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 ovarian 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 polycystic ovarian disease“. 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

Earlier with Anne Mullens

All earlier posts by Anne Mullens



  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.
    Reply: #5
  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!

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