Why Do Navy Beans Give You Gas? A Scientific Explanation

January 13, 2026 •

3 min read

The average person passes gas between 5 and 15 times a day, a normal part of digestion. So, why do navy beans give you gas with such particular emphasis? The answer lies in complex sugars called oligosaccharides, which our bodies can't break down alone, leading to fermentation by gut bacteria.

Quick Summary

Navy beans cause gas due to complex carbohydrates known as oligosaccharides, specifically raffinose and stachyose. Lacking the enzyme alpha-galactosidase, humans cannot digest these sugars, so they reach the large intestine and are fermented by bacteria, producing gas.

Key Points

Oligosaccharides are the Culprit: Navy beans contain complex sugars like raffinose and stachyose, which are indigestible by human enzymes.
Gut Bacteria Cause Fermentation: Undigested oligosaccharides travel to the large intestine, where gut bacteria ferment them, releasing gas as a byproduct.
Enzyme Alpha-Galactosidase is Missing: The human body lacks the necessary enzyme, alpha-galactosidase, to break down these specific sugars.
Soaking and Rinsing Reduces Gas: Properly soaking and rinsing dried or canned beans can leach out many of the gas-causing oligosaccharides.
Tolerance Increases Over Time: Introducing beans slowly into your diet allows your gut microbiome to adapt, reducing gas and bloating over several weeks.
Enzyme Supplements can Help: Products containing alpha-galactosidase (like Beano) assist in breaking down the complex carbohydrates before they reach the colon.

Understanding the Core Cause of Bean Gas

Navy beans are a nutritional powerhouse, packed with protein, fiber, and various vitamins and minerals. Despite these benefits, their reputation for causing flatulence often discourages consumption. The primary culprits behind this gassy side effect are specific types of complex carbohydrates called oligosaccharides.

Unlike simple sugars, which are easily absorbed in the small intestine, oligosaccharides like raffinose and stachyose are resistant to human digestive enzymes. Our bodies lack a crucial enzyme, alpha-galactosidase, needed to break down the complex bonds in these sugars. Consequently, the indigestible oligosaccharides travel intact to the large intestine.

The Fermentation Process in Your Gut

Once these undigested sugars reach the large intestine, they become a feast for the trillions of bacteria that make up your gut microbiome. These beneficial bacteria ferment the carbohydrates, a process that produces gas as a byproduct. The gases produced include:

Hydrogen ($H_2$): A major product of bacterial fermentation.
Carbon Dioxide ($CO_2$): Also produced during the fermentation of carbohydrates.
Methane ($CH_4$): Produced by certain archaea that consume hydrogen and carbon dioxide.

This buildup of gas is then expelled from the body as flatulence, sometimes causing bloating and discomfort. Interestingly, this process is a sign of a thriving and well-fed gut microbiome, indicating good bacteria are doing their job.

Reducing Gas from Navy Beans: Proven Methods

For those who wish to enjoy the nutritional benefits of navy beans without the unpleasant side effects, several preparation techniques and dietary strategies can help. The goal is to either reduce the oligosaccharide content before consumption or to help your body break them down more efficiently.

Soaking and Rinsing

One of the most effective methods for reducing oligosaccharides is through soaking. Since these sugars are water-soluble, soaking dried beans leaches them out into the water.

Best Practices for Soaking:

Sort and rinse dried navy beans to remove debris.
Soak beans in a large bowl of water for at least 8 hours, or overnight.
For maximum effect, change the soaking water every few hours.
After soaking, thoroughly drain and rinse the beans with fresh water before cooking.
For canned beans, rinsing them well in a colander can wash away some of the starches and sugars in the canning liquid.

Comparison of Bean Digestibility and Preparation


Preparation Method	Impact on Gas	How It Works
Soaking Dried Beans	High Reduction	Leaches out water-soluble oligosaccharides (raffinose, stachyose).
Rinsing Canned Beans	Moderate Reduction	Washes away starchy canning liquid containing oligosaccharides.
Slow, Gradual Introduction	High Reduction	Allows gut bacteria time to adapt to new fiber load.
Using Digestive Enzymes	High Reduction	Supplements like Beano add alpha-galactosidase to break down oligosaccharides.
Pressure Cooking	Moderate Reduction	High heat and pressure can break down some of the complex sugars.
Adding Digestives Aids	Varies	Herbs like epazote or cumin may help break down gas-producing fibers.

Dietary and Supplemental Approaches

Increase intake gradually: If your diet is not accustomed to high fiber intake, a sudden large serving of beans can cause significant gas. Start with a small portion (2-4 tablespoons) and slowly increase it over several weeks to allow your gut microbiome to adjust. Studies show that for many people, increased gas symptoms subside after consistent daily bean consumption.
Use digestive enzyme supplements: Over-the-counter products containing the enzyme alpha-galactosidase, such as Beano, can be taken just before a meal. This enzyme helps break down the oligosaccharides in the beans before they reach the large intestine. It is important to note that these supplements are not regulated by the FDA, and dosage and efficacy can vary.
Cook with natural aids: Certain herbs and spices have traditionally been used to aid digestion. Adding a piece of kombu seaweed, or herbs like epazote, fennel, or cumin to the cooking pot can help break down some of the gas-causing compounds.

Conclusion

While navy beans may give you gas, it is a perfectly normal and, in some ways, beneficial side effect of a healthy digestive process. The gas is produced by beneficial bacteria feeding on indigestible oligosaccharides, indicating a robust gut ecosystem. By using simple preparation methods like soaking and rinsing, or by gradually introducing beans into your diet, you can significantly reduce the potential for discomfort. For more immediate relief, supplements with alpha-galactosidase can provide additional assistance. Don't let the fear of flatulence prevent you from enjoying the rich nutritional profile and health benefits that navy beans offer. For further reading, see this authoritative resource on Fabry disease, which highlights the importance of the enzyme alpha-galactosidase: National Institutes of Health (NIH).

Frequently Asked Questions

The gas is caused by complex sugars called oligosaccharides, particularly raffinose and stachyose, found in high concentrations in navy beans. These are resistant to digestion in the small intestine.

Our bodies lack the specific enzyme, alpha-galactosidase, required to break down the bonds in these oligosaccharides. Without this enzyme, the sugars pass to the large intestine largely undigested.

Yes, soaking dried beans for several hours or overnight is an effective way to reduce gas. Since oligosaccharides are water-soluble, they leach out into the soaking water, which should be discarded before cooking.

Rinsing canned navy beans thoroughly under running water can wash away some of the starches and oligosaccharides present in the canning liquid, reducing the gas-producing compounds.

Yes, many studies show that consuming beans regularly allows your gut microbiome to adapt. Initial increases in gas often subside after a few weeks of consistent, moderate consumption.

Alpha-galactosidase is a digestive enzyme that breaks down the carbohydrates in beans into simpler, more digestible sugars. It is available in over-the-counter supplements like Beano, which can be taken before eating bean-containing meals.

Some sources suggest that certain beans like lentils, adzuki beans, and black-eyed peas are easier to digest for some people and may cause less gas than larger beans like navy beans. Individual tolerance can vary, so it's recommended to experiment with different types.