How Long Does It Take to Get Into Ketosis?

Quick answer: Getting into ketosis runs on a clock of days: once your stored glucose is used up, your liver starts making ketones. Feeling good on keto runs on a clock of weeks, because your body needs time to get efficient at running on fat. KetoDick's figures for that second clock are about 2–4 weeks for thinner people and longer, up to around 8, for heavier people. Mixing the two clocks up is why so many people quit in week two.

In this article

• Clock one: getting into ketosis
• Clock two: becoming fat adapted
• What month one feels like, week by week
• How to make the wait easier
• What the research says
• KetoDick's take
• Key takeaways

Clock one: getting into ketosis

Your body keeps a short-term fuel reserve called glycogen, in your liver and muscles. When you stop eating much carbohydrate, you burn through it. KetoDick says people normally get through their stored glucose in two or three days of not eating carbs (video 1vyxuWlxT5M). The Men's Health article he reads through puts it at about 48 hours, and he agrees with that part (video 1JbK1_ClDmY).

Once glycogen runs low, insulin falls, stored fat becomes easier to reach, and the liver starts turning fatty acids into ketone bodies (video s_sNd1v8Low). That's ketosis. It isn't a switch that flips at an exact hour, and how fast you get there depends on how many carbs you were eating before and how low you go now.

One thing that doesn't speed it up: eating more fat. KetoDick is blunt about this. At no point does adding dietary fat fire up ketosis; restricting carbs is how you get there (video NUJNFG6lLWw).

Clock two: becoming fat adapted

Here's the catch. Being in ketosis and being good at ketosis are different. In the early weeks your glycogen is gone, but your liver hasn't yet built up enough of the enzymes it needs, and your cells haven't adjusted to using ketones well. So you have less glucose and not yet enough of the replacement. KetoDick calls the finished state "fat adapted" (video NUJNFG6lLWw).

His timelines vary a little by video, which is honest, because people vary:

He also names things that change the speed: sex, age, where someone is in their menstrual cycle, and more (video NUJNFG6lLWw). So if your friend felt great at day ten and you don't at day twenty, that's not failure.

What month one feels like, week by week

KetoDick made a video specifically so people would know their experience is normal (video uDw65ERtsA0):

1. Week one: mostly water weight. Glycogen is stored with roughly twice its weight in water, so losing it shows up on the scale as a quick drop of a few pounds, more for heavier people. It comes back quickly if you go back to high carbs.
2. Weeks two and three: "a slog," in his words from the video. Low energy, stomach upsets as your gut bacteria adjust, and usually a plateau.
3. From about week four: real fat loss starts.

He suggests skipping the scale for the first 30 days and giving the whole thing 60 days before you judge it (video uDw65ERtsA0). Back-of-envelope, using the figures he gives elsewhere: about 700 g of glycogen plus about 1,400 g of water is around 4.4 lb (video UygKGoP_BtA). That's your week-one "loss," and it isn't fat.

The rough patch in weeks one and two is usually what people call keto flu. KetoDick's view is that the fatigue is the gap before fat adaptation, cramps point to electrolytes, and a lot of the rest is carb and sugar withdrawal. He flags that last part as more his opinion than science (video 9r2Y74AnjUQ).

How to make the wait easier

So what you do is stop expecting clock two to run at the speed of clock one.

• Taper in if you want a softer landing. Going strict from minute one, he says, is close to guaranteed to make you crash; he recommends dropping starches first, then sugary drinks and sauces, while keeping salads (video qfy0IBkPF4A). He's upfront that he didn't taper himself.
• Don't restrict calories in month one. Count carbs, get your protein, eat fat until you're full (video 7Aixw4uRksI).
• Handle electrolytes. Cramps are the sign he points to (video 9r2Y74AnjUQ).
• Use the first weeks to learn. Labels, shopping, recipes. Month one is for learning, not suffering (video 7Aixw4uRksI).

If you want to confirm the first clock has started, cheap urine strips will show it. Their shade says little about your blood level, and they fade as you adapt (video 8wOheKcBEd8). More in signs you're in ketosis.

What the research says

• The NIH's StatPearls chapter describes ketogenesis as a liver process regulated by insulin and glucagon, producing acetoacetate, BHB and acetone (Dhillon & Gupta, StatPearls).
• The classic adaptation finding comes from fasting, not diets: after weeks of fasting, BHB and acetoacetate replaced glucose as the brain's main fuel (Owen et al., 1967). That's a "weeks" timescale for the deeper shift.
• A review of starvation physiology describes the body moving from glucose to fatty acids and liver ketones while sparing body protein (Cahill, 2006).
• An analysis of online posts found that reported "keto flu" symptoms clustered in the first weeks and were mostly described as short-lived (Bostock et al., 2020).

What the evidence pages here don't give is a precise hour count for nutritional ketosis on a typical diet, or a validated timeline for "fat adaptation" as KetoDick uses the term. His week counts are his reading and experience, not a measured figure.

KetoDick's take

I've said the first 30 days just don't look at the scale; from day 30 to 60 you start to make the real adaptations, and that second month is real fat loss (video cTGYIFOTPl8). The light at the end of the tunnel, once you make it those 30 days, is that you won't be hungry anymore.

I've also said I can't tell you how to taper from experience, because I didn't (video DoSUgIr2rNo).

If you have type 2 diabetes or any kidney risk, a dark ketone strip can mean something different for you, so talk to your doctor about what your readings mean (video GojQvo_2GS0). If you take any medication, review the plan, and the dosing, with your doctor before you start (video UygKGoP_BtA).

Key takeaways

• Ketosis starts within days, once stored glucose runs down. Fat doesn't speed it up; cutting carbs does.
• Fat adaptation takes weeks: about 2–4 for thinner people and up to around 8 for heavier people, in his estimates.
• Week one's scale drop is mostly water. Weeks two and three are often flat and tired. That's the normal schedule.
• Give it 60 days before judging, and skip the scale for the first 30.
• Diabetes or glucose-lowering medication: doctor first.

Related

• Guide chapter: Keto basics · What ketosis is · Fat adaptation · The month-one timeline · Tapering in
• Blog: Signs you're in ketosis · Your first week on keto · How long keto flu lasts · The week-three stall
• Videos: What is the ketogenic diet · Common beginner questions · Eating too much fat · The typical weight-loss schedule