BACKGROUND
Intermittent Fasting (IF) is an increasingly popular approach to dietary control that focuses on the timing of eating rather than the quantity and content of caloric intake. IF practitioners typically seek to improve their weight and other health factors. Millions of practitioners have turned to purpose-built mobile applications to help them track and adhere to their fasts and monitor changes in their weight and other biometrics.
OBJECTIVE
This study aimed to quantify user retention, fasting patterns, and weight loss by users of two commonly used IF mobile apps. We aimed to describe starting BMI, amount of fasting, frequency of weight tracking, and other demographics as correlates of retention and weight change.
METHODS
We assembled height, weight, fasting and demographic data for adult users (age 18-100yo) of the LIFE Fasting Tracker and LIFE Extend apps from 2018-2020. Retention up to 52 weeks was quantified based on recorded fasts and correlated with user demographics. Users who provided height and at least two weights and whose first fast and weight records were contemporaneous were included in the weight loss analysis. Fasting was quantified as Extended Fasting Hours (hours beyond 12 in a fast) averaged per Day (EFH/Day).
RESULTS
792,692 users were followed for retention based on 26 million recorded fasts. 132,775 (16.7%) of users were retained at 13 weeks, 54,881 (6.9%) at 26 weeks, and 16,478 (2.1%) at 52 weeks, allowing 4 consecutive weeks of inactivity. Weight loss in the qualifying cohort (n=161,346) was strongly correlated with starting BMI and EFH/Day. Users with BMI ≥ 40 lost 11.3% of their starting weight by 52 weeks versus a slight weight gain on average for users with starting BMI <23. Additionally, EFH/Day was an approximately linear predictor of weight loss for a given time point and starting BMI. By week 26, users lost over 1% of their starting weight per EFH/Day on average. Furthermore, users who recorded their weight monthly lost considerably more weight than those who did not (eg, 8.5% vs 3.7% weight loss at week 13 for users with BMI ≥25). By 26 weeks, 69.2% (2985/4313) of users with starting BMI ≥ 25 who recorded monthly weights lost at least 5% of their starting weight, and 39.9% (1722/4313) lost at least 10% body weight.
CONCLUSIONS
Intermittent Fasting with the LIFE mobile apps appears to be a sustainable approach to weight reduction in the overweight and obese population. Healthy weight and underweight individuals do not lose much weight on average, even with extensive fasting. Obese users lose substantial weight over time, with more weight loss in those who fast more and who record their weight more frequently.