Whole Foods Market, the US natural and organic supermarket chain, has built its successful brand around a set of company "core values" that are highly focused on corporate integrity.

But Whole Foods' reputation and its troubled $565m bid to take over main rival Wild Oats have both suffered a setback with revelations that John Mackey, its co-founder and chief executive, had been anonymously attacking his eventual take-over target on an investors' online message board.