In general, the idea is to consume only the amount of phenylalanine that's necessary for normal growth and body processes, but no more.

CNN: Phenylketonuria (PKU)

What are the small ways you can lead (and I do mean, lead, not trick) folks, following their own self-interest and in the course of their normal activity, to take the necessary steps toward more sustainable operations and personal behavior?

FORBES: The Birds and Bees of Sustainability

He said it was rewarding behaviour which should be considered normal and questioned whether it was necessary to go as far as New York.

BBC: Skegness Academy