Why is oat milk high GI? Understanding its glycemic index

January 3, 2026 •

3 min read

Despite its healthy reputation, the glycemic index (GI) of commercial oat milk can be as high as 69, placing it in the medium-to-high category. This elevated GI is primarily due to the specific processing methods that break down its complex carbohydrates into simple sugars.

Quick Summary

The high glycemic index of oat milk is caused by the enzymatic process used during manufacturing, which converts complex oat starches into simple, rapidly absorbed sugars like maltose. Without the whole grain's fiber, blood sugar levels can spike quickly.

Key Points

Processing and Maltose: The high GI of oat milk is primarily due to the manufacturing process, which converts complex oat starches into simple sugars like maltose, a sugar with an even higher GI than glucose.
Loss of Fiber: Unlike whole oats, commercial oat milk has had most of its soluble and insoluble fiber removed, eliminating the natural element that slows down sugar absorption and prevents rapid blood sugar spikes.
Unsweetened Doesn't Mean Low Sugar: Even products labeled 'unsweetened' contain natural sugars produced during processing, which can still cause a significant blood sugar response.
Impact on Blood Sugar: The rapid absorption of sugars in oat milk can lead to blood sugar spikes, especially when consumed on an empty stomach or in large amounts.
Pairing is Key: To lower the glycemic impact, consume oat milk alongside a source of protein, fat, or fiber to slow down digestion and moderate the sugar release.
Low-Carb Alternatives: For those managing blood sugar closely, alternatives like unsweetened almond or soy milk, which have much lower carbohydrate content, may be better daily choices.

The Processing Factor: From Complex Carbs to Simple Sugars

The most significant reason for oat milk's higher glycemic index is the manufacturing process. Unlike eating whole, unprocessed oats, which contain complex carbohydrates and fiber, commercial oat milk production uses enzymes to break down the starches.

Enzymatic Hydrolysis Explained

This process, known as enzymatic hydrolysis, uses enzymes to convert complex oat starches into simple sugars, most notably maltose. Maltose has a very high glycemic index of 105—higher than pure glucose. This conversion creates the naturally sweet taste and creamy texture that consumers enjoy, but it also increases the speed at which the body digests and absorbs the sugars, causing a rapid rise in blood sugar levels.

The Role of Fiber: A Missing Component

When you eat a bowl of whole oats, the soluble fiber (beta-glucan) creates a gel-like substance in your gut that slows down digestion and the absorption of sugars. During the straining process of making oat milk, however, much of this beneficial fiber is removed. This leaves behind a liquid that, while having some fiber content, lacks the bulk needed to slow down the glucose release effectively. The result is a quick influx of sugar into the bloodstream, rather than the steady release from eating whole oats.

Other Factors That Influence GI

Beyond the core manufacturing process, other elements can influence oat milk's glycemic impact:

Added Sugars: Many commercial oat milk brands, especially flavored varieties, contain additional sweeteners that can further elevate the GI. Even unsweetened versions contain processed natural sugars.
Added Fats: To achieve a rich and creamy texture, some manufacturers add oils like canola oil. While healthy fats can help slow down digestion, the impact on GI is not as significant as the sugar content.
Fortification: Many brands fortify oat milk with vitamins and minerals like calcium, vitamin D, and B12. While beneficial for nutrition, fortification doesn't alter the GI.

Oat Milk Versus Other Milk Alternatives: A Glycemic Comparison

To put oat milk's glycemic impact into perspective, consider how it stacks up against other popular milk types.


Milk Type	Estimated Glycemic Index (GI)	Key Factor Influencing GI
Oat Milk (Unsweetened)	Medium (59–69)	Enzymatic processing and high carbohydrate content
Cow's Milk	Low (30–35)	Contains lactose, a less impactful sugar, and is higher in protein and fat
Almond Milk (Unsweetened)	Low (25)	Very low in carbohydrates and high in fat
Soy Milk (Unsweetened)	Low (~30)	Higher protein content helps slow sugar absorption

Strategies for Minimizing Oat Milk's Glycemic Impact

If you enjoy oat milk, there are several ways to mitigate its effect on your blood sugar levels:

Choose Unsweetened Varieties: Always opt for unsweetened options to avoid additional hidden sugars.
Pair with Protein and Fat: Consuming oat milk alongside foods rich in protein, healthy fats, and fiber can help slow down digestion and stabilize blood sugar. For example, a latte with oat milk is better with a protein-rich breakfast than on an empty stomach.
Mind Your Portions: Use oat milk in smaller quantities, such as a splash in coffee, rather than drinking large glasses on their own.
Consider Fermented Alternatives: As research and technology progress, fermented oat milks may become available, where microbes consume the carbohydrates, resulting in a lower-GI product.

Conclusion: Making Informed Choices

While oat milk offers a creamy, delicious, and allergen-friendly alternative to dairy, it is not a low-glycemic beverage. Its high GI is a direct result of the processing that breaks down starches into rapidly absorbed maltose and the removal of the whole grain's fiber. For most people, consuming oat milk in moderation as part of a balanced meal will not pose a significant problem. However, for those managing diabetes, insulin resistance, or following low-carb diets, it is important to be mindful of its effect on blood sugar. By choosing unsweetened options, controlling portions, and pairing it with protein and fat, you can continue to enjoy oat milk while minimizing its glycemic impact. For more information on food and its effect on blood sugar, consider consulting the Glycemic Index Foundation, a resource for GI data.

Frequently Asked Questions

Yes, even unsweetened oat milk contains natural sugars created during the processing of oats. Enzymes break down the oat's complex starches into simple sugars, primarily maltose, which still impacts blood glucose levels.

Oat milk has a significantly higher glycemic index (GI) than cow's milk. Cow's milk's GI is typically low (~30-35) due to its lower-impact lactose sugar, higher protein, and fat content, which slows digestion.

The difference lies in the fiber content. Whole oats contain soluble fiber (beta-glucan) that slows the absorption of carbohydrates. In oat milk, this fiber is largely removed during processing, allowing for rapid sugar absorption.

To minimize the glycemic impact, you can pair oat milk with protein, healthy fats, or extra fiber. For example, have it with a meal containing eggs and avocado instead of on an empty stomach.

The GI of oat milk is considered medium-to-high. Raw or unsweetened oat milk can have a GI around 60–69, while sweetened varieties can be even higher.

Oat milk isn't necessarily bad for diabetics, but it needs to be consumed mindfully due to its higher carbohydrate and sugar content. Diabetics should choose unsweetened options, watch portion sizes, and pair it with balancing nutrients like protein and fat.

Yes, unsweetened almond, soy, and coconut milk generally have a lower glycemic impact than oat milk because they contain fewer carbohydrates and sugars.

Homemade oat milk might be slightly lower in sugar than some commercial versions, but because the oats are processed into a liquid, it will still result in a quicker glucose response than eating whole oats. Processing methods still break down starches into simpler sugars.

The glycemic load of a standard serving of oat milk is relatively low (around 3.5–4), as GL considers portion size. However, this increases with larger quantities. The GI remains an important metric for how quickly the sugar is absorbed, regardless of portion.