Inclusion criteria  18 years or older Fluent in English Low adherence to cancer prevention dietary guidelines, operationalized as a score of ≤ 2 out of 4 using the National Cancer Institute method for assessing adherence to World Cancer Research Fund/American Institute for Cancer Research (WCRF/AICR) lifestyle recommendations. This three-level scoring system (meeting/partially meeting/not meeting each recommendation) includes 4 items specific to diet. Participants must score equal or less than 2, meaning that they are fully meeting recommendations for no more than 2 of the 4 dietary recommendations. Performs the majority of the household's food shopping, and do so at stores that can passively stream item-level data from a store loyalty card to the Information Machine API (e.g., Walmart, Target, ShopRite, Wegman's, etc.) Has a smartphone with iOS or Android operating system that is compatible with the program app Lives in a household with at least one other adult who consents to being randomized to possibly receive messages on his/her own cell phone through the program app  Exclusion criteria  Medical condition or psychiatric condition (e.g., active substance abuse, eating disorder) that may limit appropriateness of or ability to comply with program dietary recommendations Planning to enroll in another lifestyle modification program in the next 6 months Bariatric surgery history Currently pregnant or breastfeeding or planning to become pregnant in the next 6 months