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.

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  • Abby

    My husband went keto for awhile and lost a fair amount of weight, but the second he transitioned into a more normal (but still much healthier than his prior habits) eating routine he gained it all back. He said he felt great but had way less stamina at the gym.

  • Hayley


  • Ruth

    I am a fan of ketogenic diet and also intermittent fasting!

  • CMA

    This is a great article, thanks for sharing! Here is another interesting perspective about a person who tried and failed the Keto Diet, but found success doing a different diet!

  • Alex S

    Thoughts about Bulletproof’s Brain Octane for the average woman???

    • Jeanie

      The Bulletproof stuff is all bs :p You can google about his scammy ways and make your own judgment though.

  • Jeanie

    I tried it. I eat gluten free already so it was easier for me. I only did it for a few weeks and was having a blast. I actually had fun and it was working really well for weight loss. I stopped craving sugar too. However, one day I broke out all over my back!!! I had big acne spots as well as rashes. I found out some people get a thing called Keto rash. I have a bad history of dealing with acne, so no way I was gonna spend time and energy figuring out how to stay with Keto and get rid of the rash problems. It’s a shame cause the diet was working so well otherwise.

  • 808kate

    We educate on the ketogenic diet where I work for kids with seizures when medication isn’t successful.. a typical day for them is something like: fried eggs with butter and heavy cream for breakfast, tuna salad with extra mayo and a bit of lettuce for lunch with a side of a few strawberries, snack of peanut butter, and for dinner more heavy cream, and some baked chicken breast with cheese. Sooo much fat. I couldn’t do it! / don’t ever want to

    • Adrianna

      There was a Radiolab podcast episode about this, where a father tried this out of desperation about 30 years ago

  • B4B

    I personally like a keto diet..carbs make me crash. But women indulging in IF beware, there are a few studies that show that IF can adversely affect glucose tolerance in non obese women specifically. Obviously there aren’t enough studies to unequivocally say this is the case, but it’s something to think about before starting IF.

  • Kristin

    <3 editors footnotes.

  • pamb

    Because I am Old, I remember my parents going on the Atkins Diet in the 70s. They had the pee strips and everything! My dad even made up a song about ketosis (only a few lines long, because what rhymes with ketosis?) to sing loudly as he tested his urine…

    • Hayley

      Oh my god you could almost PERFECTLY sub the word imitosis in Andrew Bird’s song “Imitosis” with ketosis and it WOULD BE SO CATCHY!

      • pamb

        Again, because I am Old, I don’t know who that is! Off to check… 😉

  • Shelby

    I know I’m late to the party here, but I had to chime in. While I appreciate the editor’s notes, this piece still doesn’t feel balanced. Anyone considering a ketogenic diet should dig into more research, specifically from peer reviewed, scientific journals. I see a lot of people on social media touting the benefits of this diet and various others. In an age where perceived “wellness” has become more important than scientific fact, it’s important to look at the motivations of who is sharing the information and whether there is any basis to their claim.

    • Jay

      Yeah… Keto seems to be the new frenzy… but I fully agree, it is – with you and with Mrs. Berzin – it is not something for everyone and it’s not something to do just so…

      Getting in a state of ketosis may really take some time – and it can actually be dangerous if you have certain conditions…

      For athletes it show very weird results which are not studied sufficiently, I’d say (and PN is going to agree…)

      So if anyone is really interested in this – or just moderately – or just trying to follow up with trends…

      Keto is super hard to follow (even though eggs and bacon might sound nice when you’re coming from any other kind of weird diet… just recall: Icecream remains off! And so does chocolate! – or even that peach?!) – personally I don’t even wanna try.

      It might have it’s place in treating certain conditions.

      But for the rest… to me it seems like just another big fat marketing thing…

      Oh, and a good source to educate yourself:

      (PN is pretty much the sanest approach to food out there anyways, though…)

  • Ellie

    I’m on this diet for seizures and lupus autoimmune and bc of it my seizures are almost GONE and I have very few autoimmune symptoms! It’s great for sick people. Got to kick the steroids and lost 60 pounds in 3 months because of it. So happy. Read books/consult with a good Dr who knows natural and conventional medicine first. 🙂

  • Lindsay

    I just want to add as a Physician Assistant that this diet can be extremely dangerous! It can cause permanent kidney damage and seizures if not done under medical supervision. Yes its been very effective for uncontrolled pediatric seizures, but those are patients with a serious medical condition with close monitoring. Diabetic Ketoacidosis is when patients with type 1 diabetes don’t have proper insulin. Advertising this as weight loss is misleading.

    Plus if you’re a healthy person, why would you want to be so restrictive with your diet and “force” your body and brain not to have the carbs it wants? We don’t feed our car anything other than gasoline so let’s be nice to our bodies and provide the energy it likes!