A radical experiment seeks to put something that our bodies routinely reject back inside us - all in the name of solving a global epidemic.
Professor Wayne Cutfield and Dr Justin O'Sullivan are part of the research team for The Good Shit, a documentary series on Three exploring cutting-edge Kiwi research that's using faecal transplants to retrain gut microbes and hopefully create a cure for obesity.
Studies show if you take the gut bacteria from a thin mouse and put it in a fat mouse, the mouse gets thinner - and scientists are hopeful the same could be true of humans.
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"We know that our gut bugs actually influence how much weight we put on, how much food we absorb, other immune and allergic disorders," Professor Cutfield says. "It isn't just about obesity."
Faeces are the obvious way to get one person's gut bacteria into another person, explains Dr O'Sullivan.
"When you're born, you pick it up from your mum, from your environment - you eat it. It's just a natural process."
It's a world-first in many respects: it's the first time such an experiment has been carried out on teenagers, and the intricate capsule process is ground-breaking as well.
"They're like handmade chocolates," Professor Cutfield said to disgusted groans from The Project audience. "They go in one capsule, then another capsule, and then you swallow them - odourless, flavourless, easy."
In the unlikely chance any viewers are tempted to sample their thinner friends' droppings to lose weight, the researchers have a warning: don't try this at home.
"It's quite dangerous," Dr O'Sullivan says. "We're very careful and we screen people very, very strictly.
"There are very strict criteria to have to be a donor - you have to pass similar things to what you would for blood donations and organ transplants."
He says gut microbiomes are already used to treat chronic diarrhea, and there are possibilities they could treat other conditions such as diabetes and inflammatory bowel disease.
Professor Cutfield says even mental disorders like depression, Alzheimer's and autism could be improved through gut bacteria, which has a direct link to the brain.
"The range is potentially amazing, but until you do the study in humans we don't know," he said.
"The story's been well built up from animal studies, but we've got to do studies like ours to actually answer the question 'will it work in humans?'"
The researchers were reluctant to talk about whether the experiment showed promising results, as they're sworn to secrecy until the show is over.