Fasting vs. low carb – which is more powerful?

What is most effective for weight loss – fasting or low-carb, high-fat diets? It’s like asking if Superman or Batman is more powerful.

You probably already know the answer. If not, Dr. Jason Fung explains it in his latest post:

Dr. Fung: Power: Fasting vs Low Carb

Spoiler: The most powerful one is Superman… and fasting. No diet will ever beat no diet, when it comes to weight loss.

However, depending on how you look at it, an LCHF diet might give you around 70 percent of the benefits of fasting, without the fasting. Not too bad.

In fact, pretty superheroic. Like Batman.


Low Carb for Beginners

Intermittent Fasting for Beginners

Read Dr. Jason Fung’s new great book The Obesity Code for many more insights:

The Obesity Code

More About Intermittent Fasting

What is Fasting? – Dr. Jason Fung
How to Maximize Fat Burning – Dr. Jason Fung
How to Fast – The Different Options – Dr. Jason Fung
The 7 Benefits of Fasting – Dr. Jason Fung
The Top 5 Myths of Fasting – Dr. Jason Fung
Breakfast! Is It Really That Important? – Dr. Jason Fung
The Most Common Questions – Dr. Jason Fung
How to Get Started with Fasting – Dr. Jason Fung
Who Is Dr. Jason Fung?
The Perfect Treatment for Weight Loss and Diabetes – Dr. Jason Fung
The 2 big lies of type 2 diabetes – Dr. Jason Fung
The Key to Obesity – Dr. Jason Fung


  1. Jo
    I've finished the book and it's fantastic.
    Reply: #11
  2. dylan
    I do both, is this an implication they are mutually exclusive?
    Reply: #3
  3. BobM
    No, it's not. I also do both. They're both good.
  4. Karlyn
    I am a tall 51 yo female, current weight 203, starting weight 266. and I've lost 63 pounds in 6 months on various eating plans (~30 more to go!) I have been doing Keto/LCHF about 10 weeks now (I love it!), and added 16/8 IF about 2 1/2 weeks ago. For me they go hand-in-hand so well. I really don't believe I could do IF without LCHF. The first week on 16/8 was more-or-less 15/9, but by the next week it wasn't an issue anymore. It is too soon to measure any results, but so far I am averaging a loss of 3 1/2 pounds per week by adding IF. That is about 1 pound more than on just LCHF, and a good 2+ pounds more than when I was just doing a traditional low-fat high-carb. (My calories and exercise have stayed very close to the same though all of these eating plans.) I do like this method of eating quite a bit, and I plan to stick with it. When I first heard of IF I thought the world has gone completely crazy! But not having blood sugar swings makes this so doable. I look forward to reading your book.
  5. Apicius
    For me, LCHF maintains my weight - I can eat as much bacon/cheese/butter...and weight stays the same. And then I use fasting when I want to force weight loss. Gives me lots of control in what I want to do with my body.
  6. Becky
    Well I could never do fasting more than once if I was on a "normal" diet. But with lchf I fast most days and only eat one meal a day. Love it. On the "normal" diet if I didn't eat every 3-4 hours I thought my throat had been cut and I was staving.
    Reply: #7
  7. chris c
    Me too - plus a few thousand others. On my "healthy" diet with every meal based on starchy carbohydrates I would need to snack on carbs every few hours or I could literally fall over. After the dietician lowered my fat and increased my carbs even further I was constantly hungry and semipermanently stunned, my lipids and BP got rapidly worse and for the first time in my life I gained about 15kg all around my gut.

    Yesterday I ate an oatcake (5 - 6g carbs) slathered with butter and topped with smoked salmon. I spent much of the day shovelling compost and spreading it on the garden. I had a small handful of nuts with one of my cups of coffee.

    EIGHT HOURS LATER I had my only proper meal, a bolognese type sauce liberally topped with melted cheese, with broccoli.

    Several hours later I had another small snack. So not entirely fasting but close enough for jazz.

    The only problem I've found from doing this for eleven years now is that I am eleven years older. This wouldn't have happened if I'd continued low fatting - I'd almost certainly be dead.

  8. ApexOmnivore
    I get his point that fasting is Superman with respect to diabetes and insulin levels, but I think it's a matter of perspective and what you're optimizing for. Without eating low carb, fasting would become supremely unpleasant and require lots of willpower (not to mention the associated hangry moodiness), at least for me. After eating low carb consistently for a couple of years now, I've found that 16-18 hour fasts just happen naturally a few times per week. At least for me, the better analogy is that fasting is Batman's tool belt -- something of dubious utility in the hands of someone who isn't the Batman!
  9. Mary Titus
    Yes fasting and LCHF are both ketogenic and support each other yet they are not the same. Fasting allows the system to rest , regroup / reboot re-energize and prepare for the next meal...whenever that may be. It enhances ketone production, growth hormone ( which affects other hormones in a domino affect ), nutrients from the previous meal are better absorbed. Full digestion of various foods can take up to 3 days. The system is cleansed and ready for the next meal. Carbohydrates such as bread, candy and granola bars ruin the power of fasting since they destroy ketosis. Meats, plenty of fats and a few LC veggies or fruit ( avocado especially ) extend the power of the fast and injects further nourishment. There is a difference between fasting and LCHF diet . I can tell by the way my body reacts to both events.
  10. BobM
    Personally, intermittent fasting (IF) for me has been a revelation. I "had" to eat (even on low carb) 5+ times a day, as that's what everyone said you needed to do. I also would get cranky if I did not eat breakfast. IF has helped all of that tremendously. Also, if I do go off a low carb diet (say while on vacation, where it can be quite difficult to stay very low carb), I can use 1-3 days of fasting, and I'm back on track. Also, it's very freeing: if I'm traveling, I don't eat (which stops my system, meaning I don't have to find a bathroom on the highway or in an airport); if I'm working on a project and it's lunchtime and I don't want to stop, I skip lunch; if I'm on a plane and there's terrible food, I don't eat; if I know I'll be at a park all day with terrible food, I might eat breakfast, then skip lunch at the park. To me, IF is freeing in a way that low carb is not. I can skip breakfast (usually do), lunch, or dinner, or multiple ones of those, or none at all.

    I now know that if I eat breakfast, which I do periodically, if I eat lunch, I'll eat more calories over the course of the day than if I skipped breakfast.

  11. Dorothy
    Fasting for three days now but no weight loss - ? Dorothy
  12. Valeria Jones
    What does one do when one WANTS to fast, but one is taking a medication that is actuated and made bio-available only when taken with a meal of 50% fat? I want to do a water fast for the healing benefits, weight loss secondary because I understand Keto, but I'd prefer to fast completely. I understand that carbohydrate digestion derails many metabolic and hormonal processes, essentially reseting everything, but what about having a meal of only fat? I came to understand the value of low carb dieting while researching fasting, but now that I'm in a position to fast, it seems I may be constrained to only a low carb diet, at least till I can get off my meds.
  13. Dean
    I tried low carb/keto 2 days and I'm sick of avocados already. How I'm I supposed to get that many calories in fat being 200lb plus bodybuilder. I may give another shot. I also found I felt more bloated. Not sure if it's from all the fat my liver is processing or the new veggies . Good luck to everyone , I may try IF as I can still eat burgers . Ha
    Reply: #14
  14. Tom
    I've got rid of avocados from my daily diet for the time being as I felt bloated. Eggs, meat, and fish is now more my approach.
  15. Cathy
    I started out doing keto, then added fasting... and now, nearly one year later, I'm able to fast regularly (24-42 hrs) while eating whatever I want the rest of the time - including carbs. I find that if I delay eating carbs until night, they put me to sleep and help me avoid getting into a vicious hunger cycle. When I wake up the next day, I'm not the least bit hungry and stay that way all day (and sometimes into the next) so long as I don't eat. I should also mention that thanks to fasting (with and without keto) I've lost 50lb and feel absolutely fantastic!!
  16. Gypsy
    On a fast day with Keto what do you have? Anything at all? What drinks? Anyone tried one broth or stock? Or is that not fasting?
    Reply: #17
  17. Kristin Parker Team Diet Doctor
    Black coffee and bone broth will generally not break a fast. Aside from those, water is your best option.
  18. Albert Decker
    When I click on "Dr. Fung: Power: Fasting vs Low Carb", this comes up instead: "Your connection is not secure", and: "The owner of has configured their website improperly. To protect your information from being stolen, Firefox has not connected to this website." The other links work fine, just not that one. Of course, the one I most want to read. Is there another way to get to that post?
  19. Judy
    You are already on that post as I just discover myself
  20. Rose C.
    This is a perfect analogy for fasting vs low carb.

    Fasting is Superman. Best.
    Low Carb is Batman. Very good.

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