It's normal to have day-to-day fluctuations in body water content, which actually follow variations in calorie intake (energy) as well as variations in the macronutrient (carbohydrate, protein, fat and alcohol) and sodium content of the diet. Carbohydrate and sodium in particular can both cause rapid changes in extracellular water. Additionally, intracellular water increases or decreases (along with increases or decreases) in glycogen (the storage form of carbohydrate) and protein.
Adult humans are 55 to 60% water by weight. The leaner (more muscle relative to fat) the individual, the higher his or her body-water content. So men are generally 5% to 10% more water by weight than women.
Water fluctuations mean scale fluctuations. Understanding this phenomenon should help desensitize you to the morning numbers on your scale!
The less welcome news is it takes some of the fun out of early weight loss, as 50 to 75% of the drop on the scale the first week to ten days is water.
Your "actual" loss of body-cell-mass (mostly fat, and some protein) over those days is limited to whatever energy deficit you achieved. This early water loss creates the illusion of slowed weight loss as soon as the water loss slows.
Here's how this works: When you start a diet, you reduce your intake of calories and a substantial part of that reduction is from carbohydrates. The reduction in carbohydrates leads to the depletion of glycogen (how your body stores sugar) from both your muscles and liver. Each gram of stored glycogen normally holds 3- to 4-grams of water with it.
This is the mechanism behind most of the early weight loss at the beginning of any diet--again, anywhere from 50 to 75% of the scale loss is water! Low-carbohydrate (high-protein) diets especially accentuate early (excess) water losses because it takes as little as 3-days on a low carbohydrate meal plan to deplete two-thirds of muscle glycogen. Thus, when you start a diet, it looks like you're losing more than you actually are.
Fad diets are based on this trick, because initial calorie reductions can produce the illusion of significant weight loss.This illusion, however, also leads to highly unrealistic expectations about ongoing weight loss!
Furthermore, when your glycogen stores are depleted from following that low carbohydrate diet, a carbohydrate binge will lead to excessive glycogen repletion (up to two times normal levels). And along with the glycogen, comes one heck of a water-weight-gain!
Actionable Points:
1) Remember that when you cut down on calories, that most of the drop (the first 7- to 10-days) on the scale is water. Get over it and trust your body--it's working exactly as expected!
2) Learn more about how your body works, for instance if your goal weight is 150-pounds (or you fill-in the number), then what calorie intake and weekly amount of physical activity, would be required to maintain at that weight? [Learn more]
3) Remember that due to water-weight fluctuations, that weighing yourself on a single day is hit or miss. To use the scale properly weigh yourself daily, and track the trend in the readings. Also it's best to weigh yourself at the same time, undressed and after voiding in the morning. Don't bother stepping on the scale at other times.
Your questions or comments are welcome!
Best,
-Dorene
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References:
-Hall KD and Chow CC. Am J Clin Nutr. 2011;94:66-74.
-Heymsfield SB and Thomas D. Obesity Reviews. 2011;12(5):e348-e361.
-Kreitzman SN, et al. Am J Clin Nutr. 1992;56(1 Suppl):292s-293s.
- The Water in You