by and nitrogen girls consuming
three
protein”
levels
Paula M. Howat,4 R. P. Abernathy,5
of dietary Ph.D., Ph.D.,
Man’ K. Korsiund, and S. J. Ritchey,
ABSTRACT
A nitrogen
nitrogen the
intake
protein
needs
total
body
sweat
and
weight
of
collected
under
g, 57 g and fairly
constant. of
nitrogen
Clin.
balance
subjects
Mean day
was of
for growth
0.3
for
Nutr.
28: 879882,
to determine
and
were
to assess
a mean
132
and
28.9
kg,
cm
conditions,
The
balances the
in 8 and g which
per
inclusion
day
2 subjects has
girls
were on
been
through age 201
0.04
recommended
263
g, 0.55 loss,
g and
and
57 g protein by
NRC
may
fur
319
the
than
that
of normal
height losses,
mg/day
on 34
study
remained
the
respective
g on
a negative
intake. for
intakes higher support
1.42
of on
of 24-hour, Mean nitrogen
the
however,
children, protein be required
mg
throughout
nitrogen
34 g and
collection sweat
levels nitrogen
7 months.
Mean mg,
ofthree
of sweat
the
of 8 years,
conditions
of sweat
impact
respectively. were
environmental
the effects
the
determined
with
intake.
preadolescent
sweat
girls
of preadolescent
NRC-RDA
undertaken
Values
environmental
with
found
was
through
I 5 healthy
were
nitrogen
intake,
study girls.
from
uncontrolled
retention
allowance the
the
Ph.D., Ph.D.
of nitrogen
of preadolescent samples
nitrogen per
loss
88 g of protein
levels balance
on the
2,3
After
nitrogen considering
minimum
nitrogen
recommended growth.
by Am.
J.
1975.
Most studies undertaken to assess protein requirements have dealt primarily with adults and have excluded protein needed for the physiological stress ofgrowth and integumental nitrogen losses (I). In 1964, the Food and Nutrition Board of the National Research Council recommended for the first time that an allowance for nitrogen lost through the skin should he included in calculating protein requirements. The value, 0.8 mg/basal kcal per day was based on studies of adult subjects (2-4). Spence et al. (5) recently speculated that the NRC allowance for integumentary nitrogen loss may be inadequate for preadolescent girls consuming a protein intake greater than marginal or too low to support normal growth. The effect of nitrogen loss through the skin on protein needs has not been clearly defined for the growing child. Such losses may represent a significant percentage of the total intake when protein consumption is above the minimum. Only after the extent of nitrogen losses are determined can realistic recommendations for maintenance and growth be calculated.
The present investigation was conducted to study the amount ofcutaneous nitrogen losses and to relate these losses to protein intake, nitrogen retention and total nitrogen excretion of preadolescent girls. The subjects were maintained on three levels of dietary protein ranging from that estimated for maintenance to an amount estimated to be ample for maintenance plus growth. Activity and sleep patterns during the study were typical of this
The
1975,
American
Journal
of Clinical
Nutrition
28:
AUGUST
age/sex
group.
Procedure Subjects were 15 healthy Caucasian girls who ranged in age from 8 to 9.5 years. Their mean heights were 132.9 ± 6.0 and I 33.3 ± 6.0 cm at the beginning and end of the 1 From the Department Foods, Virginia Polytechnic sity, Blacksburg, Virginia 2 Presented in part at Societies for Experimental 3Supported by National
of Human Nutrition and Institute and State Univer24061 the Federation of American Biology, April 1974. Institutes of Health Grant
HD 07250. Present address: University, University, “Present address: tion, Purdue University,
pp.
879
882.
P.O.
Drawer HE, Mississippi State Miss. 39762. Department of Foods and NutriWest Lafayette, Ind. 47907.
Printed
in U .S.A.
879
Downloaded from https://academic.oup.com/ajcn/article-abstract/28/8/879/4732957 by University of Otago user on 16 December 2018
Sweat nitrogen losses balance of preadolescent
880
HOWAT
TABLE Sweat
1 nitrogen
by’ subjects
loss
expressed
consuming
three
in mg/day levels
and
of dietary
mg/m2
34mg
intake
nitrogen
loss
per
day
g/day
57mg
Protein 34 mg/rn2
88mg
intake
g/day
57 mg/rn”
88 rng/rn’
100 101 102 103 104 105 106 107 108 109 110 Ill 112 113 114
170 197 131 203 162 294 173 208 202 216 261 204 126 304 170
229 221 188 284 309 254 142 218 254 180 289 424 227 416 312
470 462 235 433 472 325 179 279 213 227 301 343 234 411 203
160 158 129 211 172 274 163 226 225 192 235 182 134 255 171
210 176 186 292 328 237 139 239 282 160 260 378 241 352 315
431 370 233 446 496 300 170 307 245 200 271 309 251 345 207
Mean
201 ±52
263 ±80
319 ±106
192 ±43
253 ±72
305 ±96
SD
study. The corresponding weights were 29.2 ± 5.0 and 29.4 ± 5.0 kg. The mean increases in height and weight were 0.5 ± 0.4 cm and 0.2 ± 0.6 kg. Subjects lived in university housing converted to a metabolic unit and under continuous supervision by adults during the 34-day study. The study was divided into a 3-day adjustment, two 10-day and one I I-day experimental periods designed to allow all subjects to consume three levels of protein: 34, 57 and 88 g daily. During the adjustment period (period I), all subjects consumed 34 g protein daily. The subjects were then randomly divided into three groups of five each. These groups rotated through the experimental treatments in random order during the remaining periods, II, III, and IV. The diets, including supplements, were calculated to supply 2,070 kcal, and with the exception of protein, to meet or exceed the 1968 recommended dietary allowances (3). All subjects were given weighed quantities of foods and beverages from a 3-day cycle menu. Subjects were supervised during meals, were expected to consume all portions, and were not allowed access to other food sources. The dietary protein included a mixture of animal and plant sources, and compared favorably by chemical score to the amino acid pattern ofegg, and was similar in composition on the three experiment treatments. Differences in dietary treatment were in amount of protein from the same food sources rather than foods with varying concentration of protein. Subjects followed a daily schedule of activities normal for this age/sex category. There was no attempt to control environmental temperature and relative humidity. Recorded mean temperature and relative humidity values forexperimental periods II, Ill and IV were 69,71 and
surface,
75 F; and
85,
83 and
80%,
respectively.
On each level of protein intake, the following data were collected: mean nitrogen intake by periods; sweat nitrogen during 2 days at the end of periods II, III, and IV; nitrogen in the bedding; urinary nitrogen daily; and nitrogen in feces from a marked collection corresponding to the last 5 days of each experimental period. Nitrogen balance was calculated from data collected during the last 5 days of periods II, III, and IV. Sweat was collected by the total body method similar to techniques described by Spence et al. (5) and Sirbu et al. (6). Towels, washcloths, bedding and clothing were treated to remove trapped nitrogen by the procedure described by Spence et al. (5). The clothing worn, the procedures followed during the sweat collection periods, and the sampling of sweat collection for analysis were similar to those described by Spence et al. (5). Nitrogen in food, urine, feces and sweat collections was analyzed using a modified Kjeldahl-Gunning-Arnold method
Results Cutaneous
using
and
copper
and
selenium
catalysts
(7).
discussion nitrogen
losses
The mean sweat nitrogen losses expressed per 24 hours and per square meter of body surface per 24 hours increased as the level of dietary protein increased (Table 1). Individual subjects varied somewhat from the general trend, but differences in sweat nitrogen losses, as determined by analyses of variance, were significant. (P < 0.05). The observation
Downloaded from https://academic.oup.com/ajcn/article-abstract/28/8/879/4732957 by University of Otago user on 16 December 2018
Subj No.
of body’
AL.
protein Sweat
Protein
ET
SWEAT
NITROGEN
LOSSES
AND
Nitrogen
balance
A summary of respective levels of trates the effects of losses. When sweat TABLE Summary experimental
nitrogen protein omitting nitrogen
balance (Table sweat losses
at the 3) illusnitrogen were in-
2 of sweat period
nitrogen
Sweat
loss
nitrogen
loss
period II. rng Me an ± SD (n = 15)
227
TABLE 3 Mean urinary, at three levels Protein level
±
(mg/day)
according
day
per
period IV rng
period III. mg 234
77
fecal, and sweat of dietary protein
±
58
nitrogen
322
losses,
.
.
to
Urinars nitrogen
±
112
and
881
BALANCE
cluded, eight gen balance
subjects were in negative nitroon 34 g of protein; the range of nitrogen balances was from 1.25 to + I .05 g of nitrogen daily on the lowest level of dietary protein. Two subjects were in negative balance when consuming 57 g of dietary protein with the range of retention from -0.61 to +1.37 g daily. The subjects in negative balance or having the lower retention were not the largest or smallest subjects. The status in nitrogen balance did not correspond with weight. The 34 g protein/day may not have been adequate to support maintenance and growth for these subjects. The 34 g protein level is not greatly different from the 36 g protein recommended in the 1973 revision of the Recommended Dietary Allowance for this age group (12, 13). Even the diet which provided 57 g protein daily was apparently inadequate for some subjects. If the positive 0.3 g nitrogen/day recommended by NRC (2, 3, 12, 14) forgrowth plus an addition of at least 0.2 nitrogen/day to cover any unavoidable losses of nitrogen in the collection of excreta is considered, the resulting nitrogen retention deemed necessary for a growing child could easily reach 0.5 g/day or more. With these criteria, only three subjects at the 34 g protein level, and nine subjects at the 57 g protein level retained enough nitrogen to support growth, when sweat nitrogen losses were included in the calculation of total balance. Under conditions of the present study, the integumental nitrogen losses were probably less than 0.8 mg/basal kilocalorie recommended by the NRC. However, data from the present study and cited references (I , 5, 9, 1 1,
nitrogen
Fecal nitrogen
-
balance
Balance
Sweat nitrogen I-U-F”
g/day
g/day
34 57 88 a
Nitrogen
take-urinary
4.12 7.26 I 1.15 balance nitrogen-fecal
=
g/day
g/day 0.56 0.58 0.80
± ±
±
nitrogen
.02 1.05 1.14
± ± ±
0.25 0.25 0.22
intake-urinary
nitrogen-sweat
nitrogen-fecal nitrogen.
0.20 0.26 0.32
± ± ±
I-U-F-S”
g/day’ 0.05 0.08 0.10
nitrogen.
0.24 0.81 1.74 bNitrogen
± ± ±
g/day 0.59 0.54 1.15 balance
0.04 0.55 1.42 =
± ± ±
0.60 0.52 1.08
nitrogen
in-
Downloaded from https://academic.oup.com/ajcn/article-abstract/28/8/879/4732957 by University of Otago user on 16 December 2018
that sweat nitrogen loss is affected by level of nitrogen intake is contrary to the observations of Mitchell and Hamilton (8), but in agreement with other reports (6, 9, 10). When the mean sweat nitrogen loss was determined on the basis of experimental penod rather than protein intake, the values increased as the study progressed (Table 2). When the dietary regimen progressed from a lower to higher level of protein, sweat nitrogen losses increased. However, when the sequence of feeding various protein levels was different, sweat nitrogen values did not consistently correspond with an increase in protein intake. The increase from period to period could be attributed to differences in environmental conditions, activity, and mdividual characteristics. The environmental influence on sweat nitrogen losses was probably minimal since the mean temperature increased only 6 F while relative humidity increased 5%.
NITROGEN
882
HOWAT
16)
have
teracting
Summary
I 146. 3.
4.
5.
6.
7.
losses through sweat were deterin 15 preadolescent girls participating in a 34-day metabolic study. Mean sweat nitrogen losses were 201 mg, 263 mg and 319 mg/day on 34 g, 57 g and 88 g of protein intake, respectively. There was a significant difference in mean sweat nitrogen loss among the three levels of protein intake. There was also a significant difference in mean sweat nitrogen loss between the experimental penods, but the difference was not as great as that caused by protein level. Individual fluctuations in sweat nitrogen values were attributed to variations in environmental conditions, activity, and individual characteristics. Nitrogen balance was negative in eight and two subjects on 34 g and 57 g protein intake, respectively. All subjects were in positive balance on 88 g protein daily. The mean nitrogen balances on the three levels of intake were 0.04 g, 0.55 g, and 1.42 g/day, respecNitrogen
mined
tively. Sweat
nitrogen
nificant
in
losses
estimations
preadolescent
were
that they of total
enough
considered
should protein
10.
I I.
13.
14.
IS.
research
M. I., AND D. M. of protein
101: 385, 1971. Recommended
HE;s1ED.
requirement
A conspectus of man.
J.
of
of Sciences-National
Allowances. Research
National Council.
AcadPubI.
National
Acad-
1906.
of in
arm
nitrogen, and
total
calcium
body
sweat.
and
iodine
Am.
Nutr. 18: 443, 1966. ASIIwORTti, A., AND A. D. B. HARROWER. requirements in tropical countries: nitrogen sweat and their relation to nitrogen balance.
Nutr. 17.
Dietary
I: 263, 1905
cretion
Nutr.
1964.
Allowances.
Recommended Dietary Allowances. National Academy of Sciences-National Research Council. 8th Revised Edition. Washington, D. C., 1973. HARPER, A. E. Recommended Dietary Allowances: are they what we think they are’ J. Am. Dietet. Assoc.64: 151, 1974. Recommended Dietary Allowances. National Academy of Sciences-National Research Council. PubI. 589. Washington, D. C., 1958. C0NSOI.AzIo, C. F., L. 0. MATousil, R. A. NELSON, G. J. ISAAC AND J. E. CANHAM. Comparisons
El
girls.
D. C., Dietary
emy of Sciences-National Research Council. PubI. 1694. Washington, D. C., 1968. CALLOWAY, D. H. Recommended dietary allowances for protein and energy, 1973. J. Am. Dietet. Assoc. 64: 157, 1974. SPENCE, N. P., R. P. ABERNATHY AND S. J. RITCIIEY . Excretion of nitrogen in sweat by preadolescent girls consuming low protein diets. Am. J. Clin. Nutr. 25: 275, 1972. SIRBu, E. R., S. MARGEN AND D. H. CALLOWAY. Effect of reduced protein intakes on nitrogen loss from the human integument. Am. J. Clin. Nutr. 20: 1158, 1967. Association of Official Agricultural Chemists. Official Methods of Analysis (7th ed). Washington, D.C., 1950. MITCHELL, H. H., AND T. S. HAMILTON. The dermal excretion under controlled environmental conditions of nitrogen and minerals in human subjects with particular reference to calcium and iron. J. Biol. Chem. 178: 345, 1949. CUTHBERTSON, D. P., ANI) W. S. W. GUTHRIE. The effect of variations in protein and salt intake on the nitrogen and chloride content of sweat. Biochem. J. 28: 1444, 1934. WEINER, J. S., J. 0. C. WILLSON, H. EL-NEIL ANI) E. F. WHEElER. The effect of work level on dietary intake on sweat nitrogen losses in a hot climate. Brit. J. Nutr. 27: 543, 1972. EIJKMAN, C. 1893. Verchow’s Arch. Pathol. Anat. Physiol. 131: 170. Cited by F. G. Benedict. The cutaneous excretion of nitrogenous material. J. Biol.
Chem. 12.
16.
I. IRwIN,
emy
9.
sig-
be included needs for
References
2.
8.
Washington,
Recommended
21:
833,
ex-
J. Clin. Protein losses in Brit. J.
1967.
ABERNATHY,
R. P.,
requirements 64: 56, 1972.
of preadolescent
ANI)
S. J. RITCIIEY. girls. J. Home
Protein Econ.
Downloaded from https://academic.oup.com/ajcn/article-abstract/28/8/879/4732957 by University of Otago user on 16 December 2018
illustrated that protein intake inwith various external conditions can increase the sweat nitrogen losses. The present study demonstrates that the level of protein in the diet influences the nitrogen loss through the skin. The findings also supported the recommendation of Abernathy and Ritchey ( I 7), that the recommended allowance for protein should be increased to at least 60 g/day for preadolescent children.
ET AL.