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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