There has been widespread media attention over the past week, some of it my own, to a study published in JAMA that compared low-fat and low-carbohydrate diets for weight loss and health improvement. Significant weight loss, and health improvement measured in all the usual ways, occurred in both treatment assignments. Going from the generally poor baseline diet that prevails in America to either a healthful, low-fat diet that emphasized vegetables, and whole, minimally processed foods; or to a healthful low-carbohydrate diet that also emphasized vegetables, and whole minimally processed foods — produced significant, and very comparable benefits.

This study verified the relevance of calories, and the merits of controlling them without counting them. Study participants were not told to track or reduce calories, but by shifting to a much higher-quality diet, they did so as a byproduct. Both treatment groups cut their daily calorie intake by about 500 to 600 kcal daily, and lost the amount of weight that would portend. They achieved this by eating wholesome foods in sensible combinations, and by applying some rules and discipline to diets that had neither at the start. Since both low-fat and low-carbohydrate diet assignments reduced calories almost identically, and produced almost identical weight loss, this study suggests that when it comes to weight loss, per se, calories and energy balance are really all that counts — and you can get there whatever your macronutrient preoccupations (or preferably, absent any).

Genetic markers of expected success on one type of diet versus the other proved to be of no value. Weight loss in each diet arm was indistinguishable between those with a genetic profile saying they should do especially well, and those with profiles suggesting they should struggle. Nutrigenomically customized weight loss, despite the buzz it generates, is clearly not ready for prime time.

Even more provocative, the study found no relationship between baselines insulin status and success on a given diet assignment. The high-profile claims that weight loss is all about reducing carbs to reduce insulin prove to be apocryphal. A shift to wholesome foods in sensible combinations is effective at lowering weight and improving health regardless of fat or carbohydrate levels, even among those with insulin resistance at the start.

Fundamentally, then, this study suggests that the best way to lose weight and improve health with diet is not by fixating on macronutrients or calories, but by eating wholesome foods in some sensible combination, and emphasizing whole, minimally processed plant foods. The study also indicates that the fundamentals of generally healthful eating pertain to us all, regardless of our genes or insulin levels.

These findings of science may surprise some, but they don’t much surprise me, and the reason is: sense. Horse sense, in particular.

We tend to look right past genetic and physical variation when it comes time to feed horses, and instead prioritize the fact that they are…horses. With horses, as with every species other than our own, we tend to think about the kind of diet that is generally right for the kind of animal, rather than the need to customize diet to each individual. Of course, the one does not preclude the other; horses can all be fed like horses, but some horses will need extra grain to maintain their weight, some will do better on certain varieties of hay. But from the start, the focus is on the common theme of a healthful diet for an entire species, and only after that — variations on the theme.

The DIETFITS study findings collectively indicate that the fundamentals of a health-promoting dietary pattern for Homo sapiens matter more than customizing on the basis of inter-individual variations. As with horses, the one does not preclude the other — but the science we own at present better empowers us to customize diet based on preference, rather than genes. It is good to know that when it comes to dietary patterns that are best for health, we do have choices among the variants on a common theme.

Importantly, though, there is a common theme of eating well for Homo sapiens as for all other species, which we know this week on the basis of the latest science, and might have known last week on the basis of horse sense.