If you have a condition like irritable bowel syndrome (IBS), a finnicky gut or just want to keep your microbiome in top condition, you might be tempted by products and treatments that offer a microbial tune-up. But what really works? Here are the main tools to engineer a better gut.
Probiotics
Probiotics are microbes that may help to restore healthy gut microbiota. If they also improve your mood, they are called psychobiotics. You can typically get them from eating naturally fermented foods like yogurt that contain beneficial bacteria, such as Lactobacillus or Bifidobacterium.
But as an adult, these microbes are unlikely to colonise your intestines. To the extent that they are helpful, their benefit comes while they are passing through. Such probiotics , increase mucus production and deter pathogens by producing lactic acid. But as mere visitors, they need daily top-ups.
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Probiotic supplements have been used (with mixed success) for more than a century to help with the gut conditions of Crohn鈥檚 disease, colitis and IBS. They have also been shown to help with weight loss in people who are overweight and are increasingly being used for , including bacterial vaginosis and urinary tract infections. What鈥檚 more, they reduce the risk of antibiotic-associated diarrhoea.
As the gut microbiome can affect our mental health, it is perhaps unsurprising that psychobiotics are also being used to target our minds. Some studies suggest they may be able to help , and in older people.
But there are caveats. Regulations governing the safety of these products vary widely from country to country. In the US, the Food and Drug Administration applies a soft touch to , as long as manufacturers don鈥檛 claim to treat or cure specific conditions, so look for solid science behind any assertions and be wary if they sound outrageous. The European Food Safety Authority, however, isn鈥檛 convinced of probiotic efficacy and .
Clinical trials are proceeding apace, but around a third of them are industry funded, so should be handled with care. Some of the best-studied probiotics include Bifidobacterium longum, Lactobacillus rhamnosus, and Akkermansia muciniphila. Clinical studies show that these appear to by reducing bad bacteria and boosting beneficial ones. But it is still early days, and unless you have a specific condition, there are other ways you can keep your gut healthy (see 鈥淗ow to care for your microbiome and keep it healthy as you age鈥�).
Prebiotics
A prebiotic can be a dietary fibre that is food for bacteria, including probiotics. Prebiotics are mainly comprised of sugars too complex to be digested by our own bodies, but just right for microbes. Prebiotics also include polyphenols, natural chemicals that act as food for gut bacteria and as antioxidants.
Plants are the best source of prebiotics, while meat contains no dietary fibre. Somewhat confusingly, the prebiotics that feed psychobiotic microbes are also referred to as psychobiotics.
Eating a wide variety of vegetables and berries will give you the prebiotics you need. Many of the ills of modern life have accelerated since the advent of processed fast food, which often removes the fibre from key ingredients such as grains to make a lighter, less filling product. That encourages extra consumption, a definite plus for the industry, if not for the consumer. Without sufficient fibre, your good microbes will starve. The diversity of microbes in the gut, which we know is good for health, will also suffer. If you don鈥檛 get enough veggies, a , especially a blend of prebiotics to support a diverse microbiota.
Postbiotics
Probiotic microbes, fed by prebiotics, produce two groups of substances that are uniquely beneficial to us: neurotransmitters and short-chain fatty acids. These products of microbial digestion in the gut are known as postbiotics and can profoundly influence our health.
The neurotransmitters produced include dopamine, serotonin and GABA, which are known targets of psychoactive drugs. Your microbes use these substances to talk to each other, but also to you. This grants them the superpower to drive some of your cravings, for better or worse. The vagus nerve communicates these signals from nerve cells lining the gut to the brain, which .
The short-chain fatty acids include butyrate, a molecule that both nourishes and heals the cells lining your gut, preventing microbes from leaking into the bloodstream. Butyrate travels to your brain, where it can stimulate new neuron growth. It also boosts the production of Could you cut out the middle man and just take these substances as supplements? Perhaps in future, but for now, a working microbiome is still the best way to generate these substances on your own.
Faecal transplants
If fiddling with your gut microbes to get a perfect internal ecosystem doesn鈥檛 work for you, there is the nuclear option: a faecal microbial transplant.
Here, your poorly working microbes are wiped out by antibiotics and then faecal matter from a donor with no major health conditions is inserted via an enema. Your gut microbes are like a fully fledged organ in your body, so this is akin to an organ transplant.
As unpleasant as it may sound, it is a godsend for people with hospital-acquired Clostridium difficile infections, with a 90 per cent cure rate. The connection between the gut and the brain implies that your faecal donor should not only be healthy, but happy as well.
For now, faecal transplants are , not simply a bad gut or other conditions. Despite this, advances are being made, including an oral version of such transplants, known affectionately as a 鈥渃rapsule鈥�.
COULD WE EVER MAKE DESIGNER MICROBIOMES?
When it comes to altering our microbiome, the aim is simple. We want more beneficial microbes and fewer harmful ones. But achieving this isn't easy.
If people ingest beneficial strains of microbes, often called probiotics, they usually die out rather than becoming established in the gut. And antibiotics, the main tool we have for killing off harmful microbes, such as the ulcer-causing Helicobacter pylori, are blunt weapons. They also kill many beneficial bacteria, resulting in side effects such as nausea and diarrhoea.
As a result, many teams worldwide are working on more precise ways of altering our gut microbiota. The simplest is to harness viruses that naturally infect bacteria.
Our guts are already teeming with so-called bacteriophage viruses, also known simply as phages. There can be more than a billion of them per gram of faeces. By finding and dosing people with viruses that kill specific bacterial strains, the numbers of those bacteria can be reduced. For instance, phages have been used to kill off bacterial strains associated with inflammatory bowel disease, though so far.
Another approach is to use . This method has been used to kill dangerous bacteria in the guts of mice, but hasn't yet been tried in people. Such weapons can even delete undesirable genes from bacteria without killing them, such as the genes for toxins that make some strains harmful.
Similar tools could be used to add extra genes to gut bacteria. Researchers are exploring many different possibilities, including modifying bacteria to mop up harmful substances or to produce beneficial nutrients or even drugs. Another idea is to turn bacteria into living sensors for the early detection of diseases such as cancer.
However, these ideas involve creating genetically modified organisms that might spread to other people. One answer to this is to make modified bacteria dependent on nutrients not found naturally, so they can survive only in the guts of people who feed the bacteria by regularly taking pills containing those artificial nutrients.
Even so, regulators are going to need a lot of convincing of the benefits and safety before giving the go-ahead for this kind of approach.
Michael Le Page
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Speak to your doctor before seeking new treatments for medical conditions
