# Use the fasting timer even if you don't fast (TRE)

It records when you eat, which is a circadian measure in its own right; time-restricted eating is one use of it, not the reason for it.

Type: practice · Unit: h:min · Domain: Metabolic Health · Accuracy: Self-reported · Importance: Core

Also called: fasting timer, overnight fast, eating window, time-restricted eating, intermittent fasting, 16:8, last meal time, first meal time, when to eat

## Do this

- Tap the timer at your last bite of the day and again at your first bite the next day; if you forget, correct the time afterwards.
- Do it every day, fasting or not.
- Keep the last meal's time honest, including the late snack.
- Read your eating window and your overnight fast on the timeline beside your glucose, your sleep and your morning readings.
- Treat time-restricted eating as one experiment you can run with the timer, not the reason the timer exists.

## Why VT asks for it

The timer records when you eat, which is a circadian measure in its own right, and the one most people have never looked at. A late last meal moves the next day's glucose: in 20 healthy volunteers, a dinner at ten instead of six, with sleep fixed, raised overnight glucose, delayed the fat the body burned during the night, and raised cortisol, most in the early sleepers (Gu 2020). It moves the night's readings too, which is why a late or large late meal is one of the things Symptom Radar gives less weight to when you have logged it, judged against your own habits once VT has about 20 logged examples. The first meal's time explains many morning readings: your glucose line marks it, with the length of the fast before it. And the consistency of your window from day to day is one of the few circadian levers under your control, which the circadian entries take up.

## What the evidence says about fasting itself

Enough to be interesting, not enough for a verdict, and VT does not give one. In a controlled feeding study, men with prediabetes who ate within a six-hour window with dinner before 3 p.m. for five weeks, at a weight held constant, improved insulin sensitivity, beta-cell responsiveness, blood pressure, oxidative stress and appetite compared with a twelve-hour window (Sutton 2018), which showed that timing can matter independently of weight. In 116 adults with overweight or obesity, twelve weeks of eating between noon and 8 p.m. produced no more weight loss than three structured meals a day, and the in-person subgroup lost some lean mass (Lowe 2020). In 139 adults with obesity, a year of eating between 8 a.m. and 4 p.m. on top of a calorie limit lost 8.0 kg against 6.3 kg for the calorie limit alone, a difference that was not statistically significant (Liu 2022). And in a tightly controlled crossover study, eating the same meals four hours later increased hunger, shifted the hunger hormones, and lowered daytime energy expenditure and core temperature (Vujović 2022). Read together: when you eat changes glucose and appetite, an earlier window has the better evidence, and a restricted window on its own is not a weight-loss method. Whether it suits you is what the timer and your record will tell you.

## What the timer gives VT

The overnight fast, from yesterday's last meal to today's first; the eating window, from first to last; markers on your glucose line for both; and the late-meal flag for the overnight comparison. The energy engine does not need it, and nothing scores it.

## What it does not do

It does not need a plan: the app starts on an 18:6 window, and choosing No plan leaves it only recording your times. A window you pick shows your progress through it, and nothing scores it. If fasting makes you lightheaded, sleep badly or eat more later, that is a finding, and your record will show it.

## Sources

1. Gu C, et al. Metabolic effects of late dinner in healthy volunteers: a randomized crossover clinical trial. J Clin Endocrinol Metab 2020;105:2789–802. [doi:10.1210/clinem/dgaa354](https://doi.org/10.1210/clinem/dgaa354)
2. Sutton EF, Beyl R, Early KS, Cefalu WT, Ravussin E, Peterson CM. Early time-restricted feeding improves insulin sensitivity, blood pressure, and oxidative stress even without weight loss in men with prediabetes. Cell Metab 2018;27:1212–21. [doi:10.1016/j.cmet.2018.04.010](https://doi.org/10.1016/j.cmet.2018.04.010)
3. Lowe DA, et al. Effects of time-restricted eating on weight loss and other metabolic parameters in women and men with overweight and obesity: the TREAT randomized clinical trial. JAMA Intern Med 2020;180:1491–9. [doi:10.1001/jamainternmed.2020.4153](https://doi.org/10.1001/jamainternmed.2020.4153)
4. Liu D, et al. Calorie restriction with or without time-restricted eating in weight loss. N Engl J Med 2022;386:1495–504. [doi:10.1056/NEJMoa2114833](https://doi.org/10.1056/NEJMoa2114833)
5. Vujović N, et al. Late isocaloric eating increases hunger, decreases energy expenditure, and modifies metabolic pathways in adults with overweight and obesity. Cell Metab 2022;34:1486–98. [doi:10.1016/j.cmet.2022.09.007](https://doi.org/10.1016/j.cmet.2022.09.007)
6. Vitality Tracker, How it works: Symptom Radar; What VT measures (catalogue of 15 October 2026).

## Related

- [Eating window: first and last meal](https://vitalitytracker.app/knowledge/eating-window)
- [Fasting glucose](https://vitalitytracker.app/knowledge/fasting-glucose)
- [Blood ketones and the breath reading](https://vitalitytracker.app/knowledge/blood-ketones-and-breath-reading)
- [Symptom Radar and Symptom Trend](https://vitalitytracker.app/knowledge/symptom-radar-and-symptom-trend)
- [Why log meals even if you are not trying to lose weight](https://vitalitytracker.app/knowledge/why-log-meals)
- [Dip after](https://vitalitytracker.app/knowledge/dip-after)

Reviewed October 2026 · v1

Source: https://vitalitytracker.app/knowledge/use-the-fasting-timer