Date: 20 Aug 1994 07:44:59 -0700 From: taltar@vertigo.helix.net (Ted Altar) Subject: What are RDAs? (repost) Newsgroups: rec.food.veg Organization: Helix Internet Lines: 156 WHAT ARE RDA'S? Ted Altar Topics briefly covered: A. General Preamble B. The American Rda's C. Toxic Effects Of Vitamins D. The Example Of How A Rda For Protein Is Obtained. A. GENERAL PREAMBLE Let us remember that a public health official recommendation like that of a country's RDAs, actually only represents: "optimal values for a population often FAR above the simple and strict average of the basic biological needs" (Millet et al, AM. J. CLIN. NUTR. 50:718-727, 1989) Margins of safety are built in to not only protect healthy adults but some of those with unique needs or absorption problems. For example, Victor Herbert, who is probably the leading authority on B12, puts the actual requirements to be round .1 microgram/day (hence, even the recently reduced NRC recommendation of 3mcg is still some 6-30 times greater than the actual requirement of healthy adults who suffer from no unusual absorption problems other than the general inefficiency of not being able to absorb all dietary nutrients consumed (remember, over 95% of B12 deficiency cases are a result of absorption problems). Hence, the American RDA levels of 3mcg for B12 is somewhat ethnocentrically based upon the American population, whose meat-eating diet incurs a greater loss bodily stores of B12 through the excretion of more bile. The WHO recommended daily allowance of B12 for adults is only 1mcg. Personally, I think the WHO recommendations are more useful, especially for vegetarians, since they are less ethnocentrically biased upon a gluttonously high fat, meat-eating diet. In general, the RDAs are NOT requirements for an individual but are simply recommendations for the daily amounts of nutrients that *POPULATIONS* should consume over a period of time to protect almost all members of that population. While single numbers have been employed (for simplicity to help inform a nutritionally naive public), sometimes ranges are used, as in the case of the 1980 RECOMMENDED DIETARY ALLOWANCES (9th edition) of vitamin K, pantothenic acid and biotin. B. THE AMERICAN RDA'S The American RDA are standards developed by the FDA for use in the nutrition labelling of the general food supply and for labelling dietary supplements and special dietary foods. They are based mainly on the 1968 RDA as formed but the then judgements of the COMMITTEE ON DIETARY ALLOWANCES of the then constituted FOOD AND NUTRITION BOARD. In the USA, RDAs are set 2 standard deviations above the mean requirements of subpopulations (as categorized by age, weight, sex and pregnancy or lactation) so as to encompass the needs of 97.5% of the population. For simplicity, the Amer. RDA uses only 4 pop. groups (compared with 26 groups listed in the 1968 RDA and 17 in the 1980 RDA editions). Too bad nobody has seen fit to devise tables for lacto-ovo vegetarians and vegans :-( Generally the HIGHEST values for the all ages combined are used in the US RDA. C. TOXIC EFFECTS OF VITAMINS Undesirable effects ranging from trivial to lethal have been reported in the literature in association with use of inappropriately high does of vitamins. For instance, serve illness has resulted from the excessive use of vitamin A, and death has occurred from large doses of vitamin D. Even an intravenous does of 80 g of good old vitamin C caused the death of one patient with a glucose-6-phosphate dehydrogenase deficiency. Excessive doses of vitamins are conventionally defined as around 10 or more times the RDA, but toxic effects from long-term ingestion of, say, vitamin A has been well documented with supplements ranging in only 5 times U.S. RDA. [see "Council Report: Vitamin Preparations as Dietary Supplements and as Therapeutic Agents", JAMA, 1987, 257(14, April 10):1929] D. THE EXAMPLE OF HOW A RDA FOR PROTEIN IS OBTAINED. To help make more concrete the above, I thought it might be helpful to here give a more concrete example of how a RDA is actually obtained. The RDA for protein is fairly precise, unlike that of the vitamins which due to lack of information on base allowances, upper limits are often chosen. The following RDA by the COMMITTEE ON DIETARY ALLOWANCES of the NATIONAL ACADEMY OF SCIENCES, FOOD AND NUTRITION BOARD, comes from Frances More Lappe, in her recent edition of "DIET FOR A SMALL PLANET" 1991:. step 1. Estimating average need. Since nitrogen is a characteristic and relatively constant component of protein. . . experimenters put subjects on a protein-free diet. . . measure how much nitrogen is lost in urine and feces. They add to this an amount to cover the small losses through the skin, sweat, and internal body structure. For children additional nitrogen for growth is added. The total of these nitrogen losses is the amount you have to replace by eating protein. . . step 2. Adjusting for individual differences To allow for individual differences and to cover 97.5% of the population, the committee sets this protein requirement 30% above the average, arriving at 30 grams per day of protein for a 154-lb man, or .45 gram per kilogram of body weight per day. This assumption that 30% above the average requirement will cover 97.5% of the population is one of the issues in dispute by nutritionists. step 3. Adjusting for normal eating compared to experimental conditions. Scientists have discovered that protein is used less efficiently when people are eating a normal diet containing some extra protein than when they are eating at or near their protein requirement, as they do under experimental conditions. Apparently, when people are deprived of protein their bodies compensate by more fully using what's there and excreting less. So to account for the less efficient use of protein in ordinary eating patterns, the committee adds another 30% This brings the allowance up to 42 grams for a 154-pound "average" American, .57 gram per kilogram of body weight per day. step 4. Adjusting for protein usability The protein in our food is not fully used by the body. The above estimates are all based on ideal "reference protein". Scientists estimate the average usability of protein in the U. S. diet at 75% Therefore, the allowance of 42 grams of protein for a 154-lb man is pushed up to 56 grams because it is assumed that only 75% of what is eaten is actually used. Note that by setting the intake 30% above average right at the beginning, already we have a RDA that is in excess of what most people really need. Still, even a vegan diet will easily meet this RDA of protein and more. ted