In Mantikas v. Kellogg Co. (2018) [1], the 2nd Circuit allowed a false-advertising class-action suit to proceed against Cheez-Its labeled 'Made with Whole Grain' that only had 8g of whole grain in a 29g serving, whose primary ingredient was white flour.
The opinion explicitly rejects the situation you describe:
> Such a rule would permit Defendant to lead consumers to believe its Cheez-Its were made of whole grain so long as the crackers contained an iota of whole grain, along with 99.999% white flour. Such a rule would validate highly deceptive marketing.