The

effects

of sweat

in evaluating

protein

preadolescent

ABSTRACT

A nitrogen on

needs

of preadolescent

sweat

samples

from

twelve

weight

of the

subjects

were

relatively

constant

height

and were

mg/day

day

were

on daily 0.39,

and

for

both

for

this

a series

of

nitrogen

reported

sweat and including in

evaluating

protein

0.09,

288

sexes.

and

1.95

age

group.

of

studies data

600

growing

g when

sweat

for

girls

Am.

to

cm

study.

Mean

54, and

further

31.0

sweat

kg,

losses

age

levels

impact

of sweat

the

of 8 years,

respectively.

nitrogen

were

of three

through

a mean

84 g, respectively.

nitrogen

the

determined

having

and

the effects

assess

were

boys

131.4

lost on the loss of

needs

Journal

the

Nutr.

labora-

nitrogen

protein

boys,

nitrogen

mg/basal

J. Clin.

in this for

and

of 0.5

of

child

The American

the

of 29,

estimation

have speculated a figure for this the

during

intakes

and

Values

healthy

M.S.,

to determine

sweat

children.

(1, 2). As early as 1964, the Food and Nutrition Board of the National Research Council (3) acknowledged the need to allow for nitrogen lost through the skin in calculating protein requirements. The value, 0.8 mg/basal kcal per day, recommended at that time was based on studies with adults. The need to determine nitrogen losses in the growing child seems obvious in order to provide a basis for realistic recommendations for maintenance and growth. The present study was a follow-up to the work of Howat et al. (2) and was conducted to relate the losses of cutaneous nitrogen to the

conducted

through

Meiners, Ph.D.,

included

collection 8 months,

Environmental

losses Mean

of

were

208,

nitrogen

in the

287,

balances

calculations.

and per

At the

levels of protein intake, nine and six subjects were in negative nitrogen balance were considered. Sweat nitrogen losses in the boys were similar to a previous study girls. Based upon published basal metabolic rates and mean sweat nitrogen losses

mg/day An

of nitrogen

was

total

body

loss

study

on protein

368

the

balance

nitrogen

of 261

through effects

by

Christine R. P. Abernathy,6

of 24-hr.

lower and moderate when sweat losses with preadolescent

have

Y. Leung,5 M.S., Taper, M.S., R.

intake

conditions

we

utilization

nitrogen

Mean

Through

losses

children1-4

Mary K. Korslund, Ph.D., Eva Michael G. Crews, B.S., Janeue and S. J. Ritchey, Ph.D.

tory,

nitrogen

communications

of Clinical

kcal 29:

lost for

600-603,

sweat

was

nitrogen

0.25 loss

mg/basal

kcal

appears

realistic

1976.

protein

intakes,

total boys.

nitrogen Comparisons

boys made

through

integumental

to

nitrogen

excretion of

and the girls in this report.

retention,

by nitrogen

from

and

preadolescent losses by

Howat

et al.

to the

(2) are

Procedure Subjects age

were

from

7 years,

12 preadolescent 8 months

boys to 9 years,

who

ranged

8 months.

in The

‘From the Department of Human Nutrition and Foods, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061. 2 Presented in part at the i-ederation of American Societies for Experimental Biology, April 1975. ‘Supported by National Institutes of Health Grant 07250. Address reprint requests to Dr. S. J. Ritchey. 6 Present address: Charlotte Memorial Hospital, Charlotte, North Carolina 28234. 6 Present address: Department of Foods and Nutrition, Purdue University, Lafayette, Indiana 47907. HD

Nutrition

29:

JUNE

1976,

pp.

600-

603.

Printed

in U.S.A.

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original

mean

NITROGEN

LOSSES

IN EVALUATING

heights

and weights were 131.4 cm and 31.0 kg, the beginning of the study. The mean change in weight was 0.25 kg with the extreme changes being a 1.0 kg loss and a 0.5 kg gain. Subject lived in a university dormitory converted to a metabolic unit for the study. The subjects were under the continuous supervision of adults during the 34-day study. The study was divided into a 3-day adjustment period and three

respectively,

at

experimental periods, two of which were 10 days and one of which was 11 days in length. The experimental design permitted all subjects to consume three levels of dietary protein: 29, 54, and 84 g daily. During the adjustment period (period 1) all subjects consumed the diet containing 29 g of protein. Subjects were then randomly divided into three groups of four each. The groups of subjects rotated through the experimental treatments in random order during the remaining periods, 2, 3, and 4. No attempt was made to control the environmental conditions. However, the mean temperature and relative humidity recorded for experimental periods 2, 3, and 4 were 74, 69, and 64 F, and 76, 73, and 77%, respectively. Throughout the study, the subjects followed a schedule of activities normal for this age/sex group.

On were

each level of collected: mean

protein nitrogen

intake, intake

the following by periods;

data sweat

nitrogen

in clothes and bath water during 2 days at the each experimental period (2, 3, 4), nitrogen in the bedding during the same 2 days; urinary nitrogen daily; and fecal nitrogen from a marked collection representing the last 5 days of each experimental period. Nitrogen balance was calculated from data collected during the last 5 days of each experimental period. Methods for sweat collection, measurement of nitrogen in clothing and bedding, and the analytical method for nitrogen have been described in previous publications by Spence et al. (I) and Howat et al. (2).

end of

PROTEIN

and

Cutaneous The

TABLE

2

Comparison girls according

of sweat nitrogen to experimental

per

24

Sweat

Sweat

nitrogen

2

Period

and

nitrogen

loss

by boys

and

loss/day 3

Period

4

mg

losses

sweat

hr

TABLE

loss (mg/day) period

discussion nitrogen

mean

601

surface area per 24 hr increased as the level of dietary protein increased (Table 1). Losses of sweat nitrogen for individual subjects varied somewhat from the general trend, but mean losses increased significantly (P < 0.05) as protein intake increased. The data for the boys agree with the results of Howat et al. (2) for preadolescent girls and of other investigators (4, 5, 6). The mean sweat nitrogen values for the boys in this study (Table 2) decreased as the study progressed and were significantly different (P < 0.05) between periods. These observations differ from those reported by Howat et al. (2) for girls. The effect of experimental rotation on sweat nitrogen losses may be the result of numerous contributing factors, including environmental conditions, activity, general adjustment to the experimental regime, and individual characteristics. Temperature fluctuations may have been a significant factor in the different results with boys and girls as the mean temperature decreased 5 F between collection

Period

Results

UTILIZATION

nitrogen per

losses

square

Boys(l2) Girls(I5)#{176}

expressed

meter

of

6Data

body

from

330±75 227±77 Howat

272±111 234± 58

246±52 322± 112

et al. (2).

I expressed

in mg/day

and

mg/m2

Sweat Subject

SD

nitrogen

loss/da

29 mg/day

115 118 (19 120 121 122 123 124 125 126 (27 128 X

of body

190 266 270 179 215 218 235 181 162 220 212 154 208

±37

surface

by boys

y with daily

consuming

protein

intake

three

165 207 267 211 224 202 233 172 147 222 204 132 199

±38

mg/day

of dietary

protein

(g)

54

mg/rn’

levels

84

mg/rn’

mg/day

mg/me

182 270 239 318 295 271 438 402 210 232 249 345 287

159 209 236 378 307 251 434 379 191 234 239 294 276

349 427 314

306 331 311

207 380 297 471 466 390 321 396 399 368

244 396 275 466 444 355 318 381 341 347

±77

±84

±75

±65

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SWEAT

ET AL. though a small percentage of the total nitrogen excretion (Table 4), may have a meaningful effect on nitrogen retention figures and may alter conclusions of nitrogen balance studies. Losses of nitrogen through sweat were similar for preadolescent girls and boys (Table 4). A comparison of the two studies, one a replicate of the other except for sex of the subjects, confirms the magnitude and variation of sweat nitrogen losses in the growing child. The sweat nitrogen excretions of approximately 4.0, 3.2, and 3.0% of the total nitrogen excretions may be useful guidelines for estimating sweat nitrogen losses when subjects on balance studies are consuming low, moderate, and high levels of protein, respectively. Recognition of the environment as a major influence on sweat losses is important in using the above figures which were determined in a relatively moderate climate. Under conditions of these studies, the integumental nitrogen losses were less than the 0.8 mg/basal kcal recommended by the National Research Council. By using the basal

days of period 2 and 3 and between collection days of period 3 and 4 with the boys whereas, the mean temperature increased 6 F during the study by Howat et al. (2). However, in both studies, the effects of dietary protein level clearly affected losses of nitrogen through sweat, and in both studies the experimental design was established to reduce the effects of environmental conditions on the major variable, level of protein intake. Studies under controlled conditions are required to determine the effects of temperature, humidity, and activity on sweat nitrogen losses in the growing child; this was not the objective of this study or the previous one with girls (2). Nitrogen

balance

A summary of nitrogen balance at the respective levels of protein (Table 3) demonstrates the effects of utilizing sweat nitrogen losses. When subjects were consuming 29 g of protein, the mean nitrogen balances were negative with 8 or 9 of the 12 subjects being in negative balance depending on whether or not sweat losses were included in the calculations. Individual nitrogen retentions ranged from -0.94 to 0.63 g nitrogen/day on the 29 g diet when only urine and fecal losses were used and ranged from -1.12 to 0.46 g nitrogen/ day when the sweat loss was added to other losses. At the 54 and 84 g of protein levels, the number of subjects in negative balance were one and zero when sweat loss was not used and were six and zero when sweat nitrogen was used in the determination. The mean retention values were 0.09 and 1.95 g nitrogen daily at the moderate and high levels of intake when sweat losses were included in calculating nitrogen retentions. The data confirm the previous reports of Spence et al. (1) and Howat et al. (2) that sweat nitrogen losses, TABLE Mean

TABLE

4

Comparison

girls’

and

of

boys

sweat

nitrogen

consuming Sweat

-

Protein

High

of dietary

preadolescent

Boys

± ± ±

protein

Girls

mg/day

201 263 319

Moderate

by

levels

nitrogen

Girls

level”

Low

losses

three

Boys

% excretion

52c 80 106

208 287 368

±

37d

±

77 7S

±

3.8 3.0 2.6

4.3 3.3 3.2

‘Data from Howat et al. (2). bprotein intakes were 34, 57, and 88 g/day for the girls and were 29, 54, and 84 g/day for the boys at the low, moderate, and high levels, respectively. cMean ± SD; 15 subjects. dMean ± SD; 12 subjects.

3 urinary

,

fecal

and

sweat

nit rogen

losses,

nitrogen

balance

Fecal nitrogen

Urinary nitrogen

Protein level

and

at t hree

levels

of diet ary

protein

Balance

Sweat nitrogen

l-u-F-S”

I-U-F’

g/day

29 54 84

sweat

‘Nitrogen N.

3.80 7.09 10.08 balance

± ± ±

=

0.97 1.02 1.16

0.39 0.50 1.00 intake

-

urinary

±

0.19

0.21

±

±

0.23 0.26

0.29 0.37

±

±

N

-

fecal

N.

±

0.04 0.08 0.08

“Nitrogen

-0.18 0.49 2.32 balance

=

± ± ±

-0.39 0.09 1.95

0.49 0.51 0.87

intake

-

urinary

N

-

± ± ±

0.48 0.56 0.86

fecal

N

-

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KORSLUND

602

NITROGEN

LOSSES

IN EVALUATING

metabolic rates for weight and sex from Food and Agriculture Organization/World Health Organization (7) for these subjects and using mean nitrogen losses in sweat of 261 and 288 mg/day for girls and boys, the nitrogen lost through sweat was 0.25 mg/basal kcal for both sexes. Doubling this figure to a value of 0.5 mg/basal kcal appears to provide a realistic estimation for the loss of integumental nitrogen for growing children with normal activity in a moderate climate. LI References 1. SPENCE, N. P., R. P. ABERNATHY AND S. J.RITCHEY. Excretion of nitrogen in sweat by preadolescent girls consuming low protein diets. Am. J. Clin. Nutr. 25: 275, 1972. 2. HOWAT, P. M., M. K. KORSLUND, R. P. ABER-

PROTEIN

NATHY

S. J.

AND

UTILIZATION RITCHEY.

603

Sweat

nitrogen

and nitrogen balance of preadolescent ing three levels of dietary protein. Am. 3.

4.

28: 879, 1975. Recommended Dietary Sci.-Natl. Res. Council D.C., 1964. Effect

from 1158, 5.

E. R., S.

SIRBU,

of

reduced

the human 1967.

Allowances. Publ. 1146.

MARGEN

AND

protein

intakes Am.

integument.

D. P.,

CUTHBERTSON,

6.

J. S., J. 0. C.

WEINER,

F.

WHEELER.

The

intake on sweat nitrogen Nutr. 27: 543, 1972.

D. H.

of

losses

CALLOWAY.

on nitrogen J. Clin. Nutr.

H.

work

loss 20:

The

GUTHRIE.

and salt of sweat.

WILLSON,

effect

by

Nail. Acad. Washington,

W. S. W.

AND

effect of variations in protein nitrogen and chloride content 28: 1444, 1934.

losses

girls consumJ. Clin. Nutr.

intake on Biochem.

EL-NEIL level

in a hot

on

the J.

AND

climate.

Brit.

J. 7.

Food

and

Organization.

WHO

Tech.

Agriculture

Organization-World

Energy Rept.

Ser.

and No.

protein 522, 1973.

E.

dietary

Health

requirements.

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SWEAT