A new, 25-year study of rhesus monkeys is muddying the waters around the theory that heavily limiting the number of calories you eat can prolong your life. You’ve probably heard about the studies with worms, and mice, and rats, showing that those animals live longer, healthier lives when they eat significantly less food than control animals. But, as Nature News points out, those results aren’t always consistent from study-to-study—a fact which suggests we don’t really understand all the factors in play just yet. In fact, the new rhesus study flatly contradicts a previous rhesus study. But that previous experiment could have been flawed because control monkeys were fed high-sugar foods in unlimited quantities, rather than a reasonable, healthy diet. Basically, if animals really do live longer on super-low calorie diets, there’s probably more going on there than just super-low calorie diets.