When planning national screening programs, it is important to investigate potential changes in health behavior initiated by the screening. Knowledge of the consequences of different colorectal cancer (CRC) screening modalities for health behavior is limited. We aimed to investigate differences in 1-year health behavior changes after testing negative in CRC screening by one of two screening modalities. Participants of both sexes aged 50–74 years assigned randomly to five biennial rounds of fecal immunochemical test (FIT), one round of flexible sigmoidoscopy (FS), or no screening (control) were invited to complete a self-reported lifestyle questionnaire on smoking, body weight, physical activity, alcohol intake, and consumption of selected dietary items at baseline and at 1-year follow-up. In total, 1809 and 1327 individuals in the FIT and the FS arm, respectively, completed the lifestyle questionnaire, as did 1029 controls. We analyzed differences in 1-year health behavior changes between the arms at follow-up by analysis of covariance and logistic regression. Overall, 1-year changes in health behavior were moderate and probably of no clinical relevance. Participants with negative CRC screening test results in the first round of the FIT arm reduced their alcohol consumption significantly more than controls [−0.29 glass/week (95% confidence interval −0.54 to −0.04)]. Body weight decreased more in participants with negative screening test results in the FS than in the FIT arm [−0.31 kg (95% confidence interval −0.55 to −0.08)]. The present study did not suggest unfavorable short-term consequences in the health behavior of individuals who received a negative CRC screening test result from either a first round of FIT or a once-only FS screening.