Can Keto Actually Work For Hard-Training Endurance or Power/Strength Athletes?

inline_sami_rowingKeto is red hot these days, and it’s not going away anytime soon. Call it the latest dietary fad, but keep in mind a great insight Robb Wolf told Joe Rogan on his podcastketo was “likely the default human metabolic state” over the past 2.5 million years of human evolution. Only with the extremely recent (on the evolutionary timeline) advent of civilization have we been stuffing our faces with carbs and snuffing out our magnificent ability to generate ketones as a clean-burning alternative fuel source to dietary carbohydrates. And we certainly were compelled to evolve a highly efficient mechanism to keep our high energy demand brains fueled with glucose or the glucose-like substitute of ketones at all times—for this was a matter of life or death in primal times. When our ancestors were starving, they needed to keep working hard, and concentrating hard, to find food!

The thought leaders and scientists in the keto scene have been establishing the case for keto very well: ketogenic eating really works for virtually everyone if you follow the correct approach. You can expect not only the efficient reduction of excess body fat, but a profound anti-inflammatory effect that can correct assorted autoimmune and inflammatory conditions; improved cognitive function and protection against the disturbingly prevalent conditions of cognitive decline (that are being increasingly connected to high carb, nutrient deficient diets); and assorted anti-aging benefits such as enhanced autophagy (the natural cellular detoxification process) and apoptosis (the programmed death of dysfunctional/pre-cancerous cells).

Keto has also been touted as potentially improving athletic performance for both endurance and strength/power efforts. However, this has become a matter of some dispute in the fitness world, as high calorie burning folks have a hard time embracing the idea that they can benefit from consuming fewer calories and rejecting the obsession with immediate refueling to restore glycogen after vigorous workouts. Today’s post will introduce you to the amazing Sami Inkinen, one of the world’s most accomplished endurance athletes who also has a high profile career as a Silicon Valley entrepreneur. Sami has taken keto experimentation to the extreme, and quantified everything beautifully to illustrate the amazing transformation that happens when you become a fat- and keto-adapted as an athlete.

The Keto Reset Diet goes into great detail about how keto can benefit endurance performance by making athletes virtually bonk-proof—able to perform for hours on end with a dramatically reduced need for carbohydrates as a fuel source. Sami’s story is told in further detail in Primal Endurance and on his blog. Here, he has taken the time from his busy schedule to share some extensive thoughts on how you really can succeed in endurance sports while eating ketogenically, if you follow the correct approach.

Being fat- and keto-adapted is an obvious benefit for endurance, since endurance performance is predicated on being burning more fat and sparing glycogen. The benefits of keto for strength/power athletes is less logical, because high intensity, high glycolytic (high glucose burning) workouts would seem to beget carbohydrate consumption in order to recover and replenish glycogen-depleted muscles. However, keto pioneers in the power scene have discovered amazing results, which are being increasingly validated by science at places like the Applied Science and Performance Institute in Tampa, FL, with Ryan Lowery and Dr. Jacob Wilson. Luis Villasenor, the legendary “DarthLuiggi” in the keto scene, has followed a ketogenic diet as a competitive powerlifter and bodybuilder for some 16 years! Through his program, he and his team have coached thousands of high intensity athletes to improved performance and improved body composition. Luis is a living, breathing example that you do not have to destroy your health with massive overconsumption of carbs and protein to maintain a bodybuilder physique.

We’ll hear more from Luis and others about how to utilize keto for high intensity performance in the future. Briefly, fasting and ketogenic eating have been shown to have a remarkable protein-sparing effect. It makes evolutionary sense that your body would initiate assorted mechanisms to preserve lean muscle mass when you are starving. Unfortunately, in the carbohydrate dependency paradigm, your body routinely converts lean muscle tissue into glucose via gluconeogenesis to meet your energy needs, especially for the brain (only two percent of body weight, but consuming 20-25 percent of total calories!)— a ravenous consumer of glucose. For carb dependent athletes who don’t remain constantly glycogen stocked, bad things happen with fatigue, delayed recovery, and loss of lean mass. This is why bodybuilders have been urged to eat their six small meals throughout the day and obsessively overconsume protein and carbs to spur growth. Luis and others have shattered this paradigm by getting big, strong, and lean in full keto mode.

Back to endurance, where for decades the conventional thinking was to carb load with your evening pasta feeds and morning cereal troughs, train super hard so you can go harder and longer without falling apart, and possibly train the body to store more glycogen (yes, it’s possible to a minor extent, but soon you will learn how irrelevant this is), and to stuff sugary drinks, gels, and cubes down your throat, hopefully without gagging. Finally, it was believed essential to stuff your face with more carbs immediately after workouts in the so-called “window of opportunity,” when your muscles can restock glycogen optimally.

We are in the age of a transformation in the endurance scene to the extent that I might boldly proclaim that the endurance champions of the future will possibly be full keto or at least cyclic keto to gain a performance and recovery boost. To date, our endurance champions have fueled their efforts with sugar and beige glop—my pet nickname for grains. Who can forget when Olympic swimming legend Michael Phelps’s diet was presented with great fanfare a decade ago as totalling 12,000 calories a day, featuring heaps of refined carbohydrates. Phelps later admitted to exaggeration, and readers at this site can appreciate the irony of his correction that he really only ate 8,000-10,000 calories…featuring heaps of refined carbohydrates. I still get giggles for a quip I wrote over 30 years ago in my first endurance training book relating to the prevailing ethos of the endurance community: “if the furnace is hot enough, anything will burn.” I related my impressive pre-race meal before my fastest marathon performance: a couple beers, a bag of frozen peas, and a half-gallon of rocky road ice cream—pretty much all that was available at my bachelor pad that night!

As our sophistication in training methods and health and nutrition science grows, we can all appreciate the destruction caused by eating garbage while pursuing ambitious fitness goals, especially when training patterns become chronic. The awakening is upon us, but unfortunately it seems like many athletes are stuck in the old paradigm. Sugary drinks, bars, and gels are still flying off the shelves, and the community as a whole is freely dispensing hall passes to each other and themselves to indulge in nutrient-deficient foods on account of their impressive workouts.

Sami and his mind blowing performances and self-experimentation results serve as a true inspiration for endurance enthusiasts to try something new with an informed and disciplined approach, and reap phenomenal benefits. Not just performance benefits (how about Sami moving his theoretical “time to bonk” value from 5.6 hours while carb dependent to 87 hours when fat adapted?!) but also health and freedom from disease risk factors driven by high carb eating and burning patterns. Enjoy the following commentary from Sami, encouraging athletes to consider a ketogenic approach.

Traditional advice for endurance athletes is to “carb-load” and to consume enough carbohydrates before, during, and after a race for fuel through the entire event and for recovery. But what if I told you that you could run or ride your bike for longer without hitting the dreaded wall? What if I told you that you could even recover faster and improve your metabolic health? All of this is possible, but only if you throw out the advice we’ve all been given about carbohydrates and exercise.

There’s a different path when it comes to fueling our bodies—a ketogenic diet. Restricting carbohydrates and relying on most of your calories as fat induces a state of nutritional ketosis, meaning that your body will use fat—both dietary and body fat—as its primary source of fuel. Even the most lean athlete has tens of thousands of fat calories on hand, so it makes sense to use them! The key is knowing how.

Here are 3 of what I believe to be the most compelling reasons for an endurance athlete to make the switch from a high-carb to a high-fat nutrition plan:

1. You can become virtually bonk-proof

As athletes, we want to be our best and be able to compete at our best. We prepare for months or even years with training plans for both our performance and our nutrition in hopes that we leave our best out on the course. Despite our strongest efforts, many of us know it’s possible to get to a point during exercise when we ‘hit the wall,’ regardless of how well-trained and prepared we are going into an event.

‘Bonking’ or ‘hitting the wall’ typically occurs after about 2 ½ hours into continuous, hard exercise, which corresponds to when glycogen (glucose stores) is really low. When exactly this happens depends on how long and how hard you’re pushing, but when your body can no longer meet the energy demands, it is essentially an energy crisis for the brain. You’re fatigued, not able to think clearly, and if you’ve ever experienced this during an event, you know that it’s simply miserable.

Ever since I experienced my first bonk on my bike, I’ve tried to figure out how to make myself bonk-proof, and eventually realized that I couldn’t do this by simply adding more and more carbs to my nutrition plan. When we eat and train with carbs, our bodies rely on them, but we have a limited ability to store them with a capacity of only 500-600 grams of glycogen (glucose stores), or about 2,000 calories. I’d have to eat gels and bars every 30 minutes to extend the point at which I’d run out of energy, but the ability to eat and absorb that energy while exercising is limited. Alternatively, we have the ability to store nearly unlimited amounts of fat. Even a very lean and small (~120lbs) athlete with low 7% body fat still carries about 30,000 calories of fat. Imagine being able to use that during a race!

So I learned how to rely on fat instead and my brain can rely on ketones (that are produced from fat by the liver) for a nearly unlimited supply of fuel. I’ve essentially made myself bonk-proof, and with fat as my primary source of fuel, I don’t need to eat anything at two hours anymore. It’s literally a game-changer! But becoming a fat-adapted athlete takes time. It doesn’t happen overnight. Just like training for an Ironman doesn’t happen in a week or two, neither does training your body to more efficiently burn fat. Once you become adapted to nutritional ketosis, or keto-adapted, there are several benefits. You rely less on the limited amount of carbs your body has and can more easily and quickly rely on your body’s fat for fuel. You increase the rate at which you utilize fat and you no longer ‘hit the wall’ at 2 ½ hours into an endurance event, even if you don’t have food available. In fact, the recent FASTER study demonstrated that fat-adapted athletes oxidize (i.e. burn) fat at a rate more than twice that of high carb athletes, which means the body has a better ability to access its fat and oxidize it for fuel.

2. You can recover faster

Being a successful high-performing endurance athlete isn’t just about the moments when you are working out or competing. It is also about how quickly you recover so that you can resume your usual workout regimen. Most athletes are familiar with the inflammation, soreness and swelling that comes after any hard workout or race. While some inflammation is necessary to increase muscle strength and is part of recovery from exercise, too much inflammation can interfere with the body’s repair process. It’s a balancing act. Many athletes will try just about anything to reduce post-workout inflammation, from ice baths to taking anti-inflammatory medications to chugging beet juice.

The less pain and soreness you have post-workout, the sooner you can go hard in your workouts again, and the better you might perform in the next race. After fully adapting to nutritional ketosis, I felt (subjectively speaking) a lot less sore and got rid of frequent nagging things like inflamed achilles tendons following the same workouts—racing my wife up Mt. Tamalpais [A 2,500-foot peak in Marin County, CA—just North of San Francisco], while just as strenuous as the times I had done it as a high-carb athlete, didn’t leave me with the same muscle soreness in the days after. It turns out that ketones don’t just function as important energetic molecules, but they have positive effects on cellular processes as well. Studies show that a well-formulated ketogenic diet reduces inflammation levels. Furthermore, I can get right back on the bike the very next day, meaning that I can train more frequently and don’t need as many recovery days.

3.  Your health may not be what it appears

The appearance of physical health and “fitness” can hide serious medical issues. Even if you are fit, strong, and lean, you may not be metabolically healthy.

I had no idea that this was true for me until around 2011-2012. I became a triathlon world champion in my age group and found out that I was prediabetic and metabolically unhealthy—my glucose values were consistently way above healthy ranges. Despite my years of high-level endurance sports, strict performance diets that perfectly aligned with the dietary guidelines, and very low body fat, I was on my way to developing type 2 diabetes. I was shocked to find out that following the low fat and ‘quality’ high carb dietary recommendations had led me to the brink of diabetes, but I was also determined to dig myself out of this hole. Type 2 diabetes and prediabetes are typically treated with medications (and, for some people, eventually surgery), but I wanted to try fixing my metabolic health myself. If following the dietary guidelines had led me to prediabetes, I thought there might be a way to reverse prediabetes—perhaps even by following the opposite approach.

My deep dive into published research led me to realize that the high carb diet recommended for athletes instigated my prediabetes by constantly spiking my blood sugar, and that my intense, regular, high-volume exercise had not been enough to keep my blood sugars in control. It turns out you can’t exercise enough to outrun bad nutrition advice. After finding peer-reviewed clinical research demonstrating that a high-fat, moderate protein, and low-carb ketogenic diet could help me reverse my prediabetes, I completely changed my nutrition plan and started tracking my blood sugar and ketone levels. I was amazed at how useful the regular biomarker information was to tweaking my diet around my body’s individual response.  Everyone truly responds differently to the same foods based on genetic differences, and you never know for certain until you test regularly. By switching to a well-formulated ketogenic diet and a data-driven approach, I successfully reversed my prediabetes and improved my metabolic health across the board.

The bottom line is that sustained nutritional ketosis has allowed me to:

  1. Increase my endurance capacity by providing me access to a larger fuel tank
  2. Reduce post-workout inflammation and thus recovery time, increasing valuable training time
  3. Reverse my prediabetes and improve my metabolic health

You can learn more about nutritional ketosis here in an FAQ by Dr. Stephen Phinney.

In Sami’s journey to becoming bonk proof, he painstakingly tracked his progress in repeated laboratory tests where he measured fuel substrate utilization while riding a stationary bike at a comfortable pace. The results as explained in this graph series (below) are astounding. Ditto for the details of the highly regarded FASTER Study, which compared the fat oxidation rates among elite ultramarathon runners who were on a low-carb, fat adapted diet to elite counterparts consuming a traditional high carbohydrate diet. Dr. Peter Attia, one of the most brilliant minds in the keto scene who now focuses on longevity medicine at his private practice in San Diego and New York City, has also chronicled his amazing transition from sugar burner to fat adapted cyclist. Attia went from burning 95 percent carbohydrate calories at anaerobic threshold to burning 25 percent carbs and 75 percent fat at the same threshold heart rate after a devoted period of dietary transformation. What’s more, Attia achieved an increase in wattage output at anaerobic threshold when fat adapted—in other words, he went faster on fat! This data shatters the notion that keto is only for long, slow endurance performance.

Take a look at Sami’s graphs from repeated performance tests in the Stanford laboratory, as he progressed from pre-diabetic sugar burning machine to a fat burning beast:


Graph 1 (above): Results of Sami Inkinen’s initial performance test from 2009. At 300 watts, he is burning almost all carbohydrates—destined to bonk after a couple hours, maybe three if he can slam down some gels en route.


Graph 2 (above): Sami’s second performance test at Stanford, coming off three months of devoted carb restriction and fat emphasis in the diet. Here, at 300 watts, Sami has doubled his fat oxidation to over 400 calories per hour, going from burning almost all carbs to about half carbs, half fat.


Graph 3 (above): Sami’s third performance test, on the heels of his amazing Clydesdale-style Wildflower victory, where he beat some of the nations best amateurs despite carrying 200 pounds (due to preparing for an interesting trip to Hawaii—details follow.) Notice the fat utilization at low intensity of around 85 percent of total energy and 750 calories per hour—triple that of the levels he delivered on his first test!

Sami’s successful transition to fat adapted athlete tee’d up one of the most remarkable endurance performances you will ever hear about. He and his wife Meredith Loring rowed a small boat from San Francisco to Hawaii—2,400 miles in 45 days. In the process, they raised $300,000 for the Institute of Responsible Nutrition, an advocacy group headed by anti-sugar crusader Dr. Robert Lustig. Because their journey was unsupported, Sami and Meredith traveled with some one million calories—ultra low-carb, high-fat selections like dehydrated beef, salmon, and vegetables, along with fruit, nuts and olive oil. Sami also lost 26 pounds on the journey, indicating that a combination of ingested fat and stored fat were his main fuel sources. A feat like this completely reframes the carb paradigm that endurance athletes have long existed in, whereby sustained endurance efforts were highly dependent upon successfully ingesting and absorbing a steady stream of carbohydrate calories. No, there was no bonking allowed aboard a twenty-foot rowboat in the middle of the Pacific Ocean! I don’t know how much more convincing you need to try ditching carb dependency and become fat adapted than this absolutely mind blowing data and enthusiastic message from Sami.

Check out our Primal Endurance Mastery Course to get the step-by-step guidance you need to achieve this objective without the high risk of backsliding and burnout that comes from an ill-advised approach. This online multimedia portal is the most comprehensive educational experience ever created for endurance athletes, with a robust video library of expert interviews as well as bite-sized video presentations that take you through the entire content of the Primal Endurance book. We also have a free sample video series so you know what your course experience will be like.

Note: After co-founding and selling the popular real estate website, Sami has embarked on a fantastic new venture as the CEO of Virta Health. They offer, “the first clinically-proven treatment to safely and sustainably reverse type 2 diabetes without the use of medications or surgery.” Their mission is to reverse Type-2 diabetes in 100 million people by 2025. Check out their cutting edge program.

Thanks for reading today, everybody. Let me know your thoughts below, and have a great week.

TAGS:  Keto

About the Author

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

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

44 thoughts on “Can Keto Actually Work For Hard-Training Endurance or Power/Strength Athletes?”

Leave a Reply

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

  1. Thanks for posting this, Mark. I’m not an intense athlete by any means, but I’ve been wondering how keto works with strength and endurance training exercise. I usually hear about how athletes need more carbs and more protein than fats, but it’s encouraging to hear that some serious athletes benefit from keto.

    Will share with the athletes in my family!

  2. Super excellent article, saving this for reference and re-reading and of course evernoting it

    1. Nicely put:

      “It turns out you can’t exercise enough to outrun bad nutrition advice.”

  3. Just a measly 81.4 more hours before bonking? That should tell us everything we need to know about our ancestors.

  4. Is there an elite female out there that trains high intensity that has successfully trained through a ketogenic diet long term? All I ever see is males in endurance fields.

    1. Check out Nikki Kimball. She has been fat adapted for a few years I believe.

  5. Keto-Smeto…what’s with all this latest dietary fad stuff!? There must be a pecuniary incentive of some sort. And who wants to exercise for hours on end? Deleterious to musculoskeletal integrity, if not presently, eventually (I know from experience). To longevity in general, as any extreme endeavor.

    So, the only non-laboratory , non-animal human longitudinal studies to date reveal through Dan Buettner’s 5 “blue zones” throughout the world the following: “…the longest lived people ate a high complex-carb (approx. 65%) diet with medium levels of fat and medium to lower levels of protein.” “…cornerstone of every longevity diet in the world is the lowly bean.” And, from a 5/22/15 Wall Street Journal article summarizing Buettner’s work: ” People are afraid that eating carbs–potatoes, squash, corn, rice, beans–will lead to chronic disease and early death. It did just the opposite for the world’s longest lived people.”

    Turner Howard

    1. I’ve been trying to add a bit more healthy fats to my diet because I think it’s important and the keto articles have triggered that a bit but I have posted similar missives, I don’t recall the Blue Zone folks embracing a keto diet. One person responded “maybe if they did they’d live even longer” LOL. How do you even respond to logic like that?
      Mark is one person I really look up to in the health and fitness realm, but I’m seeing this site morph into something targeted for the CrossFit and Keto crowd. Still a lot of great info and products so “pick and choose” I guess. 🙂

      1. “…I’m seeing this site morph into something targeted for the CrossFit and Keto crowd.” I’ve noticed this too. I’m afraid MDA will lose mainstream readers by targeting the 5 or 10 percent that are into extreme exercise and diet. That would be unfortunate since Mark has helped a lot of people with the more moderate, nutritionally sound Primal approach.

    2. I agree. Most complex carbs are good for us and should make up the bulk of a healthful diet. A short term (several years) ketogenic diet can work wonders in some instances, such as for weight loss or medical purposes, but IMHO (which keto adherents will disagree with), is that it’s too nutritionally restrictive to be a good idea over the long haul, particularly when employed on a “just cuz” basis versus having a real need. Moreover, a ketogenic diet does not work well for everyone, women in particular.

      I disagree that ketosis is “likely the default human metabolic state.” That’s painting all of humanity with a very broad brush. I also dislike it that few articles on the subject, including this one, make the distinction between beneficial complex carbs and the various destructive junk food carbs. This leads people who don’t know any better to believe that carbs are carbs, and they should all be reduced to a bare minimum or eliminated entirely. Then it becomes very much a case of throwing the baby out with the bath water.

      1. “Moreover, a ketogenic diet does not work well for everyone, women in particular.”

        So true! I did strict Keto for over a year and it tore my digestive system apart and I was perpetually ill with either a cold or some digestive issue. I was afraid to leave the house, tbh! I quit Keto about 7 months ago and the past few months I can tell I’ve gotten my health back. Sure, I put on a few pounds, but I truly believe I was suffering from malnourishment during the Keto period.

        I think it’s dangerous and very likely to trigger eating disorders when Mark suggests/writes that Keto is for everyone.

    3. This Blue Zone has become a sort of sacred book and nobody seems to challenge its goals. I am Italian and travel in my country, I’ve checked directly how the people in the blue zones of Italy live/eat, they by no means eat a starch-based diet, not at all. In Sardinia for instance they eat huge quantities of sheep/goat meat and cheese, which is made with raw milk of free range cattle. The common denominator could be beans because they are the cheapest and traditionally well known form of starches for many peoples in the world (I don’t think we should avoid all carbs) but this doesn’t mean they are the main staple to be consumed in huge quantities, on contrary they are the cheap starch on a meat/cheese/fish/vegetables/olive oil centered diet. Don’t be fooled by the vegan propaganda hindering behind some “researches”

    4. Blue-Zone, Shmoo-Zone….

      1. This article is about fitness, not longevity. Looking at the life of centenarians reveals a surprisingly sedentary lifestyle. My Nana lived to 94 sitting around smoking cigarettes and drinking wine. Good for her for living so long, but I’d rather be active and die younger.

      2. My Nana was also thin as a rail. The only thing that has been proven to increase life expectancy is overall caloric reduction. There is growing evidence time-restricted eating, taking in all your daily calories in 12 hours or less, may also. Giving your digestive system a break everyday seems to mean we can handle foods we’re not evolved to eat and are also spending part of the day in ketosis.

      3. As the article states, and is unarguable, ketosis was the default state for humans through history. Most westerners now walk around in permanent glycolysis. The results are clear to those that strive to be in ketosis at least some of the time. My digestive issues cleared up. I’m leaner, stronger and have more endurance.

  6. Please put the disclaimer at the top, not the bottom. Its annoying to read through an entire article only to find out at the end that it is a plug for a new business/commercial venture.

    Mark, this website is only as valuable as its commercial independence and objectivity. Disclaimers should not be seen as an annoyance – they should be placed upfront so that credibility is not damaged.

    1. A bit more than just a plug, surely? I think you’re being rather unfair.

      1. Mark keep us informed of other like minded excellent programs such as Virta Health. Type 2 diabetes is now an epidemic with all the low fat nonsense out there so it is good to know of programs such as Virta for my friends who are nearly all over weight and pre diabetic.

    2. SpottedChui, thanks for commenting. I, too, put a premium on the independence of this blog. That said, it is a personal blog, and I do occasionally (and very selectively) highlight programs, products, and sources I’ve either used or am interested in following – and believe might be of interest to a Primal audience. Sami’s story and his lab experiments stand on their own for their value to the keto conversation, but I also am looking forward to seeing how his new business can serve growing health needs in this country.

      1. Your diet causes diabetes. You have done no research and are putting yourself in a liable position by promoting such a deadly diet.

  7. Anyone British will be laughing about the “bonking” No bonking on a small boat? Since it’s a slang term for having sex, maybe not such a good selling point!

  8. I’ve been keto for the last 8 weeks while training for a half marathon in May. The first 4 weeks of the diet were concurrent with an aerobic base training phase (primal endurance protocol) while transitioning into the diet. The first 4 weeks were a challenge and I felt slow and sluggish, but like I could run for a long time, just not quickly. Week 5 was a turning point and I started increased distance and speed at a gradual rate moving from base training into the active training phase for the event. Speed is picking up, there is minimal muscle soreness, and the diet is easy at this point as I’m in the groove. I feel great. Mental clarity is much improved, sleep is better than in years, and I’m down 23 lbs. since January 29th. I’ve run as far as 8.1 miles without any additional fuel and maintain less than 50g of carbs per day. All food is tracked in My Fitness Pal. I’m 46 and no where near a world class athlete – 13.21 goal is sub 2 hours. I’ve run 2 other half marathons and one full marathon, but didn’t have the nutritional piece in place before. My results have been amazing and I’m progressing further and faster than I anticipated. I’m on track to achieve my goals for the May half and am considering another marathon in October. I’ve also noticed significant changes to my mental state – I’m more positive and suffer less anxiety and racing thoughts. Keto for me has been a huge success thus far. It’s my intention to remain keto for a total of 12 weeks minimum until my weight is 190 or so and at some point transition back to Paleo on some days but dipping back into ketosis regularly to maintain the fat burning adaptation. I also plan to do an annual base train/keto phase during the first couple of months of the year. That’s worked well for me this year and I can see the benefit of periodizing my training. I’m still experimenting but could not be more pleased with the results. The first few weeks were challenging but totally worth it. My running, health, and overall sense of well being are better than they’ve ever been.

  9. Thank you Mark. Whilst I agree with the article, last summer you wrote about how not replenishing glycogen stores can lead to increased levels of cortisol. I eat primal and generally low-carb (always gluten free), however when I go very low carb / keto I do end up very stressed and short-tempered. I enjoy lots of sports and practice them regularly, some of which are high-intensity, and have an active lifestyle walking or biking to work, climbing stairs, and moving around a lot whilst treating patients. I do not do any chronic cardiovascular exercise, but I do more intense exercise than a pure primal blueprint, as I love mountain sports and it is a big part of my social life and play-time. After a few months of very low/carb, I was highly stressed and experiencing a lot of emotional liability, despite having taken a few years to slowly and healthfully reducing carbohydrate and increasing fat. When your article about the relationship between not replenishing glycogen stores and stress came out, it all made sense with my experience. So how does being athletic and going keto fit in with glycogen replenishment and stress?

  10. Any hockey players out there that have gone low-carb? I’ve experimented with both low- and moderate- carb and I feel that I lose some of my jump in the third period of my games with low carb. I’m assuming that means that I’ve used the up my stored glycogen and I’m on fat metabolism at that point. Recently I’ve tried taking some carbs in the water bottle toward the end of the game, and that seems to restore the jump. If anyone knows of someone working on low[-er] carb hockey please feel free to pass it on. Thanks.

    1. You are a hockey player, therefore you will burn massive amounts of carbs with 1 minute of ice and 1 minute of rest (or so). Your sport shares similarities with 400m to 800 runners or combat athletes and less so with pure endurance sports. What is your total carbs for the day? 100 to 150? More? How much do you weight? How often do you train? All factors to consider.

      1. I’ve been playing hockey for 60 years, 3-4 times a week and up until I discovered primal, I ate a ton of carbs and carbed up before games. After reading Primal Blueprint I lowered my carbs significantly, maybe 200 a day, but my first game I hit the wall in the warmups. I was toast.

        So I read primal for athletes and it suggested adding carbs before playing so I ate a couple of baked potatoes and hour before and that worked pretty well. Now I’m down to about 100g of carbs a day but have never gone full keto to try hockey. As a backup I take a Hammer gel just before playing and that’s where I’m at. My fear in going full keto is the amount of time to not suck at games before it actually works.

    2. You need to eat a lot of healthy carbs. This low carb crap is nonsense particularly if you are active. If you want endless energy, then the diet of long distance runners is a good model.
      Who wins all the long-distance races? Athletes from Kenya and Ethiopia.
      What do they eat? A diet extremely high in carbohydrates. Fruits, grains, legumes and whole plant foods.
      Also, all plants have protein, so a diet high in plants is also high in healthy protein. Simply eat plant based, lift weights and you will turn yourself into a hockey playing machine.

  11. Hi Mark: What are your thoughts about the “Lean Mass Hyper Responder” as coined by Dave Feldman? Those of us who are generally, thin, athletic and show a (dramatic) increase in LDL, and increase in HDL but a decrease in Trigs when on a keto diet.

  12. After five months of keto my experience agrees.

    Something neglected by most keto advocates: benefits flow not only from reducing carbohydrate, but from increased consumption of fat and Vit A, D, E and K, all of which are limiting factors for many processes.

    Something from my experience but unconfirmed: reducing reliance on glycolysis doesn’t just upregulate fat oxidation, but phosphocreatine as well, leading to improved maximum force output manifesting in heavier one-rep maxes.

  13. While ketosis is meant to sustain us during fasting so the trick of eating mostly fats should be used carefully, I’ve gained a lot from the reduction of carbs to about 100gr./ day mostly from greens and very few starches. It is liberating to be fueled for hours and in fasted state too, and I’ve seen huge improvements on the health that was compromised by one year of vegan whole starch/fruit wfpb bla bla diet that made my triglycerides and LDL go higher than on a standard diet and made me crash after any meal even a small one. When you do sport on a low carb then your body naturally start to use ketones and burn fats in the muscles, no need to go on the carb’s total deprivation spectrum, that’s probably good for sedentary overweight people to start losing fat but not a good long term strategy for athletes.

  14. The information for these types of atheletes is compelling but what about for people that work in highly physical jobs. Construction workers participating in strenuous labour for 10-12 hours a day that are also doing weight training? I would be very interested to see how someone like that could utilize a keto diet and what that diet would look like.

  15. After spending many many months on keto. I can say (for my body) it was a total failure for strength training and heavy lifting. I felt like I had the energy but just lacked the physical strength over the long haul. My lifts started decreasing and my reps were nearly half of what it is on a 40/40/20 diet. I still love keto for cutting and it is amazing for losing weight. Took me less than 3 months to drop 45 lbs so I can not knock the keto too much. It still has great benefits.

  16. Our bodies were always historically fat adapted. You even learn this in health class…well, at least back when I was in school, in the late 90s. Your body uses fat first, for reasons mentioned above, stemming back into primal times. It burns more efficiently, longer etc. So this translates over to such activities as running as well. It also coincides with a lower heart rate. Sugar/ carbs is what your body uses when there is no more fat to burn. Sugar, alone, increases your heart rate with no activity involved. It’s also cancer feeding. No wonder cancer is common these days. We love our sugar! I can name off several people, namely fellow runners, who would not subscribe to this idea. They are very pro high-heart rate, carb loaders. That is very old-school…a tradition hard to break. I would much rather train my heart to move more blood and, therefore, O2 with less pumps than see how long I can keep my heart at muscle tissue ripping speeds. When you constantly push your heart, you are literally tearing it up. There are primal diet athletes out there that can run 6 minute miles with a heart rate as low as 124, trouble is it’s very hard and long process to retrain yourself. It’s even may be pride splitting and embarrassing. Why? Because you may be a sub 7 minute miler, but taking on a low carb diet, opting fats and going out for those first several runs, you have to stop when you heart hits a certain rate, in order to keep it in the fat burning zone. And there is where the training starts. So even though you odn’t feel tired, exerted, you have to swallow your pride and either slow, or walk. until your heart learns to accomplish more with less. It can take months, to years. Much easier to just back carb loading and continue with pushing the limits of the human heart.

  17. I have lost 94 pounds since 1/18/17 following a keto diet with little exercise. I feel amazing from the weight loss. I wasn’t type II diabetic, however my blood pressure, cholesterol, joint pain, and overall cognitive function have significantly improved. I plan to add in an exercise regime soon. I plan to eat this way for the rest of my life. Great article!

  18. Keto diets are not without their risks:

    “Keto diets should only be used under clinical supervision and only for brief periods,” Francine Blinten, R.D., a certified clinical nutritionist and public health consultant in Old Greenwich, Connecticut, told Healthline. “They have worked successfully on some cancer patients in conjunction with chemotherapy to shrink tumors and to reduce seizures among people suffering from epilepsy.”

    “Blinten, who has used a keto diet for some cancer patients in specific circumstances, cautioned, “people will do anything to get the weight off.” However, a keto diet will do more harm than good for the majority of patients, especially if they have any underlying kidney or liver issues.”

  19. “I once knew a person that could” insert comment XYZ here. Such as my grandpa quit smoking cold turkey one day, thus everyone can… This is anecdotal for now. One can’t make sweeping generalizations after seeing how the results turned out for ONE person. Possibly this persons genetics are set up to do this better, possibly the researcher had a bias. Much more research needs to be done. Possibly with this article, it may lead to killing some people through ketoacidosis??

  20. Keto is complete stupidity. The research has already fully proven how harmful and dangerous high fat diets are.
    We evolved eating primarily fruits, nuts, seeds and vegetables. Claiming otherwise reveals the profound ignorance of this article. Bordering on criminal.

    1. Wow… so you’re suggesting that your grandparents or great grandparents didnt eat high fat high protein diets? They did because thats what was on the farm – pig, chicken, steak, lard to cook with, eggs, butter etc etc. Your comment is complete stupidity. “The research” goes both ways here. Its like arguing religion.. go with your belief vs being condescending. “The research” has proven that cholesterol, inflammation and basically every other health concern has improved on Keto. An all farm based diet would do the same, but being in ketosis serves a different purpose and obviously isnt for you.

  21. I have read that mountaineers get fat before embarking on their treks so that they can burn body…fat. So, Keto makes sense to me!

  22. Thanks for sharing i really love to know about how can keto actually work for hard training and endurance

  23. Direct informative basics, like yours, get a person started. Thank you! I will share your newsletters, book, and blogs with my clients.

  24. As a track cyclist, I was hoping for some info on how a carb-cycling approach might be useful for some athletes, some of the time. This is an n=1 of some guy in Silicon valley. I. Do. Not. Care. Let’s see his Wingate numbers if you want me to take this seriously.

    If a full-blown kept approach worked for real athletes, they’d do it in a heartbeat. The incentives are too high to ignore things that are genuinely ergogenic. But I’ve seen nobody serious doing anything more than a little fasting or carbs cycling – and admittedly, it appears that a lot of enduros ARE doing these things, to a moderate degree… but you still need glucose to lift and sprint repeatedly, and therefore to perform at an elite level in MOST endurance events too, as they tend to involve a more significant anaerobic component than many people realise. As an ex-real athlete, Mark should know this. Bodybuilders are impressive at their thing and all, but they’re hardly strength and power/sprint athletes so provide a poor example for those of us who are. In cycling, we really only see the Chris Froomes of the world even trying to get anything close to this level of fat adaptation, as frankly, in my experience (n=1 also, but I have other people’s anecdotes on my side here) it kills your anaerobic capacity, even if you may squeak out a few more watts at lactate threshold, due to being unable to produce lactic acid (which is recycled back into glucose and ATP, remember, to reuse for your next sprint).

    I’d be happy to see some advice or evidence on a more moderate approach that would work for real athletes and especially sprint athletes, but this isn’t it. Frankly, when I’ve been more-strict on my primal eating, I’ve had to add a lot of carbs (pumpkin, rice, etc) just to maintain performance; salad, fish and avocado alone just makes for a hangry, slow, weak athlete in my experience.

  25. Anyone British will be laughing about the “bonking” No bonking on a small boat? Since it’s a slang term for having sex, maybe not such a good selling point!