The scientific jargon behind the humble yoghurt

The Small Print: Choosing a yogurt takes about 10 times longer than it used to, thanks to the array of pots, tubs and jars promising…

The Small Print: Choosing a yogurt takes about 10 times longer than it used to, thanks to the array of pots, tubs and jars promising to do everything from protecting your immune system to making you feel more relaxed.

Yogurt is being marketed as a solution to our increasingly unhealthy lifestyles - as a cross between a natural snack and a superfood - but how do you know which one to buy?

First, check the name on the label. If you have a pot of "strawberry yogurt", you should be eating some fruit but if it says "strawberry flavour yogurt", don't expect any natural fruit at all. Vegetarians should read the small print carefully as some yogurts contain cochineal, a red food-colouring made from crushed beetles.

"Yogurt is a healthy snack, in comparison to biscuits or cakes," says Margot Brennan, a dietician with the Irish Nutrition and Dietetic Institute.

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Nevertheless, fruit yogurts and yogurt drinks can be surprisingly high in sugar and low in fruit. Danone's orange Actimel has over seven times more sugar than fruit (16 per cent sugar vs. 2.2 per cent orange pulp) while Tesco's Probiotic orange yogurt drink contains almost 12 per cent sugar and 5 per cent orange puree. A "low-fat" yogurt should contain no more than 3 per cent fat but some have added sugar or artificial sweeteners.

Although yogurt is a useful source of vitamins and calcium, some types - far from being a natural food option - are highly processed. They may contain modified starch as a thickener, preservatives (such as E202), artificial sweeteners, glucose syrup, added vitamins, colourings and "nature identical" flavours.

One problem in choosing a yogurt is the scientific jargon. What exactly are L. Casei imunitass in Danone's Actimel, LGG in Yoplait's Everybody and L.acidophilus La-5 in Tesco's Probiotic Drink - and what do they do? These are all probiotics (live bacteria) added to yoghurt because they are thought to strengthen your body's defences and to be beneficial to your digestive health by maintaining a balance between healthy and harmful bacteria in your gut.

More research is needed but it seems that probiotics may reduce the risk of diarrhoea, especially antibiotic-associated diarrhoea; may help to improve digestion and possibly irritable bowel syndrome; and may help symptoms associated with lactose intolerance. Danone's research found that a daily Actimel can help to reduce diarrhoea in children and can reduce the number of days an elderly person might suffer from winter infections.

One problem is that there are millions of types of bacteria in your gut so consuming just one type will have limited effectiveness. "Most healthy people eating a balanced diet shouldn't need probiotics," says Breda Gavin, nutritionist with Superquinn. "They might be useful if you have been taking antibiotics, because antibiotics destroy the good bacteria and leave the gut vulnerable to harmful bacteria."

The jury is still out, according to the British Dietetic Association. "When it comes to probiotics, at the moment we don't really know how effective they might be so can't make specific recommendations about their use." However, it views probiotics as safe except for anyone with a condition that affects the immune system, such as cancer or HIV.

The latest addition to the heaving yogurt shelves is Zen from Danone. Clearly aimed at stressed-out adults, Zen "helps the body to relax". The main ingredients are semi-skimmed milk and sugar (11 per cent) followed by cream and 90 mg (or 30 per cent RDA) of magnesium. So how does magnesium help us to relax?

"Magnesium is essential for good muscle function. If you are stressed, you excrete magnesium and so have less in the body," says Colette Kelly, nutritionist with Danone. "It is important to eat foods that contain magnesium, such as meat, grains and nuts. The more stress you are under, the more you need to ensure you have enough magnesium."

But extra magnesium is not usually necessary, says Brennan: "It is plentiful in food and people are not generally deficient".