Scales don't always give you the whole story about your body or your weight loss progress. For that reason, scales aren't the best way to track what's really going on inside your body. The scale can't tell you what you've lost or gained, which is important information if you're trying to lose weight—and by weight, what we really mean is fat.

Why Your Weight FluctuatesThe numbers you see on the scale vary with these factors:

Water weight gain. Because the body is about 60 percent water, fluctuations in your hydration levels can change the number on a scale. If you're dehydrated or have eaten too much salt, your body may actually retain water, which can cause scale weight to creep up. Similarly, many women retain water during menstrual cycles, which is another thing that can make that number change.Food weight gain. Weighing yourself after a meal isn't the best idea simply because food adds weight. When you eat it, your body will add that weight as well. It doesn't mean you've gained weight, it simply means that you've added something to your body (something that will be eliminated through digestion over the next several hours).Muscle gain. Muscle is more dense than fat and it takes up less space, so adding muscle could increase your scale weight, even though you're slimming down.4That doesn't mean the scale is useless. In fact, it's a wonderful tool when you combine it with your body fat percentage. Knowing both of these numbers will tell you whether you're losing the right kind of weight: fat.