I won't repeat exactly what Dave said as it was a tad bit colourful but putting it short its a myth. Carp will eat what they want to eat whether its fish meal, bird food or nut based every lake is different for instance, people have been Pike fishing with an oily chunk of mackerel and have in turn caught a Carp and I don't think that there is an angler in the land who hasn't caught on a piece of plastic or foam.
Not too long ago I was having a discussion with a good friend of mine and he mentioned smelly baits and there is a massive misconception that smelly bait works. He explained this in the most simplest way I've ever heard which is, we all love the smell of Vimto but you wouldn't drink it undiluted. Boilies leak flavour into the water column which carp in turn taste and if they are hungry will go and investigate further. The leakage happens from the break down of the bait itself and in the same way as PVA it is effected by the oil content. When it comes to oils it is all dependant on the type of oil some oils have a high lipid content. This is what historically puts people off fish meal products in winter.
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