Marks Daily Apple
Serving up health and fitness insights (daily, of course) with a side of irreverence.
19 May

A Metabolic Paradigm Shift, or Why Fat is the Preferred Fuel for Human Metabolism

There’s a good reason so many people (mostly the sugar-burners, whose disparate group includes fruitarians, veg*ans, HEDers, body-builders, most MDs, the USDA and virtually every RD program in the country) can’t seem to grasp why a lower carb, Primal approach to eating is a better choice for health and fitness: their fundamental paradigm – the core theory that underpins everything else in that belief system – is flawed. They remain slaves to the antiquated notion that glucose is the king of fuels, so they live their lives in a fear of running low. The truth is, fat is the preferred fuel of human metabolism and has been for most of human evolution. Under normal human circumstances, we actually require only minimal amounts of glucose, most or all of which can be supplied by the liver as needed on a daily basis. The simple SAD fact that carbs/glucose are so readily available and cheap today doesn’t mean that we should depend on them as a primary source of fuel or revere them so highly. In fact, it is this blind allegiance to the “Carb Paradigm” that has driven so many of us to experience the vast array of metabolic problems that threaten to overwhelm our health care system.

It boggles my mind that such a large segment of the so-called health and fitness community would continue to defend high carbohydrate diets with such tenacity. It should all be very obvious by now. The studies keep piling up indicating that carbohydrate intake is the major variable in determining body composition and that excess glucose from carbohydrate intake (especially from processed grains and sugars) is the primary culprit in obesity and in many disease processes. It follows logically that if you can limit carb intake to a range of which is absolutely necessary (and even up to 50 grams a day over) and make the difference up with tasty fats and protein, you can literally reprogram your genes back to the evolutionary-based factory setting you had at birth – the setting that offered you the opportunity to start life as a truly efficient fat-burning organism and to continue to do so for the rest of your life as long as you send the right signals to your genes. Becoming an efficient fat-burner is the major premise of the Primal Blueprint eating and exercise strategies.

But logic doesn’t rule when you are stuck in the Carb Paradigm, so I still see some misguided bloggers decrying the Primal Blueprint eating strategy as potentially harmful for its relatively low carb intake or stating that my advice to “generally keep carbs under 150 grams a day unless you’re an athlete” is ridiculous. How many more times do I have to overhear a trainer advising a still-portly client to “eat 5 or 6 small meals throughout the day, always with some carbs, so you keep your blood sugar up and don’t go into starvation mode.”? It’s time to stop this nonsense and reframe the current views of human metabolism to accurately reflect the two and a half million years of evolution that shaped the current human genome – a perfect DNA recipe that fully expects us from birth to function largely on fats.

It’s time for a Metabolic Paradigm Shift within the health and fitness world.

The Faulty Carb Paradigm “Logic” Goes Something Like This

The basic underlying assumption is that glucose is the preferred fuel of most cells; BUT, because we can’t store very much glucose (as glycogen in liver and muscles), we need to provide a continuous source of glucose in the form of exogenous carbohydrate (high carb meals) to keep the brain, blood, and certain organs humming along and the muscles primed for activity. AND, if we don’t feed ourselves enough carbohydrate every few hours, our blood sugar will drop and we’ll go into “starvation mode” and cannibalize our precious muscle tissue. AND any lack of regular glucose refilling (i.e. skipping a meal or fasting) will cause cortisol to rise, which will have additional deleterious effects. FURTHERMORE, an excess of glucose in the bloodstream is known to raise insulin and will predispose excess calories (from all sources) to be stored as fat. THEREFORE, we should also be doing a lot of moderate-to-heavy cardio or lifting activity most days to burn off this excess stored body fat. HOWEVER, if we want to be ready and able to exercise frequently and strenuously to burn off our stored fat, we need to eat lots of complex carbohydrates between workouts to refill our glycogen stores. And ULTIMATELY, the only way to lose weight is to restrict calories (calories in<calories out), BUT if you’re working out regularly, it’s almost impossible to maintain a calorie-restricted regimen and still be able to work out hard enough to burn appreciable calories. Sheesh.

Sure, there are exceptions, like the driven and genetically gifted types, who can train long hours, refuel on carbs and not add much body fat (hey, I was one). But unless you love to work out incessantly and have really lucky familial genes, the Carb Paradigm is an unsustainable and ridiculous literal and figurative treadmill, a self-fulfilling prophecy for most people who tend to gain weight steadily and insidiously over the years and wonder why. If you are one of the 60+% of the American population who is overweight, the above scenario plays itself out because you have spent your life programming your genes in the direction of being an effective sugar burner and, as a result, have become dependent on a fresh supply of sugar (carbs) every few hours. Naturally, in the presence of all that glucose, and provided you actually do some exercise, your genes will eventually get the signals to up-regulate the enzyme systems, pathways and receptors involved in sugar-burning and fat storage and they’ll down-regulate all those involved in accessing and burning fat for energy. Of course, that doesn’t make it right, but it sure makes it appear as if glucose is king. What makes it worse, if you don’t exercise, you head down the path to insulin resistance and/or obesity.

The Problem: The Basic Assumption of the Carb Paradigm is Wrong

Glucose is not the preferred fuel of muscle cells under normal human resting metabolic conditions or even under most normal human movement patterns (exercise). Fat is. Sure, given an unlimited supply of glucose and regular refilling of glycogen stores, skeletal muscle will burn through it during exercise the same way a fire burns through kindling when that’s all you have to offer. The body can shift carbohydrate oxidation to keep up with intake. But skeletal muscle can burn fat with great efficiency (and far less oxidative fallout) at relatively high outputs for very long bouts. Cardiac muscle actually prefers ketones, and the brain can run just fine (maybe even optimally) on a blend of ketones and minimal glucose.  Our survival as a species has depended on these evolutionary adaptations away from glucose dependency. Entire civilizations have existed for ages on what is practically a zero-carb diet. Think about this: there is actually no requirement for any “essential dietary carbohydrates” in human nutrition. It’s possible to live a very long and healthy life never consuming much – if any – in the way of carbs, provided you get adequate dietary protein and fat. The same can’t be said for going too long without protein or fat. Cut too far back on either of those macronutrients and you will eventually get sick and die.

The Evolutionary Model

Fat and protein were the dominant macronutrients (when food was even available) over the majority of our two-and-a-half million years as evolving humans. The lack of regular access to food and a scarcity of carbohydrates for much of this time necessitated that we adapt efficient pathways to readily store and access body fat for energy if we were to survive day-to-day and generation-to-generation. Our movement patterns were such that we never required large amounts of glucose or that we needed to store very much glycogen. It was predominantly fats, ketones and the minimal infusion of glucose via gluconeogenesis that got us here. Dietary carbs were insignificant. In fact, when you consider how ridiculously small the body’s glycogen reservoirs are, you understand that it would have been impossible for us to survive as a species if glucose were truly the “preferred” fuel. The liver, the main back-up glycogen/glucose storage facility for the brain and other glucose-burning organs, can only store about 100 grams of glycogen. Less than a day’s worth. Your muscles can only hold another 350-500 grams, barely enough to run for 90 minutes at a reasonable clip, and that glycogen isn’t even available to provide fuel for the brain. Meanwhile, we have a virtually unlimited storage capacity for fat (like 100,000 grams or close to a million calories on some people). The reason glycogen storage wasn’t necessary is because, between our copious fat storage capability, easy access to fats as fuel, gluconeogenesis and ketones, we just didn’t need much. Evolution tends not to reward structures or functions that take up unnecessary space or waste energy.

So How Much Glucose Do You Really Need?

Much less than most people assume. At any one time, the total amount of glucose dissolved in the bloodstream of a healthy non-diabetic is equivalent to only a teaspoon (maybe 5 grams). Much more than that is toxic; much less than that and you pass out. That’s not much range for a so-called “preferred” fuel, is it? Several studies have shown that under normal low MET conditions (at rest or low-to mid- levels of activity such as walking and easy work) the body only needs about 5 grams of glucose an hour. And that’s for people who aren’t yet fat-adapted or keto-adapted. The brain is the major consumer of glucose, needing maybe 120 grams a day in people who aren’t yet on a low carb eating program. Low carb eating reduces the brain’s glucose requirements considerably, and those who are very low carb (VLC) and keto-adapted may only require about 30 grams of glucose per day to fuel the brain (and little-to-none to fuel the muscles at <75% max efforts). Twenty of those grams can come from glycerol (a byproduct of fat metabolism) and the balance from gluconeogenesis in the liver (which can actually make up to a whopping 150 grams a day if you haven’t metabolically damaged it with NAFLD through fructose overdosing). Bottom line, unless you are a physical laborer or are training (exercising) hard on a daily basis, once you become fat-adapted, you probably don’t ever need to consume more than 150 grams of dietary carbs – and you can probably thrive on far less. Many PBers do very well (including working out) on 30-70 grams a day.

The Fat Paradigm

The Fat Paradigm, under which the human species has thrived quite effectively for two and a half million years, recognizes that human metabolism is pre-programmed by evolution to be primarily fat-based (the real preferred fuel). In other words, our genes expect us to function optimally when we consume fats and can easily access our stored fat. The Fat Paradigm acknowledges that the body is able to manufacture adequate glucose as needed. It acknowledges that most typical human movement patterns can be fueled almost entirely by fats and/or ketones (PDF) if need be, but can draw on glycogen when energy bursts are required (and which can then be replaced over time). It acknowledges that fat (and cholesterol) are not the proximate cause of heart disease. It acknowledges that fat cells are designed to release stored fatty acids as required, especially during times of scarcity or fasting. It allows for intermittent fasting as a means of accelerating fat loss without sacrificing muscle tissue. It increases insulin sensitivity, modulates energy and mood swings, and allows for a normal and healthy drop in hunger and cravings. There is a downside, however: you can’t train long and hard day-in and day-out in the fat paradigm.

Now then, having explained all this, please understand that I am not carb phobic. I actually permit more carbs in the Primal Blueprint than many other low carb eating strategies. I prefer to view carbs as the “elective” macronutrient, as a tool to use to manipulate your glycogen levels as needed. Low carb isn’t even the main objective of eating in the PB: eliminating grains, sugars and seed oils are the primary objective. Of course, when you get rid of that crap and naturally limit your carb intake to veggies, root tubers and a few fruits, you almost invariably decrease carbs to under 150 grams a day. And that emulates our ancestral dietary intake.

I came up with a simple Carbohydrate Curve a few years ago that offers a pretty concise picture of where most people ought to fall if they are seeking optimum health and energy, depending on their size, weight, sex, age, goals, etc. Now, many hundreds of thousands of user experiences later, I am finding that the Curve is pretty much spot on for a large segment of the population.

When I say generally that a chronic intake of over 150 grams of carbs can lead to insidious weight gain over a lifetime, I am factoring in the concept that many people are at the effect of a familial genetic predisposition to storing fat easily under the carb paradigm (the 60+% overweight). I am also factoring in the drop in metabolism that happens naturally with age, as well as the fact that PBers don’t NEED to purge and refill glycogen stores every day via exercise. Yes, there are some people (a small percentage of outliers) who might maintain pretty decent body composition at up to 300 grams a day on little exercise. I would bet that they also are selective about the carb sources and do a better job of controlling overall calories, so there’s little excess to store. For most of the population, that 150 mark remains a good average level for maintaining ideal body composition.

Well, that was a lot to digest today. You see where I’m going with this. I need your help in showing the health community that their basic assumptions are wrong and that they need to make a Metabolic Paradigm Shift. I’m sure there will be lots of specific questions, so bring  ‘em on and I’ll do a follow up post in a week or two.

You want comments? We got comments:

Imagine you’re George Clooney. Take a moment to admire your grooming and wit. Okay, now imagine someone walks up to you and asks, “What’s your name?” You say, “I’m George Clooney.” Or maybe you say, “I’m the Clooninator!” You don’t say “I’m George of George Clooney Sells Movies Blog” and you certainly don’t say, “I’m Clooney Weight Loss Plan”. So while spam is technically meat, it ain’t anywhere near Primal. Please nickname yourself something your friends would call you.

  1. Mark,

    I thoroughly enjoyed this post as it contradicts nearly everything my nutrition professor lectured about in college last semester. I do have one question though that is foggy to me. Generally, health advice often states that when the body does receive enough carbohydrates for energy, it turns to the protein in muscles first, as opposed to fat. Why is this used as an answer, and is there any evidence to support this statement?


    Andrew wrote on May 19th, 2011
    • It may contradict what your prof was emphasizing, but if the course taught any science, you should still have gotten this same info. That was always my experience, that it was there all along, just ignored.

      Fat is what your body will burn after running out of glucose, such as in longer moderate exercise.

      Real Food RD wrote on May 19th, 2011
    • Andrew, your prof is mostly right. If you live in the Carb Paradigm ,where all your energy systems crave glucose and can’t access or easily burn fat, then, yes, that’s exactly what happens: you run out of glucose and the body turns to protein (usually in muscle) to make more glucose. It’s why fasting is not as effective for sugar-burners.

      In the Fat Paradigm, once you have become fat adapted (up-regulated enzyme system to increase beta oxidation of fats and down-regulated glucose oxidation mechanisms), your body will look to fat stores for energy instead of muscle. No problem.

      Mark Sisson wrote on May 19th, 2011
      • The main reason is that fatty acids can’t cross the blood-brain barrier, so the body needs to either make glucose from protein to feed the brain, or start making ketone bodies.

        Using ketones is rather inefficient, which is why this pathway only happens after a few days of starvation (or during hypoglycemic shock when a diabetic injects too much insulin).

        Tim wrote on May 19th, 2011
        • “…only happens after a few days of starvation (or during hypoglycemic shock when a diabetic injects too much insulin)…”

          …or when I eat my normal diet.

          Also, please Google “Fatty Acid Transport Through the Blood‐Brain Barrier”. Some of the shorter-chain fatty acids are transported and metabolized.

          Ed wrote on May 20th, 2011
      • Ahh, I see the difference. Much appreciated!

        Andrew wrote on May 19th, 2011
  2. Great article! Thanks! Also, just wanted to say thanks for writing the book – I just finished it and it was great! I learned so much! Thanks!!!

    Diana wrote on May 19th, 2011
  3. Mark, you’re on FIRE! Love it!

    I know youse a busy man, but I have a question I’m not seeing an answer to yet, and maybe some kindly comment readers will know as well.

    So those “lucky” ones who don’t get overweight eating the SAD, are they also susceptible to the other health ramifications or are they somehow immune to those to? Is it the body’s response to the SAD that begins the cascade of other health problems and if you don’t have that response, then you’re in the clear?

    Just curious since many of my friends are these “lucky” ones and can see no reason to entertain a dietary regimen change. *sigh*

    Karen P. wrote on May 19th, 2011
    • Yes, skinny people can still develop all the “diseases of civilization,” including heart disease and diabetes. So being naturally skinny doesn’t automatically mean they’re healthy.

      Renee wrote on May 19th, 2011
      • It’s so frustrating when skinny folk think they’re immune. As though all this diet is about is weight loss…ugh.

        Karen P. wrote on May 19th, 2011
  4. I think I love you.

    … But on a more serious note, this was incredibly informative and further solidifies my choosing this lifestyle.
    Thanks so much for everything that you do, Mark!

    Venne wrote on May 19th, 2011
  5. Thanks for this timely posting, Mark. Yeah, the debate over on Don’s blog (since removed — evidently a little back-peddling on Don’s side) did confuse me about whether I should be cutting down on the animal fat and upping the carbohydrates. I’m glad to get your position on this. I’ll stick with my Primal BP shopping guide until I hear otherwise from you!

    Clarissa wrote on May 19th, 2011
  6. Foraging wild foods is one of my hobbies and with the exception of the fall when the various nuts are available and a few wild tubers there are not many carbs out there for the picking. Depending on the season and where you forage there may be close to none.

    Occasionally I try and do a weekend where I only eat wild foods that I have collected one way or another. I always find myself falling back to the fish and game for a majority of my nutrition.

    I imagine that Grok was in the same position much of the time.


    John wrote on May 19th, 2011
  7. Pro-carb bloggers however always refer to people in the far east who eat 500 grams of carbs a day (or something to that effect according to them). How do you explain that?

    kash money wrote on May 19th, 2011
    • They do eat rice, but they still eat fewer carbs than we do. And virtually no sugar or refined flour. I wish I could remember the source, but I read that the average Japanese man consumes 1800 calories per day, roughly 50-60% of that as carbs, which comes out to about 270g carbs per day. The average American, in comparison, eats 350-400g of carbs per day. Plus ten times the amount of soda!

      Renee wrote on May 19th, 2011
    • I think the China Study, when you look at the data and not the conclusions, shows that white rice comes out almost neutral, whereas gluten is absolutely shown to follow morbidity.

      Karen P. wrote on May 19th, 2011
    • As of March 2010, China passed up India as the diabetes capital of the world. Sounds like a good explanation to me.

      Jerry wrote on May 19th, 2011
  8. Great post. I just wish all the S.A.D folks and other slaves to the status quo would read this article and embrace it. I’m in my third year of college as a Fitness and Nutrition major and I am sooooooo sick of hearing the same old bull about glucose and carbs and the food pyramid. It’s just so frustrating and it gets in the way of my willingness to learn.

    Rhys wrote on May 19th, 2011
    • Hang in there Rhys, the world needs you.

      Sharon wrote on May 20th, 2011
  9. Mark, I’ve always thought of you as the gentle soul among the best-known proponents of a primal/paleolithic lifestyle. But you showed us in this post that you have quite a bit of fight in you. Bravo! Keep it up. We need strong voices like yours.

    Franklin Mason wrote on May 19th, 2011
  10. Im so glad Mark posted this. I know myself, I already feel amazing on a Primal Blueprint diet, but lately Ive been staying in keto, and I dont know if its mental but its like Primal x 10. I feel the difference, I literally feel like a beast in the gym in keto, and I manage to stay in keto even eating potatoes a couple of times a week. Although that is cause Im mostly carnivorous haha. Anyway, great to see Mark finally shed some light on this subject since many low carb gurus have different opinions on ketogenic diets.

    Jerry wrote on May 19th, 2011
  11. Thank you for this post! I can’t tell you how much grief I’ve gotten over the last 48 days. 48 days ago, I started eating Primal, cleaned up my diet (and my body!), and let go of my carb addiction. Since changing my eating style, I’ve lost weight (20 pounds!), started sleeping better/longer, and have had way more energy.

    When people ask me how I’ve done it and I describe a Primal diet, I’m amazed at the (occasionally angry) response. In the same conversation, someone will praise me for looking fit and then berate me for not eating a ‘well-rounded’ diet.

    I know I’m talking to Noah about the Flood here, but ever since I hard-core committed to eating Primally, I haven’t eaten so many vegetables in my life!

    Love this post. Thank you!

    Jenn wrote on May 19th, 2011
  12. This blog post really hits home to me. Maybe I’m so vain that I actually think this post is about me (laugh), but I’ve recently discovered the effectiveness of the carb refeed.

    I would never advocate a high carb diet and I definitely agree that fats are the ideal fuel for humans. Yes, we burn glucose more readily than fat, but we’ll also burn alcohol more readily than glucose. Do I hear anyone advocating a diet composed primarily of ethanol? I love my 60/30/10 fat/protein/carbs ratio, but when you get in the leaner body fat percentages, a 48 hour low-fat carb-up can really get the metabolic fires burning again.

    I don’t think carbs are evil – particularly starches. I think they’re great if you know how to time them, and you don’t make them a staple. A sweet potato every day would probably be a poor choice for your weight loss, but a pound of sweet potatoes once a week with half coming pre-workout and half coming post-workout could really help you break through those plateaus.

    ChocoTaco369 wrote on May 19th, 2011
  13. You only got one thing wrong. Hard work every day is possible on a vlc diet, and I’ve been doing it for some time now.
    Weight lifting 3-4 days a week, sprinting and walking whenever the weather is nice enough for it. VLC works just fine for this, although I have noticed that lifting 3-4 days a week generally doesn’t give you a break from DOMS.

    Alex Good wrote on May 19th, 2011
    • @Alex, nice going. For high-intensity work, muscle glycogen is still the limiting factor. If you keep your HIIT stuff short and sweet, you can be VLC and still refill stores every two or three days without a lot of carbs. You just can’t go long and hard every day. And why would you want to? There’s no strength or fitness benefit to going hard every day.

      Mark Sisson wrote on May 19th, 2011
    • I’ve been doing low carb for probably a year now. I did keto for 8 weeks last year and worked out hard every day before I knew any better. Even on keto, I ran 17 miles a week and lifted 4 times a week. It was brutal.

      Since going Primal 3 months ago, I’m seeing far better results, and I started taking up sprinting. I typically take in around 80g of carbs a day and HIIT is no issue. Carb refeeds are something I’ve only recently incorporated in the past month. I honestly don’t feel working out is any easier during a refeed, but it does help me shed some body fat.

      ChocoTaco369 wrote on May 19th, 2011
  14. I think people are becoming less health conscious
    these days because they don’t car about eating healthy

    Suboxone Doctors wrote on May 19th, 2011
  15. Great article, thanks for lighting the way!

    I struggle with the proportions, personally. Im still finding my balance. There is a big part of me that just wants to eat butter & steak all day, because that is what I crave… and the other part that worries I am not getting enough veggies if I do. Dont know if that is my inner carb-addict talking.

    Mia wrote on May 19th, 2011
  16. I’d love a response to my earlier comment…

    “Pro-carb bloggers however always refer to people in the far east who eat 500 grams of carbs a day (or something to that effect according to them). How do you explain that?”

    Kasha wrote on May 19th, 2011
    • Kasha-

      In my experience, the perception that Asians (living in Asia) eat a lot of carbs is more anecdotal than factual. I’ve been to Japan and Thailand, countries where the diet is indeed based on rice. Rice was indeed eaten at every meal, but not very much. Maybe 1/2 cup or so, or about 25 grams of carbs. For 3 meals that’s still only 75 grams of carbs, which really isn’t much. And unless they are dining out at the now-ubiquitous KFC or McDonald’s, their overall carb intake is still quite low compared to the SAD. Of course, if you go to a Chinese or Thai restaurant here in the US, they are happy to give you big bowls of rice. Only Americans eat lots of rice, at least in my experience. I know I did years ago, before I knew any better!

      Rob wrote on May 19th, 2011
      • That’s true Rob. Same in the Philippines. Rice with every meal, but no where near what an American would typically put on their plate. And when I was there bread was pretty much a treat for tourists. Locals commented on my love for it. They are not loading up on carbs the SAD way.

        Heidi P. wrote on May 19th, 2011
        • And, according to Konstantin Monastyrsky (Fiber Menace) white rice is actually very LOW in fiber.
          It does not cause any digestive upsets such as hard stools and constipation and moves through the bowels quickly.

          Primal Palate wrote on May 20th, 2011
      • Also, factor in that people in Asian countries are poor, the cities are overcrowded and they WALK EVERYWHERE. 100g of carbs from white rice a day is easy to burn off when your source of transportation is your feet. Pair that with how pure and clean white rice is compared to wheat, corn, legumes and soy and you have basically an intake of nearly pure glucose. The only side effect of eating white rice is weight gain due since toxin levels are so low, but if you’re burning it off walking around, it doesn’t matter much.

        ChocoTaco369 wrote on May 20th, 2011
  17. Good timing as there have been many blog posts of late that are re-evaluating the fat issue. Always good to see different opinions on an issue as important as this.


    Chris Sturdy wrote on May 19th, 2011
  18. Mark,

    Great insights on carb vs. fat metabolism. I think it’s a good rule of thumb when in doubt to ask yourself “what would Grok do?” Low-carb is the eating plan that we evolved on, so it’s no wonder that today’s high-carb diets cause inflammation and all kinds of other health problems.


    Alykhan wrote on May 19th, 2011
  19. Wait wait wait! Are you telling me, that I DON’T need to take the skin off my chicken? Hallelujah! :)

    Mayan Fox wrote on May 19th, 2011
    • better still…. stick the skin under the grill until crispy and sprinklemwith sea salt. Now THAT is a chicken crisp!!!

      KL (almostGrok'd) wrote on May 20th, 2011
    • Just chose chicken that is free-range organic–lower in omega 6. Yum!

      fritzy wrote on May 20th, 2011
      • or “choose,” which ever works better 😉

        fritzy wrote on May 20th, 2011
  20. Great post, Mark! I love any article you post that relates to metabolism.

    One point related to everything you said that wasn’t explicitly stated is that if our bodies, as CW insists, prefer glucose for fuel, why do we convert the excess to fat? As you said, Mark, you’d think we would have found a more effective way to hold onto copious amounts of this “prefered fuel” without having to convert it to something else.

    So our bodies are even trying to tell us something here that we stubornly try to ignore: “Hey, look, if you’re going to keep giving me this crap fuel, fine; I’m going to turn it into my prefered form of fuel, reagardless. Idiot.” 😉

    fritzy wrote on May 19th, 2011
    • That doesn’t really follow; fat has a higher energy density by weight than carbohydrate so it pays to convert it, because you spend less energy carrying it around. That’s true regardless of whether it’s a better fuel for you or not.

      Uncephalized wrote on May 19th, 2011
      • Actually, that’s one of the many reasons fat is the prefered fuel. Natural selection isn’t going to “reward” an organism that effectively stores massive amounts of glycogen and uses that as it’s primary source of fuel as much as an organism that efficiently converts, stores and uses fat, a macronutrient that as you pointed out is much more calorie dense by weight. You’re not really saying anything different from what I’m saying.

        fritzy wrote on May 20th, 2011
  21. Thank goodness for this post! I hope that some of the newer forum members are reading this. I have been seeing far too many conversations about calories and low-fat there these days. I actually saw one poster say that “75g of carbs is not enough to cover even your basic physiological functions!”
    Have they not even read The Primal Blueprint?!
    Thank you Mark for a well-timed post.

    Emma wrote on May 19th, 2011
    • Seeing a resurgence of low-fat talk, too. Wife’s frind, a skinny young lady, who is trying to “lose weight” pulls fat off thinly sliced grilled beef belly at the Korean grill house. It looks ridiculous, but I keep my mouth closed because I have learned that my wife and her friends are serious afflected by the the carb belief system.

      Julian wrote on May 19th, 2011
      • It’s like a cult all women are signed up to at birth. I feel her pain.

        Mia wrote on May 19th, 2011
  22. I apologize if this is a silly question, but I have to ask. I eat a TON of veggies every day. Clearly, they contain carbs. I know it’s often said you don’t have to limit your veggie consumption because of how nutritiously dense they are, but I have to wonder, should I in fact be limiting my veggie consumption if I want to accelerate weight loss? How can I reach a state of ketosis when veggies are bringing my daily carb intake above 50 grams? Does Mark’s carbohydrate curve refer to total carbs or net carbs (subtracting out dietary fiber)? Any feedback from fellow PBers is greatly appreciated!

    Sean wrote on May 19th, 2011
    • You can subtract out fiber for sure. Fiber is indigestible and does not change your blood sugar.

      Uncephalized wrote on May 19th, 2011
  23. I’ve been low-carb primal for about 3 years now and recently added in more carbs like Sweet potato and even moderate amount of rice for some variety…I’m not athletic or particularly sporty. Not overweight either.

    I don’t quite understand why the Primal/Paleo-sphere is so insulin-phobic! Given that there are tons of ancient hunter-gatherer civilizations out there like the Kitavans, Hadza, Kung, and – more recently on the evolutionary scale – Asians, all of these peoples thrive on varying levels of “high-carb-ness” but are devoid of toxic neolithic “foods” such as gluten, high levels of omega-6 oils and sugar.

    Why does primal/paleo have to equal low carb?? It does not make sense to me. I find that guys like Don Matsz, Kurt Harris, Stephan Guyenet, Paul Jaminet and Richard Nikoley have a more balanced and realistic view on ancient nutrition than simply looking at effects on insulin and blood sugar levels.

    David wrote on May 19th, 2011
    • “Why does primal/paleo have to equal low carb??”

      It doesn’t, that’s just often the net effect. And that’s pointed out over and over and over and over by all kinds of people, including Mark. Ultimately, it’s about finding a balance within your environment that leads to the best possible health for YOU, which is measurable in many ways – i.e. via scientific methods and n=1 testing of your overall well-being mentally and physically.

      Todd wrote on May 20th, 2011
    • Have a look at the work done by Prof. Cynthia Kenyon of University of California about the effects of insulin on the body and life expectancy. Put her work alongside that of say Loren Cordain and the whole insulin/carb thing becomes clearer. The more we turn on our insulin, by eating carbs, the more damage it does to our bodies.

      Paul wrote on May 20th, 2011
      • All interesting stuff but still does not explain the H-G civilizations that thrive on high carb diets. There is a view that post meal insulin spikes are not necessarily the problem. Rather, elevated *fasting* insulin is. Big difference…are carbs *per-se* driving this? Don’t know, but I suspect that toxic carbs like fructose and wheat are the big confounders in this whole carb debate. It’s just like the CW folk lumping all fats together as bad. I just don’t see that safer starches like sweet potatoes and tubers etc, the staples of many H-G civilizations, are inately problematic. The “insulin hypothesis” of the paleo world does not play itself out in those societies who live on these types of foods.

        David wrote on May 20th, 2011
    • I don’t know what Asian countries you’ve been to where they are thriving, but to me most of them look clearly undernourished. They are very short and very skinny.

      wozza wrote on May 21st, 2011
    • There’s one thing you have to keep in mind: the Kitavans and other primitive peoples you mention typically eat one big meal per day in the evening. Their diet may be high in carbohydrates but when you eat one meal per day you only have one insulin spike per day so chances are you’ll never develop insulin resistance to begin with.

      If you’re going to compare a primitive diet with a western diet you need to take into account meal frequency. My guess is that once you’ve been on the Primal Blueprint for a while and your body is back to normal you can probably eat a rather high carb diet with no negative consequences if you eat one big meal per day (as long as you keep the food more or less primal).

      One big insulin spike per day shouldn’t send you on the road to insulin resistance but since there’s no precise way to assess if your body has been permanently damaged or not from all those years of breakfast cereals, sodas, wheat products, fruit juices, grain oils, etc. you’ll have to try it and evaluate how good it is for you.

      Michael wrote on September 15th, 2011
  24. This could be the best article you’ve written

    Nidalee wrote on May 19th, 2011
  25. An excellent post and great comments. All around me, except one student of mine, gorges on carbs. I’ve just about convinced my wife to reduce hers but she just have to have bread(!) which pushes her daily carb intake up over 120 grams. I regulate mine to around 60 gms perday and have never felt better, fitter or slimmer, with no effort whatsoever. And here too in the UK everything on the supermaket shelves is ‘Reduced fat’ or ‘Fat Free’ and what folk don’t realise is that they take the fat out and replace it with carbohydrate! Love your Paleo I say!

    Paul wrote on May 20th, 2011
  26. Chris Masterjohn, over at the Daily Lipid, has recently touched on very low carb/ketogenic diets. While it does show promise, he warns:

    “The body may be able to survive without dietary glucose, but only because it can make glucose from protein. Give it only fat, and it will make that glucose — and oxaloacetate — from lean muscle tissue.”

    In order to avoid muscle wasting on a ketogenic diet, there is strong evidence that either protein or carbohydrate should be included. For those in favor of keeping it low carb, of course protein would be the preferred choice.

    Either way, I’ve noticed improved health on a lower carb diet. Whether or not a 0 carb diet could work for me, perhaps a self experiment in the future could answer that question!

    Great article!

    Nutritionizt wrote on May 20th, 2011
  27. The timing of this post is great. Men’s Journal just came out with an article entitled “The Man’s Guide to Carbs.” Of course, it parrots the CW regarding carbs. It’s gonna take time and continued education to change the CW.

    Justin wrote on May 20th, 2011
  28. I recently watched an old Japanese comedy from around 1963. The father is gorging on rice at breakfast, and hands his bowl to his wife for a refill.

    She says: “You’ve had enough, dear!”
    The daughter chimes in: “You’ll get fat eating that much rice!”

    garymar wrote on May 20th, 2011
    • That’s how the Japanese have traditionally “built” 500+ pound sumo wrestlers. Just significantly increase the amount of rice and beer.

      Mark Sisson wrote on May 20th, 2011
    • it’s still common knowledge in Japan, I think. if you ever eat at restaurants there with a female, you’ll notice they give a half portion of rice to females so they won’t get fat

      justin wrote on May 23rd, 2011
  29. Love it Mark. Carb control is key! Thanks for this!!

    John M. Rowley wrote on May 20th, 2011
  30. Mark, hands down one of the most informative articles I’ve read on your site. It also is greatly going to help me to explain to my questioning friends/family why fat is better than carbs. I have one question though.

    I’m sure someone else has asked this and it might have been answered, but in the year that I have been following your site I don’t remember it being mentioned.

    At the end of the article you are mentioning the Primal Carb Curve and taking into account those that consume above 150 gms of carbs are probably predisposed genetically to weight gain AND “I am also factoring in the drop in metabolism that happens naturally with age”

    Can you shed anymore light on this metabolic drop with age? EVERYONE in society talks about it as they get older, but I’ve never seen anything about it being real. Does it only affect people running on carbs? I’ve been skinny my whole life and jealous coworkers always say “wait til you get older”. I’m eating very primal almost 100% with the occasional cheat. I did seem to notice that I was starting to add on lbs when I got to be 27 and had horrible nutrition and wasn’t being active. I’ve done some research online on the topic but would love to hear your take on it. What gives with our metabolisms slowing down as we get older?

    Jesse wrote on May 20th, 2011
  31. re: “It boggles my mind that such a large segment of the so-called health and fitness community would continue to defend high carbohydrate diets with such tenacity.”

    Look no further than the FDA/farming lobby/government schools/main stream media/food merchants.

    The health and fitness community, like every community, tends toward attachment to what is both familiar and promoted.

    tim_lebsack wrote on May 20th, 2011
    • People also refuse to do their own research. Its much easier to repeat society norms when forming opinions.

      Jesse wrote on May 20th, 2011

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