they blow their nose and touch everything and bring home germs. teachers get sick all the time. that's why the c.b.c. says school-aged kids need to be immune. >> brian: germs are not always a bad thing. helps bring up immunity. i heard a story about d.n.a.-based diets, that there is testing available to determine what kind of diet might actually work better for individuals. >> well, you know, i do believe in genetic variation in testing. i think that they will find this. now these tests are kind of simplefied. it was low fat versus a low-carb diet. there are genes that tell us why can some skinny person eat like a pig and stay skinny and why an obese person can be obese and hardly eat anything and there are jennetgenetic determination for that. the simplistic tests, i'm not sure we're there yet. but if you believe it and it will deep you on a diet,