Your body is about two-thirds water. Dehydration reduces the amount of water in your body. Severe dehydration can lower blood pressure and the amount of oxygen available to your cells, which may lead to coma and death. Besides the usual causes of dehydration, like excessive sweating from heat exposure, vigorous exercise, fever, diarrhea, vomiting or just not drinking enough, some foods can reduce water and other body fluids. When you eat these foods, avoid dehydration by drinking and extra glass or two of water.

Diuretics

Diuretic foods increase urination and thereby reduce the amount of water in your body, making you feel dehydrated. Foods known to have this effect include parsley, celery, asparagus, artichokes, and melons. Two common diuretics, alcohol and caffeine, affect millions of people daily, with alcohol having a stronger diuretic effect than coffee. To offset the effects of alcohol and caffeine, drink one glass of plain or sparkling water in between each glass of wine or coffee.

Sodium

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Foods high in sodium boost your body's sodium levels. To dilute the salt, your cells excrete water and send a thirst signal to your brain saying they need more water. Foods that taste salty, such as french fries and salty snack foods, contain high amounts of sodium. But you might not be able to detect the high sodium levels in other foods, such as fast food meals, canned foods, deli meats, frozen dinners, processed baked goods and bottled condiments such as salad dressings.

Sugar

Sugar affects your body in the same way salt does, drawing water out of your cells and making you feel thirsty. Ironically, sports drinks with sugar can actually quench your thirst more slowly than plain water because the sugar draws water from your cells. Moreover, the sugar in beverages such as fruit juices, vitamin water and sports drinks is absorbed by your body more slowly than plain water. You should eat snacks from two food groups to avoid feeling dehydrated, such as a piece of fruit plus a piece of cheese or fruit plus whole grain crackers.

Diarrhea

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Any food that causes diarrhea can also dehydrate you. If you are lactose intolerant, those foods include most dairy products. Some lactose-intolerant people react to smaller amount of lactose in baked goods, cereals, soups, drinks, lunch meats, salad dressings and powdered drink supplements. Excess iron, either through iron supplements or too much red meat, also can cause diarrhea, according to the President’s Council on Physical Fitness and Sports.