Dear Mark: Rapid Weight Loss



I’m a big guy (okay, obese, if I’m being honest) who’s getting smaller fast. I adopted the PB a couple weeks ago, and I’ve already dropped twenty pounds, going from 300 to 280. Don’t get me wrong, I’m not complaining. I’m just confused. How does that work? You always hear that initial weight loss for the really overweight is fast, but why? Is it really just water weight? It seems metabolically impossible that I’ve actually burned that much body fat… I can’t help but feel a bit let down if all I’m doing is losing water. If there’s one thing I learned from your writings, it’s weight isn’t just weight (and calories aren’t just calories). So… what gives?



Thanks for the question, Todd.

It’s a common weight loss experience. You’re overweight. You decide to take control of your health and shed some body fat. You go Primal, drop a bunch of weight and the first thing you hear from detractors is “Oh, it’s all water weight.” Uggh. How frustrating. But it’s also absolutely true that the bulk of the initial weight loss from a low-carb diet is from the expulsion of previously retained water. The question is: is that loss of water necessarily a bad thing? The answer is, as always, complex and we’ll need to look at it in the context of all the changes taking place when you start eating and exercising Primally.

Most obese people have accumulated their extra adipose (fat) tissue through eating a diet that is higher in pro-inflammatory agents (insulin-promoters, anti-nutrients and omega 6 fats) and generally also higher in sodium. One of the side effects of such a diet is substantial water retention both within the cells and in the spaces between cells (interstitial space). This retained water can amount to 10, 20 or more pounds depending on how large the person is. Even in non-obese people, this effect often manifests itself most obviously in a “puffy” look around the face or a feeling of “bloatiness.” It’s a testament to the power of eating Primally when you realize that often within just a week of decreasing grains and other simple carbs and sugars, as well as cutting omega 6s and the huge amounts of sodium found in the SAD, the body no longer needs to hoard all this water. Understand that this was water you never really needed in the first place; it was just there because agents in the diet sent signals to different systems to hold onto it. As long as you continue to eat Primally, the need for this retained water ceases and you not only weigh less, your body shrinks accordingly. Nothing wrong with that as long as you retain muscle, which you do easily on a Primal program.

The other (albeit secondary) source of rapid weight loss can happen in the muscles. It’s also a short term adjustment to a decrease in carbohydrates that – over time – levels out and soon becomes insignificant. This is the idea that muscle glycogen is stored with water and when you deplete glycogen, you deplete that water as well. You see, for every gram of stored carbohydrate – also known as glycogenthree to four grams of water are stored as well (PDF). So, if you burn, say, 400 grams of glycogen through exercise without refueling with carbohydrate in a short span of time, you might drop close to a kilo of water, too. This can happen when a new Primal convert gets overly enthusiastic and hammers the first few workouts. (Nothing wrong with that, it’s just that we are looking to burn relatively more fat than glycogen over the long haul.)

Why would the body be “built” this way? It turns out that glycogen burning releases water as a metabolic byproduct and that this fulfills an athlete’s hydration needs.

Think about it: glycolytic work, as a general rule, makes you thirsty. What do hiking a steep mountain in the summer heat, going for a long grueling bike ride, and running fifteen sprints to absolute exhaustion have in common? They make you thirsty and they force you to burn glycogen for energy. You see, in the real world, glucose demand and hydration needs go hand in hand. You don’t engage in a glycolytic activity without also increasing your requirement for fluids. It appears as if your body stores water and glycogen together because it “knows” that when you call upon the glycogen for energy, you’re also going to be thirsty.

This should make intuitive sense to most of my readers, especially those with a knack for dipping into their adipose tissue for energy. After all, that’s what body fat is: stored energy for later use. The amount of fat on most modern humans these days is excessive, but the body is simply doing its job and storing energy. It can’t help that we provide dysfunctional environmental and dietary inputs, like overtraining or large amounts of wheat soaked in vegetable oil.

Water weight in the case of glycogen is simply stored hydration. You can’t expect a human, especially a Paleolithic human without a cool neoprene water bottle, to have exogenous water on hand at all times. No, you need a storage mechanism for water, just as you do with fat energy and glucose energy. Energy/nutrient/mineral/water storage is just a basic facet of living organisms. It makes survival possible in a relatively harsh world that doesn’t care one whit about whether you live or die.

So, wait – are the detractors right? Is a low-carb diet for the massively overweight ultimately fool’s gold? Is Todd subsisting on false hope?

Not at all. He – all of us, in fact – simply needs to understand that yes, the initial exodus of weight is mostly water, but that doesn’t detract from his overall goals. Water no longer retained because you are no longer in a state of systemic inflammation is a good thing. Water no longer retained because you have cut sodium intake (without really ever trying) is a good thing. And it’s not like the water loss from glycogen depletion is even restricted to low-carb diets. Any diet that restricts calories and results in a reduced input of carbohydrates (rather through willful macronutrient restriction or by overall calorie reduction) will mean less glycogen is getting restored, and less water is being retained.

It’s always important to be equipped with the facts so you’re ready to deal with naysayers and temper your own expectations. Family members or friends with naught but “water weight, Atkins, cholesterol” comments can be pretty influential if you aren’t prepared. Losing half a toddler’s worth of weight can be exciting early on, but it can set you up for future disappointment if you come to expect those results on a regular basis. Real fat loss takes longer (not so long, though; fairly quick results are common on the PB). Once it’s there, though, you’ll shut up the detractors and quiet your silent, secret doubts. Low-carb isn’t magic, but it’s also not smoke and mirrors and a heart attack waiting to happen.

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.

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55 thoughts on “Dear Mark: Rapid Weight Loss”

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  1. My response to the “all water weight” downers is, “So what?”

    It is extra weight you no longer have to carry around, and by not retaining that water you WILL be more slim. All that lost weight might not have been fat, but it’s still lost weight.

    And once you get used to not carrying around that excess water, bloating becomes very noticeable and uncomfortable when it does happen. The average person on the SAD just does not realize how bloated they are.

  2. It was actually water, that made me uncertain about my health. Last summer, I had an extreme thirst, and a friend of mine said “maybe you got diabetes”. This stuck into my head, and I started to look for ways to solve this issue. When I went primal (still not 100% though), I don’t consume that much water any more (mainly because I don’t feel “heated” (inflamed?))

  3. Mark — thanks once again for a very interesting post. It leads me to ask a glycogen/hydration question of you and the PB community that I have not been able to find an answer to, either on the interwebs or from my fairly CW doctor or a nutritionist I visited. I have noticed that when I get hungry I have to pee–a LOT. Sorry if I veer toward TMI here, but it’s basically almost clear water. I figure there’s got to be some sort of nutrient burning/expelling of something going on here, but I can’t figure out what. Any ideas out there?

    1. Glad you are asking this question — I have noticed the exact same thing happening immediately as this is week 1 of going Primal. Thanks! Wish I had an answer but will stay tuned for someone who does.

      1. April – Very happy to hear that I’m not the only one out there with this problem! Not a simple situation, however. It seems to happen whether I’m eating primal or slipping back into more conventional food/carbs–doesn’t matter what I ate, when I’m hungry I gotta’ go! And go…and go…and go…

        1. Sorry I’m late to the party, but the same thing happens to me when I’m hungry, and it has nothing to do with the quality of food I’ve been eating. Based on my intuition about the body, here is what I think is happening.

          The body needs food to absorb water into the digestive system. In the absence of digestion, the expulsion of excess water is not slowed down by the digestive process.

          I know that’s not a very detailed answer, but I really think it’s that simple. I don’t think there’s anything wrong with you or that you’re peeing out nutrients.

  4. So how do you know when you actually start burning fat and you are losing said fat? When your body measurements change?

    1. The typical time range, if you stick with Primal eating/drinking 80% (or more) of the time, is about 2-3 weeks until your body is “fully” transitioned to burning body fat as your primary source of energy.

      1. Technically, the ratio of carbohydrate to fat we are burning at any one time is related to our VO2 max (maximum oxygen consumption) at that particular time. If we are in a state of jogging, we are likely using mainly carbohydrates, but while I sit here at work typing on the computer, my body is using mainly fat stores. From a weight loss perspective, what Primal/Paleo/PaNu does is allow the body to more efficiently burn those fats by increasing the time we spend in lipolysis (fat burning) and, secondary to this, increase the amount of fat burned. By limiting carbohydrates to a certain level in our diets we limit the effect of insulin (which is the main hormone in charge of fat storage locally), therefore the effect of insulin after a meal is short-lived (comparatively).

        If you are aiming for ketosis, then it takes about 2 to 3 days to deplete your glycogen stores (or go out and pretend you are running a marathon–you should be able to deplete your stores in an hour or a bit more). Once you are glycogen depleted, you’ll enter ketosis as your body is no longer using carbohydrates, even under anaerobic exercise. However, for maximal ketosis efficiency, your mitochondria need to adapt, which is the 2-3 weeks I believe you are talking about PrimalBrett. I was under the impression that this runs about 6 weeks given it needs genetic modification at the cellular level. Regardless, the point is that it takes time for your body to convert to full ketosis, but once it does, it’s a fat burning machine.

  5. Mark – I always thought that the amount of glycogen stored was a direct function of muscle mass, since glycogen is stored in the muscles. According to your post, this would tell me that the amount of stored water is also a function of muscle mass… but it doesn’t really make sense. Could you expand on this, please?

    Also, to validate your point: I do notice that if I add grains to my diet, I will start to look bloated around my mid-section in a matter of a few days. I do believe that this is retained water…

    1. Ballpark figure: 2/3 of glycogen is stored in muscles and 1/3 in the liver plus minor amounts in other location like red blood cells, etc). Hope this helps a bit too.

  6. Mark – Do these same tenants and concepts about losing water weight apply to those who are not obese? I ask the question because I recently went Primal about 1 month ago…before going Primal, I was 200lbs with 13.5% body fat and considered myself physically fit. Now that I have gone Primal, I am down around 190 lbs but with noticeable strength gains…I thought if I was building muscle I would not lose so much weight? Does going primal affect my weight loss the same as it does an obese person?

    1. I have been primal for 2 months now and have gained weight (up to 190 from 180). I think it boils down to your individual body at the end of the day.. I certainly feel a whole lot better and have lost body weight (I wish I knew percentages, but I was probably under 10% to start). At your weight, your body doesn’t have to put such a huge emphasis on water eradication and fat loss, so it is likely focused on muscle building and cell recovery.. which would explain your strength gains.. just my thoughts!

  7. Forget the people who try and doubt what you are doing is correct Todd. Continue to live a primal lifestyle and the weight will continue to shed. Sure, it might be initial water loss but you are still on your way to looking good naked.

    I have a good friend who lost about 70 lbs. in a year by simply avoiding fried foods, fast food, etc. He still did not eat great but never really ate veggies or fruits so it was low carb for the most point.

    He finally went primal and within 6 weeks he lost 15 lbs. He continues to drop weight and looks like an entirely different person. I will have to push him to submit his success story when he ends up with the weight he wants.

    Be patient and never give up. Have a passion for the lifestyle you are living and you will do great. Make sure you are getting adequate amounts of protein so you can build muscle while shedding the fat (or water in the initial stages).

    Good luck to all and anyone who is out there losing weight and grok on!

  8. “if I add grains to my diet, I will start to look bloated around my mid-section in a matter of a few days”

    I second that. Probably a lot of other folks will, too. If I have cornbread or tortillas for dinner I’ll put on 2 lbs. overnight–and usually pee it all out by mid-morning the next day. (Of course I feel lousy for a couple days and it tend to make the weight creep up, so I don’t recommend it!)

  9. Great post. I notice that on very brief relapses into eating refined carbs during kids birthdays etc. (cake is too delicious to resist I am afraid) that even small amounts cause me to pack on weight. The weight gain seems to massively outstrip the actual calorie content – 600cals of refined carbs shouldn’t cause a 1.5lb weight gain based on conventional thinking. So the water/glycogen link is really helpful. Thanks Mark. As always a voice of clarity amid the confusion.

  10. There’s also quite a few pounds of bacteria in your gut that can be trimmed down if you stop eating certain food groups.

  11. This answers a lot of the questions I was having about my own dramatic weight loss (at least to me). Certainly not as fast as Todd, but I have lost 30 pounds since June going Primal.

    Like Todd, I’m not going to complain either. Any weight loss is fine by me at this point.

  12. If I have a couple of non-paleo “cheats” over the weekend, my weight creeps up by anywhere from 4-7 lbs. Then I spend most of Monday and Tuesday peeing out all the water I’ve retained.

    Losing excess water is not a bad thing; it only becomes so when fad diets mislead their prospective adherents by touting “lose 8 lbs in the first week,” without explaining that the first 8 lbs is probably just excess retained water.

  13. This is quite fascinating, thank you, Mark!

    Me, I started at 240 pounds only two weeks ago myself, and I’m very obviously slimmer now (don’t have a scale so I don’t know pound loss). I’ve dramatically lost inches and I look much more healthy and vibrant. I really don’t care if those inches lost are fat or water. I look good and feel great and I love the way I live.

  14. I started eating semi-primally a month ago. I lost 6.7 pounds of fat, which I calculated with the U.S. Navy Circumference Method. In real terms I lost 3.8 pounds. My before and after pictures show a significantly reduced gut.

    WTG – Todd. Sounds like you are on the right track.

  15. I started right at 300 lbs like Todd and have been mostly Primal since mid-April. I was initially concerned with the larger weight loss I experienced initially too. After I got into true fat-burning mode though (about 3-4 weeks), the weight loss was slower, but always steady. Now, at the end of August, I’m at 248 and losing about 2 lbs weekly. I just tell people not to worry, stick to the 30-day challenge and you’ll know for sure that going Primal is the best thing you can do for yourself.

  16. The eliminating of pro-inflammatory elements from one’s diet is sound advice based on sound science.

    To my understanding, however, the science behind sodium’s apparent water retention abilities (which is also the science behind its “hypertensive properties”) is Ancel Keyes-ish. Most nephrologists that I know who don’t subscribe to conventional wisdom think this is nonsense. We have a good pair of kidneys that can re-establish homeostasis quite rapidly to deal with excess sodium. So I doubt sodium is a culprit or has much to do, if anything, with water retention. Is there good, hard science behind this? I’d be interested in correcting my view/belief on this if there is.

    Keep at it Todd. Step one is the toughest one in one’s journey to health.

    1. I don’t know if it sounds Ancel Keysish, but Gary Taubes follows similar pattern. /this is copypaste form GCBC):

      The “remarkable sodium and water retaining effect of concentrated carbohydrate food,” as the University of Wisconsin endocrinologist Edward Gordon called it, was then explained physiologically in the mid-1960s by Walter Bloom, who was studying fasting as an obesity treatment at Atlanta’s Piedmont Hospital, where he was director of research. As Bloom reported in the Archives of Internal Medicine and The American Journal of Clinical Nutrition, the water lost on carbohydrate-restricted diets is caused by a reversal of the sodium retention that takes place routinely when we eat carbohydrates.
      Eating carbohydrates prompts the kidneys to hold on to salt, rather than excrete it. The body then retains extra water to keep the sodium concentration of the blood constant. So, rather than having water retention caused by taking in more sodium, which is what theoretically happens when we eat more salt, carbohydrates cause us to retain water by inhibiting the excretion of the sodium that is already there. Removing carbohydrates from the diet works, in effect, just like the antihypertensive drugs known as diuretics, which cause the kidneys to excrete sodium, and water along with it.

      1. This seems to suggest that it is the carbohydrates that cause the body to retain the sodium (well, it’s actually stated implicitly), which in turns causes the retention of water. So, if I understand this correctly, it is not the ingestion of extra salt that is causing the water retention. It is the ingestion of carbohydrates. The sodium is only along for the ride. So, it is the salt that is already there that is involved–the kidneys spill less to compensate for the extra need to maintain homeostasis. It’s not necessarily extra salt from the diet.

        I’ll read up on it a bit more as, like many here and Mark, I’m in the pursuit of healthy diet backed by sound science. But I’m glad that so far, if I’m reading this right, I’m not challenging Taubes–I have him to thank for bringing me to the Primal/Paleo lifestyle. Thanks for the feedback.

        1. Yes you got it right. Cut down on carbs and kidneys will do the rest of the job. Personally I drink considerable less water than before and therefore it makes sense to me. Not that it matters to me in the sense of losing wight. My BMI was never higher than 18 and I am quite happy I haven’t lost a pound since starting low carb. Hopefully the lost water was substituted by lean muscle. 🙂

          You are welcome, Poisonguy.

  17. Here’s some advice….

    Throw away your scale and eat real food. Your mental state will thank you.

    Stay away from recipes especially baked stuff, and you’ll lose even faster.


    1. What do you consider real food? In all my books on nutrition, the main food group stressed is the dark green leafy vegetables. I don’t like them much, so that is a challenge. I just got interested in learning how to bake homemade whole grain bread. Now you said to stay away from baked stuff. So why is it bad, the carbs?

  18. It is possible that some of the 20 lbs Todd lost was fat. Just remember, once the water weight is gone, for every 2 pounds you lose, 1 of them is muscle. As little as 2 strength training sessions per week can prevent that muscle loss.

    1. Sorry to disagree with you Susan, but as long as Todd’s protein intake is adequate, he will not lose muscle mass (unless he was active before and suddenly became sedentary, which seems like the opposite is true in his case now). The body will use ingested amino acids for it’s metabolic needs before dipping into muscle–that’s basic physiology and biochemistry (albeit one has to keep mind that amino acid turnover in muscle is a dynamic process). Can’t argue that a little exercise is beneficial health wise.

      1. Bits of my response sounded nasty. Of course I believe there’s micromanagement at the muscle level (the dynamic stuff I was talking about), but nothing remotely close to 50% muscle to fat loss. That’s what I was trying to say, without offending of course. But if I did, I’m sorry. It wasn’t my intention.

        1. well I started the pb 2 weeks ago at 191 lbs and now Im down to 175 I am verry siked! but Ive noticed that Im not looseing the weight as fast, why is this?? and what can I expcect for a helthy weight for me? Im 34 5ft. 3inches and I have a lot of muscle. I would like to get to 130lbs that was when I was a size 3 but I would be happy with 150.

  19. I have been full on Primal for 5 months now (inadvertently partial for 2 years before reading Mark’s book). I cannot seem to drink large amounts of fluids without running to the washroom shortly thereafter. This is hard evidence in support of Mark’s reply to Todd. Very little water retention!
    Great job Todd, keep it up!

  20. Very interesting article and comments. What about people like me….71 years young, marginally diabetic for years and taking Medformin….went on Primal back in March, didn’t so much drop a lot of weight (5-8 pounds), as I lost inches…and could tell I had lost fat..and I hope not muscle. Only walking on occasion for exercise.
    Should I be concerned?

    1. Concerned about what, Larry? Sounds to me like you replaced fat with muscle. Nothing to be concerned about at that level. And what you are doing is only going to help with your diabetic status. Plenty of folks doing the Primal/Paleo/PaNu thing are eventually able to come of meds. So keep at it.

      BTW, are you still overweight or obese?

  21. in relation to this is this video

    from robb wolf

    don’t know if you’ve seen it?

  22. Todd, consider that initial water-loss as a nice bonus to get you started. After that, eating primally will result in a steady sustainable loss. Actually not exactly steady for me–I stay the same weight for 2 to 3 weeks, then drop a couple of pounds overnight. I’ve taken off 36 lbs since January, reducing my fat percentage such that my lean body mass is not changing. Yay!

    By the time you have lost 50 lbs, people will stop saying “water weight” since a person would die who actually lost 50 lbs of water.

    1. That would depend on how much water they were retaining.
      My wife went into hospital with partial heart failure and was put on IV Lasix (a powereful diuretic)and dropped 34 lbs of water weight OVERNIGHT, and 50 within five days.
      Far from dying, she felt much better.
      Of course, there is the fact that, with that kind of retention, she was close to dying, but she continued to lose weight in the form of retained water (on oral Lasix) for nearly a month before leveling off.

      1. Art, I believe ColoGrassFed meant water loss not related to a pathological condition–just from dieting.

        1. Yes, I get that, I was only pointing out that a person could lose 50lbs of water weight without dying. particularly over the course of a month.
          Do I believe it happened here? No.
          I believe the poster lost probably 10+ lbs of fat, 10 lbs of inflamation based reatained water, and gained a pound or two of muscle.
          how much weight in water one can lose without death, however, is different for each person, depending on size, amount of water retained (beyond a healthy level) and simple differences of individual biology.
          Fixed numbers are arbitrary, and no two people are the same.

  23. Great work Todd! Keep it up! I started with PB around the end of March and atb 346. I am now down to 299-303 depending what day of the week it is. I feel great and am not sure if it was water or not, but my goal is to lose 10 pounds per month and hopefully get back to 195. Maybe it’s unrealistic, but if I can get between 195 and 215 lbs. I will be a very satisfied happy guy. My goal is also to be able to do 10 pull-ups and run a few miles with my son! I can only keep at it as I sure don’t want to go back to how I was!!!!

  24. I’m right there with you partner. Started about a month ago when I met woman that called herself Primal Jane. I asked her what’s “that” about… then picked up Primal Blueprint… yadda yadda yadda … and I’ve dropped from 340 to 320lbs. I could care less whether it’s water weight. What amazes me is how much better I feel. And talking about medical things, nut just weight loss.

    It’s kind of intimidating when there is such a long way to go but what I did was make up a list of “rewards” for every 20lbs I drop. The last one… when I reach 200lbs… is a motorcycle trip across Alaska!

  25. I like this post, very educational!

    Been Primal since 07. April 2010 and lost 20 lbs. But … I had no muscle and a lot of fat, also internal fat so the weight loss was probably more like 30 lbs of fat lost and 10 lbs of muscle gained.
    Went from 164 lbs down to 144 lbs at 5’10” (female).

    Need to get rid of my belly flab still but it’s summer and I’m not going to give up all those seasonal fruits quite yet! 🙂

  26. I’m getting ready for the 30 day challenge. Why? I wasn’t able to go on a zip-line because of my weight, which told me I had a problem. I guess I know what my “reward” will be when I lose the first 20 pounds.

  27. I’m typically to running a blog and i actually admire your content. The article has actually peaks my interest. I am going to bookmark your site and hold checking for brand new information.

  28. I don’t care if it’s water weight. All I care about is that I look better, with a more defined face instead of a bloated fat face.

    I see that I’m making lots of ketones from the strip test. I know I’m no track. I went from 310 lbs to 275 last year, and now I’m back on the diet once again going from 275 to 260 already in the last week. I worked out twice in the last week, so I’d say 5-7 lbs is water weight, but the rest must be fat because I’m in the purple for the strips…plus I’ve been skipping some meals (intermittent fasting).