WTF is Ketosis and Why Are People Talking About it Again?

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“Ketosis” is suddenly (hyperbolically) everywhere. Ketosis surged in popularity alongside the Atkins Diet in the aughts, but it seems to have snuck back into the cultural lexicon. As reported in December, “ketogenic diet foods” was one of the top diet searches of 2016, perhaps as a result of people like Kim Kardashian and Gwyneth Paltrow publicly praising the benefits of low-carb diets in recent years. Ketosis is a little controversial, though — particularly because the research is mixed and still in its earlier stages. But what the hell is it? If you’re thinking of trying it out or just generally curious, Dr. Robin Berzin, Columbia-trained MD and founder of Parsley Health, weighs in below on what ketosis actually is and how to decide if a ketogenic diet is worth exploring.

What is ketosis?

Ketosis is a normal metabolic process that occurs when the body uses fat for energy instead of sugar. Typically, the body (specifically the brain) uses glucose (sugar) for energy. Entering into a state of ketosis where the body uses fat instead requires severely limiting carbohydrate consumption. You can do this by fasting or by following an extremely low-carb diet. In other words, you essentially force your body to utilize fat for fuel by depriving it of sugar. This type of diet is known as a ketogenic diet, and it typically includes getting around 75% of your calories from fat, 20% of them from protein and 5% from carbs.

What health benefits does ketosis potentially have?

The original medicinal use for a ketogenic diet was established in the 1920s for the treatment of pediatric epilepsy. Researchers found that a ketogenic diet dramatically helped to decrease the number of seizures in epileptic patients. Since then, the ketogenic diet has also shown to improve symptoms and cognitive function in individuals with both Alzheimer’s and Parkinson’s disease. Promising new research has also shown that following a ketogenic diet may help to kill cancer cells and reduce tumor size in addition to preventing the development of precancerous cells altogether.

Aside from the treatment of disease, the ketogenic diet is often used, quite simply, for weight loss. It’s shown to be mostly effective in this regard, especially in obese individuals. Some evidence also indicates improved moods are experienced by those following a ketogenic diet (Edit note: some find the extremely restrictive nature of the diet to do the opposite.) Biohacking enthusiasts are increasingly using ketosis on a regular basis to achieve target body fat percentage and achieve states of metal focus and clarity.

What are the signs of being in ketosis?

There are three ways in which ketosis can be detected in the body. The first is a blood test, the second is urine and the third is breath. When you have a large amount of ketones in your blood, your body eliminates them through both urine and breathing. Ketone urine test strips sold at most local pharmacies are probably the easiest way to identify if your body has entered into ketosis.

People in ketosis also often have a characteristic breath odor often called “fruity breath.” This is the result of the lungs releasing the built up ketone body byproducts which results in the sweet fruit-like odor. This way of assessing ketones is the most subjective.

Edit note: Research shows it can also cause things like dehydration, fatigue, headaches constipation and kidneys stones.

Should I try a ketogenic diet?

Getting your body into a state of ketosis is not something that happens overnight. It can take somewhere between one day and a full week on a very low-carb/high fat diet, usually kicked off by a period of fasting, before the body starts to utilize ketone bodies for energy.

At Parsley Health, we guide people through an individualized nutrition program and sometimes that includes short periods of ketosis. Most often we use this for people with issues like weight gain, fatigue, brain fog and cancer, along with other treatments as appropriate.

Since there is not enough research to determine the effects of following a ketogenic diet over the long-term, it’s hard to say if everyone should try it or not. For some people with cholesterol problems, a ketogenic diet can make them worse in the short term. (Longer term, these effects appear to reverse, but it’s advisable that you know what your cholesterol looks like before trying it.) Some also report that a ketogenic diet might reduce testosterone production and thyroid function.

If you have any chronic conditions, while you may benefit from a ketogenic diet, you should certainly talk to your doctor first. For most people at Parsley, we do not recommend doing a ketogenic diet long-term, but it can be an effective tool used short-term and periodically, if approached carefully and thoughtfully.

Please consult your doctor before trying a ketogenic diet.

Robin Berzin

Robin Berzin is the founder of Parsley Health, which combines nutrition prevention and wellness with cutting-edge medicine and testing from top doctors who help you live a healthier life. To learn more, visit You can also schedule a free consult call by visiting

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