Diet Moderation, Variety Stressed in RDA Update
The National Research Council announced its long-awaited revision of the Recommended Dietary Allowances last week, putting to rest five years of controversy and mystery, and reinforcing the current nutrition edict of variety and moderation.
Despite the volume of recently published research correlating diet and health this is the first update since 1980. And, as in previous editions, the subcommittee’s report defines the RDAs as suggested levels of intake for essential nutrients that are “adequate to meet the known nutrient needs of practically all persons.” These are flexible, generous yardsticks by which consumers can maintain good health.
The 10th edition of the nutrient intake guidelines added RDAs for two nutrients, Vitamin K and selenium, and makes changes in some others, including increased intake of calcium for youngsters and additional Vitamin C for smokers.
Otherwise, “variety and moderation remain the keys,” said Darlene Dougherty, president of the American Dietetic Assn., at the organization’s annual meeting in Kansas City last week. She explained that no major change from a varied, well-balanced diet is necessary for most individuals in order to accomplish these goals.
The RDAs are based, according to NRC, on the needs of groups of people, not individuals, and they should be considered recommendations, not requirements. Medical needs, the council emphasizes, alter nutrient needs and must be addressed separately.
For example, separate guidelines are established for individuals based on age, sex, height and weight. This allows people to assess the nutritional adequacy of their diets and make adjustments, over time, the report states. RDAs are not daily objectives, but time-averaged goals.
“In planning meals or food supplies,” the report said, “it is technically difficult and biologically unnecessary to design a single day’s diet that contains all the RDAs for all the nutrients.” A span of five to 10 days is an acceptable design for planning menus, NRC advises.
The new RDAs suggest intakes for protein, 11 vitamins and seven minerals. Carbohydrates and fat are not included. Most figures are given in milligrams, although micrograms also are listed for some nutrients. (There are about five grams per teaspoon; 1,000 illigrams per gram, and one million micrograms per gram.)
Here is a list of how they break down:
Vitamin K: This vitamin is essential for the maintenance of blood clotting mechanisms within the body. A common symptom of deficiency is hemorrhaging. Recent studies have helped define the specific amounts needed: The new RDA is set at 80 micrograms for men and 65 for women. Green leafy vegetables, particularly the cabbage family, and liver are good sources, while dairy products and red meat also contain appreciable amounts.
Selenium: Although selenium is considered a trace mineral (one that is found is small quantities within cells) it has been shown, along with Vitamin E, to have an antioxidant function. Deficiency has caused a major health problem in China. When Chinese children and women of child-bearing age consumed low-selenium diets, they developed a heart disease known as Keshan disease. Scientists suspected that a requirement might be necessary, and subsequent research established a precise ammount. The RDA for men is set at 70 micrograms, 55 micrograms for women. Seafood, meat and grains are sources.
Vitamin C: Since Vitamin C is among the nutrients with a role in strengthening resistance to infection, it is perceived as important for smokers who tend to process and eliminate the vitamin more rapidly than others. Although there is no proof that Vitamin C reduces risk for lung or other cancers, the subcommittee recommended that cigarette smokers consume at least 100 milligrams daily. For others, the RDA remains at 60 milligrams a day. Good sources include: citrus fruits, cabbage-type vegetables, dark green vegetables, strawberries, peppers, tomatoes, potatoes, papayas and mangoes.
Calcium: Previous RDAs recommended the average daily intake of this valuable mineral at 1200 milligrams for adolescents through age 18, and 800 for all others. But research has suggested adequate calcium intake during development of peak bone mass, which takes place throughout the growing years to age 24, is the best insurance against osteoporosis later in life. Thus, the allowance for this mineral was lengthened to age 24. Milk and milk products are primary sources. Fish with bones, tofu, some greens and legumes are others.
Iron: The RDA for iron, which is an important part of the protein hemoglobin, was decreased to 15 milligrams for adolescent girls and premenopausal women, a drop of three milligrams. Meanwhile, pregnant women were advised to increase their daily intake of iron by an additional 15 milligrams. Protein containing foods including red meat, fish, poultry, some grains and vegetable are sources.
Protein: The addition of protein to the diet for women during pregnancy was dropped from 30 grams to 10 grams a day. This change was based on theories about protein accumulation during pregnancy.
Folate: The committee reduced the RDA of folate, also known as folacin, to 240 micrograms for men ages 25 to 50 and 190 micrograms for women of the same age, based on observations of adult populations who maintain good health on diets containing an average of 200 micrograms a day. The previous recommended intake was 400 micrograms for both sexes. Folate is found in liver, leafy vegetables and some fruit. Anemia is a result of severe deficiency.
Vitamin B12: The RDA for this vitamin also was reduced from three micrograms per day for men and women to two micrograms a day. This nutrient is essential for maintaining normal metabolism and blood functions. It is prevalent in animal products.
Magnesium, Zinc and Vitamin B6: All of these nutrients were lowered. Daily allowances of magnesium, an important component of bone mineralization and maintenance of the teeth, dropped for women during pregnancy and lactation. It is found in nuts, legumes, whole grains, dark green vegetables, seafoods and chocolate.
The RDA for zinc was reduced to 12 milligrams a day for adult women, but remained the same, 15 milligrams, for adult men because of its role in reproduction. Zinc is important for taste perception and wound healing and is found in protein containing foods such as meats, fish, poultry, grains and vegetables.
RDAs for both sexes were decreased for Vitamin B6, but the amounts vary depending upon age.
Last week’s announcement represents the second attempt at the 10th edition of RDA. The previous effort was back in 1985 when the report was rejected by the National Academy of Sciences, the council’s governing body because it advised reduced levels of vitamins A and C.
A subsequent controversy surrounding the dispute over the two changes resulted in the delayed publication of the 1985 report and the ultimate disbanding of the committee due to “differing scientific opinions.”
Under normal circumstances, however, the RDAs have been reviewed every five years since their debut in 1943. The National Resource Council is a five-member subcommittee of nutrition experts from the Food and Nutrition Board of the National Academy of Sciences.
