New studies show that prebiotics, found in leeks and garlic, play a key role in gut health
Ever since gut health became a hot topic, the popularity of probiotics (otherwise known as friendly bacteria) has soared. But now scientists are suggesting there may be an even more effective way of supporting our gut function.
Instead of gulping down live bacteria in the hope of adding to the population already in our gut, we should focus on the food that will feed those billions of microbes. Enter prebiotics, a kind of indigestible fibre — mainly inulin — found in hundreds of vegetables, and which are especially prevalent in Jerusalem artichokes, onions, garlic and leeks.
One large raw onion a day keeps the doctor at bay
The bad news is that you’d have to eat a whole large onion a day or seven cloves of garlic just to get the minimum 5g of prebiotics recommended by scientists to help you to keep your gut ticking over healthily, never mind the 12g you might need to see real improvements. There aren’t yet any official daily recommendations for prebiotics, but recent researchers found that 12g a day had an effect.
“It’s really hard to get that level of prebiotics from your diet,” admits Professor Bob Rastall, the head of food and nutritional science at Reading University, although he recommends you buy Jerusalem artichokes, which are particularly high in inulin at up to 20g per 100g.
There is now a whole industry of powders and supplements springing up offering prebiotics created in the laboratory, usually galacto-oligosaccharide, or GOS. Dairy Crest is preparing to launch a prebiotic “shot” this year, which uses GOS from the cheese-making process.
The advantage of prebiotics is that they are not killed off before they reach the gut, as many scientists fear happens to probiotic drinks. “After you ingest them they target the beneficial bugs straight away — you don’t get the survivability problems you have with probiotics,” says Professor Glenn Gibson at Reading University, who has written more than 30 research papers on prebiotics since coining the term in 1995.
Prebiotic efficacy backed by studies
Studies have shown that taking prebiotics (as a supplement) can help those with irritable bowel syndrome, ulcerative colitis, and abdominal pain and bloating. They also strengthen the immune system, most of which is based in the gut, so you’re less likely to get infections. It also means your body’s inflammatory response to possible threats is less easily triggered, which could mean fewer allergy symptoms.
Gibson believes prebiotics could also help to combat the obesity crisis because gut bacteria influence the hormones that regulate appetite. He is publishing a study on overweight people and prebiotics this year, but his previous work has revealed that prebiotics can combat insulin resistance and cholesterol.
“If we can develop a product you could add to a drink or sprinkle on food that could regulate hunger and feelings of fullness, it could help an awful lot of people struggling with obesity who have tried and failed to manage it with diet. I genuinely think that’s possible within a few years,” he says.
Gut vs. Brain Axis
There’s also emerging research that prebiotics may even have the power to make us feel happier, sleep better and reduce stress and anxiety. Bacteria in the gut make substances (metabolites) when they’re breaking down prebiotics. These metabolites produce neurotransmitters such as Gaba and serotonin, the hormone associated with happy feelings. In fact, 90 per cent of the body’s serotonin is made in the gut.
Intriguing studies on animals in the past two years have shown that prebiotics can reduce levels of the stress hormone cortisol and sharpen brain function. The only study in this area on humans was carried out by the neuroscientist Professor Phil Burnet at Oxford University on 45 healthy volunteers who were given the Bimuno prebiotic supplement for three weeks. Their cortisol levels fell, and they also paid more attention to positive imagery than negative imagery compared to the control group.
“Their mood didn’t change — it wasn’t like they skipped out of the lab with beaming smiles,” says Burnet. “But what did happen was that one of the underlying psychological mechanisms involved in mood did change, which is promising — anti-depressant medication has the same effect. But further research is needed before we can say that prebiotics make you happy.
“It’s still early days, but we know prebiotics help gut health and if you improve gut health you help the brain.”
Gibson recommends that we improve the prebiotic content in our diets and take supplements, particularly if you’re taking antibiotics, have a weak immune system or are about to go into hospital or on holiday.
“You probably won’t feel a massive difference if you start taking a supplement, although some people do feel more energised,” he says. “But what you’re doing is fortifying yourself against what might be around the corner.”
Prebiotics (inulin) are in hundreds of fruit and vegetables, but these are the top sources:
- Chicory root (roasted as a coffee substitute)
- Jerusalem artichoke
- Dandelion greens
- Globe artichokes
- Salsify root