Actually, it means you are doing well and on your way to a fit, healthy, and leaner body. One of the first things you may notice as you embark on a Paleolithic diet plan and exercise routine is that you will drop a lot of weight in the first few weeks. This will continue, but most likely at a slower pace unless you are very aggressive and strict with your eating habits.

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 glycogen – three 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.

Fat is simply stored energy for later use, water is simply stored hydration for late use, so it goes without saying that when you eat a healthy diet you will experience...

 
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.

Thank you, Mark Sisson