Can Beta-Glucan Cause Tiredness? Unpacking the Link

November 23, 2025 •

4 min read

A 2024 meta-analysis revealed that beta-glucan supplementation significantly reduced feelings of fatigue in healthy individuals, challenging the idea that can beta-glucan cause tiredness. As a soluble fiber known for supporting stable blood sugar and immune function, beta-glucan is more often associated with improving energy rather than causing tiredness.

Quick Summary

Studies suggest that beta-glucan is more likely to help combat fatigue by stabilizing blood sugar and supporting immunity rather than causing tiredness. Any potential side effects are typically related to gastrointestinal issues, not directly causing fatigue.

Key Points

Fatigue Reduction: Multiple meta-analyses and studies indicate that beta-glucan is associated with a reduction in fatigue and an increase in vigor, particularly in healthy individuals.
Steady Energy: Beta-glucan's function as a soluble fiber helps to stabilize blood sugar levels, preventing the energy crashes that cause lethargy and tiredness.
Common Side Effects are Digestive: The most common side effects are gastrointestinal (bloating, gas, diarrhea), usually occurring when intake increases too quickly, and are not typically linked to systemic fatigue.
Immune Support: Yeast and fungal beta-glucans are powerful immunomodulators that prepare the body's defenses, which can help fight fatigue associated with illness.
Source Matters: Beta-glucan from oats and barley is mainly beneficial for blood sugar and cholesterol, while yeast and fungal varieties are known for immune support.
Rarely a Problem: There is very little evidence to suggest that oral beta-glucan causes tiredness as a direct negative side effect, especially when consumed as part of a regular, healthy diet.

What Is Beta-Glucan?

Beta-glucan is a type of soluble fiber, a polysaccharide made of glucose units, found naturally in various sources. As a dietary component, it's a non-starch carbohydrate that moves through the digestive system largely unabsorbed. It's celebrated for its many health benefits, from lowering cholesterol to supporting the immune system. Key natural sources include:

Oats and Barley: Contain linear beta-glucans with mixed 1,3 and 1,4 linkages. These are most known for their metabolic effects, like cholesterol reduction and blood sugar control.
Yeast and Fungi: Possess beta-glucans with a 1,3 backbone and 1,6 side-chain linkages. These are more renowned for their powerful immune-modulating properties.
Certain Mushrooms: Such as maitake and shiitake, also provide beta-glucans known for immune support.

The Anti-Fatigue Evidence: What the Research Shows

Contrary to the question "can beta-glucan cause tiredness," a body of scientific evidence points to the opposite conclusion. A systematic review and meta-analysis published in 2025 concluded that beta-glucans may be effective in reducing feelings of fatigue and increasing vigor in healthy individuals. The research analyzed data from sixteen randomized controlled trials involving 1,449 participants and found significant improvements in energy levels and mood. In another study focused on mice, researchers found that a specific type of water-soluble beta-glucan, Salecan, had a significant anti-fatigue effect, improving exercise performance and reducing signs of fatigue-related injury. This was attributed to better energy metabolism and antioxidant defense mechanisms. While some studies show inconsistent results or smaller effect sizes, the prevailing scientific consensus suggests a positive, not negative, effect on perceived energy levels.

Stabilizing Energy Levels through Blood Sugar Control

One of the primary ways beta-glucan positively influences energy levels is through its impact on blood sugar. As a soluble fiber, it forms a gel-like substance in the digestive tract that slows down the absorption of glucose into the bloodstream. This leads to a more gradual, sustained release of energy, preventing the rapid spikes and subsequent crashes that can cause feelings of lethargy and fatigue. Without sufficient fiber, particularly soluble fiber like beta-glucan, diets high in refined carbohydrates can lead to these undesirable energy fluctuations. By smoothing out the glycemic response, beta-glucan helps maintain balanced energy throughout the day.

Addressing Potential Side Effects of Beta-Glucan

While the direct link between beta-glucan and tiredness is unsupported, the side effects associated with high fiber intake could, in some cases, indirectly influence well-being. These side effects are generally mild and related to the digestive system.

Gastrointestinal Distress: Increasing fiber intake too rapidly can cause bloating, gas, and diarrhea. While not systemic fatigue, persistent digestive discomfort can certainly be tiring. The best way to mitigate this is to increase intake slowly and drink plenty of water to help the fiber pass through the system more smoothly.
No Known Negative Side Effects: Several sources state that beta-glucans, especially when taken orally, are generally recognized as safe and have no known negative side effects, particularly regarding immune overstimulation or toxicity at typical doses.

Beta-Glucan and Immune Function: A Modulatory Role

Beta-glucan is a well-known immunomodulator, meaning it helps to regulate the immune system. It is recognized by receptors on immune cells, helping to prime the body's defenses against pathogens. Some supplements derive from yeast or fungi specifically for this immune-boosting property. While a strong immune response to an infection can sometimes cause fatigue, oral beta-glucan is not known to trigger this in a way that causes general tiredness for healthy individuals. On the contrary, some studies suggest that yeast beta-glucan can help reduce symptoms of upper respiratory tract infections and improve overall mood and health, even in endurance athletes after intense exertion.

Comparison of Beta-Glucan Sources and Effects


Source	Primary Beta-Glucan Type	Main Effects	Relevance to Tiredness	Potential Side Effects
Oats/Barley	Primarily (1,3/1,4) linear linkages	Cholesterol-lowering, blood sugar stabilization	Helps prevent fatigue caused by blood sugar crashes	Bloating, gas if increased too quickly
Yeast/Fungi	Primarily (1,3/1,6) branched linkages	Immune modulation, immune support	Can reduce fatigue associated with infections	Mild digestive issues possible
Mushrooms	(1,3/1,6) branched linkages	Immune-modulating, anti-tumor properties	Supports immune health, may indirectly help with fatigue	Very low incidence of side effects reported

Conclusion: The Bottom Line on Beta-Glucan and Tiredness

The current evidence overwhelmingly suggests that beta-glucan does not cause tiredness. In fact, numerous studies indicate it can help reduce fatigue and boost vigor through its positive effects on energy metabolism and immune function. While gastrointestinal side effects can occur when first increasing fiber intake, these are manageable and not the same as systemic tiredness. The notion that beta-glucan causes fatigue appears to be a misconception, likely conflated with general dietary fiber adjustments. For most people, incorporating beta-glucan-rich foods like oats and barley, or supplements from sources like yeast, is a strategy for supporting sustained energy levels rather than depleting them. For optimal health and energy, increasing fiber intake should always be combined with sufficient water consumption and gradual introduction. For more information on the immune-modulating effects of fungal beta-glucans, see this review on the topic.

Note: While beta-glucan is generally safe for oral consumption, it's always best to consult with a healthcare professional before starting any new supplement, especially if you have an autoimmune condition or are on immunosuppressants.

Frequently Asked Questions

The primary effect of beta-glucan on energy is a positive one. As a soluble fiber, it helps stabilize blood sugar, leading to a more consistent, long-lasting supply of energy rather than causing tiredness.

No, taking too much beta-glucan is more likely to cause gastrointestinal discomfort, such as bloating and gas, rather than making you feel tired. These symptoms are manageable by increasing fiber intake gradually and staying hydrated.

Beta-glucan helps prevent energy crashes by forming a gel in the digestive system that slows down the absorption of carbohydrates. This leads to a more gradual and stable release of glucose into the bloodstream, avoiding the rapid spikes and dips that cause fatigue.

Yes, the source of beta-glucan affects its primary function. Beta-glucans from oats and barley are known for their metabolic effects, while those from yeast and fungi are particularly potent as immune system modulators.

While a major immune response can cause fatigue, the mild and beneficial immune-modulating effects of oral beta-glucan are not typically known to cause systemic tiredness in healthy individuals. In some cases, it may even help combat fatigue associated with stress or infection.

Yes, beta-glucan is generally considered safe for daily use, especially when consumed from food sources like oats and barley. As with any supplement, consulting a doctor is recommended, especially for specific health conditions.

Excellent food sources of beta-glucan include oats, barley, and various types of mushrooms like shiitake and maitake. Yeast-derived beta-glucan is also a common supplement.