Dear Mark: Ketosis

CarbsDear Mark,

What are ketones? How does ketosis play into the Primal Blueprint? Did our bodies evolve to run on ketones? If not, why do they exist?

Ketones, to put it briefly, are compounds created by the body when it burns fat stores for energy. When you consume a diet very low in carbohydrates, the body responds to the significantly lowered levels of blood sugar by flipping the switch to another power source. The body converts fatty acids in the liver to ketones. Ketones, then, become the main energy source as long as blood sugar levels remain low.

Recently, researchers have discovered more about the unique mechanisms behind this energy “switch.” It turns out a specific liver hormone, FGF21, is essential for the oxidation of the liver’s fatty acids. Furthermore, animals who were fed a ketogenic diet over time showed “increased expression of genes in fatty acid oxidation pathways and reduction in lipid synthesis pathways.” In other words, their bodies adapted metabolically and genetically to the diet.

Ketosis was crucial to our evolution. Given the relatively minor role of carbohydrate-rich foods (even the consumption of many tubers is thought to have come later with the advent of cooking practices), our bodies were fairly frequently operating in the arena of ketosis. Add to this the fasts and famines of primal living, and it’s clear that ketones served as an essential energy source.

The Primal Blueprint recommends “generally” about 100-150 grams of carbohydrates a day, but many who follow it or the related paleo principles choose diets that fall in the realm of 50-80 grams a day, a practice (along with IF) that spurs the body to turn on ketosis as needed. These practices encourage “upregulation” of the body’s fat-burning metabolic functioning and “down regulation” of fat storing systems. For those looking to lose fat, this becomes an extremely effective tool. On the other hand, after spending a few days or weeks in a predominantly ketosis mode, it may behoove you to do an occasional higher carb day (maybe 250-300 grams) to simply readjust insulin sensitivity. This is particularly appropriate if you have achieved an ideal body composition (lean body mass and body fat) and don’t need to lose more fat. An essential part of the Primal Blueprint includes both the fat-burning upregulation and the periodic honing of the body’s systems and adaptive responses.

Finally, ketogenic diets, which are generally lumped together by critics, have gotten a lot of bad press. While experts have generally recognized their effectiveness for weight loss, very low carb diets that result in ketosis (like the Atkins) have been criticized on health grounds. The problem with these criticisms? They’re based on diets that allow for 20 grams or less of carbohydrates a day. While I believe we are not meant to run primarily on carbohydrate energy, I do believe we depend on the nutrients offered by low carb vegetables and even some low glycemic fruits. A diet of 20 carbohydrate grams simply can’t allow for the plentiful intake of nutrient-rich vegetables.

When your carb intake is low enough, say 50-80 grams a day, ketosis kicks in when it needs to. Over time, this process becomes efficient as the body “unfolds” in its genetic expression. Yet this carb intake is high enough that you can freely include copious amounts of nutrient- (including potassium) rich vegetables to offer the body sufficient nutrition, fiber, and alkalizing minerals. At 100-150 grams a day, again all from just veggies and fruits, you probably won’t hit ketosis, but you also won’t prompt a rise in insulin or fat storage.

Thanks, as always, for your questions. Look for more on low carb living this week. In the meantime, keep the questions and suggestions coming!

insearchofbalance Flickr Photo (CC)

About the Author

Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.

If you'd like to add an avatar to all of your comments click here!

57 thoughts on “Dear Mark: Ketosis”

Leave a Reply

Your email address will not be published. Required fields are marked *

  1. Sounds like the ultimate “hybrid” fuel technology, doesn’t it?

    I hear and read lots of “expert” opinion that the brain needs a lot of glucose to operate properly, yet pediatric neurosurgeon Dr. Larry McCleary (& other neuro-scientists) indicate that the brain can use ketones for fuel, too. www dot drmccleary dot com

  2. Great post,
    I quite don’t get this “carb up day once in a while to readjust insulin sensitvity”. Sounds tempting for a low carber to be allowed to order a pizza w/ a beer every other week 🙂 but could you just elaborate more on what exactly do I expect of my pancreas to do? thanks in advance 🙂

  3. Hi.
    Like zbiggy, I’m interested in exactly what you mean by the “carb up day”. I am most definitely insulin resistant (since I was 9years old) and I have been low carbing since 2003. I went off-plan for about a year, gained some back, and am now on plan seriously for the duration. I tend to get cravings from eating starch/sugar so I don’t allow them at all. Do you mean “carb up” with more low glycemic veggies/fruits or actual starches/sugars?

  4. Hey, Mark. All this low-carb and fasting got me thinking: Is it possible to be a pro, or a semi-pro athlete and still run on 100-150g of carbs with a couple of fasts per week? I have done a lot of experiments on myself with switching from high carb to low-carb&high-fat but… I never ever managed to have a good workout followed by a normal recovery with fasting. When I say good workout, I mean 1.5 hours of wrestling or weightlifting or gymnastics. Ofcourse, I have to be partially recovered for the workout the next day. If I don’t eat anything 3 hours after my post-workout meal (25g of protein and 70g of carbs from dried berries or pure glucose) I’m a wreck the next day. If I don’t eat my breakfast, the same thing happens. I won’t even start about the days when I have two workouts.

    So… How about a little sport-tuned Paleo diet? (Does it then become the Zone diet?)

    P. S. Sorry about my English, I’m from Croatia.

  5. whole fruit and veg are nice and nutritious – and that’s why i eat them – but they are not unnecessary – organic outdoor naturally reared liver, eggs and whole dairy will provide almost all your mineral and vitamin needs in abundance, along with protein and fat. The only issue is vitamin c, and on a low carb diet you only need a fraction of the RDA. so a little fruit goes a long way


  6. markus,
    I think you are probably right about that, but hardly anyone eats liver anymore, let alone from animals naturally raised on pasture. Now that I have some non-factory farmed source of liver, I’m trying to cultivate an appreciation for it, abut it isn’t happening overnight and especially for beef liver, requires a lot of mustard or other distraction.

    I was very interested to learn how sugar and Vit C compete for uptake in the cell and that a high sugar/grain diet is probably what caused scurvy on the long distance European exploration ships, not so much lack of Vit C. Those crew sailors lived on a high glucose diet of hard tack (dried flat bread), molasses, jams, and only bits of dried meat/fish – non-perishables mainly and very little fresh food (I think the captain and officers had better fare). Eventually some provisions included barrels of sauerkraut, which would have displaced some of the high glucose foods as well as provided extra Vit C to compete for uptake. And of course limes were added to the British navy’s rations.

    1. Did you know that most pirates and private sailing vessels did NOT have limes? They didn’t need them. They carried animals on board and slaughtered them as needed in addition to catching fish. You only need citrus when you eat carbs, because carbs leech it.

      1. Also spleen has decent amounts of vitamin C. There are animal sources of vit C, and VLCer’s DRI is much lower than the average (or FDA) RDI

  7. Zoran,

    It’s probably impossible to compete as a pro athlete – or even a top age-grouper – on only 150 grams carbs a day…unless your events last less than 45 minutes and you train hard for less than 45 a day. I guess I will have to do a post just for the athletes who want to be “primal” but also want to train incessantly long and hard.

    Maya, zbiggy,

    I do mean to “carb up slightly” with some healthier choices, like yams, sweet potatoes, berries, fruits etc. Only to 250-300 grams total for that day and only once in a while (not the 1000 grams that some body-builder sites suggest for “mass”). It would mimic a day Grok found a stash of tubers or honey. That little added carb-up simply has your pancreas secreting a bit more insulin for that day, which is OK if you haven’t been secreting much for a few weeks. If you are coming off years of insulin insensitivity, it might make sense to stay “primal” for a few months before experimenting with a slightly higher carb day. OTOH, if you were to never “carb-up” you’d be fine – it’s just that we want to try to mimic the non-linear, feast-or-famine style of Grok in a more controlled fashion.

    1. I have heard quite the opposite regarding ketosis and high endurance athletics. It can be done.

  8. Dear Mark and friends,

    I’ve started going paleo Jen 2009, joyfully rediscovered my 6pack after years and felt better than ever 😀
    ..only to find that training brazilian jiujitsu 3 days/week + 2 sessions of weights + the occasional walk/sprints ate away some kgs of lean mass as well, making me gaunt!
    Guess I should have eaten more carbs..

    I’d love to know your suggestions for “intense trainees” like me and Zoran! Thanks again,


  9. Hey everyone. My girlfriend is a Type 1 diabetic and has often mentioned “going into keto(acido)sis” and “ketones”, referring to an abnormally high blood sugar level. Since ketones are produced in fasting, which implies low blood sugar, I’m seeing a possibility of contradiction in terms. (In other news, I’m trying to get her to go paleo. Health benefits, people!!)

    Does anyone have any experiences with Diabetes and info on this? Thanks!

    1. Only Type 1 diabetics can be in a state of ketosis and have high blood sugar which will lead to ketoacidosis.

      In normal humans, insulin will down regulate the production of ketones in proportion to the presence of sugar in the blood, preventing ketoacidosis.

      I hope that helps 4 months late.

      1. Ketoacidosis is not ketosis as low carbs refer to it. You can also go into it as a type 2 diabetic, but it happens when you become so insulin resistant that even your fat can’t take in sugar. Your body starts starving to death because it can no longer use carbs at all. Your fat starts breaking down and flooding the blood. You’re talking a difference of like a 5 point ketosis vs a 250 point … major different animals. Normal humans also go into ketosis at night when you haven’t eaten!

  10. Many of the complaints made about Atkins center around the extremely restrictive “induction” phase, a two-week period during which only 20 grams of carbohydrates are allowed. This is not, however, the basis of the entire diet – it is meant as a “detox” period to purge the body of carbohydrate dependence before gradually reintroducing healthy carbohydrates to the diet. The purpose of this is to determine an individual’s ability to deal with carbohydrates, as the number of grams one can consume while continuing to lose weight varies from individual to individual.

    1. Might I add, that during an extreme low carb phase, you begin to crave carbs no matter what kind. As you begin to reintroduce healthy carbs after this extremely low phase, these health carbs are much more pleasing than they would be if you were still used to having tons of non healthy carbs.

      to sum up, its not only physiological but also psychological.

  11. My dad told me today that ketosis can kill you, and once you’ve been in it too long, it’s hard to reverse. I find this very hard to believe…is their any legitimate proof of this? I personally thinking my parents are freaking because at 5’3 and 124lbs I am by far the skinniest person in our obese family. They don’t know what “healthy” looks like unless it’s looking like an elephant…no offense to elephants. So I’m trying to prove to them that what I’m doing is healthy and better for my overall health. It’s so hard. They always come up with something to try and refute the primal lifestyle.

    1. At 5’3″ 124lbs is perfectly healthy! Even your doctor will tell you that. What’s more important than weight is maintaining a healthy body fat percentage. If you are active with a good amount of muscle 124 will be lean but not gaunt. I’m 5’5″ and 137 and often called “curvy” even at a weight closer to yours. Yet people who are overweight say I am too skinny and think I am unhealthy even though I am probably way healthier than them. Don’t let your family’s fear of change and ignorance get you off track!

    2. Ketosis is just a normal body state, its ketoacidosis thats problematic, which occurs when theres an insulin deficiency, its basically uncontrolled ketosis leading to high blood sugar, dehydration, and all kinds of problems. I know about this because I used to be a vegan because it was the “heart healthy” thing to do, or so my doctors told me. Ketoacidosis happened to me on a very high carb diet though, so it’s quite a bit different from ketosis…

  12. I think I may be in the midst of ketosis. As Mark indicated, I didn’t experience ketosis, even with a pure paleo diet. I think this is because I was still getting a fair amount of carbs in a day, probably at least 100 grams.

    Lately, I’ve been experimenting with IF. I use a combination of the Fast Five plan and some recommendations in the book “Eat Stop Eat” by Brad Pilon. (Pilon recommends not eating for two non-consecutive 24 hour periods a week).

    Now that I’ve been fasting, my hands and feet have become extremely cold. I also notice far more muscular definition, presumably from fat loss. (FYI, I’ve been doing resistance training lately, as well.)

    In addition to the cold feet and hands, I’m noticing far more energy and alertness on a routine basis. I guess this makes sense from an evolutionary perspective. Our early ancestors were probably at their most alert and energetic when they were in a “fasted” state and needed extra energy to hunt down their next meal. They were probably relaxed, even drowsy, after polishing off a big meal.

  13. Please note that the Atkins diet 20 grams of carbs is what Atkins calls NET or usable carbs. Fiber is subtracted and/or not counted.
    For example one of my days would have 70 grams carbs but only 30 grams net carbs.
    The 20 Net carbs is only for the “induction” period of 2 weeks and some very obese people stay there longer..but in reality their carbs are closer to 30-35.
    Atkins is designed for you to learn your carb tolerance with gradual increases in levels.
    Please be sure you understand something before you knock it!

  14. I know a guy with a three year old daughter who is on a ketogenic diet to treat her severe epilepsy. It seems to work extremely well as she rarely has seizures anymore, so maybe glucose isn’t so good for the brain.

    Apparently this was a much more common treatment before more effective drugs were developed.

    1. epilepsy is a disease so i dont believe it should be used to show that glucose may not be good for the brain. However, fasting many many years ago used to be the main tool to help with epilepsy. Then the ketogenic diet was “invented” to mimic fasting while being able to keep the ketogenic environment that helped to reduce epileptic seizures

      1. ASD – Autism spectrum disorder is not a disease, yet the same neurological efficiencies seem to apply to this (as it does to epilepsy).

  15. I’ve been transitioning over to paleo for about two months. For the last month I’ve been tracking my food and today I took my measurements. Almost no change! I don’t think I’ve lost any weight and my clothes all fit about the same. I don’t consume ANY grains. I’ve reduced even my fruit intake. When I do have it, it’s between 5-10 berries, maybe half a banana. Plenty of eggs, bacon, grass-fed beef (when I buy it for my house), vegetables, some nuts. No veggie oils. I’m guessing that I’ve increased my dairy intake too much as a result of cutting out so many comfort foods, and I still drink (probably too much!) but have cut it down to wine, tequila and bourbon… very few mixed drinks. I have stevia in my coffee or tea in the morning with full fat cream.

    What I’m trying to figure out is what to pare down to start burning fat. Has anyone else had problems? I see lots of success stories, but I haven’t had mine yet.

    1. Hi Ruby,
      I think I’ve gotten in to a similar habit: Upping my dairy to replace the greater evils I used to eat. You said you’ve been tracking what you’re eating, have you been looking at total fat and total protein intake each day?
      A few months into a primal diet, and I’ve also not been losing excess body fat as I had expected, even with starting CrossFit two months ago! But I came to realize that my protein intake was pretty low and my fat intake was high (relative to the protein).
      I’ve been meaning to re-read this post: and from there get a better picture of how much protein I should be getting, and then adjust my carb and fat intake from there. Give that a shot maybe? I hope you find something that works for you!
      Also, might be helpful in keeping track of everything.

    2. i know this was a few months back, but i got this from the atkins web site. not primal, but low carb anyway:

      Can I drink Alcohol while on the Atkins Diet?
      When you consume Alcohol, it is the first fuel to burn. While that’s going on, your body will not burn fat. While this does not stop weight loss, it will postpones it until the alcohol has been used up. If you must drink alcohol, straight liquor such as scotch, rye, vodka, and gin would be the best choices as long as the mixer contains no sugar. If you have added alcohol to your diet and suddenly stop losing, give it up.

  16. I for one would love to estimate the amount of carbs I am ingesting daily. As I am having no cereals and no sugar, most of it must be from fruits… can anyone tell me how to do this, or point me in the right direction? Thanks!

    1. I recommend using It’s a free site that features, among other things, a nutrition tracker with thousands of foods pre-loaded. I haven’t met a whole or natural food yet that isn’t in it. They’ll try to set you up on a nutrition plan with goals and all, and you might have to set up a profile to get to the main part, but once you’re there you can use their nutrition tracker and ignore their “goal ranges”.

      I’ve been using the site for a couple of years, and even though I’ve just switched to primal-eating, I’m planning to keep keeping track for a while, to get an idea of how many carbs and how much protein and fat I have going on.

  17. What about the Japanese, Vietnamese and Burmese that eat a lot of white rice? Are their bodies in ketosis or are they burning fat without ketosis? The truth is that they are still very slim even if they do eat a lot of white rice.

    1. I have exactly the same question. I live in Singapore and everyday I see all these slim, slender people tuck into rice and noodles at the food courts…almost nobody cooks at home and most people eat at food courts and hawker centres. They eat a lot of rice/noodles along with lots of meat and seafood and some veggies. How do they stay so slim? They have super flat bellies!

        1. Hi Rama and Peter,
          I am from Singapore too! Looking for like-minded Groks to maneuver this new life-style I am trying to embrace. Any tips will be welcome!

      1. I think it has something to do with how much walking and labour they do daily. Even now, Singaporeans are starting to get fat as we start becoming more modern. I got one obese person and two severely overweight people in my family. When Singapore first became a nation, there were fat people, but very few, and there was white rice too.

    2. Asians generally have a lot more coies of the AMY1 gene that controls how much amylase you can make and therefore how well you use carbs. It isn’t and can’t be the only factor because breaking down a lot of carb is not a solution all by itself. There’s the problem of glycemic index. But it shows that genetic differences may be in play. Also note that if you tried the Macrobiotic diet like I did in the 1980-90s, and read the old Japanese classics, they were advice on how to stay healthy in the “new diet” of rice and veggies and reduced meat and fish. Interestingly, the low carb Japanese on Okinawa are the longest lived. Although maybe the Hokkaido Ainu are neing ignored once more. Sorry, idk about Singapore.

    3. As someone who relies on on nutritional ketosis or whatever you call it today, to keep neurological disease down, let me chime in. I was delighted by the Paleo/Primal movement making high quality meat visible and available, but as NK is still the red headed stepchild of everyone except French Chefs, (if you stay away from the dessert), we still need a movement for brain and fat to be available in places other than asian or ethnic markets. That said, there are three metabolic cycles I am aware of, glycolysis, beta oxidation and oxidative phosphorilation. If you take the time to understand them, then you will see why you get an antiaging effect from ketosis and why it is a medical diet that stops diseases. Basically it chokes off metabolic free radicals. The debate about whether it is safe effective or any good, has raged since at least around 1919, when the arctic ethnologist Stefansson published his work and then proved his all meat and high fat diet with no vegetables and at the time.. all game and grass fed animals, was complete and adequate for a very active outdoor lifestyle. Phinney and Volek wrote one current book on this subject. For a more neurology aspect look for Kossoff and Freeman. As for me I would be on 7 more meds if the keto diet had not come my way.

  18. I’m a college student and taking an anatomy and physiology course. In my lab book, ketosis is defined as a condition when ketone bodies are found in the urine when cells do not have enough glucose to breakdown fatty acids. How does this fit in?

    1. Ketones found in urine are acetoacetate, which many low-carb dieters use urine dipsticks to check for ketosis… there are also beta-hydroxybutyric acid ketones which are found in the blood.

      To awnser your question, Ketones go out and breakdown fat cells into fatty acids which are then used for energy.

  19. I find that I generally run better on the lower carb spectrum with a little MCT oil to kick in the ketones.

  20. From above, Mark Says:
    “When you consume a diet very low in carbohydrates, the body responds to the significantly lowered levels of blood sugar by flipping the switch to another power source.”
    Here’s my problem. I’ve been primal for 4 months. I don’t eat any carbs except for what’s in veggies. And my blood sugar doesn’t drop! I’ve been type II diabetic for about 4 years. I take a glucose pill (glipizide). I’ve been experiencing “dawn phenomenon” which means my liver makes glucose while I’m sleeping so my blood sugar is actually higher than when I went to bed! I have to take the glucose pill to lower my blood sugar. The pill tells the pancreas to create more insulin. Now I’ve got more insulin in me, so I go in to fat storage mode! How can the liver keep making so much glucose?

  21. Ketosis diet counts NET carbs (total carbs – dietary fibers)! You can eat plenty of vegetables and be below 20g net carbs because most of those carbs are from dietary fibers!

  22. This is a great article! I could never seem to stick to Atkins on the “induction” phase because staying under 20 gms of carbs is simply not comfortable for mw. So this time around I started on a low carb plan with about 40 gms a day which allows a small organic apple, some sugar fee yogurt, and some nuts. But I didn’t ketosis was possible at this higher level. Now I LOVE my food plan and I am happy that it is still low carb and possibly ketogenic when needed.