Your body weight can fluctuate by a great degree on a day to day basis -- in some cases up to a few pounds. This is often caused by a change in your body's level of stored carbohydrate, known as glycogen. Changes in glycogen are normal and while they can make it seem like your weight loss progress has stalled, or even reversed, this certainly isn't the case.
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The Role of Glycogen
When you eat carbohydrate, only a certain amount can be used, or circulated in the bloodstream at any one time. What can't be used immediately needs to be stored. The carbohydrate is broken down and converted to a substance called glycogen, ready to be stored in the liver or the muscle cells to be used at a later date. About 8 percent of the weight of your liver is glycogen and about 1 percent of your muscle mass.
When Glycogen Drops
A healthy adult can store around 400 grams of glycogen in the liver and about 100 grams in the muscle cells. If your glycogen levels drop, you can lose half a kilogram -- over 1 pound. Additionally, every gram of glycogen carries with it 3 grams of water, meaning that if you deplete your regular stores of glycogen, this can show up as a 2 kilogram loss on the scale. This often happens in the first few days or the first week of a diet when you restrict your carbohydrate intake, or, if you're an athlete, it can happen on a daily basis if you're training at a high-intensity for a long duration. In the short-term, this can lead to muscle fatigue and a drop in performance and in the long-term, chronic glycogen depletion can place extra stress on your liver, warns sports nutritionist Ben Greenfield.
Glycogen levels become depleted through exercise, but you're more likely to experience a substantial drop off when making dietary changes. When you start to diet and cut calories and carbohydrates, your body has to dig into its glycogen reserves, causing them to be used for energy, notes dietitian Zoe Hellman. This is why many dieters -- particularly those following low-carb diets -- can often notice a loss of 3 to 5 pounds in the first week or two on a diet.
The Whole Picture
When aiming to lose weight, don't get too caught up in small body weight fluctuations. If you've had a high-carb meal, or have been carb loading for an athletic event, your weight will be higher due to increased glycogen stores. Likewise, if you switch to a lower-carb diet, your weight will drop as glycogen diminishes. Use other measures, such as pictures or measuring body fat percentage to gauge progress, or perhaps weigh yourself every day and take a weekly average to get a clearer picture of your overall weight loss.