Sodium

Sodium know best as table salt, but salt and sodium are hidden in all kinds of products, including packaged, frozen, canned, and fast foods, condiments, and many others. Excess sodium can raise your blood pressure and slow your metabolism.
Your body needs a steady flow of water in and out to effectively metabolize your fat. If the water gets stuck in your cells, it will slow your metabolism and, therefore, your ability to burn fat. Now, don't make yourself crazy over this, because there is sodium in everything, you can't avoid it. Just be conscious of it and minimize it where you can.