Not since Jennifer Aniston first stepped out of the shower and uttered the immortal words “here comes the science bit…” have we been so spellbound by TV commercial “science”.

Probiotic yoghurts and drinks have convinced so many of us of their power to make us healthier, more vibrant people that the industry will soon be worth about $30 billion. Not bad for posh yoghurt.

Probiotic yoghurts are sold in various small, colourful pots and marketed on an idea based on real science. Containing high concentrations of digestion-aiding bacteria, they are billed as being able to improve health and digestion.

But watch those TV ads of women jogging around parks very closely: at no point will the commercial say that it is the strawberry yoghurt that gives her more energy and vitality – it will just be implied. That’s because there’s no evidence that probiotic yoghurts offer any real benefit to the people who buy them.

Within your bowels there are huge numbers of bacteria (about 100 trillion, give or take). They are a heaving mass of microscopic chompers that feed off the remnants of your last meal. They help you digest your food, absorb nutrients and keep your immune system in tiptop shape. They also produce those aromatic gases that escape from time to time. Yet within this brown-coloured world of bugs there is a surprising amount of harmony: acting like a planet’s ecosystem, the types and amounts of different gut bacteria species are kept in a continuous balance. Probiotic products are designed to help ensure this balance of bacteria is healthy.

Occasionally, due to illness or a long course of antibiotics, the balance of gut bugs can be upset: some harmful types of gut bacteria can ‘overgrow’ and predominate. This can cause you to become very unwell. Probiotics contain high numbers of ‘good’ bacteria which, when eaten or drunk, put beneficial bacteria back into the gut.

For someone suffering diarrhoea due to antibiotics, then probiotics are proven as a useful treatment for replacing lost bacteria. However, for pretty much everyone else, the balance of bacteria will probably be absolutely fine; adding ‘helpful’ bacteria into an already nicely working mix will do nothing. You could think of taking a probiotic yoghurt like taking a medicine when you’re not unwell.

In 2012, the European Food Safety Authority ruled that probiotic yoghurt manufacturers cannot make general health claims about their products. So while probiotic yoghurts seemed like a good idea, research has repeatedly shown that they offer no benefit to people who are in good health.

That said, drinking a probiotic yoghurt or two will do you no harm – so if you enjoy it, and don’t mind the expense, then feel free to carry on. Or you could save your cash and spend it on some premium shampoo instead.