Inclusion Criteria:  Participants must:  have a body mass index between 27-45 kg/m2 have had a knee replacement (including primary, staged or independent bilateral, or revision) <12 weeks prior to baseline assessment have a computer, tablet, or smartphone with active internet access to self-monitor online and/or have a device or computer compatible with Fitbit completion of baseline assessment measures (height, weight, function tests, surveys, ≥4 days valid of activity monitoring, and ≥2 days of dietary recall) be English-speaking and able to read consent and study materials written in English be willing to attend 4 in-person assessments.  Exclusion Criteria:  have any contraindications to diet or weight loss undergo simultaneous bilateral knee replacement or have a scheduled or anticipated knee replacement for the contralateral knee within the next 18 months have a mobility limiting comorbidity unrelated to knee replacement (e.g. spinal stenosis, fibromyalgia, peripheral vascular disease, stroke) are taking anti-obesity medications are enrolled in a formal weight loss program had or are planning to have bariatric/gastric/lap band surgery are planning to relocate out of the Columbia or Greenville, SC areas in the next 18 months.