Intermittent Fasting Calculator.

Time-restricted eating (TRE) confines all caloric intake to a daily window — 8 hours, 6 hours, 4 hours, or a single meal — without prescribing what to eat inside it. The mechanism is twofold: it lowers total daily calories for most people without conscious tracking, and it aligns feeding with the circadian regulation of insulin sensitivity, which is highest in the morning and degrades through the day.

The most-cited human trial (Sutton et al., 2018) used early TRE — eating finished by mid-afternoon — and produced improvements in insulin sensitivity, blood pressure, and oxidative stress markers independent of weight loss. The effect size shrinks but does not disappear when the eating window is shifted later in the day.

TRE produces modest weight loss compared with continuous calorie restriction — meta-analyses converge around 1–4% body weight loss over 8–12 weeks, similar to what an unenforced 10–15% calorie deficit achieves. The advantage is adherence, not metabolic magic: many adults find a 16:8 or 18:6 window easier to sustain than logging macros.

The 2022 NEJM trial by Liu et al. compared TRE plus calorie restriction against calorie restriction alone over 12 months and found no significant additional weight loss from the time restriction itself. Read that as confirmation that calories still drive composition — TRE is a behavioral tool that helps you eat fewer of them.

16:8 is the entry point — skip breakfast or dinner, eat in an 8-hour window. Most adults can maintain it indefinitely. 18:6 and 20:4 compress the window further and tend to produce more spontaneous calorie reduction but require more planning around protein distribution. OMAD (one meal a day) is the most extreme and is hardest to hit a 1.6–2.2 g/kg protein target on; reserve it for short-term experiments, not long-term habit.

Earlier windows beat later ones in the controlled data. If you can finish eating by 6–7 PM and skip late-night calories, you capture most of the metabolic upside. Late-night eating windows undo much of the circadian benefit even with the same total fasting hours.

TRE is contraindicated or risky for: anyone with a history of disordered eating, pregnant or breastfeeding women, type 1 diabetics, adults on insulin or sulfonylureas without medical supervision, and competitive athletes in a heavy training block (it makes hitting protein and carb targets harder). Adolescents should not run aggressive TRE — they have growth and developmental requirements that extended fasting can compromise.