title: Diet and Physical Activity Apps: Perceived Effectiveness by App Users.
abstract: BACKGROUND
  Diet and physical activity apps are two types of health apps that aim to promote healthy eating and energy expenditure through monitoring of dietary intake and physical activity. No clear evidence showing the effectiveness of using these apps to promote healthy eating and physical activity has been previously reported.
  
  
  OBJECTIVE
  This study aimed to identify how diet and physical activity (PA) apps affected their users. It also investigated if using apps was associated with changes in diet and PA.
  
  
  METHODS
  First, 3 semi-structured focus group discussions concerning app usability were conducted (15 app users and 8 nonusers; mean age 24.2 years, SD 6.4), including outcome measures such as motivations, experiences, opinions, and adherence. Results from the discussions were used to develop a questionnaire. The questionnaire, which contained questions about behavior changes, app usage, perceived effectiveness, and opinions of app usability, was answered by 500 Norwegians, with a mean age of 25.8 years (SD 5.1).
  
  
  RESULTS
  App users found diet and PA apps effective in promoting healthy eating and exercising. These apps affected their actions, health consciousness, and self-education about nutrition and PA; and were also a part of their social lives. Over half of the users perceived that apps were effective in assisting them to eat healthily and to exercise more. Diet apps were more effective when they were frequently used and over a long period of time, compared to infrequent or short-term use (P=.01 and P=.02, respectively). Users who used diet and PA apps, perceived apps as more effective than users who only used one type of app (all P<.05). App users were better at maintaining diet and PA behaviors than nonusers (all P<.05). Young adults found apps fun to use, but sometimes time consuming. They wanted apps to be designed to meet their personal expectations.
  
  
  CONCLUSIONS
  App usage influenced action, consciousness, self-education about nutrition and PA, and social life. It facilitated maintaining a healthy diet and exercising more. Diet and PA apps of the future can be further strengthened by being tailored to meet personal needs.
authors.affiliation: Department of Chemistry, Biotechnology, and Food Science, Norwegian University of Life Sciences, Aas, Norway. qing.wang@nmbu.no.
authors.forename: Qing
authors.identifier: http://orcid.org/0000-0002-1910-7540
authors.initials: Q
authors.lastname: Wang
authors.forename: Bjørg
authors.identifier: http://orcid.org/0000-0003-0877-4628
authors.initials: B
authors.lastname: Egelandsdal
authors.forename: Gro V
authors.identifier: http://orcid.org/0000-0001-7797-6464
authors.initials: GV
authors.lastname: Amdam
authors.forename: Valerie L
authors.identifier: http://orcid.org/0000-0001-9641-3333
authors.initials: VL
authors.lastname: Almli
authors.forename: Marije
authors.identifier: http://orcid.org/0000-0002-0997-0041
authors.initials: M
authors.lastname: Oostindjer
keywords: behavioral changes; diet app; perceived effectiveness; physical activity app