Excess weight is a major risk factor underlying leading causes of death globally, including cardiovascular disease, type 2 diabetes, and some cancers. Among participants assigned to the same lifestyle intervention arms in prior weight loss randomized controlled trials, large inter-individual differences in weight loss success have been observed, ranging from >50lbs of weight loss to >10lbs of weight gain. Both genetic and non-genetic factors underlying differential adherence and weight loss success are poorly understood.

23andMe aims to recruit 91,227 adults to participate in a web-based weight loss intervention. Primary aims include: a.) to confirm whether AG/GG individuals at MTIF3 rs1885988 lose more weight on lifestyle interventions; and b.) to test the performance of a randomized controlled trial vs. self-selection study design in terms of weight loss, drop-outs, and adherence. Secondary (exploratory) analyses will focus on discovery of genetic and non-genetic predictors of weight loss success overall, and examination of potential interactions by intervention type. Web-administered intervention content, videos, and forums will be surfaced to participants every two weeks, and self-reported surveys will be surfaced weekly for the active intervention duration.

Inclusion Criteria:

• US-based men and women in self-reported 'good' or better health
• Consented to participate in research
• BMI 25-40 kg/m2
• Not actively on a weight loss plan
• Willing and able to modify eating and physical activity patterns
• Not under a doctor's care for a serious medical condition

Exclusion Criteria:

• Are pregnant, lactating, within 6 months postpartum, or planning to become pregnant in the next 6 months
• Have diabetes (type 1 or 2) or are on hypoglycemic medications
• Had a heart attack or stroke within the past year
• Are unable or unwilling to follow a physical activity or diet intervention due to a medical condition or doctor's orders
• Have an eating disorder
• Have severe depression, anxiety, or other psychiatric conditions