Prebiotics, probiotics and synbiotics: what is the difference

Your gut is home to an enormous community of bacteria, and most of them are doing useful work for you. Two words come up constantly when people talk about looking after that community, and they are easy to mix up. Probiotics are the helpful bacteria themselves. Prebiotics are the fibres that feed them. A synbiotic is simply both together, on the principle that sending bacteria in with something to eat gives them a better chance than sending them in alone.

Picture your gut as a garden. Probiotics are the seeds, the helpful bacteria themselves. Prebiotics are what makes them grow, the fibre they feed on. Neither does much alone, which is the whole point of the comparison.

There is a practical difference too. Prebiotics are ordinary fibre and survive cooking and storage without difficulty. Probiotics are alive, so heat and time can reduce them, which is why fermented food is usually eaten fresh rather than boiled.

Prebiotics feed the bacteria already living in you, help digestion along, and in the process the bacteria produce compounds that appear to support blood sugar and heart health. Oats, bananas, onions, garlic, apples, beans, lentils and flaxseed all carry them.

Probiotics add more helpful bacteria to the mix. They are most useful after a course of antibiotics has thinned things out, and some people find they ease certain kinds of upset stomach or irritable bowel symptoms. Curd with live cultures, fermented batters and fermented vegetables all bring them.

The idea is straightforward once you picture it. Bacteria arrive in the gut, the fibre that came along with them gives them something to live on, and they are more likely to settle in and multiply rather than passing straight through. That combination is what the word synbiotic describes, and it is why the two are often sold in one product.

You do not need a product to do this. The pairing happens naturally at the table, and your own kitchen is full of it. A bowl of curd with a sliced banana is a synbiotic. So is buttermilk alongside a meal with onions and garlic, or steamed rice cakes and pancakes made from properly fermented batter served with a lentil and vegetable broth. Fermented pickles and other fermented foods all bring the bacteria; bananas, onions, garlic, oats, whole grains, lentils and beans bring the fibre that feeds them.

It is worth being clear about what this is and is not. Some people find their digestion settles, feels more regular, or is less uncomfortable, and some find no difference at all. Responses vary a great deal from person to person, and the research is much stronger on some uses than others. These foods are not a treatment for a digestive illness, and no supplement replaces one.

For most people the sensible approach is the unglamorous one: eat fermented foods you enjoy, eat plenty of fibre from vegetables, fruit, whole grains and lentils, and let the two arrive together as they naturally do in a good meal. If you have a serious medical condition or a weakened immune system, or you are thinking about a supplement rather than food, speak to your doctor first. This is general food guidance, not medical advice.