Ketosis: what it is and how to tell if you're in it

Ketosis is the real goal of the ketogenic diet. You hear about it everywhere, but what exactly is it — and how do you know if you're truly in it? Let's explain it without the jargon.

What ketosis is

Normally the body uses glucose (from sugars and starches) as its main fuel. When carbs are scarce for a long time, the liver starts turning fats into ketones: an alternative energy source that fuels the body and the brain. This state is called ketosis.

In practice: in ketosis your body burns fat as fuel. That's why keto aims to keep carbs low (on the insulin/glucose mechanism, see this article).

The signs you might be in ketosis

Less hunger and fewer sugar cravings
More stable energy throughout the day
A metallic taste or slightly different breath (due to a ketone, acetone)
Greater mental clarity (after the adaptation phase)

These signs are indicative, but not precise. For certainty, you measure.

How to measure ketosis

There are three ways, from most to least precise:

Blood ketones — the most reliable method. With a ketone meter and a drop of blood you get your beta-hydroxybutyrate value (nutritional ketosis is generally considered to be between ~0.5 and 3.0 mmol/L).
Urine strips — cheap, useful at the start; they become less accurate once the body adapts.
Breath — breath acetone meters, convenient and reusable.

In addition, monitoring your blood sugar with a glucose meter helps you understand how foods affect your metabolic state.

Why there's no single carb threshold that works for everyone

Grams of carbs, on their own, don't confirm that someone is in ketosis. Whether — and how deeply — you're in ketosis can only be assessed by measuring ketones, taking into account the method and timing of the measurement.

A study that measured blood ketones in people with type 1 diabetes at different carb intakes found an exploratory inflection point below 30g/day, where ketones tended to rise more sharply — but at the same carb intake, different people had different values. That inflection point doesn't establish a general clinical threshold: it concerns a specific group, with food diaries covering just a few days, and participants who had chosen the restriction themselves.

What can affect your personal threshold, besides carbs:

Physical activity and energy availability: exercise, fasting and energy balance can change how ketones are produced and used.
Overall diet composition: it's not just carbs that matter; energy intake, protein and fat also shape the metabolic context.
Timing of measurement: values can change throughout the day and as your body adapts.
Individual characteristics: insulin sensitivity, medication, health conditions and other metabolic factors can change the response.

In the literature, ketogenic diets are often described as intakes below roughly 50g of carbs a day, sometimes lower. Definitions aren't uniform, and not every source calculates carbs the same way. On Deketox we show net carbs, expressed net of fiber, using the same method already used in our recipes.

For our sample weekly menu we chose to stay under 20g net carbs a day, to offer a conservative setup that also works for people following a stricter limit. It doesn't mean 20g is necessary or sufficient for everyone, nor that going over that amount automatically means leaving ketosis.

How long it takes to enter ketosis

Usually 2 to 4 days of very low carbs, but it depends on your metabolism, physical activity and how strict you are. To figure out what macro split to start from, use our keto macro calculator.

Sources

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