THE ENERGY SPECTRUM Part 3: Benefits of Fats Plus Ketones, and their effects on aging.

It was around 1972 that I first experienced the wonders of super high fat burning and ketosis. It occurred during a two week fast (water only). Although a busy student and working part time in a fancy steakhouse restaurant, my energy levels soared, sleep was more restful, creativity and other brainpower improved in an amazing way. Little did I know that this experience would play an important role in helping future patients improve fat burning and overall health and fitness.

Long before glucose was the primary energy for the human body, fat burning was a key component of our physiology. Paleolithic ancestors enjoyed a diet high in fat with adequate protein and little carbohydrate. It was the ultimate natural therapy—the perfect eating plan that got us to where we are today. Of course, it was the only menu as no other foods were available, or required.

Millions of years later, this same eating plan has been “discovered” once again to have therapeutic benefits.

Just like we can raise the amount of fat we use for energy by reducing insulin, ketones follow the same pattern too, with their production increasing as carbohydrate intake is further diminished. This offers huge benefits for the body.

Ketones are a key energy source for the liver, brain, intestines and other body areas. The increased fat available to the aerobic muscles for faster activity and for longer periods can improve endurance. In addition, there is a real potential for increased health and fitness on many other levels. Here are some of them.

Exercising Muscle

The state of nutritional ketosis influences the body to use more fat for fueling muscles. In doing so, glycogen is conserved. This is important during competition, and for maintaining stable blood sugar during sleep.

Increased fat and ketone burning also reduces the body’s reliance on food and carbohydrate drinks during long training and competition. In a recently published scientific paper (“Rethinking fat as a fuel for endurance exercise,” European Journal of Sport Science, 2014) the authors state: “Common lore dictates consuming about 6000 kcal of carbohydrates during a competitive 100-mile race, but low-carbohydrate runners commonly finish (and often now win) these events on 1500 or less ‘in-race’ calories.”

Some athletes who develop their fat burning aerobic system very well don’t require any added nutrient. For example, World Champion Hal Walter relied only on water and his stored body fat for fuel for more than five hours of rigorous running in 2014 to win another World Championship Pack Burro Race.

Inflammation and Free Radicals

The significant reduction in dietary carbohydrate also dramatically influences the body’s balance of the inflammatory mechanism. The reason is simple: lower insulin reduces the production of inflammatory chemicals. This can reduce physical injuries, which are often associated with “itis” conditions such as tendonitis, plantar fasciitis, and arthritis, and problems elsewhere in the body such as gastritis, colitis and others. Ketones also have a positive effect in controlling our genes, and in regulating free radicals to help speed recovery from a workout, a race or a season.

Speedy Recovery

Because high fat burning and increased ketone bodies reduce inflammation and oxidative stress, we can recover faster from physical activity. This can even help us better tolerate the other stresses of life too. Without a healthy body, recovery takes longer because of increased production of free radical stress. But with increased fat burning and more ketones, athletes could train better, race more often, and increase performance—the trifecta of endurance sports.

Reduced Body Fat/Weight Loss

Many of my articles refer to the benefits of increased fat burning for weight loss and reductions in stored body fat (see The Fat Burning Journal).

Transitioning from moderate or high carbohydrate diet to a very low carb/adequate protein and higher fat regime can take a various amount of time depending on the individual. While the beneficial changes begin quickly, they can take up to two weeks or more to occur. The complete change may take a couple of months or more. So if you tried the Two-Week Test or eliminating junk food and you didn’t feel great, you may not have continued the process long enough. Not eating enough fats or total calories, not eating frequently, or cheating here and there are other reasons for little or no success.

With very low carbohydrate intake the levels of ketone bodies rise significantly. During this period of ketosis, some people experience bad breath. This is due to the release of a ketone body called acetone into the lungs where it is exhaled. The concentration of breath acetone may correlate with another key ketone, β-hydroxybutyrate, in the blood. However, once well adapted to increased fat burning and ketosis, the bad breath should be much reduced or eliminated.

The Brain

For about a hundred years, medicine has used a high fat-burning ketosis state to treat epilepsy in children and adults. This condition includes seizures, a serious sign of brain injury. Those who are successful can often reduce or eliminate the need for medication. However, since the development of antiepileptic drugs starting in 1930, these medications became the more convenient therapy despite “the continued failure of even newer drugs to offer significantly enhanced clinical efficacy” (Jasper’s Basic Mechanisms of the Epilepsies, 2012).

The increased use of ketones and decreased reliance of glucose in the brain also provides other recognized benefits referred to as neuroprotection. From Alzheimer’s disease and other cognitive dysfunction to Parkinson’s, most brain problems are preventable. Protecting the brain is one way to accomplish this, and a healthy eating plan promoting high fat and ketosis can have great value. Other brain and head conditions that have responded well to ketosis include headache, traumatic brain injury, sleep disorders, cancer, autism, and multiple sclerosis.

Another important feature of eating well is a high-energy brain that’s creative with great stamina, not to mention better learning and concentration.

Cardiovascular Disease

Lower carbohydrate intake can quickly and significantly reduce a variety of cardiovascular risk factors. Reductions in triglycerides occur rapidly in patients with high levels, typically within a few days. In addition, maintaining a reduction in carbohydrate intake can significantly balance cholesterol, lowering LDL and raising HDL, further reducing cardiovascular risk. Some individuals respond to modest amounts of carbohydrate reductions, while other must go further along the spectrum to ketosis for this to occur.

Low carbohydrate intake also quickly lowers insulin, which can significantly reduce abnormally high blood pressure. People should be cautioned that this sometimes happens in a few days too. Those with hypertension who are performing the Two-Week Test or just going off carbs “cold turkey” should monitor their blood pressure carefully. A health professional can do this while adjusting or eliminating medication as blood pressure normalizes.

Carbohydrate Intolerance

Whether diabetes, insulin resistance, low blood sugar or other names associated with the inability to properly metabolize glucose and insulin, these problems can change rapidly in response to healthy eating. By shifting metabolism to increase fat burning significant improvements in overall health follow. In fact, carbohydrate intolerance can diminish to the point where patients can live healthy lives often with reduced or no medications, including insulin. These changes can often take place very quickly too.

The Gut

By reducing carbohydrate intake, intestinal stress is often reduced too. Starches and disaccharides can impair gut bacteria, not to mention cause a high amount of gas production.

Athletes who no longer need large amounts of carbohydrate during training and racing also get relief with significantly less gut stress. In addition, because of reduced free radical stress and lower levels of inflammation, those who consume less carbohydrate foods may have overall healthier intestinal tracts, often able to rid themselves of conditions such as colitis, gastritis and other chronic gut disorders.


Sure, the addition of ketones to a high fat burning state offers many additional health and fitness benefits. An even more amazing advantage is the effect on aging. In addition to improving the areas of the body discussed above, two other factors play a key role in reducing physiological age:

As low carbohydrate intake elevates ketone bodies, there is a significant reduction of oxidative (free radical) stress. This could be a healthy way to influence longevity.
With a higher amount of fat calories consumed, many people eating low carb with adequate protein meals eventually require less food intake to maintain great energy levels. The result is a reduction in total calories over the course of a typical day. Caloric restriction is a popular theory that has been shown in test animals to biologically slow the aging process.

With such benefits—and there are others, such as hormone balance—many of which occur within days or weeks, it would seem everyone would want to eat well. What may be the two most common reasons for people unable to maintain a healthy diet are sugar addiction and fat-phobia.

The macronutrient makeup of our diet dictates the energy sources. On one end of the spectrum, poor eating habits maintain our dependency on glucose for energy with a fat-storing, unhealthy metabolism. But by reducing carbohydrate foods we move along the spectrum to burn higher amounts of fat for energy, reduce body fat, and improve health. Moving further along the spectrum by lowering insulin even more, ketone bodies elevate considerably and contribute significantly to our energy needs, with additional fat burning raising endurance, and health, to even higher levels. Our spot on the energy spectrum is all in our hands.


  • Bernie says:


    Can I take ketones in drink form to start the fat burning process. The product claims this. I am an ultra runner working on my MAF runs but have not dialed in the diet. I found this mix that claims to help. Thoughts?

  • Mircea Andrei Ghinea says:

    Not much to say for now, just: What An Article… What Comments… I’ll read again and again.
    Thank you!
    Best regards,

  • Grant says:

    I have been trying to answer a question I have had and believe I found the answer in one of your comments as I have been re-reading articles, but just wanted to clarify I had a correct understanding.

    So have I understood this correctly: When OPTIMALLY running at MAF HR the athletes RQ should correspond with a value of 0.85 which would have the athlete burning 50/50 (sugar / fat) and remaining just under lactate production. (It is possible for an athlete to be running at MAF HR but still have a poor RQ e.g. 0.95 (poor fat burning) until they better develop their aerobic system / improve diet).

    At this point lipolysis would be occurring resulting in acetyl-CoA being produced. For acetyl-CoA to enter the krebs cycle and be used it needs oxaloacetate. Now over the other side (the 50% sugar contribution) we are seeing sugar be broken down into pyruvate which then needs to be transformed into acetyl-CoA to enter the Krebs cycle.

    Rather than using the sugar for this process the body would be better served using the pyruvate to be converted into more oxaloacetate which can then aid the abundant acetyl-CoA from lipolysis to enter the krebs cycle. Oxaloacetate can be also used by the liver for glucogenesis when needed (assuming it is converting glycerol rather than amino acids?). As more and more lipolysis occurs greater amounts of acetyl-CoA will be present and will eventually outweigh oxaloacetate production, as oxaloacetate will start to be used for its other function glucogenesis to maintain blood sugar. At this point the excess acetyl-CoA is used to produce ketones.

    Have I understood that correctly?

    Now where I did have further questions was around why is lipolysis the preferred option here from an energy production standpoint. That is does this path produce significantly more ATP. My understanding is that aerobic respiration from either fats or sugar both produce 32 ATP. But my ochem is poor and I am probably missing something. An athlete could be working primarily aerobically from simply using sugar (pyruvate > acetyl-CoA > Krebs cycle > … > ATP). Why is fat so much better, is there a better ATP gain I am missing (besides the fat of running out of sugar) is there an energy gain here of greater ATP.

    Secondly during the process of developing your aerobic system to burn more fat what are the major physiological adaptations being made? Is there a stage where even though you are burning more fat your body is still ‘accidentally’ using sugar to be turned into pyruvate to enter the krebs cycle rather than using the pyruvate to be converted to oxaloacetate?

    Thanks as always for your help.

    • Craig:

      You did understand correctly. To answer your next question, I urge you to look at the body from a macro-scale, functional, “engineer” perspective, rather than a chemist’s. Here’s why:

      The Krebs cycle for sugar and fat is the same: you get 32 ATP because the compound you’re processing isn’t really “sugar” or “fats,” it’s acetyl-CoA. Since it’s the same in both cases, it has the same cost. Here’s the thing: fats beat sugar every time as the long-lasting energy source for the simple reason that you need 3 grams of water to bind every gram of glycogen stored. To put this in perspective, a 160 lb athlete with 12% (19.2 lb) of body fat has approximately 60,000 fat calories stored.

      Now consider that 1 gram of glycogen contains 4 calories. If these fat calories were instead glycogen calories, they would be represented by a weight of 15 kg (33 lb). To store these calories, you need 3 times their weight in water, which would bring the weight of a full fuel tank to 132 lb—almost 7 times (6.875) greater than if you stored these same calories as fats.

      So, this brings us to ask the question in reverse.

      If glycogen is so heavy, why would the body keep it around, when it has a (relatively) limitless supply of fats that it can combine with a limitless supply of oxygen to create energy? Simple: To power the afterburner.

      The big big reason the body keeps sugar (glycogen/glucose) around (and why we’ll never evolve out of it) is because sugar essentially works as the body’s emergency cash: when you need to fight or run away, sugar’s your fuel of choice. Why? Because since sugar affords the body the potential for its rate of energy production to exceed the rate of oxygen supply (anaerobic work), enabling the body to essentially cash in these emergency funds in short bouts of concentration and physical exertion.

      (Remember, the brain doesn’t really need glucose—it can work perfectly fine off ketones. It would like glucose to have an easier life, but that’s a different story).

      In regards to the question about sugar, you can always convert extra pyruvate to oxaloacetate through pyruvate carboxylation by hydrolyzing ATP (using water to extract energy from it).

      In my view, the biggest and most important adaptation is actually the calibration between the sympathetic (SNS) and parasympathetic (PNS) nervous systems necessary to create the hormonal makeup that produces lipolysis as well as fatty acid transport from tissues to muscles. The reason fat-burning stops at higher intensities isn’t because fat burning stops, but because the hormonal slant towards adrenaline and ghrelin at higher intensities activates insulin pathways (to transport the “turbocharger” fuel necessary for high-intensity activity) and deactivates leptin pathways, stopping the transport of fats.

      So, fat-burning doesn’t stop because you “actively shut down the engine,” but rather because you cut off the fuel source.

      NOT cutting off the fuel source (by way of maintaining the right levels of stress hormones and the correct balance between SNS and PNS activity), is, in other words, how you become able to develop all of the systems—mitochondria, capillaries, skeletal musculature—that we typically recognize as the “real” endurance adaptations.

      This is part of the deeper rationale for the 180-Formula and the MAF HR.

      Hope this helps.

      • Grant says:

        Thanks Ivan. That is very helpful. Interesting to read your take on the nervous systems and the hormonal balance going on. That calibration could take some time considering the length of time most people have trained primarily anaerobically and / or using sugar as their primary fuel for everything.

        Another reason to be monitoring HRV I guess as if you are seeing low scores then you are naturally going to be defaulting over to the sympathetic nervous system and stressing that out, which in turn leads to the wrong hormones being produced for what you are trying to develop.

        I think I can clearly see my biggest issue to developing my aerobic system is my poor sleep. 2 little kids and disturbed sleep all night is not allowing for proper restoration and reduced stress levels. Even though training and diet might be in order, sleep is letting me down. I have just changed up my program to reduce the number of early morning sessions and ensure there is a ‘sleep in’ day between early wakes to minimise stress and maximise rest. I also have built in more micro tapers into my weekly training based off a recent article on ‘taking it easy’. So thanks for all the work you guys do here I am absorbing it like a sponge.

        • Grant:

          Excellent approach, and you’re right on about HRV.

          That’s partly why I wanted to share that side of the story: once you start thinking about the aerobic system as more than a machine you go out and train, and instead as something that is interrelated with other important systems in the body, such as the nervous system (a leap you’ve obviously already made), the better your training response just because your intuitions about why you haven’t been improving are now that much more sophisticated.

  • Grant:

    Let me try an answer these questions. The explanation will be a bit technical and extremely long—sorry about that.

    The amount of carbs is different for everyone—and importantly, will be different for the same person given their present fat-burning capability AND the expected exercise duration. It’s very difficult to say. For example, supposing that I have a sum total of 150 glycogen calories stored, if my body expects to be exercising for a very long time, it may decide to go immediately into ketosis, particularly if its is highly capable at it.

    Ketosis is the state of production/consumption of ketone bodies. So the body can’t be in ketosis without production/consumption of ketones.

    LCHF does not exist in a vacuum. For example (and this harkens to your first question) for an elite distance runner, a 30% carb diet may be extremely LCHF, since they are burning through muscle glycogen, burning through liver glycogen, and their bodies may still have to burn a couple of thousand calories in fats (which means they will most likely be in some ketosis—more on this in a bit).
    About the mechanics of ketosis (bit of a OChem lesson here): The body has a two-part energy-burning process happening in the cellular mitochondria (kind of like a hybrid engine): Glycolysis (literally: sugar breakdown) and the Krebs cycle (the main engine of the aerobic machine). Glycolysis processes sugar and creates a bit of ATP (energy), and puts out either lactate or pyruvate as a by-product. For lactate or pyruvate to be put through the Krebs cycle, they need to be transformed into a molecule called Acetyl-CoA.

    This is where fat-burning comes in: when there are very few carbs in the body (and glycolysis a.k.a. sugar-breakdown can no longer happen), the body uses fat stores. Now check this out: fatty acids are broken down almost directly into Acetyl-CoA. But in order to pass into the Krebs Cycle (which is where the real energy production happens) a molecule called oxaloacetate has to be present to react with Acetyl-CoA.

    Ketosis arises when, due to the lack of carbs in the diet and in the body, the liver is using all the available oxaloacetate to produce glucose (a process called gluconeogenesis) for use in the brain. This means that the Acetyl-CoA resulting from fatty-acid breakdown doesn’t have anywhere to go: it can’t be put through the Krebs cycle because of a lack of oxaloacetate. So, it is used by the liver to produce ketones, which are instead being used for fuel.

    So ketosis generally occurs not so much because you are burning fats—which naturally happens during all aerobic exercise in order to provide Acetyl-CoA to drive the Krebs Cycle—but because there are so few available carbs that your body has no choice but to use that Acetyl-CoA to produce ketones.

    Personally, I think that ketosis is the ultimate state of energy metabolism in the sense that a state of perfect contemplative meditation is the ultimate state of subjective experience. In other words: awesome to have as a tool in your toolkit, and awesome to practice and be capable in, but not the state you want to be in all the time. Bad for when you need to go to a meeting, solve a math problem, or have a political discussion with another human being. To use another metaphor, while 6th gear may be the ultimate gear, you actually need the other 5 gears for a whole bunch of different situations.

    Having tempered my argument with this, I think that being able to create states of ketosis (and actually doing so consistently) is a hallmark of aerobic function. Hitting the Wall (at mile 16 of the marathon) is a state of athletically incompetent ketosis: all the sugar is gone because it was burned anaerobically and turned into lactate, which necessitates further energy expenditure to be turned into pyruvate and even further expenditure to be turned into Acetyl-CoA. When the body is that exhausted, that’s not going to happen. The brain is out of sugar and can’t use fatty acids (a.k.a. the body is bad at breaking down fats) in order to produce Acetyl-CoA and drive the Krebs Cycle.

    Although the ideal race situation would be to use fats to produce Acetyl-CoA and have the brain feed itself off the liver glycogen, in an ultramarathon, when all that glycogen is depleted—because it will be—you need gluconeogenesis to provide sugar to the brain. So a trained ultrarunner will constantly be replacing their glucose with gluconeogenesis, still have enough oxaloacetate and Acetyl-CoA to drive the aerobic engine and be in ketosis at the same time, since levels of Acetyl-CoA will exceed their available oxaloacetate.

    (Now you see why we needed the chemistry lesson above).

    Your final question: there’s no real way to “train” burning acetyl sugars, in that sense. The best way to create ketosis is to drive the Krebs cycle until you are out of sugar, and then start producing sugar in the liver, using up oxaloacetate and accumulating Acetyl-CoA from fat breakdown.

    To harken back to the “gear” metaphor above, in the human body the gears would be this:

    1st: ATP-PC
    2nd: Glycolysis
    3rd: Krebs Cycle
    4th: Ketosis

    • Grant says:

      Wow thanks Ivan. I really enjoyed the long and detailed response and it really help clarify a lot of different aspects for me. It did however raise a lot of new questions, but these are now more related to how to apply this chemistry lesson to the practical aspects of training and what the desired outcomes of training are.

      Can we try link some of the chemistry / science / research papers to suggested training principles:

      – For example training in a fasted state aerobically (at or below MAF) e.g. as soon as you wake up at 6am teaches your body to start producing Acetyl-CoA from breaking down fatty acids rather than burning sugar via Glycolysis.
      – Glycogen and our bodies stores of this appear critical for racing / hard sessions. E.g. muscles store 300-400grams and liver 90-150grams hence we would need to ensure these stores are completely full before a race (1 hour sprint tri, 2 hour tri, or half or full IM). In all distances it is critical to have full glycogen stores, right?
      – By eating high fats and low carbs you are ensuring your body is utilising fat burning during the day rather than burning sugars all day aerobically. Your body due to the lack of insulin spikes allows for less fat storage and opening up of the fat stores for everyday energy which can then be shifted to exercise also (the bodies ability to just keep using fat for energy).
      – So around long training days and purely aerobic sessions it would be a good time to work on entering a state of ketosis by reducing carbs to the point that Acetyl-CoA is used by the liver to produce ketones. Putting yourself in states of ketosis throughout the week at different points teaches the body to become more efficient at producing ketones? And using them? This needs to be trained, hence the purpose of going into states of ketosis?
      – Training more aerobically (80%) is teaching the body which element of the chemistry here? To skip gear 1 (ATP-PC), skip gear 2 (Glycolysis), use gear 3 (but not from pyruvate but from the breakdown of fatty acids), and to learn gear 4 (Ketosis). However to get to Ketosis one would have to empty glycogen stores from a training run / ride? So that Gluconeogenesis would occur (using up available oxaloacetate to produce glucose) and leaving an excess of Acetly-CoA in the system to be used by the liver to create Ketones. So this would mean train in a fasted state, with already very low glycogen levels from a reduced amount of carbs in the week? (not a good race strategy I assume, but good training of these systems). However I see from your comment “For example, supposing that I have a sum total of 150 glycogen calories stored, if my body expects to be exercising for a very long time, it may decide to go immediately into ketosis, particularly if its is highly capable at it” that it is possible to enter ketosis even if there is glycogen available? Why would the body choose to produce glucose in the liver through the processes described and produce ketones for energy if glycogen still existed? Is this an adaptation we are trying to train?
      – To then complete a hard session, anaerobic or something where you wish to work max power etc, fuelling up on glycogen would be appropriate? Or are you still best to try complete these sessions from the same state as above? Can your body produce ketones fast enough to meet high energy demands? Can your liver produce glucose fast enough from gluconeogenesis to meet high energy demands? E.g. working anaerobically is this process fast enough? *
      – To aid recovery and ensure immune support, post workout should we be consuming carbs? Or do you promote something else, e.g. stay in a state of ketosis and use ketones for recovery? Allow gluconeogenesis to replace glycogen stores?
      – Training MAF and eating LCHF teaches the body to become ‘good’ at breaking down fats to produce Acetly-CoA and drive the Krebs cycle? It also teaches the body to enter states of ketosis even when glycogen is present?
      – Your description of the ideal race situation has me asking 3 questions:
      1) Is this ideal only if the athlete remains at an aerobic HR, that is they do not require any of that glucose from gluconeogenesis for the muscles but only to power the brain?
      2) What happens in shorter races where HR is more anaerobic the whole race e.g. 2 hour olympic distance triathlons? Is the ideal race situation the same?
      3) Rather than worry about gluconeogensis, what about just merely ingesting some carbs? Besides the fact that the athlete has to do this and rely on aid stations, and have the stomach to handle without GI issues are there any other benefits of not not ingesting carbs?

      *I know a large portion of training at or below a MAF HR is to increase the ability to run faster at the same aerobic HR. Hence you may be able to complete longer events purely aerobically and not have to ever go anaerobic (IM / Ultra-marathon). But what about shorter endurance events 1-2 hours? The larger aerobic engine means that this process can be supported better and at faster paces, but the anaerobic portion is going to require significant amounts of glucose. Obviously the more load you can keep on the aerobic engine the better, particularly if you can hit desired paces from mostly aerobic.

      I really appreciate your answers and I hope these long responses and explanations benefit the other readers.

      • Grant:

        It’s a pleasure to answer interesting questions from dedicated readers. So the first few paragraphs are more description, but I get to some concrete stuff farther below.

        Generally speaking, it is critical to have the glucose tank “topped off” during races, which is why ultramarathoners consume some modicum of carbohydrates throughout the event. Burning stored glucose/glycogen will give you orders of magnitude more fuel than you could ever get from gluconeogenesis. This is why, for all intents and purposes, ketosis is the highest gear, matching all the characteristics of a car’s drive train (first gear has a lot of power but uses fuel at an astounding rate; 6th gear has very little but preserves fuel) except for one: ATP-PC, glycolysis, lipolysis, the Krebs cycle, and ketogenesis (the production of ketones) are all different energy systems.

        This is relevant to your question of how to train ketosis/why the body would start burning ketones before glucose has been exhausted: anticipation. When the body has experience with ketogenic states, and is asked regularly to go all the way into ketosis, when you warm up for a long event, it’s going to anticipate the need for ketosis: it isn’t going to wait to exhaust its sugar completely because it already knows that it’s going to have to start replenishing it at some point.

        IMPORTANT: The reason that ketosis gets activated isn’t so much that there’a very little glycogen (that’s why gluconeogenesis starts) but rather that levels of Acetyl-CoA are so high that the liver feels “flooded” by Acetyl-CoA. So, if you’re the liver, and you see a lot of Acetyl-CoA in the bloodstream, you don’t really know whether it means that there’s very little glucose left or just a lot of lipolysis. This is the kicker: either way, you know you’re in an endurance situation. So you might as well do the reasonable thing and start using that Acetyl-CoA to create ketones.

        While a car has to stop using each gear when it moves on to the next, there is no good reason why the body needs to stop doing so UNLESS it has exhausted the fuel for some energy system (ATP-PC, glucose, oxaloacetate, Acetyl-CoA, etc) OR it doesn’t know it can do that. In other words, while a car can only use each gear serially (one after the other), the body can activate all of its gears in parallel. In fact, each of the later gears feeds at least one gear before it: glycolysis produces ATP, feeding ATP-PC. The Krebs Cycle feeds ATP-PC, lipolysis feeds the Krebs Cycle, and ketosis feeds glycolysis (through gluconeogenesis) and ATP-PC. So, the parallel activation of all these systems (which is what MAF training facilitates—more on this at the end) turns the body into a highly capable machine.

        So why don’t we do this in the first place? (This gets at how to train this). Because we don’t know how. Picture children playing: they’re constantly taking first gear up to the max: they sprint and then go into tripod position. Sprint and go into tripod again. They’re glycolytic machines. That’s OK—as they rest, they use mitochondria to process all that pyruvate and lactate, developing second gear. And when a teenager “gets” second gear, they use it to the max: they burn through all their sugar aerobically, and they get tired and stop exercising. In order to fuel their body the rest of the day, they ideally start burning fats—using lipolysis. Now, you’re a twenty year old, entering into marathon territory. You’re taking the gears more slowly: instead of revving the engine and taking first gear into the red (burning through all the sugar), you leave some available. You’re trained to use the Krebs cycle when glycolysis is still only at 2000 rpm. Ditto for lipolysis: by the time you turn on lipolysis (3rd), you’ve still got 3/4 of the sugar tank. And the sugar lasts you until mile 20: THE WALL. But see what happens?

        To keep the gear metaphor going, the child takes first gear from zero to 40. The marathoner takes first gear from zero to 15, second from 15 to 30, and by the time they hit 40 they’re already on 3rd. Trying to stick with first gear at 40 MPH will empty your tank very quickly, but the little kid doesn’t know that. The seasoned, 35 year old marathoner knows that the principle applies all the way to ketosis. Why? Experience. When we anticipate a long race, it’s not just a subjective event (according to Tim Noakes, at least. Check out his central governor theory). Our body is revving itself up for that particular distance/duration—even that particular race. That’s why prerunning is a thing in Le Mans and in the Boston Marathon. And for the endurance runner, that might mean getting to ketosis ASAP.

        OK. Concrete training ideas:

        1) As alluded to in the first paragraph, in order to seriously train power, you need to ingest glucose and have glucose stores. You’re not going to get it from gluconeogenesis.

        2) In shorter races, the ideal energy situation changes: Usain Bolt doesn’t even worry about the Krebs Cycle: he’s burning through far more sugar in a second than he could process through his mitochondria in a minute. In a 2 hour distance, you’re still mostly talking about lipolysis (fat-burning). Why is lipolysis so important? In a nutshell, because pyruvate is the precursor for both Acetyl-CoA and oxaloacetate. If you’re getting the Acetyl-CoA from lipolysis, then you can turn all of the pyruvate into oxaloacetate, meaning that you can drive the Krebs Cycle faster and for longer. Similarly, this means that you’ll have more oxaloacetate left over for gluconeogenesis. It’s really only after the 2 hours that you seriously start using ketones. Generally, the best way that I can think of for training this (at least for the first few months) is by going for a long walk after your long run.

        3) To produce great race results, sure, just ingest some carbs. But a body that puts all of those carbs into producing pyruvate to drive the Krebs cycle will have the best results in an endurance race. That’s why you train at an aerobic heart rate—incidentally, the heart rate at which you’re driving lipolysis at the same rate as the Krebs cycle, so that you’re getting Acetyl-CoA from fats and oxaloacetate from pyruvate, as I mentioned above.

        4) Post-race/workout, I stick with very low-glycemic carbs, and a bit of carbs: a salad, Phil’s shake; I love beans and tortillas with lots of sour cream and cheese and avocado. I don’t want to kick up my blood sugar and give my body an excuse to just produce all the ATP it needs anaerobically (which would put me in a catabolic state when I want to be anabolic), but I also want to give it the fuel it needs.

        • Grant says:

          Thanks so much Ivan. Things are a lot clearer and I am getting a better understanding of how the diet and MAF training fit in the chemistry and what you are trying to train / teach the body to do more of / be better at.

          I would love to see some more articles here on training principles and even some more science articles on the Krebs cycle and what both heart rate training and LCHF diet is achieving.

          E.g. as an athlete it appears tricky to get the balance of LCHF with training volume and balance of MAF (80%) and anaerobic (20%). For example when to work on ketosis and when to ensure glycogen stores are adequately full for particular training sessions or races. I am starting to better grasp this from your feedback and articles but I think it would really benefit to add some more articles on this.

          – Train 2 hours (long run) then walk for an hour and don’t eat any carbs post walking for an hour to get the body into ketosis. Eat some fats and protein post long workout at x quantity and here is why…
          – For your anaerobic work (20%) ensure you are adequately fuelled with glycogen by eating x amount of carbs y time before training because your body cannot produce energy fast enough from fats alone to achieve desired session…include science of energy systems, krebs cycle.
          – Training in a fasted state vs coffee with fat before hour aerobic training run? Which is better, what teaches the body what? Does the ingestion of fat promote more lipolysis that fasting alone?
          – Teaching the body to go in and out of ketosis throughout a training week by doing x and y training and ingesting of carbs for particular sessions…
          – Pre race nutrition and how much carbs to ensure glycogen stores are full, night before meal and morning of race would be extremely helpful to understand…both 2 hour races and 4-5 hour races etc.

          I would love to see more on this if possible. In fact it would be extremely helpful to see a chart / diagrams showing the energy systems and krebs cycle and how each of the principles here link to each one. E.g. by training in a fasted state you are working on this part of the krebs cycle….your body breaks down fatty acids and converts to acetyl-CoA then it enters here with x and does y.

          Love the articles and hope to see more. Thanks again for your detailed replies.

  • Jason says:

    Hi Ivan:

    Quick question: I am eating strictly according to the 2 week test (no sugar, very few carbs from veggies, etc.). I’m about 5 days in (feel great, by the way). I’m also training as I have been for the past 3-4 years (running about 40 miles/week). I’m trying to adjust to the MAF training method, but haven’t zeroed in yet on the low heart rate training. Just out of curiosity, if I’m training above the MAF recommended heart rate on a limited carb diet, what am I burning as fuel?


    • Jason:

      You may be relying on a little bit of muscle or liver glycogen stores that your body converted from fat while you were at rest. You’ll know this is the case if after a few minutes of exercise your athletic output plummets and your stress levels (and often your heart rate) shoot up. But let me answer your question a little better.

      There are two parts to the aerobic system:

      1. The cellular mitochondria, which burn sugar in the presence of oxygen.
      2. The rest of the aerobic system, which transforms fat to sugar, to feed it to the mitochondria.

      Here’s why this is important: if you don’t have that much sugar available, you are forcing your body to burn fats (or, if you have very very little sugar available, you might be burning ketones). But the problem is that if you ask your body to perform at a very high level, your stress will rise (meaning that your heart rate rises too). And a rising heart rate almost always corresponds with increasing anaerobic function. So even though may be still converting fats to sugar, a lot of times you’ll be burning some of that sugar anaerobically, either because you are too stressed or (in the case of a marathon you didn’t train well for) the mitochondria may be too tired to keep processing all that sugar aerobically. As an example of how this works from the opposite end, a lot of people who are chronically stressed but don’t exercise may be walking around 10-15 BPM below their MAF heart rate. Even then, because of their stress levels and the anaerobic function that implies, they are still producing some lactate. That, incidentally, is why chronic stress damages the body.

      Let me put it more simply: If you’re going to be below the MAF heart rate, you can get by on fats/ketones. If you want to go above the MAF heart rate, you need some sugar. If you don’t have it, your body will get unduly stressed. And when you get unduly stressed, all bets are off.

      • Jason says:

        Thanks for the very thorough response, Ivan. Incredibly helpful. It sounds as though it is a matter of efficiency. On a very low carb diet, training above the MAF heart rate places my body under stress, which makes the fat-burning process less efficient.

        One more quick question: when I train according to the MAF heart rate, I can usually run slowly for about 4-5 minutes, before I begin to approach 150 bpm (my target). I then walk for about 15-20 seconds until I drop into the low-130s, and then start jogging again. (I run mostly on trails, so the slight hills and obstacles cause my HR to climb.) After my workout, when I look at my HR chart, instead of seeing a consistent line at 145-150, I find a series of peaks that climb from 135 to 150 and back down over a stretch of about 4-5 minutes. Do the peaks suggest that my training is less effective? Is it okay to waver back and forth between a 15-20 beat range (walk/run), or should I aim for a more consistent pace (even slower running)?

        Thanks again for your help.

        Warm regards,

        • Jason:

          You’re welcome.

          The reason you want to train at MAF is to prevent stress (from anaerobic function) from accumulating so much that your body can recover from it. So, if there are a few peaks in your heart rate, you may be well below the critical threshold of stress, meaning that your body may still be able to fully recover before your next workout.

          However, as you increase training volume, and your aerobic system becomes more powerful, you’ll be increasing in speed and distance, which means that your body will be under more physical stress from the forces involved (and wear and tear) even if there is no anaerobic stress. So, ideally, as you get better, something to work towards is finding that consistent pace. But you don’t have to fret over it, as long as you improve your pacing as you improve your speed and endurance.

          Generally speaking, it pays to be conservative. For example, my MAF heart rate is 148. After a 8 mile MAF run I’ll typically have an average heart rate of 144 and a peak heart rate of say 155, because maybe my heart rate got out of hand on a hill. I don’t worry, but that lower-than-MAF average (as well as my constant checking) tells me I was in the sweet spot the overwhelming majority of the time.

  • Sebastian says:

    Hi Ivan,

    Could you please share the principles I should follow to gain weight. I’m very lean, have about 5% body fat and my low weight is a concern to me. On the other hand, I’m following the MAF method and I’ve never felt better in my life. The 2-week-test proved that I’m very sensitive to carbohydrates. I’ve read Phil’s books with understanding so I know them. Thank you.


    • Sebastian:

      The question you should ask yourself is this: is the reason I want to gain weight because my health, mobility, or cognitive function is being impaired by my weightloss?

      If not, there’s no good reason to put on weight.

      Remember, we humans are lean mean endurance machines. We’re built to be slim and slight and fast, and if your body is at its healthiest that way, then that’s the weight you should be at.

      That said, if you do want to gain weight (and I am not recommending this, but rather informing you), the best way to do so is to mix up a high-fat high protein shake (some 500 calories worth) and drink it sometime in the middle of the night. Nighttime is the period of your day that you typically spend the longest between meals. That said, if you do that, you’ll probably won’t be as healthy as you are now.

      • Sebastian says:

        Hi Ivan,

        Thank you a lot for your response. It was eye opening for me. I thought that my weight 68kg (150lb) is too little for my height of 186cm (6,10ft).


  • Hi Phil,

    Thanks for the great articles. Mine is more of a question than a comment. You mention reducing carbs is obviously beneficial. But what about effectively removing carbs entirely from your diet. Is this recommended (if one is so inclined) and is there any downsides or risks by doing this. So for example would it be safe to continue the two-week test diet recommendations permanently?

    Thanks again.

    • Robert:

      Thanks for your comment. I would say that only in very special cases. Although a low carb high fat (LCHF) diet, for example, has many benefits, a diet that has absolutely no carbs may be a problem. For example, it’s very difficult to sustain even a modicum of anaerobic activity without carbs in the diet. The first question to ask is: what are the effects on your body? (Low carbs usually means a higher proportion of protein in the diet, which can stress the kidneys). Are you in a minimal carb diet on a whim, or is there a reason that has to do with your body’s functioning?

      (Given your particular body and your body’s situation, a very low carb diet may not be a bad idea. But it’s important to know if your body is in that such situation).

      • Grant says:

        Hi Ivan,

        This article talks about the benefits of ketosis and increased ketone bodies and other comments / articles discuss athletes might need more carbs for workouts / cannot complete a modicum of anaerobic exercise without carbs.

        So I have a range of questions to help me clarify a few things:
        – At what level of low carbs does the body produce ketone bodies? ( <25grams / <50grams / <150grams / <200grams etc). Tim Noakes highlights that some of his athletes required 125grams of carbs, however what does this do to the state of production of ketone bodies?
        – Can the body produce ketone bodies without being in ketosis?
        – What are the benefits of LCHF if the low carb aspect is not low enough for ketosis which sounds like the ultimate state to be in from this article?
        – If you come out of ketosis how long does it take to get back in if you reduce carbs?
        – Is a state of ketosis achieved only when the body completely stops using glucose for energy and uses only ketone bodies?
        – If you adopt a LCHF diet and reduce carbs to a level where you feel good (e.g. 150grams) are you getting the benefits of ketosis and ketone bodies or are you just getting the benefit of looking after your insulin levels and those health benefits?
        – Is the ultimate goal to get into ketosis? Should we be reducing carbs to as close to 0 grams? Should we be striving to require 0 carbs during a 5 hour event?
        – If we adopt a LCHF diet, we become more 'fat adapted'. What does this mean if not ketosis? Can we just learn to use fats better for energy (without ketosis and ketone bodies) or is that the only way? E.g. training our bodies to become faster at using acetyl sugars in the krebs cycle and more efficient at burning ketones that are created from excess acetyl sugars?

        Some questions are similar etc but trying to better understand what you are promoting. Is it ketosis and what is that exactly (definition), or is just becoming fat adapted which references increasing the bodies ability to break down fat for energy and use that broken down fat.

        Appreciate your comments as always.

Leave a Reply