What Is a Low-Carb Diet?

By December 4, 2015 December 9th, 2016 Nutrition

Have good fats finally replaced bad carbs in the diet as the accepted approach to reach optimal health and fitness?

From the movie Midnight Cowboy, Harry Nilsson’s 1969 song still echoes in my mind: “Everybody’s talking at me … I don’t hear a word they’re saying …” That’s sometimes how I feel today when people talk about common trendy low-carb diets.

I often get confused, despite my brain being in great shape, because most of these diets have actually come and gone for decades, only with different names — low-carb, Paleo, caveman, ketogenic, etc. Regardless of what you call it, low-carb is how humans evolved eating for millions of years.

The term diet has been around longer than any of us. I recently wrote about the dangers of diets. While I don’t like the concept of diets because they make users blindly follow a list of food items instead of intuitively learning how best to eat, I could not help use the term because it is quite commonly adopted universally when discussing eating plans.

Propaganda powerfully makes its mark by maintaining the echoes in our minds. The incessant marketing of “diets” will continue but those with intelligent brains don’t have to participate. Unfortunately, too many people associate my MAF principles with the low-carb diet, and I quickly respond by saying I don’t recommended any diet — even those called ketogenic, very low-carb, or high-fat. What I do recommend is that people find an eating plan that best serves their needs (one purpose of the Two Week Test), using intuition and instinct as the best nutritional guide rather than counting macronutrient calories of carbs, fats and proteins.

I recently asked Robb Wolf of the “Paleo Solution” podcast to describe the Paleo Diet, knowing I would get a good answer. He said it’s “macronutrient agnostic.” Perfect.

For most people, improving diet usually does mean reducing the amount of carbohydrates they eat, especially those that are refined or processed.

Cutting Carbs

It’s important to understand why it may be important to reduce carbohydrate foods. Eating these foods (which are moderate- to high-glycemic) can cause over-production of insulin, even in young healthy athletes. Insulin converts a lot of carbs to stored fat, reduces fat-burning, increases hunger and triggers inflammation, the first stage of chronic disease.

Most people consume 41-60 percent of their daily food as carbohydrates or about 205-300 grams of carbohydrate. Some people even go beyond 60 percent. One problem with this is that most of the carbs are refined, despite misleading labeling as “natural” or “whole grain,” and contain various forms of processed flour and sugar. Eating this much carbohydrate puts essential fats and proteins below required, healthy levels.

Reducing consumption of carbohydrate foods may improve health, increase fat-burning and increase human performance. Incidentally, the same approach is also used to treat various conditions like seizures, cancer, diabetes and obesity.

This is accomplished simply by eating meals and snacks that are lower in carbohydrate For those who require even less carbohydrates, this may mean very-low carb meals, which are both ketogenic and high-fat. Don’t worry, I will decrypt and simplify all this gibberish as we continue.

Healthy Eating

Many people have spent their lives counting calories and can’t help it. Transitioning to a healthy, intuitive way of eating is the remedy but many require a stepping stone to get off the diet merry-go-round. So here is a general consensus of the trendy terms

As a general guide I list below the various names of eating styles without using the “D” word, using an approximate 2,100-calorie per-day eating plan as an example.

It’s carbohydrates and fats that are the revolving macronutrients. Healthy eating maintains a relatively constant protein intake of around 1.2 grams per kilogram of body weight. For a 155-pound (70 kg) person this works out to be about 85 grams of protein per day.

Moderate-carb: About 26-40 percent of daily meals, with around 140 to 210 grams of natural carbohydrates per day. The fat content is about 43 to 57 percent, or 100-130 grams. In natural forms, this amount of carbohydrate may be healthy, especially for younger, active people. However, as many children are now overfat — with insulin resistance similar to that found in an aging body — even this amount of carbohydrate may be too high.

Low-carb: About 11-25 percent of daily meals, with approximately 51 to 139 grams of natural carbohydrates per day. This would bring fat content to between 135 and 165 grams, or about 58-71 percent.

Very low-carb: about 5-10 percent of daily meals, with around 25-50 grams of natural carbohydrates. Fats are about 168 to 182 grams, about 72-78 percent. At this level of carbohydrate intake, the body makes many more ketone bodies it uses for energy in the heart, brain and other tissues.

Very low-carb also refers to:

  • Ketogenic eating — a state of healthy nutritional ketosis.
  • High-fat — obviously, if carbohydrates are reduced to 10 percent or less of the diet, with protein holding steady, the fat content will increase to higher levels. With “normal” fat intake considered to be 30 percent, low-fat is below that level with high fat well above. Don’t be concerned about eating this much natural, healthy fat.
  • The Two Week Test is an MAF Method of helping become more intuitive about food, improving health, reducing body fat and getting rid of sugar addiction. The test usually has meals and snacks on the low end of a low-carb or the high end of very low-carb, and as its name implies is only for two weeks.

The best way to convey these healthy meals — part of the stepping stones to better eating — is through recipes on this site — the photos are worth more than words.

To emphasize, if you’re eating refined carbohydrates, that’s the first problem to address, and reducing this can be accomplished through the Two Week Test. Then you can find the appropriate level of natural carbohydrates that best matches your lifestyle needs.


  • Liz says:

    Hello! I have done the two week test twice and I’ve found that I function best on the very low carb diet. However, even when only eating foods specified on the list in my everyday life, I am exceeding the carb recommendation because I am eating so many vegetables, especially green peas. Is it really possible to eat too many vegetables? Should I be concerned about reaping fewer benefits of the very low carb diet? Also, do I need to incorporate cheat meals to refuel on carbs if I want to always eat a very low carb diet? I don’t want to be malnourished or anything. Thanks!

    • Hello Liz,

      I wouldn’t worry about exceeding the carb recommendation if your carbs come from vegetables. However, if more of your carbs start coming from starchy tubers (potatoes, yams, beets) or cereals, then it might be good to cut back on those. But it may not be necessary to eliminate them entirely:

      What matters the most isn’t strictly speaking the amount of carbs you eat, but rather the quality of the foods you eat. Malnutrition, especially for Westerners, is primarily due to a lack of enough vitamins and minerals in the diet. In other words, it’s very difficult to get malnourished by eating lots of vegetables and greens. The most important thing you can do is make sure that in addition to a variety of vegetables, you have a few good animal and vegetable fats in your diet. The rule of thumb is that if you don’t have any signs and symptoms of poor health—your energy is good, your digestion is good, you rarely get ill—then your diet (and overall lifestyle) is working well for you.

      Does this answer your question?

  • San says:

    Hello There! Thanks for the great article and all the responses to the questions which also gave me further information. I’ve tried both high fat and also high carb diets. By high fat, I didn’t stuff my face all day long with fat. I had healthy natural fats from avocado, coconut oil, coconut milk, olives, ackee and nuts for breakfast, lunch and dinner. I also ate lots of low calorie veg and salad items (green beans, sugar snap peas, cucumber, kale, spinach, aubergine, mushrooms, etc etc) I did extremely well eating like this lost a lot of weight without really trying (30 lbs). I also had my lowest body fat of 16 % and lots of energy. However when upping my running distance to 10 miles and taking part in gruelling week long punishing surf sessions 4-5 hours a day in Morocco, I did start to feel exhausted and also started to crave “energy” and so I ate dried fruit in between surfs to stop the shakes and crashing which worked extremely well. I generally didn’t have cravings on this diet but would however occasionally have a bottomless pit feeling in my stomach and very specifically for muesli and yoghurt (about once a fortnight) and also for beans and pulses and so I went with it and filled up on it (eating more fat and veg just didn’t satisfy me at those times). I was also craving mangoes in particular more and more. So I decided to try a high carb diet (but still grain free, no added sugar and no processed food) – I ate lots of tropical fruit, some potatoes, and occasionally Clif peanut protein bars. But with these foods I have to eat every 2 hours or I feel hungry and it’s often not satisfying in the sense that I need to eat more fruit than I had apportioned to feel content. I do feel very energetic on a fruit/carb diet and also perform well running and swimming, but I also have gained 10lbs and feel heavier rather than light and breezy (surprisingly it’s not affecting my performance greatly though and running actually feels easier). I also ate beans and pulses in the evenings as I started craving salty food when eating mostly fruit and sometimes I started craving grains (corn and wheat), but I had no cravings at all for muesli and yogurt! Having tracked all this I’m not sure what this means (do you have any thoughts)? Potentially I’m carbohydrate intolerance. I always wake up with a sugar hangover and all consuming lethargy if I go carb heavy the day before (my tests showed that I’m not diabetic). I’m still looking for the answer to the ideal diet that will mean I feel light, energetic and don’t have cravings. Neither of the above diets that I strictly adhered to were completely satisfying and slowly led to craving food items from the “other camp”. On both diets I also ate protein smoothies from time to time (sun warrior). I wonder if you can provide some objective insights on my experience to help me out? I would really appreciate this. I exercise most days in the week for 30 minutes (running, cycling, kettle bells) and at the weekend I usually do between 3-4 hours on both days (running, cycling, swimming, rock climbing). I drink 2-3 litres of water every day. Many Thanks!

  • Gregory Cox says:

    Hi Ivan,
    I’m 58 – I’ve been doing MAF paced training (50->30->10) before a marathon this Sunday. I transitioned over to a lchf diet about 2 months ago. My dilemma is regarding carb loading. I read in one of your replies here you’re not a big believer in it, but there is some research here (https://www.researchgate.net/publication/11267836_Carbohydrate_loading_in_human_muscle_An_improved_1_day_protocol) that supports it. For my last marathon I did carb-load & had a very successful marathon (<3:22). Obviously I'm hoping that my fat burning at marathon pace has increased somewhat with my diet & training but I'm concerned that a day of (low-GI) carbs (e.g. brown rice & whole-grain bread) may switch off my fat burning system (or so I've read elsewhere). What are your thoughts on this?

    • Gregory:

      I would also be concerned that carbo-loading would switch off my fat-burning system.

      Let me put it to you this way: Eliud Kipchoge does not carbo-load. More specifically, I don’t have to know his training specifics to tell you that he does not carbo-load. To say this in more words, the study only finds that you maximize muscle glycogen levels. It says nothing about the effects that maximizing muscle glycogen has on endurance performance. (That maximizing muscle glycogen levels has benefits on endurance performance is an assumption—one I think the researchers had in mind when they were writing this paper). Endurance performance depends on the body’s insulin sensitivity, in order to allow more leptin to circulate, temper the stress response, and allow fat-burning. There’s really no way that a 70kg (130 lb) athlete who ate 1.3 kg of high-glycemic foods over the course of 3 days did not have a reduction in insulin sensitivity.

      On another topic, don’t change anything towards the race. Carbo-loading before a race is a lot like a race car mechanic tweaking the engine without taking the car out for a lap before the race. In a very real way, you’ll be racing with a (slightly) different body than the one you’ve been training with. For a lot of reasons related and unrelated to nutrition, you don’t really want to do that.

  • Ian Smith says:

    Hello Ivan,

    Many thanks for your reply. I understand what you are saying and of course remember reading about reintroducing some carbs following the Two Week Test. I guess I got carried away by the idea of fat-burning, which seemed quite miraculous at first.

    Since receiving your reply I have begun adding the odd handful of black beans and lentils to my meals and the irregular heart rhythms have stopped.

    Thanks again. And all the best. It’s a great site.


  • Ian Smith says:


    Last April I completed the Two Week Test and assumed a low carbohydrate diet. I don’t know how low exactly because I’m not good at measuring things, but I cut out all refined carbohydrate and the black beans and lentils that I love and restricted my intake to leafy greens and non-starchy vegetables. This appeared to work well and, apart from a few slack days in the beginning, I felt terrific. I lost weight, especially around my middle. And although not an athlete I continued to do plenty of exercise, making long daily hikes and doing everything from stretching to push-ups, chin-ups and light weights. My energy levels were better than ever and in fact some days I would walk for five or six hours at a stretch for the simple reason that I felt like I could go on forever. It seemed I could actually feel the fat-burning kick in, times when I’d be striding effortlessly along with not a hint of breathlessness or fatigue.

    My food intake, I thought, was good. It included plenty of healthy fats, moderate protein and carbohydrates from non-starchy vegetables at every meal. I was never hungry and after a big breakfast often didn’t feel like eating lunch, although I usually ate something. Like I say, things were great and I was cruising. I felt that I’d stumbled upon a goldmine of healthy living.

    But unfortunately at the same time I developed irregular heart rhythms. It happened from the start, although so sporadically I wasn’t bothered – it was always in the middle of the night and always after a tough day physically, so I figured I was simply acclimatizing. It was always the same. I would wake up in the middle of the night to find my heart flopping about in my chest like a fish out of water. I would get up to use the bathroom and feel weak and dizzy, with a dry mouth and the feeling that I’d been run over by a steam roller. Usually I’d still be shaky next morning, despite having slept deeply in the meantime (or at least so it felt), although the arrhythmia would stabilize after I’d eaten an omelette with spinach and drunk a cup of coffee with double cream and I’d always be able to go out and do it all again, with no ill effects.

    However over the last couple of months the condition has become more annoying. Now the arrhythmia occurs more often and not only at night but at all hours, including in the middle of exercise, which is very unsettling. It doesn’t feel as severe as before, I assume because I’m not exercising so rigorously. And otherwise I feel great and am always full of energy, although I’m afraid of pushing myself because I know what will happen. I have read about electrolyte imbalances and, although my diet may not have been optimal when I started, for the last month or so I have been very conscious about eating an abundance of green vegetables and adding a moderate amount of sea salt to my food. I have always been a big eater of vegetables, though for a long while I overdid the carbohydrates (including white bread, pasta and rice) at the expense of animal protein. Nowadays, though, my food intake appears pretty well balanced.

    I am fifty-two years old and have always been physically active, although I have not always treated my body kindly. I am the kind of person who would walk all day in the mountains and then stay up at night and drink a couple of bottles of wine to celebrate. I suffer from mild hypertension (currently off medication) and although I am sure I have issues with carbohydrates, my blood sugar levels were normal last time they were tested (Feb 2015) and my cholesterol levels were fine too. I know that another visit to the doc is in order but I thought I would write and see if you could suggest anything that I might be missing.

    Thanks for listening. Any advice you could give would be much appreciated.


    • Ian:

      Thanks for your e-mail. Generally, after doing the Two-Week Test, it’s important to find the percentage of healthy carbs that is healthiest for your body. When training at a relatively high intensity (strenuous), it’s important that your diet contain a reasonable amount of low-glycemic carbs in order to fuel higher-intensity training. Otherwise, it can be quite stressful for the body. It might be the case that the amount of high-intensity training you are doing does not fit your present diet, particularly because reducing that amount reduces the negative side-effects you are feeling. One thing you can try is to stop any high-intensity activity well before any hint of fatigue sets in.

  • Brenda says:

    Thank you for the articles, recipes and inspiration. I started following the 40-30-30 method of eating in the 90’s (before it was trendy) and have always kept the concept (if not exact practice) in mind since then. I take 3-4 oz of good protein with most every meal. I also have more recently been using Phil’s book on Health and Fitness as a day to day reference. However this article’s reference to protein requirements stumps me. I assume I’m reading incorrectly. For a 155 pound person approximately 3 grams of protein per day? I weigh 112 so would have even less. This seems very low especially thinking of discussions in Phil’s book. Is this protein requirement increased for those who exercise daily for multiple hours? Thank you.

    • Brenda:

      I’m not sure I know what you mean.

      The article reads: “Healthy eating maintains a relatively constant protein intake of around 1.2 grams per kilogram of body weight. For a 155-pound (70 kg) person this works out to be about 85 grams of protein per day.”

      If you’re talking about one of the examples below, let’s take the example that could be construed as offering the least protein: the “low carb” example. Even if you take the high range of both carbohydrate percentage (25% from 11-25) and fat percentage (71% from 58-71) this leaves you with 4% of your diet being from protein. That’s still a lot more than 3 grams of protein.

      Could you be a little more specific about your question?

  • Nuria says:

    When trying to follow a very low-carb nutrition, what range of glucemic index is considered to be acceptable? For example, once I have finished the two-week test and I want to introduce some food with carbohydrates every two meals, what type of fruits woulld be adequate. Cherries have the lowest index (23) and bannas are around 62, would these be aliminates from a low carb diet, or can they balance other meals with no carbs at all?
    Thank you very much.

    • Nuria:

      Anything below 50 works quite well. Unless you have a clear and present reason to cut carbs (such as doing the TWT because you have observed signs and symptoms of carbohydrate intolerance), it is more important to reduce the glycemic index of the carbohydrates you eat than to dramatically reduce your carbohydrate intake.

  • Eugene says:

    Hey, at least you recognize it. My diet would make you crnige. Definitely not doing myself any favors. I am VERY lucky that my metabolism is forgiving or I would be in serious trouble. On the other side I’ll burn 1400 + calories on a 24 mile ride. Even skinny guys have to do something. You’ve been on a good plan for you, so you know what you have to do.

  • John says:

    “…Pacific Islanders are now known to be very big people is because they lived in an environment where it was difficult to find adequate nutrition, so they developed extremely anabolic metabolisms—always trying to grow every chance they get.”

    Can you explain just a bit about what an ” anabolic metabolism” is, and, what is the opposite (catabolic?). Where food is plentiful, one necessarily has a catobolic metabolism?

    Generally speaking, metabolism refers to the rate at which calories are burned at rest? Likely you have a better general definition.

    Thanks, great help from you as always.

    • John:

      By “metabolism” I don’t mean “level of metabolic activity” but rather I’m talking about the metabolic process itself. In other words, I’m not talking about “how fast the factory is operating” but “the factory itself.” Although some people do use “metabolism” to mean “metabolic activity at rest,” that’s really not a useful way of defining it. A better way is to define rest and exercise in terms of units of metabolic activity, also known as METs. (For example, jogging typically happens at 3-5 mets, and “recovery” is anything at 1 MET or below).

      Everyone’s metabolism works anabolically (building up, which happens during recovery) and catabolically (breaking down, which happens during activity). But the metabolism of some people has been adaptively geared to be very anabolic: if food isn’t very plentiful, then your body wants to make sure that it’s using every bit of it to build itself, as much of the time as possible. On the other hand, if food is quite plentiful, the metabolism doesn’t really need a hair-trigger switch to go anabolic instantly, as hard as it can.

      As the hypothesis goes, the Pacific Islander metabolism is working anabolically as hard as possible every chance it gets, because there was a clear and present adaptive value that did not exist in the majority of situations. So it’s not that other metabolisms are “more catabolic”—it’s that they tend to be lazier, making the switch from catabolism back to anabolism with a lot less ferocity.

  • Paul W. says:

    Is there a food list somewhere on the website, rather than recipes?

    • We don’t have something like that yet. You make a good point, though. I’ll make a note of it.

      • Alison Harding says:

        Yes please that would help immensely

        • betty says:

          Thank you, a food list would be most helpful!

          In the meantime I’m about to embark on the Two Week Test am confused to what “real” cheese is?!
          Obviously not Velveeta, but is Swiss real? What about cheddar? Or is only hard (Parmesean) real cheese?
          Thank you for your help!

      • George says:

        I also would appreciate a food list. Until you get around to publishing one could you provide me a bit of guidance?
        I think I’m eating a low carb diet but have am wondering about a few of the foods I’m consuming:
        1. For breakfast I typically have some form of eggs, plus full fat cottage cheese mixed either with full-fat sour cream or full-fat plain yogurt. Where do these milk products fall on the glycemic range – high or low?

        For lunch and dinner I eat lots of fresh veggies plus a meat, fish or poultry

        2. I’m not clear on legumes (chickpeas, lentils, etc.) are these high or low on the carbs range? Currently, I’m excluding these until I get some clarity on them.
        3. I consume organic almond butter and raw cashews for snacks – where do these fall in the range?
        4. How about red wine?

        Should’ve started with this thanks at the beginning … your advice and information is transforming my health. Thanks you so much for what you do!

        • George:

          All of the milk products you mention are quite low glycemic.

          Legumes are good options for when you’re trying to eat low glycemic carbs.

          Almond butter and cashews are quite low glycemic as well.

          Red wine is fine, although alcohol is metabolized quite similarly to sugar inside the body. So, while 1 or 2 glasses is fine, I’ve fallen into the trap before of replacing my sugar calories with alcohol calories (and in the process became quite a heavy drinker for a couple of months).

  • Chris says:

    Thanks for clarifying what is moderate carb, low and very low carb intake. Can you shift your fuel source towards fat oxidation by moderating carbs and moving to moderate or low, or do you have to induce production of ketones to see that shift?

    • Chris:

      Yes, you can shift your fuel source to fat by moderating carbs.

      That said, production of ketones is induced by fat oxidation, not the other way around. This is whether you accomplish it by moderating carbs or by tailoring your activity level to produce fat oxidation. You can think of fat oxidation as “4th gear” in the car’s gearbox, and ketosis as “5th gear.” You have to go through 4th to get to 5th.

    • Dejons says:

      This definitely helps! Thanks! As you say; I should not see it as a performance degradation but more off the built up of an efficient energy consumption system.

      You mention I could include low- and medium-glycemic carbs the day before an interval session or a tempo run. Could you help me by specifying some healthy carbs that fall into this category? Now I am experimenting with Lentils and Parsnips but my HR is not lowering so much from it. What would be other healthy alternatives to take before tempo/interval runs?

      • Dejons:

        If you are good with starches, then you can use lentils and other legumes. Berry smoothies with carrot, apple, ginger, etc. are also a good idea. I’m also a big fan of corn tortillas (organic and non-GMO for me), so for example a bowl of chili with tortillas is a great dinner to have before a morning speed workout. A lot of other fruits also work—grapefruit, orange. I’d personally stay away from banana except as a recovery food from a session with an anaerobic component.

        Which is another issue—immediately after a strength or speed session is when you want to eat some 200 calories of easy-to-digest carbs: since the fast-twitch muscle fibers are all out of carbs, you need to allow the body to replenish them, or you’re going to be put into a lot of stress. (You don’t need more than 200 calories immediately; those calories aren’t going to hit the muscles until a few hours later—when the body feels those calories hit the stomach, the liver will kick in to help refuel the muscles in the meantime).

        But the most important thing to mention is that you don’t have to go all out on carbs the day before an interval session. What’s important is to slowly but steadily bring up your muscle glycogen levels so your body is ready to go. I call this “emphasizing” carbs. To extend this metaphor, the typical carbo-loading bread and pasta meal is like “screaming” carbs, if you will. Similarly, when you want to go for a long run, you can slowly and steadily bring up your levels of fat-burning, by reducing (but not completely eliminating) carbs from the diet.

        Going to extremes will only shock the body—what you want to do is move you diet smoothly over the course of a few meals so that it’s comfortably positioned on the side of the macro spectrum you’ll be fueling your workout with. This is really an “elite athlete” kind of intervention: most people can do wonders without messing with their macro distribution on a day-to-day basis.

        And the most important way to know if you’ve gone over the top is if you get any negative signs or symptoms.

  • Dejons says:

    Thanks for this great article!

    I am a passionate runner of 27y for about 3 years now. I keep a healthy mix between endurance (multiple day stage races), Marathons and faster races (10K, 16K, etc). I train around 50km per week (min) and 120km per week (max). The 1st of November (2015) I started with the 2-week test. The first days were very hard on a performance level > before the 2 week test I was running 5’14” at an avg HR of 130; during the 2 week test I was doing 5’38” at an avg HR of 157. After the 2 week test I included the healthy carbs again: fruit, lentils & chickpeas. I only include carbs 1 or maximum 2 meals a day. My performance went slightly up but is still far from what I am used to: this morning (5 weeks after the start of 2 week test) I did 5’13” at avg HR of 148.

    After reading your article I question my eating habit and I am wondering if I should not try to include more natural carbohydrates? Should I include it in every meal instead of only once or twice a day? Which other healthy alternatives do I have? I would love to get back to my normal performance level and would like to do that with the healthy life style (avoiding processed carbs); but as of now it seems I could not find the correct balance for myself…

    Thanks in advance for your advice!

    • Dejons:

      I’d recommend to increase your intake percentage of low- and medium-glycemic carbs the day before an interval session or a tempo run, and increase your intake percentage of fats the day before a long run. That is a really basic way to apply nutrient timing to a training routine.

      The most important indicator of good health is an absence of negative signs and symptoms. If you increase your carb intake and don’t see any adverse health effects, and your performance improves, then that’s where you should be. A lot of times, it’s very difficult for athletes to digest the sheer volume of food they need in a traditional “high fat” diet, particularly for an athlete who runs various speeds, as yourself.

      Most likely, your usual speed is derived from mostly aerobic use of sugar (which is the norm for efforts that last 2-60 minutes, since it creates more power but lasts far less than aerobic use of fats). After the TWT, you’ve been “forcing” your body to develop its ability to burn fats due to the relative absence of sugar in your diet. So, your loss in speed is likely not a loss in performance but rather an increase in using (and training the use of) a slower-burning fuel. It’s possible that what you’re experiencing as a loss of performance is actually a switch from predominantly using sugar to fuel your efforts to predominantly using fats. I’m very confident that this is the case, particularly since you mentioned that your increase in performance is due to a slight increase in carbs in your diet.

      But I’d caution you to not view this as a loss of performance: you’re training an energy system of paramount importance, which you depend on for endurance performance.

      This goes back to training specificity: The best way to create great endurance performance is to learn how to burn primarily fats for fuel (and then add carbs during race day, to fuel the afterburner). While you still need to learn how to burn sugars for fuel, that’s a different kind of training. It’s important to view and understand these systems separately, so that you can train them individually as you desire.

      Does this help?

  • Matt Trevino says:

    Thank you for the simple website and excellent presentation of so much information!! I am considered an active healthy person even though I consume a lot of food. I was exposed to your methodology reading Chris McDougalls book and have used this information as a reference ever since. I appreciate you publishing the information that you have. I am sure that you will effect many lives with the knowledge and research you have performed. Thank You.

  • wade says:

    What is the downside of substituting healthy carbohydrates such as brown rice, organic potatoes, yams and certain whole grains for unhealthy and processed carbs? It appears that most long living healthy cultures eat high carb diets with a near absence of processed food. The Tarahumara Indians, previously featured in a video on this site, eat in this manner. There is very little scientific data to support that a healthy high carb diet causes more insulin spiking than low carb, high fat diets. I love Dr. Phil’s books and approach and have recommended them to many of my patients but the long term health safety of high fat eating remains questionable compared to indigenous diets with higher amounts of natural carbs and lower fat. As a physician and research scientist, I am very open to hearing new info that i may have missed. Thank you.

    • Wade:

      A Tarahumara boy of high-school age has run perhaps 12,000 miles in his life. The sheer volume of physical activity, not to mention athletic prowess, makes comparing us and them in terms of diet nearly impossible. A Tarahumara boy is converting carbs to fats, fats into fuel, and using carbs for fuel at an incredibly high rate. When the rate of oxidative caloric expenditure is high enough, a very high carb diet can be an option.

      Most indigenous diets do have a higher amount of carbs and a lower amount of fat for the simple reason that carbohydrates exist in far higher concentrations than fat or protein in the environment. But let’s transform this into an evolutionary question: the fact that humans have a hybrid digestive system and hybrid metabolic engine does not necessarily mean that our fuel intake and usage needs to match the ratios present in the environment, particularly when, even in a lean person, fat storage dwarfs carbohydrate storage by an order of magnitude. (Which doesn’t make the LCHF argument immediately correct, either).

      However, when looking at indigenous diets, the volume, frequency, and necessity of athletic activity in indigenous cultures is a huge confound, from which we can draw very little useful comparisons to sedentary cultures, where the volume, frequency, and necessity of athletic activity is drastically different.

      The classification of foods by glycemic index and glycemic load tells us a lot about how they affect insulin levels. The key difference is that the athletic activity in indigenous cultures provides the perfect mechanism to reduce insulin levels: as soon as the volume of athletic activity creates a drop in blood sugar (which happens a lot in indigenous cultures) insulin levels drop, which means that leptin levels rise: fat oxidation (and oxidation in general) increases dramatically.

      The environmental demands typically placed on indigenous cultures provide the perfect mechanism for the development and maintenance of metabolic flexibility (regardless of diet)—a mechanism that is nonexistent in sedentary cultures. (The environment places no such demands on us; we have to go out of our way to find metabolic challenges). Because of this, we have to be a lot more careful with our dietary choices.

      Why make the choice for LCHF diet? Because a high-carb diet allows for the possibility for the body’s energy needs to be met predominantly by glycolysis. On the other hand, a LCHF diet forces the body into oxidation: fatty acids break down into Acetyl-CoA, which goes directly into the Citric Acid Cycle. The diet kicks up levels of leptin (in order to allow fatty acids to get to oxidative muscle fibers), and leptin in turn controls insulin levels.

      Don’t get me wrong—you may be able to control insulin levels on a high-carb diet. But on a high-fat diet, you have to.

      • wade smith says:

        Thank you for your detailed and well considered response. If i have processed correctly: if you are highly active on a daily basis and not dealing with overfat, sedentarism etc, then natural higher carb diet combined with high quality protein and fats is a reasonable “longevity” diet (which mirrors my experience). However, if you are not highly active, dealing with overweight issues, then a LCHF whole foods diet is a better bet to stabilize weight, insulin etc. I realize this is somewhat oversimplified but seems consistent with the 2 week test and adding back in complex carbs as tolerated. tx and keep up the excellent work!

        • Wade:

          That’s a very good reading of my words. The only thing I’d add—just to make it explicit—is that the presence of a high volume of athletic activity mitigates the possible adverse effects on insulin and aerobic function that a high-carb diet may have. (It would be very interesting to find an indigenous culture that lives off a LCHF diet).

          • Mcbeauty says:

            There are several indigenous peoples that live off o LCHF diet, Eskimos and the Nasal are the first that spring to mind

          • Mcbeauty says:

            That was supposed to say the Masai, thanks auto-correct!

  • Scott says:

    Hi there, I’d like to ask a question about rice and the Asian population. Ive just moved to Asia (South China) and it seems as though rice is a staple for the majority of the population. Ive never seen so much rice in supermarkets in very large packets. The other thing is that the obesity epidemic doesn’t seem to have reached this part of the world yet, although with the Westernising of Asian culture it won’t be long. So where does rice sit in the whole carb/low carb debate?


    • Scott:

      I’d say that the key is the difference between highly sedentary and highly active lifestyles. I don’t like to think of high-glycemic foods as “fattening”—I like to think of them as “rocket fuel.” If you’re someone that’s constantly moving (either because you’re working all day or because you’re a very high level endurance athlete), you may be able to use fuel that looks a lot more like rocket fuel, particularly because you need to replenish your fuel stores very quickly, in order to start moving again. But if you’re not moving, it’s a really bad idea to ingest a large amount of “rocket fuel.” You’re better off with milder, more slow-burning fuels such as fats.

      • James says:

        Hi Ivan,
        Great reply as usual. I think it is interesting that lots of people in western culture eat a lot of carbs and are always ‘on the go’ and working out yet can’t get lean and in fact there bf% increases over time. I think to eat a lot of carbs (‘good’ or ‘bad’) you have to have the genetics to tolerate them AND a high amount of daily activity.

        • James:


          The discussion of genetics is very interesting: for example, it is hypothesized that the reasons that Pacific Islanders are now known to be very big people is because they lived in an environment where it was difficult to find adequate nutrition, so they developed extremely anabolic metabolisms—always trying to grow every chance they get. When you match this sort of metabolism with a calorie-rich, carb-rich Westernized diet, we see that the growth effects (and health effects) of the westernized diet are compounded in the Pacific Islander peoples that fit this criteria (and any others who fit this criteria around the world).

          This research, perhaps surprisingly, perhaps not, stemmed partly from interest in the 1980s to investigate the dominance of New Zealand, Samoa, and Australia on the world rugby stage.

          (While this research is interesting, and seems to be on to good things, I call it a “hypothesis” because to be perfectly honest, I think that a lot of rugby research in those times was influenced by racist attitudes emerging from apartheid South Africa. South Africa was an is a big driver of rugby research, and also prominent on the world rugby stage.) So I’ll take it with one big grain of salt.

          I bring up this example because it complicates the way we think about what it means to “tolerate” a diet. A lot of people with very anabolic metabolisms not only can be great athletes, but sometimes have to be in order to tolerate the typical western diet. (Or they have to change the way they eat).

      • Karl Borman says:

        Is there evidence to show that the Chinese or other Asian cultures are that much more active than western cultures?

        • Yes, for now. But this evidence pertains to non-urban areas, which sustain themselves primarily from farming or hunting. The examples that Scott was discussing have this characteristic. For this population, there are boatloads upon warehouses of evidence. A lot of people are interested in this: a population migration very similar to what we saw during the industrial revolution has been happening in a lot of Asia in the past 3 or 4 decades.

          The activity levels in Asian cultures aren’t peculiar to them: they occur simply because the present rural lifestyle of a majority of Asian people necessitates them. However, the activity levels of the majority of the population in Asian cultures (and across the world) is quickly beginning to approximate western culture. It is the very same effect, for example, that happened in Mexico. So you’re seeing a drop in activity levels in Asian cultures because more people are moving to population centers. Wind the clock back 100 years in the West and the exact same thing was happening, with the exact same health effects.

          So, in addition to having very good data on diet and activity levels in Asian cultures, there is also very good data on how (and presumably why) that diet and those activity levels are changing, and what the effects are.

          Generally speaking, insofar the diet approximates a Western diet, and activity levels approximate western activity levels, you’ll get similar results. You can find a more detailed answer on this topic in this answer to Wade’s comment.

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