified sports nutritionist.  In addition to being an author for FeastGood.com, she fact checks the hundreds of articles published across the website to ensure accuracy and consistency of information.