When you eat sugary foods, your kidneys work to excrete the excess sugar in your body through your urine. While this is beneficial, you unfortunately lose water along with that sugar. This process, known as osmotic diuresis, causes increased urination due to the presence of certain substances in the fluids filtered by the kidneys. Basically, your body is trying to get rid of the substance, which is perceived by the body as waste, so it flushes it out through your urine, with water. The result is dehydration. This type of dehydration is common among diabetics, who need to urinate frequently to eliminate excess sugar.
Have you ever had the experience of your fingers swelling up like little sausages after eating a lot of salt? While it seems as if you body is retaining water, this is actually a sign of your body trying to get rid of, or dilute the salt. When you consume salt, the ion concentration in your blood increases, which pulls water out of your cells via osmosis. Your body will then try to eliminate the excess salt through your urine, thereby causing you to lose more water than you retain, dehydrating you at a cellular level.
Avoid unnecessary dehydration from the food you eat by eliminating processed foods. These are the worst culprits for high sugar and salt content. Choose more foods with natural sugars and also a high water content such as fresh fruits and veggies.