SKINNIEST!
(the number is the average BMI)

1 Roseville, CA 24.5
2 San Francisco, CA 24.8
3 Houston, TX 24.8
4 Missouri City, TX 24.8
5 Sugar Land, TX 24.8
6 Boulder, CO 24.8
7 Longmont, CO 24.8
8 Highlands Ranch, CO 24.9
9 San Rafael, CA 25.2
10 Santa Fe, NM 25.2
11 Honolulu, HI 25.4
12 Champaign, IL 25.4
13 Arlington, VA 25.4
14 Denton, TX 25.4
15 Flower Mound, TX 25.4
16 Fort Worth, TX 25.4
17 Fort Collins, CO 25.5
18 Loveland, CO 25.5
19 Daly City, CA 25.6
20 Redwood City, CA 25.6
21 San Mateo, CA 25.6
22 South San Francisco, CA 25.6
23 Aspen Hill, MD 25.6
24 Bethesda, MD 25.6
25 Gaithersburg, MD 25.6

http://money.cnn.com/magazines/moneymag/bplive/2006/top25s/skinniest.html