If the proverbial Martian came to Earth and simply read press reports on consumer desires — more fresh, more healthy, more local, more organic, etc. — our other-worldly friend would surely predict that Whole Foods Market is many times larger than Wal-Mart, and McDonald’s must sell but a small fraction of what Shake Shack does. Yet, of course, our Martian would have it exactly and precisely wrong, Whole Foods Market’s total sales are a rounding error on Wal-Mart’s financials, and Shake Shack is nothing compared to the sales of McDonald’s.

As we evaluate produce sales, it is worth keeping in mind that many treat the subject as some kind of moral arc bending inevitably toward goodness, so produce — healthful and fresh — must inevitably triumph. This is a beautiful thought, but there is not much evidence that it is true.

Indeed, sometimes the evidence seems to be shifting the other way. Certainly many people want to lose weight. Recently, though, there are indications that much of what we thought we knew about nutrition is wrong. The latest version of Dietary Guidelines for Americans abandoned an upper limit on total fat intake and dropped cholesterol as a “nutrient of concern.”

Although some of these changes make it easier to consume produce — no need to skimp on the guacamole because you are worried about total fat intake — the latest research indicates that one can eat poly-and mono-unsaturated fats (such as in nuts, avocados and fish) without concern. On the whole, though, the redirection poses some challenges for produce.

Dr. Walter Willett, the Fredrick John Stare Professor of Epidemiology and Nutrition and Chair, Department of Nutrition at the Harvard T.H. Chan School of Public Health, is widely recognized as the leading authority on nutrition and public health. At a recent talk, he explained that the old advice to avoid French fries because of the oil was now moot, especially since trans-fats have been basically eliminated from the food supply. He still urged people to avoid French fries, but now the professor said the oil was the best part of the French fry; it was the potato itself, with a high glycemic load, that gave the Professor concerns.

Even saturated fat, the avoidance of which has been a religion among nutritionists, is clearly more complicated than once understood. Today, we know there are many types of saturated fats and that some may even be beneficial. Basically saturated fats are strings of carbon atoms chained together at different lengths. But recent studies indicate that those strands associated with dairy, for example, have a positive effect on heart disease risk and reduce the likelihood of Type 2 diabetes.

None of this, of course, means the health halo of produce isn’t real — only that, as an industry, we have to be careful where we hang our hats, lest the hat stand be pulled out from under us as nutritional information evolves.

There is also a challenge with embracing causes that are trendy, but for which there is little evidence. Many are intensely opposed to GMOs, but we have no evidence that eating GMOs has any impact on human health. Organic does have connotations of a healthier, more sustainable product, but, again, there is miniscule evidence that this is so. Which brings into the spotlight the consumer education piece. It is, of course, wonderful, that retailers and producers help educate consumers, but the science has to be there.

The need to stay relevant with the lives of consumers cannot be doubted, and this research points to the importance of convenience with today’s consumer. Still, we have to be careful in assessing causality on some of these statistics. Maybe consumers are rejecting whole items as less convenient, but it is also possible that higher margin convenience items are given a more prominent place in the department, more advertisement, etc., and that this marketing effort is what may drive consumption. Banana margins have been kept low, as most chains want to be competitive with Wal-Mart on this high-volume item, but low margins also discourage large placements, prime placements and advertising. It is a chicken-and-the-egg situation.

Staying on trend is important as it allows producers and retailers to ride the changes in consumer demand and come out winners. Unfortunately, there is little evidence that all these changes in demand for particular products (kale being the top example) actually result in overall change in consumer consumption of produce. It is heartening that consumers might love a kale salad with salmon and a peanut vinaigrette; but, for the most part, this just means a switch from a spinach salad. So navigating these trends can boost any firm’s business, but to move total consumption, we need to find something more.