BACKGROUND: Several studies have shown that e-mail counseling improves weight loss achieved in self-directed Internet programs. Computer-tailored feedback offers a population-based alternative to human e-mail counseling.METHODS: One hundred ninety-two adults, aged 49.2 +/- 9.8 years, having a body mass index (calculated as weight in kilograms divided by height in meters squared) of 32.7 +/- 3.5, were randomized to 1 of 3 Internet treatment groups: No counseling, computer-automated feedback, or human e-mail counseling. All participants received 1 weight loss group session, coupons for meal replacements, and access to an interactive Web site. The human e-mail counseling and computer-automated feedback groups also had access to an electronic diary and message board. The human e-mail counseling group received weekly e-mail feedback from a counselor, and the computer-automated feedback group received automated, tailored messages.RESULTS: Retention was 82% at 3 months and 80% at 6 months for all 3 groups. At 3 months, completers in both the computer-automated feedback (-5.3 +/- 4.2 kg) and human e-mail counseling (-6.1 +/- 3.9 kg) groups had significantly greater weight losses compared with the no counseling group (-2.8 +/- 3.5 kg) and these groups did not differ from each other. At 6 months, weight losses were significantly greater in the human e-mail counseling group (-7.3 +/- 6.2 kg) than in the computer-automated feedback (-4.9 +/- 5.9 kg) or no counseling (-2.6 +/- 5.7 kg) groups. Intent-to-treat analyses using single or multiple imputation techniques showed the same pattern of significance.CONCLUSIONS: Providing automated computer-tailored feedback in an Internet weight loss program was as effective as human e-mail counseling at 3 months. Further research is needed to improve the efficacy of automated computer-tailored feedback as a population-based weight loss approach.