How did eating only fermented Japanese foods for 7 days change Samurai Matcha's life?

Could fermentation be the secret to better digestion, more energy, and a clearer mind?

That’s exactly what YouTuber Samurai Matcha set out to discover in his latest video, where he challenges himself to eat only fermented Japanese foods for an entire week.

From natto and miso soup to shio-koji and amazake, his meals were packed with traditional, microbiome-friendly foods. And the results? Surprising in all the best ways.

By Day 5, he reported feeling lighter, more energized, and emotionally grounded. His digestion became smooth, his mood lifted—and most notably, his gut felt transformed.

The Game-Changer: R’s KOSO

In the middle of his week-long experiment, Samurai Matcha added R’s KOSO to his routine and noticed a difference almost immediately. He describes R’s KOSO as his “everyday partner” for gut health—a traditional Japanese fermented drink made from over 100 fruits, vegetables, seaweeds, mushrooms, and herbs, carefully aged for over a year.

Unlike many fermented foods, R’s KOSO is easy to incorporate into your daily life. No prep, no cooking—just a tablespoon a day in water, smoothies, or even coffee. It’s rich in prebiotics, probiotics, polyphenols, and postbiotics—compounds that help balance your microbiome and support digestion, immunity, and even mental clarity.

What Samurai Matcha Learned from 7 Days of Fermented Living

Since improving his gut health, he’s noticed incredible changes. His stomach feels light and clean, digestion has improved, and bathroom visits have become regular and nearly effortless.

An unexpected bonus was that his waist felt slimmer as his body cleared out waste. Emotionally, he felt calmer and more centered, even during stressful times. He also discovered the importance of balance; while fermented foods were helpful, he realized that including carbohydrates was essential too—reintroducing them brought back mental clarity.

Cooking became more enjoyable for him, especially with fermentation, which felt like nurturing something alive—like raising a tiny baby. He even began to see bacteria not as invisible threats but as little friends, partners helping him grow.

 “Bacteria became my little friends,” he shares. “They're not just invisible things. They're partners helping me grow.”

His final takeaway? Fermented foods really can change your life.

Ready to Start Small?

You don’t need to go full “fermented-only” like Samurai Matcha to feel a difference. Start by incorporating one tablespoon of R’s KOSO into your morning routine or have one fermented food every week. It’s a simple way to support gut health from the inside out—especially during stressful, busy seasons like back-to-school or late summer transitions.

Try these popular R's KOSO recipes this summer.
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Postbiotic Electrolyte Drink (AKA Homemade Gatorade)

Blended Blueberry Chia Pudding with Dark Chocolate shell

Gut-Friendly Piña Colada Smoothie

Let’s get started!

Written by Eriko Shintani

Certified holistic nutritionist/Holistic nutrition advisor

Instagram: https://www.instagram.com/vegefuldays/