The study's method by definition places an upper limit of 40% of the population meeting all 4 requirements: "Using the average of the 2-day HEI scores, partici

The study's method by definition places an upper limit of 40% of the population meeting all 4 requirements: "Using the average of the 2-day HEI scores, participants at or above the 60th percentile (ie, top 40%) of HEI scores in the population were categorized as adhering to the dietary guidelines for consuming a healthy diet." Regardless of how healthily people do or don't eat, you only have the 'healthy-diet' characteristic if you're in the top 40%.