This phase III trial compares telephone delivered Acceptance and Commitment Therapy to standard behavioral therapy for improving weight loss in overweight or obese participants. Acceptance and Commitment Therapy focuses on increasing willingness to experience physical cravings, emotions, and thoughts while making values-guided committed behavior changes. Acceptance and Commitment Therapy may work better at improving weight loss compared to standard behavioral therapy.

OUTLINE: Participants are randomized to 1 of 2 arms.

ARM I: Participants receive ACT telephone coaching over the course of 12 months, calls 1-16 weekly, calls 17-23 biweekly, and calls 24-25 monthly. Call 1 is 30 minutes in duration, while calls 2-25 are each 15-20 minutes in duration.

ARM II: Participants receive SBT telephone coaching over the course of 12 months, calls 1-16 weekly, calls 17-23 biweekly, and calls 24-25 monthly. Call 1 is 30 minutes in duration, while calls 2-25 are each 15-20 minutes in duration.

Participants are followed up at 6, 12, and 24 months after randomization.

Inclusion Criteria:

• Overweight or obese (body mass index [BMI] >= 27) but not heavier than BMI of 45.5 (measured by weight & height)
• Wants to lose weight in the next 30 days
• Interested in learning skills to lose weight
• Willing to be randomly assigned to either condition
• Resides in United States (US)
• Has daily access to their own phone and email
• Does not have a medical or psychiatric condition that would limit their ability to comply with the behavioral recommendations of the program or pose a risk to the participant during weight loss, including meeting criteria for binge eating disorder, and meeting criteria for severe depression (CESD >= 25), or a diagnosis of serious heart disease, diabetes, uncontrolled hypertension, or cancer without written confirmation of approval from their physician office
• Not pregnant, planning to become pregnant or breastfeeding in the next 12 months
• In the past 3 months changed the dosage of prescription medications that can cause a significant change in weight or appetite
• Have not lost more than 5% of their weight in the past 6 months
• Willing and able to read in English
• Not participating in or planning to participate in other weight loss programs
• Has not participated in our other ACT intervention studies
• Does not meet criteria for combined heavy plus binge drinking
• Has access to a Bluetooth-enabled device and Wi-Fi and/or data plan
• Is not planning to have or has not recently had (past 12 months) bariatric surgery
• For outcome data retention, eligibility criteria included: Willing to complete follow-up surveys, and provide email, phone, and mailing address

Exclusion Criteria:

• The reverse of the inclusion criteria