Advertising: The nutritionists know what you need but Knorr knows what you want

You should have five portions a day. You know that, of course. It's like the units you shouldn't have – another thing to worry about. Another thing to turn us into a nation of Bridget Joneses. Five portions of fruit and veg. Or is it fruit or veg? But how much is a portion? An apple? An orange? A carrot? And what exactly counts in the ledger of natural goodness? Fresh, frozen or tinned? Does the tomato sauce on your pasta do the job? Can you tank up on strawberry jam?

Just like that injunction to avoid wheat and dairy in the modern healthy diet, it's a big "how to" question – desirable in theory, difficult in practice. So any brand-owner who can offer an easy solution should be able to drum up a bit of extra business and earn a healthy reputation. Sainsbury's, for instance, has a range called "Free From", which helps you avoid sin on the wheat and dairy fronts.

And now here's the first commercial promising to deliver those healthy portions. It's Knorr, the soup people. And they're saying their Vie soups do three-fifths of the daily job – a bowl of soup, an apple and an orange and that's you fixed.

But they have to bring sex into it. Portion, you see. Portion is a bit of a saucy word in a certain kind of vocabulary – a bit of an "I'd give her one" sort of word in creative Mockney lad-speak. So we get a pair of teenagers – a bouncy Hispanic-looking girl with big hoop earrings and a scared skinny boy with a neo mid-Sixties mop-top – sitting side-by-side spooning soup in an atmosphere of mounting sexual tension. Oh the looks, the wandering eyes, the indrawn breath with every spoonful. They're in her Parents' House. And what a house, what a bit of kitsch decoration. What fun they must've had designing a thoroughly repressed suburban house – it's a triumph, in that small business, new-money style (it's a Sixties/Seventies look, really; decorators love funny retro). Mushroom-coloured vinyl damask wallpaper, lots of synthetic net curtaining, heavily cut glass and heavily framed pictures of 17th-century-ish fighting ships. Decoration that says no one's interfering with my little girl before she marries Carlo from the deli. A carton of Knorr Vie, so the voiceover tells us, gives you three of those vital veggies you need.

In 15 seconds – this is a 30-second job – the forward 14-year-old's saying to her shy boyfriend: "Come up to my mum and dad's room," and when he does there she is, sprawled seductively on one of those swirly, stitched rayon quilts. "How you get the other two is up to you..." continues the voiceover.

Now, I like a nice ready-made soup as much as the next man, but I associate Knorr with dried packet soups. And it's terribly difficult to imagine any of those dried nuggets of pure polystyrene having the slightest nutritional value whatsoever.

Peter@sru.co.uk