GutGutGoose: The YC-Backed Startup Reinventing Probiotics

GutGutGoose tests your microbiome to create personalised probiotics designed to survive and work inside your gut.

Origin

Leon had bad gut problems. Searching for relief, it cost him more than US$600 a month to import probiotics from the US to Australia.

Some of them did nothing. Others made him feel worse. A gastroenterologist gave him an explanation.

"Every gut is different."

Yet every off-the-shelf probiotic was the same.

The gut is an ecosystem with hundreds of organisms consuming resources and producing metabolites, a system which cooperates and competes. And since every gut is different, every gut should have something different.

This is where the idea of GutGut Goose began.

Leon Mojarrabi and Anis Mihrshahi at their first industry convention.

Childhood friends

Leon brought this idea to his childhood friend Anis Mihrshahi. Leon actually started university at 14 and later spent 4 years at Queensland's first tech unicorn, Go1. Anis was studying maths, AI and data science.

Together they started researching the microbiome and began creating a system that could predict which bacterial strains would survive in someone's gut.

After all their hard work they showed it to a senior microbiome researcher, and he said what they had created wouldn't even work.

So they went back to the drawing board and tried again.

They realised they couldn't just treat the gut like a normal AI problem. They had to treat it like an ecosystem. Just like an ecosystem, different strains consume different nutrients. Some support each other; others compete, and a strain can only survive if it's right for that environment.

That became the foundation of GutGut Goose.

After two years of testing and iterating, they had finished the science. Now they just had to come up with a name.

When Anis was searching for domains he was repetitively saying the word "gut" out loud. Gut... gut... gut... Then someone yelled out, "Goose!"

Which is where they came up with their infamous name, GutGut Goose.

Leon Mojarrabi presenting GutGut Goose at Lumina X.

Lumina X

Lumina X is a health tech accelerator.

In 2025 Leon approached Lumina X with just an idea, and the director, Dren Xerax, challenged them to build something that people actually want.

They created an MVP and quickly got 120 real waitlist signups. Quickly after, GutGut Goose was accepted into the Lumina X 2025 accelerator.

The program went for 14 weeks, forcing them to go from a vague scientific solution to something simpler: test your gut, we'll build a formula for it, and we'll test again to see what happens. Stop guessing what probiotic might work.

Five phone calls

In May 2026 Leon and Anis were applying for Y Combinator.

But they felt like they needed stronger evidence that people would pay for their product, so they pulled up their waitlist and called 5 people. Three of those people answered, but from those conversations they produced 7 paid signups, because customers began purchasing and then referring their friends and family.

Then, only a few days later, the beta test was full.

At 7am on May 13, 2026, they took the interview for Y Combinator, and at 1:30pm that same day they got accepted.

These two childhood friends from Brisbane were now off to San Francisco with half a million dollars.

The GutGut Goose team at Y Combinator.

Y Combinator

GutGut Goose joined YC in its summer batch of 2026, where they publicly launched.

The product was simple. Customers would receive an at-home stool test, then ship it to GutGut Goose, who'd sample it, map out the bacteria living in their gut and test what probiotics would work for it. Then the customer would receive their one-of-one personalised probiotic.

But then, only five weeks later, GutGut Goose would test again. This allowed them to see that their product was actually working, rather than just assuming it would.

By September 2026 the company had grown from 0 to just under 3,000 people on their waitlist in 23 days, with more than a hundred customers.

It was clear they had found a hair-on-fire product. People were willing to send them a stool sample, wait for a personalised formula and pay a high monthly price just to solve this problem.

As the YC summer batch comes to a close, GutGut Goose is returning to Brisbane. They've got a clearly validated product, but only time will tell how successful it is.

The wedge

They create a custom experience for the customer, made just for their body. Once you get them on it and they see measurable, clear results, they stick with it. This creates a flywheel effect as the more you use the product the more testing occurs and the better your product becomes. Which then creates more credible outcomes, which create more referrals, more customers, more intervention data, better predictions, and the cycle repeats. However Instead of a probiotic company they are a data company, thats the real value of GutGut Goose.

Founders

GutGut Goose co-founders Leon Mojarrabi and Anis Mihrshahi.

Leon Mojarrabi - co-founder

Leon began university at 14, graduating at 16. He then worked at Go1, a billion-dollar Brisbane startup, across sales, development, partnerships, team leadership and GTM over 4 years. He also built a pharmacy to roughly US$4 million in revenue to fund the company's scientific work.

Anis Mihrshahi - co-founder

Anis is studying a Bachelor of IT in AI and data science at UniSQ, supported by the Chancellor's Excellence Scholarship. He is the youngest person to win Queensland's Mathematics Olympiad. He co-built GutGut Goose's prediction algorithm, and has competed at a very high level across maths, powerlifting, discus, and even competitive Catan.

Funding

Lumina X 2025

A$50,000 in equity-free program support, mentorship and access to investors.

Y Combinator S26

YC's deal is US$500,000: US$125,000 for 7% on a post-money SAFE, plus US$375,000 on an uncapped SAFE.

Competitors

How they can win

Prove it's better — GutGut Goose currently has a lot of claims, but Anis has clearly established that their product is better than everyone else's, and it can back those claims.

Higher quality data — There can't just be a lot of data. It needs to be high quality, as that is their real moat and what keeps the customer embedded with the company.

One customer — In the beginning GutGut Goose needs to dominate one space to prove its worth, and then expand to everything else rather than being broad from the start.

The Scorecard

Insights

Problem > everything — Businesses are just solutions to problems. If you find a major problem like Leon did, that's how you make real money.

Stick with it — When they had their first solution, a microbiome researcher told them it would never work. Rather than quitting, they started again. Their conviction wasn't that the model was right, but that their problem was right.

Sell early — GutGut Goose spent 2 years developing its scientific approach, but the thing that mattered most was that the product could sell. If it's technical, don't create the entire product before you try to sell it first. You can spend 2 years and never make a single dollar.

From a VC perspective, the real value is the data. If they can create a large enough customer base, they can use that data in many ways.