Dear Dr. Blonz: I have some questions about the Recommended Daily Allowance. I am a 28-year-old woman with a family history of osteoporosis. Lately I have been using a computer program to tally up the calories, fat, vitamins, minerals, etc., in my daily diet. I have become concerned because occasionally I have not reached my RDA for some vitamin or mineral. Often, that mineral (lacking by about 10%) is calcium. So my question is: Should I be concerned? Should I take a daily calcium supplement? How accurate is the RDA?
Dear K.D.: The RDAs are based on current research and are revised every few years. The RDAs vary according to age group and sex. This is in contrast to the daily value (DV), a single set of values developed for use on food labels. The RDAs are designed to be average intakes that meet the needs of most healthy individuals.
We think of bones as being "solid," but they are constantly being made and unmade. As a 28-year-old woman, you are in what I call the "investment phase" of bone growth. This is a period during which your body has an ability to increase its total bone mass. This happens, however, only to the extent that the bone-making minerals and other essential nutrients are present. As you enter your 30s, your body slowly begins to shift gears; and by the time you reach 40, the bones are losing more than they gain. The higher your peak bone mass, the longer this process takes.
What this means is that most women will eventually develop osteoporosis--some, however, will show symptoms in their 60s and 70s, while others might not show evidence of the condition before they reach 110 (assuming, of course, they live that long). To stack the odds in your favor, it pays to take in all the calcium the body can use. One important point: It's important to realize that it takes more than calcium to make bones. Although a bone is about 90% calcium by weight, other minerals such as magnesium, phosphorus, boron and silicon are needed, as is vitamin D. It is also important to follow a program of weight-bearing exercise, as this helps to slow bone loss.
For your age and sex, the RDA for calcium is 800 milligrams per day, but you don't have to have the RDA every day. Being down 10% is not a serious matter, and you are ahead of most people your age. If, however, your calcium intake chronically undershoots the RDA, it would be in your best interest to find a way to take it up a notch--especially in light of your family history. You can take a calcium supplement, but perhaps all that is needed is a glass of calcium-fortified orange juice, a serving of a calcium-containing vegetable such as broccoli or kale, some tofu (made with calcium) or, of course, a serving of a dairy product.
Dear Dr. Blonz: My question concerns the nutritional analysis that is on most boxes of cereals, breads, pastas, etc. Is the nutritional information listed for the whole box or for just one individual serving?
--A.V., Los Angeles
Dear A.V.: The nutritional information is for one serving, and the nutrition facts panel should list the number of servings in the container.
Dear Dr. Blonz: The latest information affirms what you have been saying for years, namely, that trans-fats are the worst fats for cardiovascular disease. Do these fats show up on a cholesterol test?
--C.B., San Diego
Dear C.B.: The level of trans-fats doesn't show up on a blood test. This dietary component, however, will have an impact on raising the level of LDL (least desirable) cholesterol and lowering the level of the HDL (highly desirable) cholesterol--two factors that do show up when you have your blood cholesterol measured.
The best way to avoid trans-fats is to avoid foods made with partially hydrogenated vegetable oils. Read the ingredient statement of the foods you buy. Also be advised that most of the frying oils used in fast-food restaurants are partially hydrogenated. That means that French fries, for example, are loaded with trans-fatty acids.
Ed Blonz is the author of the "Your Personal Nutritionist" book series (Signet, 1996). Send questions to "On Nutrition," Ed Blonz, c/o Newspaper Enterprise Assn., 200 Madison Ave., New York, NY 10016, or e-mail to email@example.com. Personal replies cannot be provided.