I Tried Japan’s Most Controversial Superfood for 7 Days — The Results Surprised Me

In Japan, people often say fermented foods are the secret to a happy, healthy life.

Maybe you've heard that too.

But have you ever stopped and thought, "Is that actually true? Will this really make me healthier?"

I didn't want to just believe it. So I tested it.

I did a 7-day challenge eating only fermented foods — mostly traditional Japanese ones like miso, Japanese homemade pickles, and natto.

The first half really felt like punishment to me because I am not used to it but the second half felt like my system had quietly rewired itself.

Here's what actually happened my body and mind — and what I learned about fermented foods along the way.

Day 0 — Preparation

Before the experiment officially started, I did what anyone would do before committing to something slightly irrational.

I went shopping.

I didn't just buy a few things, I literally cleared shelves of miso, yogurt, kimchi, rice koji and an embarrassing amount of natto.

At one point, standing at the checkout line with stacks of slimy soybean packs in my basket, I wondered what the cashier was thinking "This girl is either very healthy… or very strange."

Probably both…

Back home, I laid everything out on the kitchen counter, it felt excessive slightly chaotic, but also exciting.

If I was going to live on fermented foods for seven days, I needed structure.

So I created a simple system — meals planned, ingredients prepped, fermentation projects started in advance. If I didn't organize it properly, I knew I'd give up by day three.

Looking at all that food lined up, I felt a mix of confidence and quiet doubt.

Seven days suddenly felt very real.

Day 1 — The Beginning

Breakfast

My first official meal of the experiment was simple: miso soup, natto, and yogurt.

I started with natto.

A friend once told me, "It smells like my dad's socks."

And honestly… that's not completely wrong.

The smell is strong, the texture is sticky and it stretches in strings when you lift it with chopsticks so yeah, it's not beginner-friendly.

But nutritionally, it's impressive Natto contains nattokinase, an enzyme often associated with supporting blood flow and because it's fermented, the protein is broken down into a form that's easier for the body to absorb.

It's actually great if you're training or trying to stay healthy.

Then next, yogurt. Yes, technically it's from Bulgaria but it's eaten daily in Japan, so I'm counting it.

And of course, miso — a classic Japanese superfood.

From this moment on, I committed to seven days of fermented foods only.

Making Amazake

The first thing I decided to make myself was amazake.

It felt symbolic somehow, as if I was going to live on fermented foods, I didn't just want to eat them — I wanted to understand them.

Amazake is surprisingly simple. All it takes is rice koji and hot water.

Rice koji is steamed rice cultivated with koji mould — the quiet hero behind much of Japanese fermentation.

It's what makes miso, soy sauce, sake, so many things begin with this almost unremarkable-looking grain.

I mixed the koji with warm water, sealed the container, and kept it gently heated for about eight hours.

And then… I waited.

Fermentation is pretty quiet because nothing exciting happens that you can see, it just sits there on the counter.

But inside, things are slowly changing. The starches are breaking down and turning into a bit of natural sweetness.

By the next morning, it's different (what should a say ) it tastes smoother like a little sweet, creamy, easy to eat.

You wouldn't guess how much time went into it. It just tastes good.

Lunch

For lunch, I kept it simple: fried eggs seasoned with shio koji.

If you've never heard of it, shio koji is one of those quiet Japanese ingredients that doesn't look impressive but changes everything.

It's made from rice koji, salt, and water, then kept warm — around 60°C — for several hours to activate the enzymes. There's also shoyu koji, which swaps water for soy sauce and ferments the same way.

You can make both in a rice cooker or even a yoghurt maker. It's surprisingly low effort.

But the taste?

That's where it gets interesting.

When I added shio koji to the eggs, the flavor wasn't just salty. It was rounder and deeper.

There was this gentle umami that regular salt simply doesn't have. The eggs tasted softer, almost richer, without adding anything heavy.

It was such a small adjustment, but it felt like discovering a shortcut to better cooking.

By the end of that meal, I had a quiet thought: I might not be able to go back to plain salt again.

Dinner

My dinner is almost very simple and normal.

I poured myself a small glass of sake — not for the experiment, just because it's something I genuinely enjoy at the end of the day.

Then I stir-fried whatever vegetables I had left in the fridge and added kimchi.

Yes, I know kimchi is Korean. But like yoghurt, it's fermented, and at this point, that was the only rule that mattered.

Before serving, I spooned a little shoyu koji over the vegetables. The smell alone was enough to make me pause.

It added depth without heaviness, almost like the food had been slowly simmering for hours instead of minutes.

What struck me most wasn't the flavour, though. It was how normal everything looked.

If someone had walked into my kitchen, they wouldn't have thought I was doing an experiment.

They would have just seen dinner. Even when a friend messaged me later, he had no idea I was living almost entirely on fermented food.

But inside, I knew something had shifted.

Day 2 — The Crash

By the second day, my body started changing in ways I didn't expect.

Change #1: No Focus

It began with this strange mental fog and I couldn't concentrate like my energy dipped for no clear reason.

Even small tasks felt heavier than they should have. I kept wondering whether it was the sudden overload of fermented foods or simply the drop in carbohydrates.

I hadn't changed my portions dramatically, but something in my rhythm felt off.

So, in the afternoon, I walked to a café and ordered banana yogurt and black tea, hoping a little sugar and caffeine would wake me up.

It didn't really.

Change #2: Non-Stop Gas

And then there was the digestive situation.

When you suddenly increase fermented foods, your gut doesn't quietly adjust it reacts.

Sitting in Starbucks, I couldn't stop farting. I became painfully aware of that, and I kept thinking, "Please… no one notice." because it was uncomfortable and slightly embarrassing.

But at the same time, I knew this might be part of the process. Fermented foods introduce live bacteria and enzymes.

My internal ecosystem was probably rearranging itself.

Change #3: Smooth Digestion

The surprising part was that despite the gas and the mental fog, my digestion actually felt smoother.

I was more regular, my stomach felt lighter, less bloated. Even my waist felt subtly slimmer — not from fat loss, but from not carrying that usual heaviness.

It was a strange combination because I felt worse and better at the same time.

Dinner was natto over rice. In theory, comforting but in reality, intensely sticky.

The texture clung to everything, and the smell stayed with me long after the meal ended.

By the end of day two, I wasn't sure whether I was improving or declining.

But I knew one thing, "I have to stick with it no matter what so I did."

Day 3 — Heavy Body

Breakfast looked almost identical to the previous days, but my body didn't feel the same.

During my morning run, my legs felt incredibly heavy, like each step required more effort than it should have. Halfway through, I genuinely considered stopping the experiment.

I almost gave up the challenge, that's how tired I felt.

And for a moment, I questioned whether eating mostly fermented food was actually a mistake.

Instead of overthinking it, I decided to shift my energy into something creative.

I started making nukazuke — traditional Japanese pickles fermented in a rice bran bed called nukadoko.

There's something grounding about mixing rice bran, salt, and warm water with your hands. It's messy and warm and slightly earthy. You stir it twice a day, let it breathe, and after a few days, it slowly transforms.

I started the fermentation and couldn't wait to try it.

Lunch was simple: salmon marinated overnight in shio koji. When cooked, it turned incredibly soft and juicy, almost as if it had been gently tenderized from the inside.

The flavor was deep but not overpowering just clean and satisfying.

Dinner felt warmer.

A friend from Okinawa came over, and we made a miso soy milk hot pot together.

The steam filled the kitchen, and for the first time that week, the experiment didn't feel isolating.

We drank amazake alongside it — naturally sweet, comforting, and surprisingly nourishing.

In Japan, it's sometimes called a "drinkable IV drip," even though it contains zero alcohol despite the name.

Something was reassuring about that meal.

My body still felt heavy, but emotionally, I felt steadier.

Day three wasn't about feeling good I really think it was about not quitting.

Day 4 — Creativity

Something shifted on day four.

Maybe my body was adjusting, maybe I was just getting used to the rhythm, but instead of feeling restricted, I started feeling curious.

That morning, I blended amazake with banana, yogurt, and a little matcha. While I was making it, I hesitated. Is this too much? Is this even going to taste good?

It was unexpectedly delicious, creamy, naturally sweet, slightly earthy from the matcha and you know what it didn't taste like "health food."

It just tasted good, like really good.

For the first time during the experiment, I wasn't eating fermented foods because I had to.

I wanted to.

I also tried making enzyme brown rice (not technically fermented, but enzymes change it over time in a similar way)

The process requires patience you cook brown rice with azuki beans and keep it warm for days, allowing it to soften and deepen in flavor.

That night, I finally opened the nukazuke container I had started earlier in the week.

I was nervous.

The first bite was sharp and sour (maybe a little too sour). I probably should have rinsed it more. But when I paired it with warm rice, something clicked.

I almost cried.

Not because it was perfect (it wasn't) It was slightly uneven, slightly rough around the edges.

But my body craved it in a way I didn't expect, it felt alive, real its like I had grown something instead of just cooked it.

Day four didn't feel like a diet anymore.

Day 5 — Everything Clicks

I knew something was different the moment I woke up.

There was no heaviness, no fog and my body also felt light like everything was running smoothly again.

Even my mood was better and without forcing myself I was cleaning the kitchen, it felt almost enjoyable.

The biggest change, though, came when I reintroduced proper carbs more intentionally.

Once I paired fermented foods with balanced meals — rice, vegetables, protein — my energy returned fully. My mind sharpened, my runs felt normal again.

That's when the real lesson became obvious.

Fermentation alone isn't magic balance is.

Fermented foods support you but they don't replace everything else.

Feeling inspired, and maybe slightly overconfident, I decided to make natto myself. I boiled soybeans, mixed in a little store-bought natto as a starter, and kept it warm in the rice cooker for about twelve hours.

Now it worked, too well.

I underestimated how much soybeans expand. What started as a reasonable amount turned into a mountain of natto.

Standing in front of it, I realized I had created a new problem.

Now I actually had to eat it.

Day 6 — An Unexpected Superpower

The natto I made was finally ready.

And there was a lot of it.

I had no choice but to commit. Breakfast, lunch — natto found its way onto my plate again and again.

At this point, I wasn't even pretending it was for variety. I simply needed to reduce the mountain I had created.

And then this might be slightly uncomfortable to talk about, but it's part of the story.

My digestion reached a new level of efficiency.

It was fast, effortless, smooth in a way I hadn't experienced before. No discomfort, no heaviness, no waiting around. Just a body doing exactly what it's supposed to do.

If gut health had a performance metric, this was peak optimization.

It was almost impressive.

By the afternoon, though, I realized I might have overdone it. There is such a thing as too much natto.

My appetite dipped, and I ended up skipping dinner simply because I wasn't hungry.

Day six felt whatever was happening inside me, it was working.

Day 7 — The Final Stretch

By the last day, I'll be honest — I was tired of natto.

What started as curiosity had turned into obligation. The sticky strings, the smell, the sheer volume I had accidentally produced… it was no longer an experiment.

It was a responsibility.

That morning, a firefighter stopped by for a routine safety check.

In a moment of misplaced enthusiasm, I offered him some. He smiled politely and declined.

I can't blame him. At that point, even I wasn't fully convinced anymore.

But I had one final portion left and I wasn't about to quit on the last day.

So I sat down, mixed it carefully, wrapped it in rice, and powered through the final bite.

Should You Try It?

Short answer? Maybe…

But not as a seven-day natto marathon for sure.

If there's one thing this experiment taught me, it's that fermented foods are powerful — but they're not magic on their own.

The real shift happened when I combined them with proper meals like:

• Balanced carbs
• Enough protein
• Vegetables
• Routine

Natto didn't fix my life it just help my gut.

And when your gut feels good, everything feels slightly easier — your energy, your focus, even your mood that part surprised me the most.

But I also overdid it.

There were days I felt low on energy because I didn't fuel properly. There were moments when the "experiment" became stubbornness.

So if you're curious, try adding a small portion to your meals, give your body time to adjust, pay attention and notice how you feel.

You don't need extremes to see results because sometimes consistency beats intensity.