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How To Tell If You're In Ketosis – The 9 Main Signs

Published: 13th May 2018. Last updated: 21th July 2019.

Shaun Ward MSc ANutr

Staff Writer


Ketosis is a metabolic state used to describe when the body switches its main energy source from glucose to ketone bodies.

For ketosis to occur, the body must be metabolizing fat at a high enough rate and converting enough fatty acids into ketones.

The liver produces ketone bodies from fatty acids during periods of fasting or severely carbohydrate restrictive diets. They can be viewed as a backup fuel supply that were historically needed for survival when food availability was scarce.

Although it is normal for a small amount of ketones to be present in all humans, ketosis is only achieved when serum concentrations of ketone bodies reach 0.5mM.

In practice, a state of ketosis is only found when daily carbohydrate intakes drop below ~50 grams per day, as a higher carbohydrate intake will likely provide enough glucose to avoid the need for ketosis to occur.

Ketosis gained a lot of popularity due to the scientific evidence started to note the issues with metabolizing large amounts of refined sugars and fructose, which are both associated with a wide range of metabolic diseases.

Some data, although questionable, has even suggested carbohydrate restriction is the single most effective intervention for reducing all features of metabolic syndrome [1].

Despite people often assuming they are in ketosis when they start on a low-carbohydrate diet, this does not automatically mean ketosis is physiologically apparent.

To help, here are some easy signs to help people know whether they are in a ketogenic state (keep in mind they are not always positive signs!):

1. You'll Have Bad Breath

This is caused by elevated ketone levels and is commonly known as "keto breath".

The specific culprit is acetone, a ketone that exits the body in your urine and breath.

Ketogenic dieters should brush their teeth multiple times per day to solve this issue, as well as ensure that they're scraping their tongue to remove surface level particles.

2. You'll Find You're Not As Hungry As Normal

Increased protein intake will increase satiation and alter the levels of hunger hormones such as ghrelin.

3. You May Find You Experience Higher Energy Levels

It can take a few days or weeks for a change to be noticed. It is still debated where ketogenic diets improve or worsen mental clarity and brain function, but what is continuously noted is that a noticeable change will occur.

4. Initial Fatigue

Whether someone ends up responding well or poorly to ketogenesis, nearly all users report an initial drop in energy levels.

This is due to a lack of available glucose while the body is upregulating its ability to utilize fat and ketones as an alternative fuel source.

5. Decreased Endurance Performance

As endurance heavily relies on the availability of stored carbohydrates in the muscle (glycogen), a ketogenic diet will cause athletes to fatigue quicker.

6. Digestive Issues

Before switching to a ketogenic diet, most people’s gut microbiome will be created to mainly digest starches and sugars. Switching to more fat-based foods may cause initial digestive issues such as constipation and diarrhea until there are alterations in gut bacteria.

7. Insomnia & Jittery Sleep

Quickly switching from a high carbohydrate diet to ketosis is linked with insomnia during the night. Additionally, if you're also sticking to a caloric deficit while following the keto diet, feelings of hunger could further contribute to the inability to sleep.

8. Increased Blood Ketones

If people want to be more specific, the most accurate method of measuring ketosis is to measure blood ketone levels using a specialized meter. Nutritional ketosis is defined as blood ketones ranging from 0.5-3.0 mmol/L. For this method, test kits need to be purchased online which average around ~$50 and require a finger prick.

9. Increased Breath Ketones

This is the same concept as measuring blood ketones but instead measures acetone in the breath via a breath analyzer. However, it is less accurate than a blood monitor.

The Main Benefits Of Ketosis

Below is a list of every potential benefit that's backed by credible scientific research:

It Can Help Make Losing Weight Easier

For most people, being in a state of ketosis will result in some amount of weight loss [2].

Most scientific researchers agree that the weight loss during ketosis is a product of severely restricting 1 of the 3 macronutrients, and thus decreasing energy intake, coupled with enhanced feelings of satiety stemming from the high protein intake which alter ‘hunger hormones’ such as ghrelin [3].

Other studies suggest a more unique metabolic effect of ketosis, although none of these theories have been confirmed.

Some data suggests that ketosis may potentially slightly raise levels of energy expenditure [4], however not to a significant enough extent for this to be a major reason why ketosis causes weight loss.

Animal studies also indicate that ketosis may increase the expression of genes involved in fatty acid oxidation, and reduced the expression of genes involved in fat synthesis [5], however this may not be the case in humans.

In reality, although some short-term studies how ketosis causes more weight loss compared to standard weight loss diets [6], no significant differences are seen in the long-term (1+ years) [7]. Greater initial decreases in weight during ketosis are likely just a result of a reduction in water weight as opposed to fat mass.

However, being in a state of ketosis may facilitate greater weight loss for ‘carbohydrate-sensitive’ individuals who do not have the appropriate insulin functioning to deal with high carbohydrate and glucose intakes [8].

It May Help Prevent Epileptic Seizures

Inducing a state of ketosis has been an effective non-pharmacologic treatment for epilepsy since the 1920s.

It has shown to decrease seizure frequency by ~50% in selected groups of patients and even has a prolonged beneficial effect after its discontinuation [9] [10].

Some proposed mechanisms for the anticonvulsive effects of ketosis are positive changes to brain energy metabolism, brain cell properties, and improvements in neurotransmitter function [11] [12] [13].

Investigators have also proposed that ketosis can modulate the generation of mitochondria in the brain, which may play a neuroprotective role and control cell death [14].

The potential increases in brain mitochondria may also sustain energy production and increase an individual’s resistance to metabolic or physiological stress and therefore elevate one’s seizure threshold [15].


Ketosis is a metabolic state used to describe when the body switches its main energy source from glucose to ketone bodies.

A state of ketosis may be beneficial for those aiming to lose weight, regain health, and prevent epileptic seizures.

Signs that someone is in ketosis are vast, including; bad breath, suppressed hunger, fatigue, decreased endurance performance, digestive issues, insomnia, or via measuring on a blood or breath ketone monitor.

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