in google? like i just started my own blog and about dieting and health and am wondering what are popular keywords people search for that i can write about?
You can see that on Google Analytics. It tells you what keywords people type in to get to your site from any SE.
Google analytics is an option, however if you want keyword suggestions you can use the digitalpoint's keyword suggestion tool located here : http://www.digitalpoint.com/tools/suggestion/
Or you can go get this killer software called themezoom.com....but let me tell you it's expensive ($250.00) month and it's only for the serious pros..But it actually gives you market analysis too not just keywords....It's awesome!! So much data involved it's ridiculous.