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

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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

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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-

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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.

Sweat nitrogen losses by and nitrogen balance of preadolescent girls consuming three levels of dietary protein.

A nitrogen balance study was undertaken to determine the effects of three levels of nitrogen intake on the loss of nitrogen through sweat and to asses...
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