“Am I in ketosis yet?” It’s a common question among keto dieters.
How long to get into ketosis depends on your eating schedule, activity level, carb intake, and a host of other factors. Yes, ketosis is complex.
That said, many people start producing ketones within days of going keto. But producing ketones isn’t the same as the metabolic state of ketosis, which can take longer.
Consider this article your science-based guide on ketosis. You’ll learn how long it takes, how to tell if you’re in ketosis, and tips for shifting into ketosis.
According to some sources, ketosis is defined as having blood ketone levels elevated above 0.3 millimole/Liter (mmol/L)[*]. This can be measured with a blood test.
Some people will enter ketosis following an overnight fast, while others may require several days of low-carb dieting to start making ketones. Your individual “time to ketosis” depends on a variety of factors.
You’ll learn those factors soon, but first a crucial point: having elevated blood ketones doesn’t necessarily mean you’re keto-adapted or fat-adapted.
Being fat-adapted means your body can effectively utilize stored body fat for energy.
But making ketones is not the same as using ketones as a source of energy. You might produce more ketones after a 16-hour intermittent fast, but keto-adaptation takes more time — typically two to four weeks.
And guess what? You have to fat-adapt before the health benefits of keto start rolling in.
These may include:
- Fat loss: Initial weight loss in the first week of keto is mostly water weight, but once you fat-adapt, your cells start burning body fat[*][*].
- More stable energy: Running on fat means getting off the blood sugar roller coaster that can lead to insulin resistance and hopping on the keto energy train.
- Reduced cravings: A positive side effect of using fat for energy means fewer cravings. Why? Lower ghrelin (your hunger hormone), lower CCK (an appetite stimulator), and other chemical changes take place as you become fat-adapted[*].
- Clearer cognition: After the initial brain fog of the keto flu, you can expect to experience clear-headed, clean energy. Higher ketone levels are linked to enhanced working memory, visual attention, and task switching performance in the elderly[*].
- Enhanced endurance: In 1980, Dr. Steve Phinney showed that keto dieters lasted longer on the treadmill than high-carb folks[*].
The point is: being fat-adapted is distinct from being in ketosis. Fat-adaptation can take weeks, while getting into ketosis may only take days or hours.
As you just learned, being in ketosis isn’t synonymous with being fat-adapted. Ketosis refers to having elevated ketones in your blood, breath, or urine.
Measuring your ketone levels can give you an idea of where you are metabolically. Here’s how:
#1: Blood Testing
Ketone blood testing is first on this list because it’s the most validated method for measuring ketosis. You can measure ketones in the lab, or use an at-home blood ketone meter.
These tests measure a ketone body called beta-hydroxybutyrate (BHB) in your blood. Anything above 0.3 mmol/L is considered elevated, but optimal levels may be north of 1 mmol/L[*].
#2: Breath Testing
Ketone breath tests measure acetone, a ketone body responsible for the fruity phenomenon known as “keto breath” (some people call it bad breath).
Breath testing isn’t as well-validated as blood testing, but one study did find acetone levels to be positively correlated with BHB levels in the blood[*].
#3: Urine Testing
This is the easiest way to measure your level of ketosis but not the most reliable.
Urine strips may be less accurate than blood testing, but they make up for it with ease of use. Just pee on the strips, note the color change, and find the corresponding ketosis value on the label.
According to the research, the best time to measure urinary ketones is early in the morning and after dinner[*].
Entering ketosis isn’t like cooking a turkey for four hours at a certain temperature. There are many more variables to account for how long to get into ketosis.
One person — an elite athlete, say — might be in full-fledged ketosis after a 12-hour overnight fast. Another person, however, might be low-carb for a full week before her test strips change colors.
Varying activity levels may explain some of these differences. Exercise helps dispose of excess blood sugar, which can accelerate the transition to ketosis. Ketosis, after all, is triggered by low blood sugar and insulin levels[*].
Eating and fasting schedules also matter. Intermittent fasting, for instance, can help put your body into fat-burning mode because fat is your body’s preferred long-term fuel source[*].
When you don’t eat for an extended period, you start oxidizing body fat for energy. And when you oxidize more fat, you make more ketones.
Other factors that affect time-to-ketosis include sleep, stress levels, age, body composition, and certain genetic variants affecting fat metabolism[*]. Some of these are within your control while others are not.
Yet the elephant in the room remains. The main reason people don’t enter ketosis more quickly is carbs.
The truth is, many people think they’re low-carb, but they’re not.
Hidden carbs are everywhere: snacks, sauces, soups, wraps, and so on. One or two slip-ups and you’ll steam past 20 grams daily carbs (a good keto limit) without even realizing it.
With that in mind, it’s time to review some practical tips to accelerate your keto metamorphosis.
Want to get into ketosis sooner than later? The best thing to do is to follow a clean, whole-food ketogenic diet.
Beyond that, here are five ways to support your transition to ketosis.
#1: Mind Your Carbs
Carb restriction is the key to ketosis[*]. Here’s why:
- Cutting carbs keeps blood sugar levels low
- Low blood sugar keeps insulin levels low
- Low insulin signals your cells to burn fat and make ketones
Athletes can probably go a bit higher carb and stay keto, but to play it safe keep carbohydrate intake around 20 grams per day.
For some people, keeping carbs under 20 grams per day is a cinch. But for others, it’s the single biggest obstacle to their ketogenic success.
Having a strategy can help. Track all the carbs with a keto macro calculator, and be sure to account for sneaky, hidden carbs. That honey mustard dressing, for instance, could be adding 15-20 grams carbs to your salad.
Be mindful of sauces, pastes, yogurts, and many other products you might not think are sweet, but contain added carbs or sugars. Added sugar makes food taste good, so food manufacturers put it everywhere!
Traveling and eating out are probably the hardest times to stay carb-conscious. The solution? Make special requests at restaurants — many are becoming more aware of dietary restrictions and are willing to make modifications.
#2: Increase Fat Intake
On the keto diet, you take all those calories that would have been carbs and you eat them as fat instead.
Don’t fear a high-fat diet. Fat helps you:
- Absorb fat-soluble vitamins like A, D, and K[*]
- Build your cell membranes
- Store stable energy as triglycerides
- Produce more ketones
- Curb your cravings by reducing hunger hormones[*]
You might be wondering, isn’t saturated fat bad for your heart?
The truth is, to enter ketosis, there’s no substitute for filling your plate with healthy fats. Olive oil, coconut oil, avocados, almonds, butter, lard, heavy cream, Greek yogurt, goat cheese, nut butter, fatty fish — the list is long and not very restrictive.
Be sure to check out this full list of keto-approved foods.
#3: Intermittent Fasting
When you don’t eat for a while, which energy source do you think your body turns to?
It’s not carbs. Glycogen stores (stored glucose) get depleted fairly quickly, especially if you’re active.
It’s not protein. You produce ketones during a fast, which prevents muscle protein breakdown[*].
That leaves fat. During a fast, you burn (or beta oxidize) fatty acids to meet your energy requirements.
Fast long enough and, regardless of prior carb intake, you will enter ketosis. But the more sustainable path to ketosis is to combine an intermittent fasting regimen with the keto diet.
Intermittent fasting (IF) just means taking breaks from food at regular intervals. You can intermittent fast for 12, 16, or 24 hours at a time, among other IF methods.
IF accelerates keto because it helps you fat-adapt. Your body starts running on fat stores, not sugar, making the transition to ketosis all the easier.
#4: Consume MCT Oil
Medium-chain triglyceride oil (MCT oil) is the perfect ketogenic food. When you eat this flavor-neutral oil, it travels straight to your liver for conversion to ketone bodies[*].
In one study, just 20 grams of MCTs boosted ketone levels in a sample of elderly adults[*]. Plus, their mental performance increased (compared to non-MCT controls) shortly following this meal.
If you’re just starting with MCT oil, go slowly. Start with one tablespoon and increase from there to avoid any digestive issues.
#5: Try Exogenous Ketones
You can consume ketones directly in the form of exogenous ketones.
Exogenous ketones are ketones that originate outside your body. Although they’re outsiders, these synthetic ketones are essentially the same as ketones inside your body.
Most exogenous ketones come in the form of BHB, your primary energy ketone. You’ll find these BHB products packaged as both ketone salts and ketone esters.
Ketone esters may be more potent than ketone salts, but the salts appear to last longer[*]. And for taste, most people prefer ketone salts.
Taking exogenous ketones isn’t a substitute for fat-adapting, but it does increase blood ketone levels. Researchers have shown that taking exogenous ketones:
- Enhances fat-burning during exercise[*]
- Increases mental performance (measured by mice navigating a maze)[*]
- May improve Alzheimer’s symptoms (in one human case study)[*]
- Reduces blood glucose levels[*]
Getting Into Ketosis: How Long?
To find ketones in your blood, breath, or urine, you may only need a day or two of keto dieting or intermittent fasting. How long to get into ketosis can vary from person to person, and full-on keto-adaptation can take two weeks or more.
To support ketosis, try intermittent fasting, MCT oil, and exogenous ketones. And remember the two primary keto commandments:
- Eat lots of healthy fats
- Cut carbs like it’s your job
Follow these tips, and you’ll be in ketosis before you know it.