Does Soaking Oats Increase Glycemic Index?

November 16, 2025 •

3 min read

Overnight oats have surged in popularity, but many wonder if the soaking process affects their health benefits, particularly their glycemic impact. Soaking oats does not increase their glycemic index; in fact, several studies suggest that it helps to reduce it, offering a more stable blood sugar response.

Quick Summary

Soaking oats overnight does not raise their glycemic index. Instead, this preparation method can lower the GI by increasing resistant starch, which digests more slowly, contributing to stable blood sugar and better nutrient absorption.

Key Points

Soaking lowers GI: Contrary to the myth, soaking oats overnight actually helps lower their glycemic index, not increase it.
Resistant starch is the key: The cooler temperature of soaking encourages the formation of resistant starch, which digests more slowly and stabilizes blood sugar.
Improved nutrient absorption: Soaking reduces phytic acid, an anti-nutrient that can inhibit mineral absorption, making more nutrients available to your body.
Cooking increases GI: High-heat cooking, like boiling, can gelatinize starch and increase the glycemic response compared to soaking.
Add-ins matter: For optimal blood sugar control, pair your soaked oats with protein, healthy fats, and low-sugar toppings.
Convenience for busy mornings: Overnight oats are a nutritious, easy-to-prepare breakfast option perfect for those with limited time.

The Science Behind Soaking Oats and Glycemic Index

The glycemic index (GI) is a system that ranks carbohydrate-containing foods based on their effect on blood sugar levels. The key to understanding how soaking oats affects the GI lies in two major factors: the formation of resistant starch and the breakdown of phytic acid. While cooking oats can increase their GI by gelatinizing starch and making it more available for rapid digestion, soaking provides a different, slower process.

When oats are soaked overnight, especially in a liquid with a slight acidity like yogurt or a bit of vinegar, two things happen. First, the process promotes the formation of resistant starch (RS3), a type of carbohydrate that resists digestion in the small intestine. This means that instead of breaking down quickly into glucose, it travels to the large intestine where it ferments, feeding beneficial gut bacteria. This slowed digestion leads to a more gradual rise in blood sugar, resulting in a lower glycemic impact.

Second, soaking helps reduce the phytic acid content in oats. Phytic acid, sometimes called an 'anti-nutrient,' can bind to minerals like iron and zinc and interfere with their absorption. While cooking also helps, soaking, especially when done with an acidic medium, activates the phytase enzyme naturally present in the grain, which breaks down phytic acid and improves mineral bioavailability.

How Cooking vs. Soaking Impacts Oats


Feature	Cooked Oats (Hot Oatmeal)	Soaked Oats (Overnight Oats)
Preparation Method	Cooked quickly with heat and water.	Soaked uncooked in liquid overnight, often in the refrigerator.
Starch Gelatinization	Higher degree of gelatinization, making starches readily available for digestion.	Minimal to no heat gelatinization. Starch remains largely intact.
Resistant Starch Content	Lower levels, as heat reduces resistant starch.	Higher levels of resistant starch (RS3) are formed during the cool retrogradation process.
Glycemic Index	Generally moderate to high, depending on the type of oat and cooking time.	Typically lower glycemic impact due to higher resistant starch.
Nutrient Availability	Cooking helps, but soaking may be more effective at reducing phytic acid, improving mineral absorption.	Improved nutrient absorption due to reduced phytic acid content.
Texture	Soft and creamy.	Chewy and firm.

Benefits Beyond Lowering the GI

Increased Satiety: Soaked oats, rich in resistant starch and soluble fiber like beta-glucan, promote a feeling of fullness for longer, which can be beneficial for weight management.
Enhanced Gut Health: The resistant starch in soaked oats acts as a prebiotic, feeding beneficial gut bacteria and promoting a healthy microbiome.
Convenience: Preparing overnight oats is a quick, five-minute task the night before, making for a grab-and-go breakfast that saves time in the morning.
Improved Digestion: The soaking process breaks down starches and fibers, making them easier for the body to digest and utilize.

Practical Tips for Lowering the GI of Oats

For those looking to optimize their oatmeal for better blood sugar control, consider these steps:

Choose Less Processed Oats: Steel-cut or rolled oats have a lower GI than instant oats, which are more processed and break down faster.
Add Protein and Healthy Fats: Including protein (like Greek yogurt or protein powder) and healthy fats (such as nuts, seeds, or nut butter) can significantly lower the overall glycemic load of your meal.
Use Low-Sugar Add-ins: Opt for lower-GI fruits like berries instead of higher-sugar options, and use natural sweeteners sparingly.
Try the Refrigeration Method: For cooked oats, allowing them to cool in the refrigerator and eating them cold the next day can increase their resistant starch content through a process called retrogradation.

Conclusion: Soaking is a Favorable Method

The notion that soaking oats increases their glycemic index is a misconception. In reality, the overnight soaking process is a favorable preparation method for those concerned with blood sugar stability. By promoting the formation of resistant starch and aiding in the breakdown of phytic acid, soaked oats provide a slower, more sustained release of energy compared to their cooked counterparts. For a healthy, low-GI breakfast, overnight oats are an excellent choice, combining nutritional benefits with unparalleled convenience. Incorporating ingredients like seeds, nuts, and protein further enhances their blood-sugar-stabilizing effects. It is important for individuals to note that the overall meal composition, including toppings and add-ins, plays a significant role in the total glycemic impact. Ultimately, this simple, no-cook method is a great way to start your day on a healthier foot. For more on the health benefits of resistant starch, read about it on WebMD: https://www.webmd.com/diet/what-to-know-resistant-starches.

Frequently Asked Questions

The glycemic index of overnight oats is generally lower than that of cooked oats. This is because soaking creates more resistant starch, which slows down digestion and the subsequent blood sugar response.

Yes, overnight oats can be a healthy part of a diabetic diet, provided they are prepared correctly. Choosing steel-cut or rolled oats, limiting high-sugar add-ins, and incorporating protein and healthy fats helps to manage blood sugar effectively.

Resistant starch is important because it is a type of fiber that resists digestion in the small intestine. This slows down the release of glucose into the bloodstream, helps manage blood sugar levels, and promotes a healthy gut.

Soaking oats helps reduce phytic acid, an anti-nutrient that can block the absorption of minerals like zinc and iron. While some grains have higher phytase activity to do this, soaking is still effective, especially with an acidic medium.

For those specifically trying to minimize their glycemic response, eating oats that have been soaked and cooled (like overnight oats) is often better. The cooling process creates resistant starch, which leads to a slower, more stable blood sugar increase.

Yes, adding protein powder is a great way to boost the satiety and further lower the glycemic load of your overnight oats. This addition helps slow digestion and keep you full longer.

Rolled oats or steel-cut oats are the best choices for making overnight oats. They are less processed than instant oats and have a lower natural GI, providing a better, more stable blood sugar response.