From Googling Nutritional Claims Excellent:
YES! These terms are highly regulated in the United States.
In the US, the FDA sets the following standards for food products:
- "High," "Rich In," or "Excellent Source Of" - Contains 20% or more of the DV per RACC. May be used on meals or main dishes to indicate that the product contains a food that meets the definition, but may not be used to describe the meal.
- "Good Source," "Contains," or "Provides" - 10%-19% of the DV per RACC. These terms may be used on meals or main dishes to indicate that the product contains a food that meets the definition but may not be used to describe the meal.
- "More," "Fortified," "Enriched," "Added," "Extra," or "Plus" - 10% or more of the DV per RACC than an appropriate reference food. May only be used for vitamins, minerals, protein, dietary fiber, and potassium.
Note: DV = Daily Value, RACC = Reference Amount Customarily Consumed
This is a really helpful page!