DEAR DR. BLONZ: I read that caffeinated beverages are diuretics and that when you drink an 8-ounce glass of a caffeinated beverage, such as tea, coffee or caffeinated soda, your body will lose 12 ounces of water. That would mean that these beverages are dehydrating instead of hydrating. It made little sense to me, but there were "experts" on that blog that were agreeing that this was true. I wanted to see if this was true. Where does alcohol rank as a diuretic? - O.C., Boston, Mass.
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Diuretics are substances that increase urine output. By this definition, even water could be considered a diuretic. Caffeine is considered to have a mild diuretic effect, and caffeinated beverages such as those you cite do not draw more water out of the body than they contribute. If, however, you were to take caffeine as an over-the-counter medication, such as a NoDoz product, or as an herbal dietary supplement, such as guarana, mate or cola nut, it would make sense to be well hydrated. Hydration is the key, and the Institute of Medicine recently established the Daily Reference Intake (DRI) for water. The guidelines state that adequate hydration is a daily intake of 2.7 liters (91 ounces) of water for women and 3.7 liters (125 ounces) for men. Those who are active or live in hot climates may need to consume more. About 80 percent of this total would come from drinking water and beverages, including caffeinated beverages. The rest comes from food. Vegetables and fruits, for example, are mostly water by weight.
Alcohol also has a mild diuretic effect, but it works in a different way. One of its effects is to inhibit the release of antidiuretic hormone (ADH), a hormone that limits the amount of urine produced in the body. When alcohol is around, less ADH is released, which translates to more urine leaving the body. The effects are apparent within about 20 minutes of consuming alcohol, which any beer drinker could affirm. Alcohol's diuretic effects play an interesting role, as many of alcohol's effects depend on the blood concentration of its metabolites. The body has a rate at which it processes alcohol, and it uses its fluids as a storage queue for metabolic byproducts awaiting processing and elimination. Tolerance to alcohol is said to be weight related: The larger you are, the more you can tolerate. This is not so much because larger people metabolize alcohol faster but because a larger body has a greater blood volume. As such, alcohol's diuretic effect enhances the consequences of overconsumption.
DEAR DR. BLONZ: I was hoping you might help me understand why BHT is used in breakfast cereals. I thought BHT was a food additive that was used to help prevent oils from going rancid, but there is little, if any, oil in breakfast cereals (except for the oat-based products). - O.V., San Francisco, Calif.
Dear O.V.: The letters "BHT" stand for butylated hydroxy toluene. It is a chemical antioxidant that can help prevent the oxidation of fats and oils. In low- or no-fat cereals, BHT can help protect fat-soluble vitamins that may have been added to the cereal.
This compound can also help "preserve" the packaging material, keeping it pliant so that it remains an efficient barrier between the cereal and the outside air. These functions become more important in warmer climates. Both uses require very small amounts of this compound.
Send questions to: "On Nutrition," Ed Blonz, c/o Newspaper Enterprise Association, 200 Madison Ave., New York, NY 10016. For e-mail, address inquiries to: ed@blonz.com. Due to the volume of mail, personal replies cannot be provided.
Ed Blonz, Ph.D., is a nutrition scientist and the author of "Power Nutrition" (Signet, 1998) and the "Your Personal Nutritionist" book series (Signet, 1996).
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