Abstract Numerous dietary recommendations aim to decrease fat and increase fiber in the American diet, yet obesity remains a major public health problem in the United States as indicated by excessive weight for height ratios. The purpose of the Western Regional Project 182 was to examine knowledge, attitudes, and practices of the general population in 11 states and the District of Columbia regarding dietary fat and fiber. This paper specifically discusses the survey results related to the relationships of fat and fiber knowledge and food behavior to body mass index (BMI). Using self-reported weight and height, it was estimated that more than one third of the respondents (n = 1297, 42%) had a BMI ≥ 26. Subjects with BMI scores less than 26 generally had the highest knowledge scores of all BMI groups, but no significant differences in fat knowledge were found among the BMI classifications. Behavior that was related to fat intake was significantly (p < 0.05) different in respondents with a BMI < 26 as compared to those with higher BMI scores. Gender differences for fat, fiber, and overall behavior were also highly significant (p < 0.0001) with favorable diet-related behaviors exhibited by females. Education, income level, residence, and age were consistently related to the BMI of females, but not males. Women who graduated from college, earned more than $50,000 per year, and lived in an urban location of >250,000 people were most likely to have a lower BMI than females with other educational levels, lower economic categories, and from less populated areas. Results support continued use of government and private funds to educate Americans to improve diet and achieve acceptable weights for heights.