Our stomachs are easily influenced by pictures, smells, and hunger. But none of this explains kale's popularity. It doesn't photograph as well as doughnuts, or smell as good as a barbecue, or even fit into a shopping bag easily. But it does pun well.
So it is no surprise to learn a New York publicist has been taking the credit for getting the seemingly unappealing spinach-like vegetable into every cafe, smoothie, and health-food book in the Western world. Oberon Sinclair claims she made kale popular just because she loves it, although some reports say she was working for the mysterious American Kale Association.
If you look carefully there are vested interests behind every latest craze, be it a single ingredient, dish or even style of eating.
Food historian and author Colin Bannerman says there are always three forces driving food trends: manufacturers and supermarkets trying to make money; journalists trying to impress readers; and restaurants, which are "always trying to re-invent themselves on an endless quest for novelty".
As for kale, Bannerman labels it "Scottish peasant food" and says the fad will probably end soon, given kale doesn't taste very good. The real long-term trends in food are much harder to see, such as the globalisation and industralisation of food, he says.
So what are the next trends?
London-based firm The Food People predict we will start seeing hybrid vegetables in 2015, such as "broccoflower", "rainbow carrots" and "kalettes" (yes, that's Brussels sprouts crossed with kale. So, is genetic modification cool now?). They also expect broth, table condiments and kids' menus to make a comeback.
In Australia the restaurant trends will be smoked meats, hand-made condiments, hand-made plates, cauliflower (driven by the paleo-nerds) and a new wave of South American dishes, according to Epicure editors Nina Rousseau and Roslyn Grundy.
And if New York continues being the origin of everything then 2015's food trends will be more root vegetables, vegetable-flavoured yoghurt (already spotted in Australia), huge punchbowls of cocktails served at the table, and restaurant pricing based on sharemarket conditions, according to research by consultants Baum and Whiteman. The report also claims the gourmet toast craze is close to ending in the US, although it has barely started here in Australia.
Sadly, food trends rarely start because you discovered a food that no one else has noticed. There is always someone putting the food in front of you, whether it be on the shelf, on the menu, or filling your social media feed. Of course someone looking at photos of doughnuts all week will want one on Saturday.
It may feel like food trends never end, but cast your mind back to the great sun-dried tomato craze: served at dinner parties alongside the olives, in sandwiches made with the newly discovered focaccia bread, and in cafe salads and pastas. Ah, the late 1990s.
It might be hard for anyone under 30 years of age to understand, but the range of food available at the local Coles or Woolies was very different 20 years ago. When sun-dried tomatoes first appeared in supermarkets they were a huge success. Australia was emerging from recession, the cosmopolitan Paul Keating was in power, and this new delicacy was a sign of sophistication.
Melbourne-based distributor G&K Fine Foods is now happy to claim they were instrumental in getting sun-dried tomatoes into our lives by supplying it to Coles, Bi-Lo, Safeway and Woolworths.
"The semi-sun-dried tomatoes were sourced from a number of Victorian and Queensland tomato farmers, processed by Sundown Foods and then distributed to retailers, cafes and restaurants," marketing co-ordinator Ben Metcalf explains. Sundown Foods was started in the early 1990s by former Victoria Market delicatessen owner Peter McGee (who used to run the French Deli).
Woolworths then asked G&K to create packets of antipasto foods that could be stored in open fridges. This led to "a multitude of antipasto-style packs that included marinated eggplants, artichokes and bell peppers".
But within a couple of years this ubiquity made sun-dried tomatoes mundane, and people got sick of them. Soon enough, the next food craze came along.
Over at Woolworths Justin Nolan is responsible for deciding which foods the supermarket giant sells to customers under its in-store brands. He gets information from purchasers, suppliers, strategy teams and a group of chefs who monitor trends in cafes and restaurants. Woolworths doesn't try to start trends, rather it aims to harness the popularity of new trends and create an affordable supply for customers.
Nolan says consumer tastes in 2015 are getting healthier, particularly with the introduction of health-rating system later this year. But deciding what to stock depends on availability as well as popularity. For example, quinoa demand outstripped supply last year.
While refusing to name the next trend, Nolan has confirmed staff are keeping an eye on the popularity of "natural tree birch water". If the idea of Woolies selling drinkable tree-sap sounds ridiculous, he points out that five years ago coconut water was "a very niche product and it was quite expensive, but as the supply side developed it became less expensive".
Meanwhile, Bannerman the historian has his own version of the sun-dried tomato story. Jars of Tuscan tomatoes were "sold in exclusive shops at outrageous prices" in the 1970s and '80s. Foodies tried to dry their own tomatoes, but found it hard to replicate the Tuscan conditions and "gradually the things acquired a certain amount of notoriety and the big companies exploited the fashion".
Then antipasto barges started appearing in supermarkets, and suddenly the once-expensive savoury delicacy was available everywhere, albeit at lesser quality.
"That's what happens with fashion," says Bannerman. "To exploit it on an industrial scale you have to get the price way down. And it becomes an industrial product ... Just another fad."