Current Recommended Dietary Allowance Research Articles

Effects of age on energy balance

The effects of aging on energy requirements and energy balance have been studied by several research groupsusing the doubly labeled water method. The weight of evidencefrom these investigations suggests that current recommendeddietary allowances underestimate the usual energy needs ofadults of all ages, including older adults. In addition, doublylabeled water studies have found a significant negativeassociation between body fatness and energy expenditure forphysical activity, and a significant positive association betweenenergy expenditure for physical activity and fat-free mass.Further studies are needed to refine estimates of energyrequirements for different population groups and to address therole of physical activity in the prevention and treatment ofobesity. Am J Clin Nutr 1998;68(suppl):975S–9S.

Folate Status Response to Controlled Folate Intake in Pregnant Women1–4

A metabolic study (84-d) was conducted to investigate the folate status response of pregnant subjects (n= 12) during their second trimester and nonpregnant controls (n= 12) to folate intakes approximating the current (400 μg/d) and former (800 μg/d) recommended dietary allowance (RDA). The overall goal of the study was to provide metabolic data to assist in the interpretation of the current RDA for folate. Subjects were fed a controlled diet containing 120 ± 15 μg/d (mean ± SD) folate and either 330 or 730 μg/d synthetic folic acid. Outcome variables between and within supplementation groups were compared at steady state. Serum folate was higher (P≤ 0.05) in pregnant women consuming 850 compared with 450 μg/d (44.6 ± 13.4, 26.3 ± 11.3 nmol/L, respectively, mean ± SD). No differences (P> 0.05) were detected in serum folate between pregnant and nonpregnant women within the same supplementation group. Urinary 5-methyl-tetrahydrofolate excretion was greater (P≤ 0.05) in pregnant women consuming 850 compared with 450 μg/d (198.0 ± 100.4, 9.5 ± 3.2 nmol/d, respectively). No differences (P> 0.05) in 5-methyl-tetrahydrofolate excretion were detected between pregnant and nonpregnant women within supplementation groups. Differences (P≤ 0.05) were not detected in red cell folate between pregnant women consuming either 450 or 850 μg/d (1452.5 ± 251.8, 1733.5 ± 208.5 nmol/L, respectively) or between pregnant and nonpregnant women consuming 450 μg/d. Our data suggest that 450 μg/d (dietary folate + synthetic folic acid) is sufficient to maintain folate status in pregnant women. This level of intake equates to ∼600 μg/d dietary equivalents, assuming 50 and 75% availability of dietary folate and synthetic folic acid consumed with meals, respectively.

New Views on the RDAs for Older Adults

The oldest age category in the 1989 edition of the Recommended Dietary Allowances (RDAs) is 51 years and above. Future committees on dietary reference intakes will likely define recommendations for age categories older than this. Instead of extrapolations from data derived from experiments on younger people, future RDAs should be derived directly from experiments on older people. Further, scientists are now interested in the amount of the nutrient that it takes to prevent chronic diseases from occurring rather than to prevent deficiencies, and this will likely influence RDA numbers. A review of past and current data suggests that the current RDAs for the elderly are too low for riboflavin, vitamin B-6, folic acid, vitamin B-12, vitamin D, and calcium, and are probably too high for vitamin A.

Dietary Calcium Intake Among Children Ages 4–12 Years: 1980 to 1992

The Recommended Dietary Allowance (RDA) for calcium increases from 800mg to 1200mg per day after age 10 years. Recent evidence suggesting current dietary intakes of calcium were insufficient to achieve optimal peak bone mass resulted in a National Institutes of Health Consensus Statement recommending intakes up to 1500mg per day for persons between the ages of 10 and 24 years. Dietary intake studies conducted on a national sample examined the mean daily intake of 30 nutrients for 19 age/sex groups and were the source of the data reported. Results indicate dietary calcium intakes in 1992 for children ages 4–6, 7–10 and 11–12 years of 713mg, 792mg and 832mg, respectively. This represents a decline from 1980 to 1992 of 27mg (p<.01), 6mg and 26mg (p<.05) for the three age groups, respectively. The 11–12 year olds consumed significantly higher amounts of calcium than the two younger age groups (p<.01) but not enough to compensate for the higher RDA. Over 90% of 11–12 year olds failed to meet the current RDA for calcium compared to 64% of 4–6 year olds and 56% of 7–10 year olds in 1992. Fifty percent of 11–12 year olds had calcium intakes below 66% of the RDA. Twenty-eight percent of 4–6 year olds and 18% of 7–10 years olds consumed below this level in 1992. Milk and milk products were the predominant source of calcium, contributing 59%, 55% and 52% of calcium to the diet for the three respective age groups in 1992. However, this is down from 66%, 62% and 61% for the same three age groups in 1980. The percentage of calcium contributed by fluid milk declined over time and with age from 49% for the 4–6 year olds in 1980 to 41% for the 11–12 year olds in 1992. This decline can be attributed to a decrease in fluid milk consumption of approximately 10% across all age groups. Efforts to increase calcium consumption among children of all age groups are crucial. Encouraging regular, daily consumption of at least three servings of low-fat, calcium-rich dairy products such as low-fat milk and yogurt can help children meet their daily calcium requirements. Particular attention must be paid to 11–12 year olds whose increased needs are not being met by current consumption patterns.

Mineral requirements of elderly people

Poor mineral nutrition reported in elderly people is attributed in large part to low dietary intake. Evaluation of the adequacy of mineral nutriture is limited for several minerals because of inadequate methods for assessing mineral status. In addition, there is a general lack of information about mineral nutriture and metabolism in very old people (> 85 y). Given these reservations, the 1989 recommended dietary allowance (RDA) for iron, zinc, and selenium appears adequate for elderly people, as does the estimated safe and adequate daily dietary intake (ESADDI) recommendation for copper. In contrast, the current RDAs for calcium and magnesium and the ESADDI for chromium need careful reevaluation. Current recommendations for calcium may be too low, whereas those for magnesium and chromium may be higher than necessary. For phosphorus, iodine, manganese, fluoride, and molybdenum the available data are insufficient to make a critical judgment about the appropriateness of the dietary recommendations for elderly people.

Dietary energy requirements of young and older women determined by using the doubly labeled water method

There is little information on the effects of age on energy requirements in women. This issue was investigated in a cross-sectional study of 10 normal-weight young women aged 25.2 +/- 1.1 y (mean +/- SEM) and 10 normal-weight older women aged 74.0 +/- 1.4 y. In a 9-d study, measurements were made of free-living total energy expenditure (TEE) by using the doubly labeled water technique, body composition by using hydrodensitometry, and resting energy expenditure (REE) by using indirect calorimetry. Mean values for reported levels of strenuous activity were within the expected range in both groups (31 +/- 13 min/d in the young group and 7 +/- 2 min/d in the older group). Energy requirements expressed as the ratio of TEE to REE were 1.80 +/- 0.10 and 1.62 +/- 0.06 (P < 0.01) in the young and older group, respectively. When values for REE predicted from body weight (pREE) were used, as suggested in the current recommended dietary allowances (RDAs), the ratios of TEE to pREE in the two groups were 1.85 +/- 0.10 and 1.54 +/- 0.04 (P < 0.05). The RDAs significantly under-predicted the energy requirements of the young group (P < 0.05), but there was no significant underprediction in the older group. Although obtained in a relatively small number of subjects, these results provide no evidence to indicate that the current RDAs underestimate the energy requirements of older women, in contrast with previous observations of an underestimation of energy requirements by the RDAs in older men.

Energy requirements for frail elderly females

About half the residents living in nursing homes and homes for the elderly show activity factor values less than 0.25 in daily living. However, the current Recommended Dietary Allowances (RDA) have been intended to apply to self-supporting and healthy elderly persons rather than bedridden elderly persons. Accordingly, current RDA tables do not indicate energy requirements for frail elderly people who show less values than 0.25 in activity factor. Consequently, in most institutions for the elderly, an adequate dietary energy supply for residents has been calculated on the basis of "level I (light)" in levels of physical activities. In this study, we measured the daily energy expenditures of 78 frail elderly females (age; 79.9 +/- 7.1 yrs) living in nursing homes and homes for the elderly. From these results, energy requirements for frail elderly females corresponding with 0.00 to 0.25 of the activity factor were provisionally estimated as to be 21 to 31 kcal/kg BW.

Effect of chronic endurance exercise on retention of dietary protein.

On two separate occasions, five well-trained endurance runners (VO2max = 71 +/- 5 ml/kg/min; means +/- SD) consumed a meat-free diet for 6 days. For one trial the subjects consumed the recommended dietary allowance (RDA) of protein (REC-PRO = 0.86 +/- 0.23 g/kg body wt/day). Protein intake for the other trial was 1.7 times higher (HI-PRO = 1.49 +/- 0.29 g/kg body wt/day). Each subject followed his regular training program (12-16 km running/day), and on day 5 of each diet completed a treadmill run at a similar intensity and duration (75 min at 72% VO2max). Seventy-two hour urinary urea N loss (days 4, 5, and 6 of each diet) and day 5 exercise sweat urea N excretion were measured. Serum urea N and creatinine increased significantly during the treadmill run under both dietary conditions (P less than 0.05). No significances between diet differences were observed in sweat or urinary urea N excretion; however, excretion of both tended to be higher on the REC-PRO diet than on the HI-PRO diet. The differences in protein intake combined with the nitrogen excretion measures resulted in significant differences in estimated whole-body nitrogen retention between the two treatments. Nitrogen retention (means +/- SE) remained positive during the HI-PRO trial (2.41 +/- 1.99 g/day) but was significantly (P less than 0.005) reduced to -5.29 +/- 2.58 g/day during the REC-PRO trial. These results suggest that the current protein RDA may be inadequate for athletes engaging in chronic high-intensity endurance exercise. Future studies are needed to confirm this observation.

The RDA or U.S. RDA?

An adequate vitamin intake is essential for a good nutritional status, especially in older women, who are more sensitive to nutritional deficiencies. The American, European and Italian Recommended Dietary Allowances (RDAs) derive mainly from studies on adults, and it is not clear whether they also apply to elderly people. Comparing the RDAs with the actual vitamin intake of a group of healthy older women could help to clarify the real needs of elderly people.Our aim was to compare the American, European, and Italian RDAs with the actual vitamin intake of a group of healthy older women.This was a cross-sectional study.The study included 286 healthy women aged older than 65 years.For each micronutrient, the 50th percentile of the distribution of its intake was considered as the average requirement, and the corresponding calculated RDA for our sample was the average requirement×1.2, as recommended by the US Food and Nutrition Board. This calculated RDA was then compared with the American, European, and Italian RDAs.Student’s t test or the Mann-Whitney test (after checking the normal distribution of the micronutrient) for continuous variables; the χ2 test for categorical variables.The calculated RDA were 2,230 μg retinol equivalents for vitamin A, 2.8 μg for vitamin B-12, 0.9 mg for thiamin, 1.4 mg for riboflavin, 3.6 mg for pantothenic acid, 1.4 mg for vitamin B-6, 320 μg for folic acid, and 115 mg for vitamin C.Our findings suggest that the current RDAs are adequate for older women’s intake of riboflavin, vitamin B-6, and folic acid, but should be raised for vitamin B-12 and for vitamin C.