Big brands' best customers have been defecting in droves since the beginning of the US recession, according to a study. By this year, more than half of a typical US brand's most loyal shoppers in 2007 had switched to rival products.

A two-year analysis of 685 grocery and pharmacy-stocked brands, using data from 32m consumers' supermarket loyalty cards, found that in 2008 the average brand lost a third of its formerly highly loyal customers.