I would be interested to know, for the people not eating at least one egg a day, what were those meals instead? It could be a case of "an egg is healthier than [Unknown]" instead of "an egg makes you healthier."

An even simpler paraphrase is "eating less than 1 egg a day is associated with lower CVD".

To answer your question directly, one can reasonably infer from the quote you provide that it is best to eat fewer eggs.

EDIT: change quantifying adjective from "less" to "fewer"

In my partial defense, concluding something like "eating up to but less than one egg per day is inversely associated with CVD risk" is odd and somewhat defies common sense.

My incorrect translation is a good reminder for me that scientific language doesn't always easily translate into conversational language.

EDIT: remove repeated word