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What is ketosis?

Ketosis is a metabolic state of the body in which there are elevated levels of ketones and keto acids due to insufficient amounts of glucose for the body to use as fuel. The body can use ketones and keto acids as an alternative energy source. 

How long does it take to get into ketosis?

Ketosis is a metabolic state in which the body begins to break down fat to form molecules known as ketones to but used as fuel in the absence of sufficient glucose. It usually takes 2 to 4 days of very low carbohydrate consumption (usually less than 50 grams per day) to enter a ketosis state, although this time may take longer for some individuals if they are consuming too many carbohydrates or protein and not enough fat. Other factors such as stress, sleep, and exercise may also affect how long it takes an individual to enter ketosis. 

A state of ketosis is usually identified by symptoms such as headaches, fatigue, nausea, bad breath (“keto breath”), and increased thirst. Ketosis may also be measured by urine, breath, or blood tests. 

Blood ketone levels above 0.5 mmol indicate the body is in a state of ketosis while ketone levels of 1.5-3.0 mmol are considered to be “maintaining ketosis”. 

What are symptoms of ketosis?

A state of ketosis is usually identified by symptoms such as headaches, fatigue, nausea, bad breath (“keto breath”), and increased thirst. Ketosis may also be measured by urine, breath, or blood tests. These symptoms are commonly referred to as the “keto flu”. Other symptoms of reaching ketosis include short term fatigue, loss of appetite or decreased appetite, increased focus, and weight loss. 

Blood ketone levels above 0.5 mmol indicate the body is in a state of ketosis while ketone levels of 1.5-3.0 mmol are considered to be “maintaining ketosis”. 

How to get into ketosis

It generally takes a person 2 to 4 days of following a very low-carbohydrate diet to enter the ketosis state. 

In order to transition into this metabolic state it is suggested that a person eats no more than 20 to 50 grams of carbohydrates per day and increases intake of heart healthy and high-quality fats to at least 70% to 80% of total daily calories. It is also important to limit protein intake to 20% or less of daily calories since protein metabolism may interfere with ketone production. 

Intermittent fasting, short-term fasting, and exercise may also help a person enter ketosis sooner since these techniques help to deplete the body’s glycogen stores and increase ketone production.

Learn more about Ketosis:

Photo of Kristin Ricklefs-Johnson

Medically reviewed by:

Kristin Ricklefs-Johnson, Ph.D., RD

Kristin is an RDN who also earned her Ph.D. in Nutrition from Arizona State University with an emphasis on insulin resistance, lipid metabolism disorders, and obesity. She completed her post-doctoral fellowship at Mayo Clinic where she focused on nutrition-related proteomic and metabolic research. Her interests include understanding the exact mechanism of action of various genetic variations underlying individual predispositions to nutrition-related health outcomes. Her goal is to help all individuals prevent chronic diseases and achieve long, healthy lives through eating well.

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