Your question is about an articled titled "Science and Pseudoscience in Adult Nutrition Research and Practice." Since this is clearly a non-fiction article on a technical subject, one would not expect it to use much figurative language. Still, there are some examples.
METAPHOR: a comparison that does not use "like" or "as"
a) "nutrition research...have lagged behind many other...fields."
Only a person (or animal, or vehicle) in a race can lag behind; saying that one kind of research "lags behind" another is a metaphor.
b) "such studies...are...the result of 'data-dredging."
The author is comparing some studies to "dredging," which is the process of cleaning a body of water by dragging up the mud and sewage that is clogging it. The author is saying that some researchers find a lot of "dirty," unreliable statistics, "draw" them out of the mud, and use them as the basis for their conclusions.
ALLUSION: a reference to another work of literature, or to history, etc.
a) "Are there 'fountain of youth' nutritional approaches...?"
The "Fountain of Youth" is a reference to ancient legend (see link below)
b) The author refers several times to the ancient Greek philosopher, Aristotle.