The amount of water in your body affects your scale weight, and the numbers can go up or down, depending on whether your body is losing or retaining water.

Many people believe that drinking more water makes them weigh more because it causes water retention. However, while water retention does indeed add to scale weight, drinking water actually helps to prevent water retention rather than cause it. Common causes of water retention include:

• Excess sodium/salt. The normal recommended daily maximum of sodium is 1500 mg. But just one teaspoon of salt supplies 2358 mg of sodium, and we often consume far more sodium than needed. This causes water retention and adds water-weight.

• Not drinking enough water. Although it sounds back-to-front, you need to drink a sufficient amount of water to flush out the water already in your body.

• Menstruation, constipation, and certain diseases such as heart and kidney disease may also cause water retention.

Water loss can also give you some false readings on the scale. Generally it's only possible to lose one to two pounds of actual fat per week, so if you're losing more than that you're probably losing water, not fat. Excessive calorie restriction, in particular, can cause rapid weight loss which is often about 75 percent water loss. Diuretics can also cause water loss.