The keto diet: Happy muscles running on fat

Anne paddle board

Over the last few weeks of my pretty active life — biking to and from work, hiking hills with friends, kayaking, paddle boarding, competing in dragonboat races, and even just working out at my local gym — I’ve noticed something exciting: my muscles feel just great.

In fact, at age 59, my muscles feel and perform better now, in every sphere of my life, than they ever did when I was 20, 30 or 40.

They are stronger. They don’t hurt as much when I am working out; they don’t fatigue as easily or complain under strain as much. And after a hard workout, they don’t feel as sore as they used to the next day.

I can come to only one conclusion: My muscles run so much better on fat than they ever did on glucose.

The difference really struck me this last month, after slipping off my ketogenic diet while at the family cottage. I’ve been solidly in ketosis for almost two years now, ever since a pre-diabetes scare in the fall of 2015 converted me to the low-carb keto diet. In the post I wrote about that cottage slip, I joked that one impact of falling off the keto wagon was that my reaction time and performance in our cottage spike ball tournaments significantly declined.

But it wasn’t really a joke. My performance did decline. I’m proud to say when I first arrived at the cottage I was a keto-adapted fat burner and I won the first highly competitive spike ball tournament with my niece’s partner. “Aunt Anne you rock!” the young nieces and nephews (all of whom I beat) had high-fived me. By the end of the week, same partner but now eating a high-carb diet, I performed dismally – slow and sluggish. Where we were unbeatable a mere five days earlier, we were unwinnable now. And it was all me.

That poorer physical performance while still out of ketosis really hit me the first day I got home. I ride the same route to work every day, but on my return, the hills were suddenly harder. My leg muscles hurt and felt fatigued on the inclines — rapidly, within seconds. My lungs were fine but my legs felt wimpy. I’d only been gone 10 days. I’d remained highly active. The only thing that had changed was my diet, adding back in enough carbs to take me out of ketosis.

An insight about muscles on keto

That night, I had a revelation as I was carrying a big load of clean laundry up the three flights of stairs in our old house. My legs ached and felt extraordinarily heavy by the top floor. Suddenly I recalled that for many years, pre-keto- diet, that weird leaden ache had been routine doing that regular chore. Back then I had concluded that, along with the ardent desire to do a renovation to move the laundry from the basement to the upper floor, I needed to work out more and get more fit.

But here is the thing: during those years I worked out all the time and that leaden leg feeling never went away, no matter how many leg presses and squats I did. I saw personal trainers, tried different workout routines. I would push through the muscle fatigue and ache and wonder, ‘will this feeling ever go away when I get fit enough?’ I was no couch potato either. I’d been a competitive athlete in my teens and 20s, and highly active all my life.

That odd achy leaden muscle feeling got so bad during two very stressful periods of my life — and included fatigue, weakness, numbness, fasciculations (muscle twitching) and cramping — that I was referred to neurologists to be investigated for multiple sclerosis or other neurodegenerative conditions, which fortunately I did not have. I realize now, however, that during both those times of high stress, carbs in the form of pasta and potatoes had been my daily comfort foods. Was it all related?

Carrying that laundry load I suddenly knew: it must be. I hadn’t felt that leaden heavy ache for two years in ketosis in any of my activities. My muscles had felt fantastic.

It sent me to the medical literature to inquire: Do women with polycystic ovary syndrome (which I was diagnosed with at age 19) have any evidence of reduced muscle function, muscle weakness or fatigue?

The search rewarded me with multiple articles and studies — more than a dozen — how skeletal muscle insulin resistance of PCOS causes impaired insulin action on glucose uptake, impaired mitochondrial function and increased oxidative stress.

One 2010 article, entitled Skeletal Muscle Insulin Resistance in Endocrine Disease, had this revealing summary: “In PCOS, muscle insulin resistance has been associated with abnormal phosphorylation of insulin-signaling proteins, altered muscle fiber composition, reduced transcapillary insulin delivery, decreased glycogen synthesis, and impaired mitochondrial oxidative metabolism.”

It all made sense. For years no matter how much I trained or worked out, my muscles always complained. But when I switched my fuel to fat, they hummed along happy and strong.

Earlier this year I wrote a summary for Diet Doctor “Eight reasons to adopt a low carb keto diet for PCOS“. Now I would add a ninth, at least for me: Because my muscles feel so much better in ketosis.

But I wonder: have other people experienced the same phenomenon? I’d love to hear about it. Feel free to leave a comment below.

Anne Mullens


A keto diet for beginners

Low carb for beginners


All earlier posts by Anne Mullens


Fertility and PCOS


  1. Brenda
    This. I’ve been low carb now for more than a year and a half, but it only took about two weeks to feel the difference in my muscles. Slow, stiff, sluggish and terribly sore after working out to pain free, energetic and strong. The difference is like night and day and is the biggest incentive to not cheat. I love feeling like this.
  2. David Watson
    Thanks for your post Anne. I love eating this way, but run competively and have noticed a definite drop in performance in relation to speed when only burning fat. So I think there is room when eating high fat/low carb to add more carbs pre and/or post intense physical effort to improve glycogen reserves. For me
    fruit, especially organic raisins aids performance and expedites recovery. My experience is that slower endurance based excercise responds just fine to fat burning alone. I would be interested in any other suggestions re more intense physical exercise.
    Replies: #5, #16
  3. 1 comment removed
  4. Sandra
    I'm 62 and have gone into ketosis on Atkins on and off for years,( if I gained 5lbs I'd eat this way until it was gone) Each time , I have felt more energetic and alert and wondered if I had a gluten issue or what... I am currently( about a month) eating low carb and lost 5-6 lbs. The weight loss is great but the way I feel is even better! It DOES help you not to cheat! Been trying to figure out why this occurs and saw your post.. thanks
  5. Catherine
    Hi David,
    Somewhere on this site I saw an interview with Prof Noakes where he talked about a possible need for small amounts of carbs to top up glycogen reserves for some athletes to achieve bursts of speed. But do you think I can find it now?? Maybe searching on his name here and more broadly will bring you better luck than me in finding it!
  6. Samantha Dalby
    Hi Anne
    I think there is a difference between athletic and active. Most Canadians carb load like they are competing in the Olympics and they aren’t exercising at all.
    I find my muscles are stronger on keto and also more defined. Whether that’s because of loss of body fat I’m not sure. I do not get severe muscle pain or fatigue but I have also changed my exercise regimen as I age for less long distance endurance work and shorter daily exercise that includes stress reducing activity as well as weight lifting.
    I have seen patients reduce pain in their joints and muscles and reduce muscle fatigue and general fatigue with LCHF whole foods eating. I have seen people get off chronic narcotic analgesic after dietary change. And I have helped patients to get pregnant with keto eating (when they weren’t able to before).
    Ultimately it has to be what feels right for each person. But it definitely works for me (in the post meno modifications).
    NP Samantha
  7. bob b
    I am getting the same good/great feeling (as described in this post) from my muscles on low-carb diet after years of "weird leaden ache". Wish I could see more literature on exactly why. Thanks for the info shared here.
  8. Jamie
    Thanks for the shared info!! I no longer feel crazy!! After returning from a snowmobiling trip this past weekend where we rode for over 250 miles of some pretty rough trails I suddenly realized... I'm NOT sore!! Normally a ride that size and that aggressive would have left me limping...stiff..exhausted.. but this was my first ever ride in ketosis! And I feel AMAZING! Another side effect I believe is a huge decrease in pain from my herniated disc. I truly believe it has relieved inflammation in my body! And that has also helped my intestines!! No bloating!! Regular happy guts! Wonderful feeling!!
  9. Margaret
    You are so right on! Loved your entire article! You give me the courage to keep on keeping on to educate people and follow this diet myself. I am a senior citizen who told her husband she didn’t want to die “fat”.
    You are such an inspiration! Am forwarding your article to a bunch of people. Keep up the good work!
  10. Melisa
    I've only been in ketosis for a month, went through the 'keto flu' stage and am now happily humming along as I get more and more dialed in on how to do this. I'm at 15carbs a day just lunch and dinner and have been taking potassium and magnesium supplements daily as well as drinking tons of tea. I am a 48-year-old recreational runner - I used to do trail ultra runs in my 30's and have been trying for years to get back - I keep having little injury after little injury. I have been excited about losing weight and having reduced inflammation on keto but unfortunately, I have been having severe muscle fatigue even on the shortest runs - it is incredibly discouraging. I don't want to stop keto but if I can't solve my muscle fatigue problem then I will have to - can anyone help? Thank you!!
  11. Anne Mullens
    Melissa, it can take longer than a month to get fat adapted -- some say two to three months. Taking potassium and magnesium is good, but also examine salt intake -- you may need more. I often shake some salt into my water, especially when I am feeling fatigued, or have a headache and often it solves the issue within 15 minutes. Since I had PCOS, it may have been that my muscles never preferred glucose to fat and felt so much better when I added fat back into my diet after 30 years of avoiding it.

    You may have to experiment to find where you feel your best. Consuming 15 grams is very low -- you may not need to be that low to still achieve the results you want. You can lose weight and have reduced inflammation on moderate low carb or with occasional "carb ups" - having small amounts of healthy carbs - like orange sections or apple before exercise.

    I hope that helps.

  12. Sharon Hobday
    This is great I think some of us just really adapt well to keto more than others I train really hard at the gym lifting heavy I've always felt sore muscles each week after leg day. Since being on keto taking no extra
    supplements I'm full of strength and no sore muscles the following day. Unfortunately no one I talk to about it believes it's good for me they have a ''yeah but'' to everything I say good about the diet.
  13. Amanda Dooley
    Thank you for sharing your experience. I've experienced the same. I'm 40 years old and I've been in ketosis for almost 5 months. I've always exercised on a regular basis, and I did notice my first two weeks on keto were a challenge. I struggled through my daily workouts and feared I would continue to feel exhausted like I did. WRONG!! Once I made it through the adjustment period, my endurance and stamina are better than ever. I work out harder than I ever have with no muscle soreness afterwards. I've tried mixing it up with PiYo, P90X, trail running, resistance bands, you name it....STILL no soreness! Before keto, I always had some body part aching or hurting post work-out. With keto, those days are over and I am so thankful for this new way of life.
  14. katherine
    Thanks Anne for the article. I am 48 and have a love for running . I went on a modified version of the keto diet, (high fat, low carbs, low sugar) more to monitor my sugar intake. A few months into the diet I noticed many improvements, slightly lower sugar levels, no more bloated feeling, more energy (I used to get sleepy around mid-afternoons), a 10-lb weight loss, and lower cholesterol levels! The most surprise of all was my recovery times after a long or hard run. Before the diet, it would take days before the achiness and stiffness go away after a hard run. During the diet my body thrived, I no longer felt stiff or achy after runs. I feel great after half-marathons, and can go back to running immediately afterwards without the aches and pains. My body loved it! The only downside I felt was that my leg muscles weren't as strong as before the diet; I will take faster recovery times over faster running times. Lately I fell off the wagon and went back to eating carbs. My body hates it. My body feels bloated all the times, I have less energy and the stiffness and achiness came back after hard runs. I plan on going back on the diet for all the reasons of feeling more energized, but mainly so that I can recover faster after hard runs.
    Reply: #31
  15. Brenda McIntosh
    This is no walked the dogs and then decided it was a great morning to get out Recumbent and take her for a spin. As I was approaching the dreaded first hill, which used to make my thighs burn and my muscles scream, it was a breeze. No heavy.heartbeat, no muscle screaming and burning! I maintained 8.5 miles an hour and that is good for a Recumbent bike on a hill, trust me. Then the next big incline came up and it was the same a breeze. I was like, OMG this is amazing. So I went and hit some of the other steep inclines an powered up to see if I could get that old painful burn going and remarkably I could not. I powered up the steepest hill at 9 mph and maintained it and pushed super hard for the duration of five min or so and nothing, no burn, no out of breath no, heavy heartbeat 😁 To my surprise and let me tell you I have been through wueen of lactic acid burn my whole life and hated it. Now that I am fully fat adapted and burning ketones instead of glucose I am on fire. I did this on a 18 hour fast as well. Yeah, even during fasting and feel great. I will go hit the gym next and get some laps in this afternoon. Energy levels have been so amazing and I feel so remarkable. Ketogenic way of eating is amazing. I came home and looked this up to see if I was imaging things and here is an article about this very thing. Wow bike to work is coming back.
  16. Jennifer Haagenson
    David, thank you for your post. I am 48 and have been on the Keto way of eating for only a few weeks, but I also run competitively and have been performing slower. I do feel great and have lost a few pounds, but I am worried about the running. I am like Katherine in that I appreciate the faster recovery after longer runs, but I don't want to give up the time. I love Anne's comment about trying a small amount of healthy carbs before exercise but will continue researching for other options. I am inspired by everyone's comments here. Thank you, Anne, and everyone, for sharing your experience.
  17. Lizeth
    Hello, im new to keto and something odd happened after a month of being keto. Both my legs became fatigued to the point of not being able to stand or walk. I got aches and an insane amount of twitches!! My calves which are the worst part became Stiff!!! I was left disabled from continuing my normal starbucks job and even had to shower sitting on a stool of how painful and unable i was to stand without my legs buckling and aching. I have had many tests done home to a neurologist and had an MRI of my spine. Everything seems to look normal. My neurologist suggested i might have benign fasciculation syndrom... ....but i find it odd that it happened a month after keto... i realize i did keto wrong you might say. I never consumed vegetables or leafy greens and i only took track of sodium. Im still recovering from this crippling just scared it wont go away... I've been on bed rest for 1 month now..... anyone experience this rare situation??
    Replies: #22, #32
  18. Anne
    Hi Lizeth - That sounds like an incredibly scary and concerning set of symptoms. In researching the article, I did not come across anything like this.

    I do find I will get bad muscle cramps (early hours of the morning) if I do not have enough sodium. In my 40 years of avoiding fat, I also tended to not add much salt to my food, so now I find I definitely have to up my salt content.

    Magnesium could also be an issue. Drs. Stephen Phinney and Jeff Volek, in their book "The Art and Science of Low Carbohydrate Performance" have a great section on muscles and magnesium , saying when magnesium is low "muscles get twitchy" - cramp, fatigue, twitch, ache. The section is page 83 to 85 in their book and they have an intensive magnesium supplementation protocol that takes 20 days, using slow release magnesium (trade names: Slow-Mag, Mag-64, or Mag-Delay.).

    I don't know where you are, but those formulations are available in the US, but not in Canada. I don't know about other locations. I am in Canada so have asked a friend to send me some so I can do their protocol. They say take 3 slow release magnesium a day for 20 days; if cramps/ muscle symptoms return after you stop, take two a day in perpetuity. Only contraindication to doing it is if you have chronic kidney disease or kidney failure.

    I have not done it yet, but in the meantime while i wait for Slow-Mag to arrive, I am currently adding electrolyte drops to my water and that seems to reduce my night time cramping, along with being well hydrated and getting enough salt. It might help for fasiculations and fatigue, too. Since you are under medical care to investigate this, perhaps ask your doctor whether supplementing with magnesium might help? (Phinney and Volek do note: "Magnesium resides in our cells. There is very little of it in our serum, so blood tests for this mineral cannot tell us if we are okay or not. As a result, doctors who rely on blood tests are generally clueless about magnesium.")

    A question though -- did you try adding back in some healthy higher carbs, like sweet potatoes, beets, beans, baked potatoes? Did you notice an improvement in symptoms coming out of ketosis with higher carbs?

    Good luck sorting this through as I am sure it has been a concerning and challenging time. - Anne Mullens

  19. Anne
    I have a question. What is considered healthy high fat, low carb? I did keto (25 carbs day set up by Dr on carb manager) for 10 weeks to support my husband in his weight loss. I lost about 4 lbs which was fine. I was fatigued and had severe headaches so about a month ago I switched to high fat/low carb (60 carbs a day). Headaches are gone but I struggle to jog a mile and the fatigue in my legs remain. Otherwise I feel fine. I'm 51, life long runner although I've had to cut back to 10 miles or less per week due to knee replacement 4 years ago. I'm 5'7", 140 lbs (about 10 lbs over my college training weight, but 10 lbs less than my all time high after knee surgery). Any thoughts on what I'm doing to cause so much fatigue? My legs haven't felt this way since I was running 70 miles a week and I'm running around 6!
  20. Katie
    I have been following a keto way of eating for about 15 months. From the first week onwards, I felt 10 years younger thanks to the stiffness from my joints/muscles lifting almost miraculously overnight. I have lost about 40 pounds since then; I have plateaued but am happy to stay on keto because it seems to suit me so well. This past weekend I experimented by eating whatever/whenever on a ladies' getaway. Desserts, mashed potatoes, the whole nine yards... everything I had been successfully avoiding. Now it's Monday morning and my leg muscles (minus any working out, I can assure you) are stiff and sore and my back aches. I just want to crawl back into bed! I am back on keto and interested to see how quickly I lose the 4lbs and achiness I gained from three days of indulgence!
  21. Frank
    I'm Frank, a Chinese man of 50 being in US for 25 years. 5'10", 198 lbs diagnosed as pre-diabetic and it got me into ketos. 6 weeks in and down to 180 lbs, that's 18 lbs in 6 weeks !!! amazing, ketosis works for Chinese too !! I play soccer on weekends running 1.5 hrs avg on field. used to feel big muscle sore right after Sunday game and going thru 6 days to slowly recovert day by day. I go to work with sore muscles all over body all week long. now I only tiny light sore after same game, about 10% of what used to be, taking only 1 day to recover. what a difference !!! I love Keto !!!
  22. jennifer
    This has happened to me. Not sure if it was keto or something legs did return to me though after a time. Still going through tests but beginning to catch a pattern...i get sick in January every year for three years running...and the only thing I can parallel it to is new years resolution to lose weight and going low carb.. doctors dont see a connection we spend more money hunting "zebras".

    They have determined that I am hypoglycemic...not sure how that ties to all this.

  23. Leah
    I’ve got the opposite problem... I’m nearly at the end of 2 weeks in Ketosis and I’m exhausted just going up stairs, and things like brushing my hair make my arm muscles ache horribly... hoping that I’m just still adapting...
  24. Roger Gregoire
    I've experienced this same phenomena of no muscle soreness since I've been on a low carb diet. (About 2 months now). I'm a runner, and after a hard long hilly run, prior to this diet, I would normally get acky stiffness for the next 3 days. But no more! I can run the next day with no muscle soreness, instead of having to take a recovery day or two. The drawback is that my running heartrate is higher on a low fat diet, and lower when I carb up for a race. But that is probably a good thing. "Train low, race high" seems to work very good for me. Low carbs let me train every day, and high carbs let me be very competitive on race day. My running efficiency (via Polar Running Index) is also slowly improving on my low carb training days which seems to imply that I am becoming more fat adapted athlete.
  25. Erin
    I have the same problem as Leah. I have been eating Ketogenically for 2 months approximately. I eat alot of snacks like Kale chips, unsweetened coconut, peanuts. I have unsweetened yogurt too. My concern is that I am having too many carbs. When I did this with lower carbs a few years back, I stopped due to the same condition. I was like an old woman! I could hardley get up the stairs. Lumbering sore achy muscles. What is up?? I sleep like a baby for the first time ever. This is the only positive and the only thing keeping me from going back. I didnt lose any weight and my skin is still red and pimply and scaley. I do have endometriosis and SIBO. Help!!!
  26. Priscilla
    Does anyone here give themself a carb day or two within the week ? And if so how far into keto diet before having a carb day ?
    Reply: #27
  27. Kerry Merritt Team Diet Doctor

    Does anyone here give themself a carb day or two within the week ? And if so how far into keto diet before having a carb day ?

    If you're referring to carb cycling, it's not something we recommend. The idea is to keep blood sugars and insulin levels stable, and carb cycling is counterproductive to that goal.

  28. 1 comment removed
  29. Chris
    ATP, the fundamental unit of energy within the body's cells. How body chemically makes energy.

    A single molecule of ATP contains 10 carbon, 16 hydrogen, 5 nitrogen, 13 oxygen and 3 phosphorus atoms. The formula of ATP is C10H16N5O13P3. Three phosphate groups are attached to the assembly of adenosine. Here is where need ---------------Phosphate.

    ATP (adenosine triphosphate), the main source of energy in cells, must bind to a magnesium ion in order to be biologically active. ---------------need MAGNESIUM here as binder. Magnesium ions regulate over 300 biochemical reactions in the body

    Salt is composed of sodium ( NA) and chloride( Cl), which are two electrolytes that help maintain fluid balance and the transmission of nerve impulses. When depleted in the body, sodium must be replaced in order to maintain intracellular osmolarity, nerve conduction, muscle contraction and normal renal function.

    The body needs to have a 7 pH which is neutral or water (7 pH) if too much base or to much acid will make body not work well.

    Brain needs amino acids. All of these are found in Beef. Brain clarity when start eating beef and eggs. Other lesser forms also which are not as good as beef for uptake. Real beef, not processed.

    The Vitamin B which is B1-B12 is very important for energy. Vitamin C for health. Content/CHEMISTRY OF ATOMS AND MOLECULES OF OUR BODY.pdf.......................This is a very good power point on more information.

    Krebs cycle in the mitochondria is our basic life force. Need all of above to make it work and some others not mentioned.
    Try these and see if it helps. Do not go overboard. See doctor to help as needed. Will get rid of most headaches and some muscle pain after workout.


    Tells you why need Potassium, Salt which contains NA and Cl, Calcium Ca, Phosphorus P, Magnesium Mg and Water. If do not keep a neutral 7pH in body will suffer from side effects. Too acidic or basic will cause symptoms. See the slide show from UC.

  31. TomY
    I shared the same results! Always stiff and aches after exercise. Stretching helped but didn't solve. On low carb, it went away! Stiffness after exercise gone. I don't have to stretch after exercise but still do for flexibility improvements only...
  32. robyn
    I had a very similar occurrence. After 3 months of Keto. My arms and legs became so weak and felt like bricks. It was scary!! I could hardly walk. So I decided to add rice to my meals. Shakiness is gone but feel weak still. I used to be able to run so easily until I started keto. I can now run again but running is so very hard now. I regret keto. I will slowly increase my carbs back up to before I started keto. I miss feeling strong.

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