When obtained form a usual diet, a food component that sustains or enhances physiological functions and/or prevents diseases is a nutrient. Isoflavones, tocotrienols, and carotenoids are candidate nutrients which may be of health benefit to humans by inhibiting cancer development and reducing risk of atherosclerosis. The amounts of some of these candidate nutrients in food are known. A carotenoid data base has been developed. Isoflavone content of soy foods ranges from 0.1 mg/g (soymilk) to 2.5 mg/g (soy protein isolate). Human bioavailability studies have also been performed with these candidate nutrients. For example, in young adult females fed a single meal containing soy milk, isoflavones were cleared from urine within 24 h after feeding, with about 15-20% of the total dose accounted for in urine and feces. The two major soy isoflavones, genistein and daidzein, differ in bioavailability, with daidzein being more readily excreted in urine. Isoflavones, tocotrienols, and carotenoids meet several criteria for classification as nutrients. But after appropriate animal testing, food analyses, and availability studies have been performed, human health-protective efficacy must be proven in long-term feeding trials, in order for potential health-enhancing food components to be classified as nutrients.
