See your ketones climb.
Ketones are a number you can track. Log ketones, glucose, and weight, sync Apple Health, and watch your own trends climb across a fast. Your private lab notebook.
2.1 mmol/L
Ketones
86 mg/dL
Glucose
Free · Private · No account
Fast better, for longer.
Optimize your fast with data. Fasting moves your metabolism through distinct, well-studied stages. Meridian by Kētos™ visualizes your progress so you can track your progress in real time.
Coming soon for iPhone and Apple Watch — free, always. Wellness education, not medical advice.
On-device & private
Works with Apple Health
Grounded in research
Free, forever
The science of the ring
It comes down to one hormone: insulin.
When you eat, insulin runs high to store the food you just ate as fat. As you fast, insulin falls. That drop signals your body to shift gears stored burn fat as clean ketolytic fuel.
metabolic ring
See your biology in real time.
The metabolic ring changes color as you advance into new fasting stages. A single card explains your current state in plain English, and the journey bar shows you what's on the horizon.
Deep ketosis & autophagy · ~26h
"Glycogen is largely spent and ketosis deepens, cellular cleanup (autophagy) is ramping up."
The science, hour by hour
Progress through seven stages
The complete metabolic arc at your finger tips. Each phase matches a color on your ring and is rooted in peer-reviewed science.*
*(Note: Every body is different, timings are typical ranges, not absolute guarantees).
Fed state — digesting · ~0–4h
You're absorbing your last meal; insulin is high, so your body stores energy instead of burning its reserves.
Sugar falling · ~4–8h
Insulin starts to drop and your body leans on stored sugar (glycogen) to keep blood sugar steady.
Fat-burning begins · ~8–12h
Glycogen runs lower and your body gradually shifts toward releasing stored fat for fuel.
Metabolic switch · ~12–16h
Fat-burning ramps up and your liver starts turning that fat into ketones — the well-studied "metabolic switch."
Ketosis building · ~16–24h
Your liver typically begins making measurable ketones, and your brain can start using them as fuel.
Deep ketosis & autophagy · ~24–36h
Ketosis deepens and cellular cleanup (autophagy) is thought to increase — though its exact human timing is hard to measure.
Elevated autophagy · ~36h+
Repair processes are believed to go deeper and growth hormone rises, helping preserve lean muscle.
These timings are evidence-based estimates that vary from person to person and shift with your last meal, activity, and sleep — autophagy timing in particular is inferred largely from animal and lab studies and is less certain in humans. Kētos supports general wellness and isn't medical advice. Fasting isn't right for everyone: if you're pregnant or breastfeeding, have a history of an eating disorder or diabetes, or take medication, talk to your doctor first.
The research behind the stages — 11 peer-reviewed sources
- de Cabo R, Mattson MP. Effects of intermittent fasting on health, aging, and disease. N Engl J Med. 2019;381(26):2541–2551. doi:10.1056/NEJMra1905136
- Anton SD, et al. Flipping the metabolic switch: understanding and applying the health benefits of fasting. Obesity (Silver Spring). 2018;26(2):254–268. doi:10.1002/oby.22065
- Jensen MD, et al. Lipolysis during fasting: decreased suppression by insulin and increased stimulation by epinephrine. J Clin Invest. 1987;79(1):207–213. doi:10.1172/JCI112785
- Rothman DL, et al. Quantitation of hepatic glycogenolysis and gluconeogenesis in fasting humans with 13C NMR. Science. 1991;254(5031):573–576. doi:10.1126/science.1948033
- Owen OE, et al. Brain metabolism during fasting. J Clin Invest. 1967;46(10):1589–1595. doi:10.1172/JCI105650
- Puchalska P, Crawford PA. Multi-dimensional roles of ketone bodies in fuel metabolism, signaling, and therapeutics. Cell Metab. 2017;25(2):262–284. doi:10.1016/j.cmet.2016.12.022
- Madeo F, et al. Essential role for autophagy in life span extension. J Clin Invest. 2015;125(1):85–93. doi:10.1172/JCI73946
- Bensalem J, et al. Intermittent time-restricted eating may increase autophagic flux in humans: an exploratory analysis. J Physiol. 2025;603(10):3019–3032. doi:10.1113/JP287938
- Ho KY, et al. Fasting enhances growth hormone secretion and amplifies the complex rhythms of growth hormone secretion in man. J Clin Invest. 1988;81(4):968–975. doi:10.1172/JCI113450
- Nørrelund H, et al. The protein-retaining effects of growth hormone during fasting involve inhibition of muscle-protein breakdown. Diabetes. 2001;50(1):96–104. doi:10.2337/diabetes.50.1.96
- Furmli S, Elmasry R, Ramos M, Fung J. Therapeutic use of intermittent fasting for people with type 2 diabetes as an alternative to insulin. BMJ Case Rep. 2018;2018:bcr-2017-221854. doi:10.1136/bcr-2017-221854
Coming soon to theApp Store
Free, always · No account · iPhone & Apple Watch
Your fast, at a glance
Leave your phone behind.
Focus on what is most important to you. Get instant clarity on your fast right from your Lock Screen, Dynamic Island, and Apple Watch, so you can stay in the flow of your day.
Live Activity + Dynamic Island
Apple Watch
Home & Lock Screen widgets
On-device · Free
Ketosis building16h 04m · next 2h 14m
9:41
Thursday, June 26
MERIDIAN
Ketosis building
Next in 2h 14m · Deep ketosis
16:04:38elapsed
One fast. Three glances.
The timer and ramp fill move on their own; the stage label refreshes when you cross into a new stage or open the app — an honest read, not a fake per-second countdown.
Go deeper
Your numbers, your rhythm.
Let the ring run in the background, or use our two easy tools to uncover patterns and build a lasting habit. Everything stays entirely private, giving you the space to explore your body without the pressure of rigid targets.
Set your rhythm.
Benefits deepen when fasting becomes second nature. Flexible streaks, charts, and goals that grow as you do so you can unlock all the health benefits of fasting.
10 days
Streak
114h
This week
Honest about what it is
No ads. No subscription.
Meridian by Kētos is free and fully private — everything lives on your iPhone. Optional encrypted iCloud sync stays under your control, and an Apple Watch app, Live Activity, and Dynamic Island keep your fast on your Lock Screen.
Free
Every feature, no paywall
Private
On-device, no account
No ads
Nothing tracking you
iPhone & Watch
Live Activity built in
16:818:620:4OMAD24–168h therapeutic
Kētos supports general wellness and isn't medical advice. Fasting isn't right for everyone — if you're pregnant or breastfeeding, have a history of an eating disorder or diabetes, or take medication, talk to your doctor first.
Questions, answered honestly
Before you start.
Is fasting safe?
For most healthy adults, time-restricted eating is well studied. But Kētos supports general wellness and isn't medical advice. If you're pregnant or breastfeeding, have a history of an eating disorder or diabetes, or take medication, talk to your doctor first.
Is it really free? What's the catch?
Yes — every feature, no ads, no subscription, no in-app purchases. Kētos makes a multivitamin for fasting windows, and the app's job is simply to be useful. It stands entirely on its own, and there's nothing to buy inside it.
Do I need a ketone meter or an Apple Watch?
No. The metabolic ring works from the timer alone. A blood-ketone meter and the Apple Watch app are optional extras if you want to go deeper.
Is my data private?
Completely. Everything lives on your iPhone — no account, no sign-up. Optional iCloud sync is encrypted and stays under your control. Nothing is ever sold or shared.
Where do the stages come from — are the times exact?
The seven stages are grounded in published fasting research. The hours are typical ranges, not guarantees — they shift with your last meal, activity, and sleep. Think map, not stopwatch.
Which devices does it work on?
Meridian by Kētos is a native app for iPhone and Apple Watch, with a Live Activity, Dynamic Island, and home- and lock-screen widgets. There's no Android version.
From sunup to sundown, Meridian has your back.
Meridian by Kētos is launching soon for iPhone and Apple Watch. Leave your email and we'll send one note the moment it's live. Everything's free, your data stays on your phone, and it works beautifully on its own.
