Final answer:
Jordan Baker tells Nick Carraway that Daisy Buchanan and Jay Gatsby had a past romantic relationship, a pivotal revelation in 'The Great Gatsby that affects the storyline.
Step-by-step explanation:
It appears there may be a mix-up in the context of the question, as the information provided refers to a study of nutritional biology during famines, yet the question seems to allude to a literary context, particularly to a character named Jordan presumably in a novel who is conveying some important information to another character named Nick. If the novel in question is The Great Gatsby, then a significant revelation made by Jordan Baker to Nick Carraway is that Daisy Buchanan, Nick's cousin, and Jay Gatsby, Nick's neighbour, once had a romantic relationship when they were younger. Jordan tells Nick this because Gatsby wants to be reunited with Daisy and has been throwing lavish parties in the hopes that she will attend. This knowledge is pivotal as it sets in motion the events that will unfold throughout the rest of the narrative.