Freezing your poop for later: at first it seems like a bizarre idea. But in the second instance it might sound like a very good plan.

Because suppose that in x number of years you will develop a disease that is related to the microbiome: the collection of microbes in your gut. Then it could be useful if you can ‘reset’ your microbiome with the help of your own poop.

That is why American scientists Shanlin Ke, Scott Weiss and Yang-Yu Liu argue in the magazine Trends in Molecular Science for a poop bank with poop samples. The only question is whether it is not too early for that.

Dramatic mismatch

Our microbiomes are changing, Ke and colleagues write at the beginning of their article. For example, antibiotics, processed foods, formula for babies and increased hygiene, we now walk around with fewer types of microbes in and on our bodies than a few decades ago. And that can significantly increase the risk of all kinds of diseases, from asthma to colon cancer, and from type 2 diabetes to cardiovascular disease.

So should we find out what our microbiome was before the industrial revolution and put it back in that state? According to Ke, Weiss and Liu, this has been discussed in recent years, but that strategy can lead to major problems. “That can be a dramatic mismatch between our current industrial environment and lifestyle and the microbiome of our ancestors.” Quite apart from the question of what exactly that ancestral microbiome must have been.

frozen poo

The American scientists then suggest a less far-reaching alternative. Wouldn’t it be useful if you freeze the poop of healthy people between the ages of 18 and 35? If they develop a condition related to the microbiome later in life, you can give them a poo transplant. Their own ‘old’ poop is introduced into their intestines, so that they have the same microbial composition as before.

At the moment, faecal transplants are already taking place – but this always involves faeces from someone else that is injected into a patient. In addition, donor and recipient may prove to be a bad match, write Ke, Weiss and Liu, which means that the treatment does not work or does not work well. And that problem is “avoidable, or at least minimized,” if you give people their own poop, they sue.

No defense at all

Ed Kuijperemeritus professor of medical microbiology at the LUMC and affiliated with the Dutch Donor Feces Bank there, however, tempers expectations. “Poo transplants have only been proven effective in fighting infections with the bacteria Clostridioides difficile“, he says. For all other diseases that a poo transplant can help, the research is still ongoing and no firm conclusions can be drawn at this time.

However, American researchers are looking at whether the technique could be useful in bone marrow transplants. “After such a transplant, patients have no immune system at all for a long time, which makes them very susceptible to all kinds of infections,” says Kuijper. “The idea is that their disturbed gut microbiome causes their immune system to work less well. You can then collect poop from them before they are treated, which you give them back after the transplant. This could then lead to fewer immunological complications and ensure that the new bone marrow takes root more quickly. But we are still waiting for the results of that investigation.”

So many questions

The number of conditions of which we now know that they can be treated really well with a faecal transplant is therefore very small. Moreover, we still lack a lot of other knowledge, says Kuijper. “Suppose I will soon be working at such a poo bank and someone comes forward who wants his old microbiome back. How am I going to do that? Do I thaw his poop sample and use it all at once, or do I give him a weekly dose for four weeks? Am I going to pre-treat that patient with antibiotics? Do I insert such a sample rectally, or in the form of a pill? There are still so many questions that are totally unsolved. Why start thinking about storing poop samples at a young age when you don’t even know how to administer them later?”

In certain cases, storing poop samples can be useful, says Kuijper. “Suppose that an abnormality associated with the microbiome is common in certain families. Then you could collect poop from those people at a young age, and keep it in case they show the first symptoms later. But first you have to research the relationship between a defect in the microbiome and the origin of that abnormality.”

Another idea that Kuijper would like to see investigated: people can contract a bacteria abroad that is very insensitive to antibiotics. “You could then take a poo sample from those people before departure. If they turn out to have such a resistant bacterium after their return, you can reintroduce that sample to them to displace that bacterium.”

Poo on the couch

But Kuijper does not see the point in storing poo samples from large numbers of people in a poo bank ‘just in case’. Interestingly, Ke, Weiss and Liu themselves do not assume that every citizen will soon have a small amount of poop ‘on the couch’. They believe that the patients themselves will pay for the costs of collecting and storing their poop samples, writing: “We do not expect that all individuals in our society would be willing to pay those costs.”

In other words: the poo bank would be there for people with enough money, who have been convinced that they could benefit from that little bit of frozen poo in the future. “That mainly sounds like an attractive business model,” says Kuijper. “You can make a lot of money with it, but it has little proven benefit yet.”