Does Natto Help with Sleep? Unpacking the Science

November 14, 2025 •

4 min read

According to a 2025 review in the Journal of Food Science, there is a documented link between consuming fermented foods and experiencing better sleep. This growing body of evidence suggests that incorporating natto into your diet could positively influence your sleep patterns, though the mechanism is complex and multi-faceted.

Quick Summary

Natto contains key nutrients like tryptophan and probiotics that support the body's natural sleep-wake cycle via the gut-brain axis, promoting the production of regulating hormones like serotonin and melatonin. Its benefits are linked to improved gut health and reduced inflammation, which collectively contribute to better sleep quality.

Key Points

Tryptophan content: Natto is a good source of tryptophan, an amino acid precursor to serotonin and melatonin, which help regulate the sleep-wake cycle.
Supports the gut-brain axis: The probiotics in natto promote a healthy gut microbiome, which is directly linked to brain functions like mood and sleep via the vagus nerve.
Aids in melatonin production: By supporting serotonin synthesis, particularly with midday consumption, natto can enhance the natural conversion to melatonin for better sleep later.
Provides stress-reducing GABA: Fermented foods like natto can contain GABA, an inhibitory neurotransmitter that helps calm the nervous system and reduce stress.
Offers holistic health benefits: In addition to sleep support, natto provides other benefits like improved cardiovascular health and reduced inflammation.
Requires mindful consumption: People on blood thinners or with soy allergies should consult a doctor due to potential risks, including increased bleeding.

The Gut-Brain Connection and Its Role in Sleep

Your gut is often called the "second brain" due to its direct communication with the central nervous system via the vagus nerve. This intricate pathway, known as the gut-brain axis, allows substances produced by your gut microbiome to influence brain functions, including mood, stress, and sleep. Fermented foods like natto are rich in probiotics, which are beneficial bacteria that help cultivate a healthy and diverse gut microbiome. A balanced microbiome, in turn, supports the production of neurotransmitters that are vital for sleep regulation.

How Natto's Nutrients Support the Sleep Cycle

Natto is not a sedative, but it provides several key components that support the body's natural processes for sleep. By supplying these building blocks, it can help create an optimal internal environment for restful sleep.

Tryptophan: This essential amino acid is a precursor to serotonin, a neurotransmitter that helps regulate mood and stress. As the day winds down, the brain converts serotonin into melatonin, the hormone primarily responsible for regulating the sleep-wake cycle. Natto is a good source of tryptophan, effectively feeding this natural biological rhythm.
Probiotics and the Gut Microbiome: The Bacillus subtilis bacteria used to ferment soybeans into natto contribute to a healthier gut flora. Studies have found that imbalances in the gut microbiome can negatively impact sleep, while increasing beneficial bacteria can have the opposite effect. By promoting better gut health, natto helps regulate the production of sleep-related neurotransmitters.
GABA (Gamma-Aminobutyric Acid): This is the main inhibitory neurotransmitter in the central nervous system, and it helps calm nerve activity and promote relaxation. Fermented foods can naturally contain GABA, which facilitates the body's transition to a state of rest and reduces stress and anxiety. Some studies have also shown that orally administered GABA can reduce sleep latency.
B Vitamins: Natto contains a variety of B vitamins, including B1, B2, and B6. These vitamins play a crucial role in cellular metabolism and nerve function, complementing the body's self-maintenance and repair processes that occur during sleep.

The Best Time to Eat Natto for Sleep

While natto can be enjoyed at any time, its potential sleep benefits can be maximized by strategic timing.

Lunchtime: Eating natto at midday allows the body's natural processes to unfold throughout the afternoon. The tryptophan supports serotonin production, which then converts to melatonin as evening approaches, aligning with the circadian rhythm. This can help prevent the post-lunch slump and set the stage for a calm evening.
Dinner: Consuming a moderate portion of natto with your evening meal provides the necessary nutrients for overnight recovery. It supports cell renewal and tissue repair that happens during deep sleep cycles. It's recommended to watch portion sizes at dinner, as the body's metabolism is slower at night, potentially leading to weight gain in sedentary individuals.

Natto vs. Traditional Sleep Aids


Feature	Natto	Traditional Sleep Aids (e.g., Benzodiazepines)
Mechanism	Supports natural sleep processes via nutrients (tryptophan, probiotics, GABA) and gut health.	Directly influences GABA receptors in the brain to induce sedation and sleep.
Side Effects	Few, but watch for potential interactions with blood thinners due to nattokinase.	Can cause dependence, withdrawal symptoms, daytime fatigue, and other side effects.
Long-Term Use	Considered safe for regular, long-term consumption.	Not recommended for long-term use due to risk of dependency and side effects.
Holistic Benefit	Offers additional health benefits like improved gut health, cardiovascular support, and anticarcinogenic effects.	Primary effect is on sleep; offers no other broad systemic health benefits.
Targeted Use	Supports healthy sleep patterns and overall wellness.	Addresses sleep issues directly but with potential health trade-offs.

Potential Downsides and Considerations

While natto is generally safe and beneficial, there are considerations to keep in mind.

Allergies: As natto is made from soybeans, individuals with soy allergies or intolerances should not consume it.
Medication Interactions: The enzyme nattokinase, abundant in natto, has anticoagulant properties. Those on blood-thinning medication should consult a doctor before adding significant amounts of natto to their diet to avoid excessive blood thinning. It is also advised to discontinue natto consumption at least one week before any surgery.
Hypothyroidism: Soy is considered a goitrogen, which may be a concern for individuals with hypothyroidism. It is best to consult a healthcare provider.

How to Incorporate Natto Into Your Diet

For many, the unique taste and slimy texture of natto can be an acquired taste. Here are some methods for adding it to your routine:

Traditional Preparation: Serve natto over steamed rice with soy sauce and mustard. The stickiness is a key characteristic.
Blended into Smoothies: For those who prefer to mask the flavor, blending natto into a fruit smoothie with strong flavors like banana or berries can be effective.
Added to Salads: A small portion of natto can be mixed into salads for an added protein and probiotic boost.
Natto Powder: For maximum convenience without the texture or strong taste, natto powder capsules or powdered products are available, offering similar benefits.

Conclusion

While not a direct sedative, natto can indeed help with sleep by providing key nutrients and beneficial bacteria that support the body's natural sleep-regulating mechanisms. Its content of tryptophan, probiotics, GABA, and B vitamins works to calm the nervous system, reduce stress, and promote the healthy production of melatonin. The evidence points towards a significant gut-brain connection, suggesting that improving your gut health through foods like natto can lead to better sleep outcomes. Strategic consumption, such as during lunch to support evening melatonin conversion, can further enhance these effects. However, it is essential to consider potential allergies and interactions with blood thinners. Ultimately, incorporating natto into a balanced diet is a holistic approach to promoting restorative and natural sleep. For personalized advice, particularly concerning existing health conditions or medications, consulting a healthcare professional is recommended.

Frequently Asked Questions

Natto affects the sleep cycle indirectly by providing the body with tryptophan, which is converted into the neurotransmitter serotonin. Serotonin is later converted into melatonin, the hormone that regulates the circadian rhythm and promotes sleep.

Eating natto at lunchtime is ideal for supporting sleep. This allows the tryptophan to help with serotonin production during the afternoon, which naturally converts to melatonin as evening approaches.

While it is not harmful, it may be better to eat natto earlier in the day to support the natural sleep-wake cycle. Eating a large portion right before bed may not be fully utilized due to a slower metabolism at night.

Nattokinase is more known for its cardiovascular benefits, but some studies show that supplements containing nattokinase and melatonin can have a synergistic effect on sleep, though it is not the primary sleep-promoting compound in natto.

Individuals on blood-thinning medications should be cautious due to nattokinase's anticoagulant properties. Additionally, people with soy allergies or hypothyroidism should consult a healthcare provider.

Many fermented foods contain probiotics and can positively influence gut health and mood, potentially leading to better sleep. Studies on foods like yogurt and kimchi have also shown a link between fermented food intake and improved sleep quality.

The effects of dietary changes on sleep can vary by individual. Some may experience benefits over time as their gut health improves, while the impact of tryptophan on melatonin production is part of a natural daily process.