Intermittent Fasting
Intermittent Fasting — Intermittent fasting (IF) is an umbrella term for eating patterns that cycle between periods of eating and voluntary fasting. Common protocols include 16:8 time-restricted eating, alternate-day fasting, the 5:2 diet (two low-calorie days per week), and 24-hour periodic fasts. Most clinical trials show IF produces weight loss similar to calorie-equivalent continuous restriction.
What is intermittent fasting?
Intermittent fasting (IF) is a pattern of eating defined more by when food is consumed than by what or how much. Major variants include:
- Time-restricted eating (TRE) — eating window of 6-12 hours per day, fasting the remainder; popularly the “16:8” pattern
- Alternate-day fasting (ADF) — alternating ~25% calorie days with ad libitum eating days
- 5:2 diet — five normal-eating days plus two ~500-600 kcal “modified fast” days per week
- 24-hour fasts — once or twice weekly
The pattern was popularized in mainstream weight loss culture starting around 2012 and has accumulated significant clinical trial evidence in the years since.
How does intermittent fasting work?
The two leading mechanistic claims for IF benefits are:
- Spontaneous calorie reduction — eating windows naturally limit total intake for many people, producing a calorie deficit without conscious counting
- Metabolic effects independent of weight loss — improvements in insulin sensitivity, autophagy, lipid profile
The first mechanism is well established. The second is contested. Multiple recent randomized trials, including Lowe et al., 2020 (TREAT) and Liu et al., 2022, NEJM, have found that IF produces weight loss roughly equivalent to calorie-matched continuous restriction, with no clear cardiometabolic advantage independent of weight loss.
Why intermittent fasting matters in tracking apps
For users employing IF, calorie tracking apps remain useful but with caveats:
- IF does not suspend the importance of calorie balance over time
- Some users compensate by overeating during eating windows; tracking exposes this
- Apps with eating-window timestamps (LoseIt, MyFitnessPal Premium) can visualize compliance
Concerns: IF is not appropriate for individuals with active or recovered eating disorders, in pregnancy, in growing adolescents, or in those with certain medical conditions. See related entries on time-restricted eating, carb cycling, and refeed days.