Carbohydrates love water (Hydrophilic is the scientific term), so for every gram of carbohydrates you store, you also store 3-4 times their weight in water. So low Carb diets give you an up front weight loss that is greater than you’d expect based purely on calories, since for every pound of carbs you lose, you also lose the water that is stored with them.
Now, since you store an extremely limited amount of energy in carbs (relative to the amount of energy stored as fat), this is pretty short term.
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