Kellogg's has been rebuked for "misleading" nutritional claims in a TV ad for Special K Sustain.

The Advertising Standards Authority upheld a complaint from viewers about a voiceover claiming the product contained "extra protein and fibre". Viewers said it appeared to be a comparison with Special K Original - but the new line had less protein. Kellogg's submitted evidence stating that Special K Sustain contained 5.6g of protein in a 40g portion compared with 4.5g in 30g of the original.

But the ASA upheld the complaint, saying consumers would expect a comparison to be made on a "like-for-like basis".

Kellogg's has been ordered not to broadcast the ad again in its current form. Kellogg's said the different servings sizes were used because ingredients in Sustain make it denser. Kellogg's has now changed the voiceover to "delicious new Special K Sustain contains protein and fibre".