Am J Cli,z Nutr 1995;62:621-32. Printed in USA. © 1995 American Society for Clinical Nutrition 621

High- versus low-meat diets: effects on zinc absorption,iron status, and calcium, copper, iron, magnesium,manganese, nitrogen, phosphorus, and zinc balance inpostmenopausal women14

Janet R Hunt, Sandra K Gallagher, LuAnn K Johnson, and Glenn I Lykken

ABSTRACT The effects of three diets-high meat (HM), low

meat (LM), or low meat with mineral supplements (LS)-on zinc

absorption, elemental balance, and related clinical indexes were

investigated in a metabolic study of 14 women aged 51-70 y. The

women ate each of the three diets for 7 wk in random order. Lean

beef, chicken, ham, and tuna in the HM diet replaced foods with a

low mineral content in the LM diet. The LS diet was similar to the

HM diet in K, P. Fe, Mg, and Zn contents. Compared with the

other diets, the HM diet increased zinc absorption and retention,

and slightly increased urinary zinc. Nitrogen and calcium balances

and urinary calcium were not different for the HM and LM diets.

Iron balance was not different for the HM and LS diets with

similar iron content, but the HM diet was unexpectedly associated

with lower iron status (higher iron-binding capacity and lower

ferritin than LM and LS diets). These results indicate that 0.8 g

protein/kg body wt meets protein requirements in older women,

and that high meat consumption increases zinc retention without

compromising calcium status and may reduce indexes of iron

status, in contrast with iron absorption results from studies with

radiolabeled test meals. Am J Clin Nutr 1995;62:621-32.

KEY WORDS Calcium, copper, iron, magnesium, manga-

nese, nitrogen, phosphorus, zinc, mineral balance, zinc absorption,

serum fernitin, meat, protein

INTRODUCTION

Concern about meat intake and epidemiologic associations

with certain cancers and coronary heart disease has led to a

recommendation from the Committee on Diet and Health of the

US Food and Nutrition Board to “maintain protein intake at

moderate levels” and to consume “lean meat in smaller and

fewer portions than is customary in the United States” (1).

A further concern related to meat consumption is that highprotein intake may increase urinary calcium excretion and

possibly contribute to the risk of osteoporosis (1). Increased

dietary protein from isolated, purified sources increases urinary

calcium excretion (2-6), an effect that is at least partially

reversed by increasing dietary phosphorus (3). In comparison

with the effect of isolated protein sources, the effect of protein

from meat on calcium retention is more moderate, causing a

smaller (7) or no (8, 9) increment in urinary calcium excretion

and no change in calcium balance. Spencer et al (8) found that

47Ca absorption and excretion were unaffected by a diet high in

meat protein. However, concerns about the possible negative

effects of meat protein on calcium retention persist (1), and

high-protein diets are commonly listed as a possible risk factor

for osteoporosis (10, 1 1).

Because meat provides highly available iron and zinc, re-

ductions in meat consumption may adversely affect iron and

zinc nutniture. Meat, poultry, and fish provide at least one-half

of the zinc in most US diets (12). Meat protein may enhance

zinc bioavailability because zinc absorption was increased by

additional protein in a meal (13-16). However, this effect may

be moderated by phosphorus from meat, because zinc balance

was increased by purified sources of dietary protein with a

moderate phosphorus intake, but not with a high phosphorus

intake (17). Purified sources of dietary protein also have been

associated with increased urinary zinc excretion (5, 17-19).

Substantial research with single meals suggests excellent

iron absorption from meat, both because of highly bioavailable

iron in the heme form (20-24), as well as unidentified factors

in meat that promote heme- (20, 23) and nonheme-iron absorp-

tion (20, 22, 25). The effects of meat on long-term indexes of

iron status are less clear. Most studies of vegetarians in West-

em societies have not found poorer iron status in vegetarians

compared with omnivones (26-28). In cross-sectional studies

of free-living subjects, meat consumption has been positively

associated with iron stores, as indicated by serum ferritin

(29-33). However, serum ferritin was unresponsive in experi-

mental trials intended to influence iron absorption with either

ascorbic acid (34-37) or calcium (31) supplementation. There

I From the United States Department of Agriculture, Agricultural

Research Service, Grand Forks Human Nutrition Research Center, Grand

Forks, ND.

2 Mention of a trademark or proprietary product does not constitute aguarantee or warranty of the product by the US Department of Agriculture

and does not imply its approval to the exclusion of other products that may

also be suitable.

3 The US Department of Agriculture, Agricultural Research Service,

Northern Plains Area, is an equal opportunity/affirmative action employer

and all agency services are available without discrimination.

4 Address reprint requests to JR Hunt, USDA, ARS, GFHNRC,

University of North Dakota, P0 Box 9034, Grand Forks, ND 58202-9034.

Received August 16, 1994.

Accepted for publication May 11, 1995.

High meat Low meat

g

192.5

0.55

27.5

5.5

154

66

33

5.5

5.5

2.2

99

22

44

99

1.1

3.3

4.4

61.6

5.5

126.5

5.5

3.3

0.22

5.5

33

170.5

126.5

33

2.2

82.5

5.5

6627.5

27.5

5.5

38.5

44

2.2

27.5

11154

165

38.5

5.5

220

88

27.5

5.5

13.2

192.5

0.55

27.5

11

154

33

11

22

27.5

27.5

44

99

1.1

3.3

4.4

61.65.5

126.5

5.5

11

0.22

5.5

33

264

38.5

33

2.2

82.5

116627.5

27.5

5.5

38.5

44

2.2

27.5

11

154

16538.5

8.25

220

110

27.5

5.5

22

BagelPeanut butter

Milk, skim

622 HUNT ET AL

have been no controlled feeding studies of the effect of meat

consumption on biochemical indexes of iron status, including

serum ferritin.

To investigate the effect of meat (beef, pork, chicken, and

fish) in whole, isoenergetic diets on zinc absorption, mineral

and nitrogen balances, and clinical indicators of mineral nutri-

tion, we conducted a randomized, controlled feeding study of

high- and low-meat diets fed to postmenopausal women. Three

diets were compared: 1) high meat, 2) low meat, and 3) low

meat supplemented with minerals to the amounts in the high-

meat diet, to attempt to differentiate between the effects of

meat protein and minerals in meat, and to control for differ-

ences in mineral balance with different mineral intakes. Dietary

effects on blood lipids will be reported separately.

SUBJECTS AND METHODS

Fourteen women admitted to a metabolic unit consumed the

three weighed, experimental diets-high meat, low meat, or

low meat with mineral supplements-for 7 wk each in random

order. After 2 wk of each diet, zinc absorption was measured

by labeling the entire 2-d menu cycle with 65Zn. Mineral and

nitrogen balances were determined for the last 18 d of each diet

and blood measurements were made on admission and at the

end of each diet period.

Subjects

Postmenopausal women were recruited through public ad-

vertising and selected after psychological screening and med-

ical examination to establish that they had no underlying dis-

ease and were emotionally suited for this project. Fourteen

women aged (� ± SD) 62.9 ± 6.1 y (range 51-70 y), weighing68.3 ± 10.8 kg (53-89 kg), with a body mass index (kg/rn2) of

26.9 ± 4.8 (20.6-36.8) participated. None of the women rou-

tinely used medication. The participants gave informed con-

sent. The study was approved for human subjects by the

University of North Dakota’s Radioactive Drug Research

Committee and Institutional Review Board, and by the US

Department of Agriculture’s Human Studies Review and

Radiological Safety Committees.

Diets

Registered dietitians planned three experimental diets con-

taming ordinary foods in a 2-d rotating menu cycle (Table 1).To maintain individual body weights, energy intakes were

adjusted in 0.84-MJ (200-kcal) increments by proportionally

changing the amounts of all foods. Foods were weighed to 1%

accuracy. Deionized water and limited amounts of low-energy

carbonated beverages and chewing gum were consumed as

desired. Coffee, salt, and pepper consumption were individu-

alized to volunteers’ preferences, and then served consistently

throughout the study.

The high- and low-meat diets contained 289 and 38.5 g (‘#{176}‘lO

and 1.5 oz) of meat daily, respectively, with energy from meat

protein replaced by low-mineral sources of carbohydrate (fruits

and sugars), and animal fat replaced with similar quantities of

vegetable fat (principally from corn oil margarine) (Table 1).

The high-meat diet contained beef, pork, poultry, and fish

roughly in proportion to the kinds of meat products typically

consumed in the United States (1; Table 1). The low- and

TABLE 1Menus for experimental diets’

Day 1Breakfast

Orange juiceSaltOatmeal, dryBrown sugar

Milk, skimHam, lean

Bread, whole-wheatMargarine, corn oil

Grape jelly

Lunch

Lemonade mixDiet lemonade mix

Vegetable soupBeef ground round, leanPeasCarrots

Potatoes

Onion, dry

Beef bouillon, dry

Margarine, corn oil

Cornbread

Margarine, corn oil

Apple crispApple

Lemon juiceSugar

Cinnamon

Margarine, corn oil

Sugar cookie dough

SupperApple Juice

Chicken broccoli casserole

Chicken breast, ground

Rice

Beef bouillon, dry

BroccoliMargarine, corn oil

Lettuce

Salad dressing, ranchBread, whole-wheatButterCake, angel foodStrawberries

SugarSnack

Day 2

Breakfast

Grapefruit juice

Shredded wheat cerealSugar

Milk, skimMandarin orangesBread, rye

Margarine, corn oilStrawberry jelly

MEAT, Zn ABSORPTION, MINERAL AND N BALANCE 623

TABLE 1 Continued

High meat Low meat

g

Lunch

Lemon-lime soda - 225.5

Diet lemon-lime soda 209 -

PizzaPizza dough 66 66

Pizza sauce 49.5 49.5

Ham, lean 110 -

Mushrooms 27.5 27.5

Olives 11 11

Onion, dry 1.1 1.1

Mozzarella cheese 38.5 38.5

Lettuce 66 66

Carrots 22 22

Salad dressing, French 27.5 27.5

Orange sherbet 77 77

Supper

Cranberry-raspberry drink 132 154

Chili macaroni casserole

Beef ground round 99 38.5

Chicken breast, ground 38.5 -

Kidney beans 44 44

Macaroni, cooked 77 77

Tomato soup, condensed 88 88

Onion,dry 1.1 1.1

Beef bouillon, dry 1.1 1.1

Chili powder 2.2 2.2

Salad dressing, mayonnaise-type 1 1 16.5

Tuna 38.5 -

Green beans 77 77

Bread, whole-wheat 33 33

Margarine, corn oil 5.5 16.5

Snack

Lemon pie

Vanilla wafers 16.5 16.5

Pudding, lemon 88 110

Margarine, corn oil - 5.5

‘ Amounts given are for a 9.2-MJ (2200-kcal)/d diet.

high-meat diets contained, respectively, 10% and 20% protein,

61% and 52% carbohydrate, and 29% and 28% fat (calculated

as a proportion of energy), with similar amounts of dietary

fiber [13.5 g, calculated (38)] and phytic acid [1056 mg,

calculated (39)] per 9.2 MJ (2200 kcal).

As a third experimental diet, the low-meat diet was supple-

mented to be similar in mineral content to the high-meat diet by

adding, per 9.2 Mi (2200 kcal), the following: 748 mg K, 594

mg P (both as potassium phosphate monobasic), 3.3 mg Fe (as

ferrous gluconate), 55 mg Mg (as magnesium citrate), and 5.5

mg Zn (as zinc gluconate). The zinc content of each low-meat

meal was adjusted to that of the corresponding high-meat meal.

The other mineral supplements were equally divided among the

five meals of the 2-d menu cycle, which contained additional

meat on the high-meat diet. Magnesium supplements were

added to the beverages, and the remaining supplements were

incorporated into the recipes that contained meat or into oat-

meal. As with food amounts, the amounts of mineral supple-

ments were adjusted in proportion to differences in energy

intake. The amounts of mineral supplements were based on

initial analyses of the high- and low-meat diets, which varied

somewhat from analyses of the three diets served during the

study; only the latter analyses are reported.

Low-copper diets have been associated previously with

heart-related abnormalities in an extended metabolic study

(40). As a precaution, all three diets were supplemented with

0.66 mg Cu/9.2 MJ (2200 kcal) as copper gluconate, which was

added to fruit juice at breakfast. Copper supplements were

omitted for the 2 d of each diet period when zinc absorption

was measured by radiolabeling meals with 65Zn.

The high-meat, low-meat, and low-meat, supplemented diets

contained, per 9.2 MJ (2200 kcal), respectively, 12.1, 8.8, and

12.3 mg total iron by analysis, and by calculation, 17, 14, and

17 mg total iron, 1.7, 0.3, and 0.3 mg heme iron, and 1.6, 1.0,

and 1.2 mg absorbable iron according to the method of Monsen

et al (22, 41). The three diets contained similar amounts of

ascorbic acid [187 mg/9.2 MJ (2200 kcal)}.

Chemical analyses

To minimize the possible confounding of indexes of iron

status by phlebotomy, blood samples were limited to 60 mL

per diet period. Blood samples were obtained after 6 and 7

wk on each diet; all blood measurements reported in this

paper were from the sample taken after 7 wk. Excneta, diets,

and blood were collected with precautions to avoid trace

mineral contamination.

Biochemical measurements were conducted on fasting blood

samples. Hemoglobin, hematocnit, complete blood count, and

mean platelet volume were measured with a Coulter counter

(S+4; Coulter Electronics, Hialeah, FL). Serum albumin, uric

acid, urea nitrogen, total protein, alkaline and acid phosphata-

ses, and serum (and urinary) creatinine were determined with a

Cobas Fara Chemistry Analyzer (Hoffmann-LaRoche, mc,

Nutley, NJ). Serum iron was measured by Zeeman graphite-

furnace-atomic-absorption spectrophotometry with prior pre-

cipitation by tnichloroacetic acid (42). Iron-binding capacity

was determined by saturation with iron followed by adsorption

of excess iron with magnesium carbonate; percent transferrin

saturation was calculated from serum iron and total iron-bind-

ing capacity. Zinc protoporphynin was measured by hematoflu-

orometry (43). Serum transferrmn and retinol-binding protein

were measured by nadialimmunodiffusion (Calbiochem-Be-

hning, La Jolla, CA). The following were determined by radio-

immunoassay: serum fenritin (Baxter Travenol Diagnostic, Inc,

Cambridge, MA), plasma monoamine oxidase (44), free and

total tniiodothyronine (T3), free and total thyroxine (T4),

thyroid stimulating hormone (TSH) (Diagnostic Products Cor-

poration, Los Angeles), parathyroid hormone, calcitonin, os-

teocalcin (Incstar Corp, Stillwaten, MN), and estradiol

(ICN Biomedicals, Inc, Carson, CA). Plasma ionized calcium

was measured by using Ionized Calcium 2 (Radiometer Amen-

ica Incorporated, West Lake, OH). Plasma zinc was determined

by atomic-absorption spectrophotometny (Perkin-Elmer Corpo-

ration, Norwalk, CT).

Diets were prepared in duplicate for analysis during each

balance period. Feces were collected completely for the last 18

d of each dietary treatment. Aliquots of the diet and fecal

composites were digested with concentrated nitric and 70%

perchlonic acids by method (II)A of the Analytical Methods

Committee (45). The mineral and trace element content of the

digestates and urine samples was determined by inductively

coupled argon plasma emission spectrophotometry. Analytical

624 HUNT ET AL

accuracy was monitored through periodic analyses of certified

standard reference materials from the National Institute of

Standards and Technology (NIST, Gaithersburg, MD). Urinary

copper, iron, and manganese excretion were not determined

because these are below accurate detection limits of this

method and do not contribute significantly to the balance

determination. Nitrogen content of diets, stools, and urine was

determined after digestion with sulfuric acid, hydrogen perox-

ide, and copper sulfate by using an elemental analyzer (model

7000; Antek Instruments, Inc, Houston). Elemental balance

was calculated as the difference between dietary intake and

excretion (in feces and urine). Hydroxyproline (46, 47), pyri-

dinium, and deoxypynidinium (48), were measured in 24-h

urine samples as possible indexes of bone turnover.

Zinc absorption measurements

Zinc absorption and biological half-life were measured byusing 65Zn as an extrinsic radioisotopic tracer. After 2 wk on

each diet, the entire menu (three meals per day for 2 d;

evening snack foods were served with the third meal) was

labeled with 6.66 kBq (0.18 MCi) 65Zn. The tracer was

mixed with the foods in each meal that were the best sourcesof zinc, and the specific activity (ratio of 65Zn to elemental

zinc) was constant for all meals.

Absorption and biological half-life of 65Zn were determined

by serial whole-body scintillation counting, and by using mdi-

vidual retention curves to partially correct for endogenous 65Zn

excretion. Whole-body radioactivity was determined before the

meals, after the second and sixth labeled meals, and twice

weekly thereafter. The initial total-body activity was calculated

from the whole-body activity after two meals (before any

unabsorbed isotope was excreted), divided by the fraction of

the total activity contained in those two meals. Percent absorp-

tion was calculated by extrapolating back to the time of isotope

administration along the linear portion (days 14-35 after 65Zn

administration for most volunteers; days 23-37 for one volun-

teen with an apparently longer gastrointestinal transit time-see

below) of a semiloganithmic retention plot (the natural loga-nithm of percent remaining radioactivity vs time) (49). The

retention plots for 65Zn administration associated with the

second and third dietary periods were corrected for previously

administered 65Zn by linear extrapolation of the previous

semilogarithmic retention plot.

For comparison with the above whole-body countingmethod, percent absorption was determined by three additional

methods. The first method used for comparison was the whole-

body counting method of Arvidsson et al (50), which corrects

for endogenous excretion by adjusting for the average retention

of 65Zn that was intravenously administered to a group of eight

men and women, who were monitored by whole-body counting

for 84-190 d. Because the measurement of 65Zn retention after

15 d yielded an SD of only 2.6%, they proposed applying the

mean intravenous retention function for that group to correct

for endogenous excretion when calculating zinc absorption byhealthy individuals. The mean two-component retention

function is described as follows:

R = 0.15 ‘ + 0.85 � (t � 84)

where R is the fractional retention and t is the time (in days)

elapsed since the day of administration (50). The fraction of

initial activity retained by our volunteers after 14-17 d (23 d

for one volunteer with an especially long gastrointestinal transit

time-see below) was expressed as a percentage of that derived

from the above retention function.

A second method used for comparison was the apparent

isotope absorption, calculated as the difference between 65Zn

administered and 65Zn excreted in the feces, as a percentage of

isotope administered. Fecal excretion of 65Zn was determined

by measuring individual stools in a small animal whole-body

scintillation counter for � 18 d, until isotope excretion returned

to background values. Variation from sample geometry was

minimal because the stool samples were centered between two

10 X 10 X 40 cm thallium-doped sodium iodide detectors.

Whereas most volunteers took only 1-5 d to pass � 50% of the

total isotope excreted in the feces, one volunteer required 8-10

d for 50% passage, a difference that occurred during all three

diet periods, and which was also evident from whole-body

counting. Zinc absorption values for this volunteer with a slow

gastrointestinal transit rate were within the range observed for

other volunteers.

A third absorption method used for comparison was the

elemental apparent absorption, calculated as the difference

between dietary and fecal elemental zinc analyses (the last 18

d of the diet period), as a percentage of zinc intake.

Bone mineral determinations

Bone mineral content and density of the lumbar spine were

assessed by using a dual-energy X-ray absorptiometen (Hologic

QDR-2000; DXA, Waltham, MA) at the end of each dietperiod.

Statistics

Repeated-measures analysis of variance (ANOVA), with

individual volunteers serving as their own controls (51), was

used to determine the diet effects. Tukey’s Studentized range

test was used to perform pair-wise comparisons of the three

experimental diets (51). Variance in the data was expressed as

a pooled SD, calculated as the square root of the mean square

error from the ANOVA. Because diet analyses used fewer

independent samples, only means and SD are presented for

these data. Pearson’s correlation coefficients were used to

determine the relations between absorption methods and

balance data (51).

RESULTS

Energy and general observations

The volunteers’ mean (± SD) energy intake was 9.15 ± 1.00

MJ (2185 ± 240 kcal). Mean body weights at the end of eachdiet period differed by < 0.2 kg between diets.

Two volunteers had moderately elevated (20-35 mU/L), and

two others had slightly elevated (4-7 mU/L) serum TSH con-

centnations, which were generally present on admission, and

did not consistently affect other serum thyroid hormone con-

centration. Serum thyroid hormones were not affected by the

experimental diets, with or without these volunteers included in

the statistical analysis.

Comparison of zinc absorption methods

Methods used in this study provided the opportunity to

compare results of the sensitive whole-body counting tech-

H

H

H

S

S S

S LS H L H rr=o��

S

L L

S

H

H

TABLE 2

MEAT, Zn ABSORPTION, MINERAL AND N BALANCE 625

I Means with the same superscript letter are not significantly different.

nique with other commonly used methods for estimating zinc

absorption. The serial whole-body counting method (49),

which adjusts for endogenous excretion by using only the

slower component of an individual two-compartment exponen-

tial retention function, yielded results within one percentage

point of those measured by the method of Arvidsson et al (50),

which corrects for both components of a representative group

retention function (Table 2). The two methods were highly

correlated (r = 0.98, P < 0.0001). Mean absorption measure-

ments from either whole-body counting method were reduced

by three percentage points if the administered whole-body

activity was determined by counting the subjects after the sixth

meal and correcting for fecal excretion up to that time, instead

of adjusting the whole-body count after the first two meals for

the amount of isotope administered in six meals (data not

shown). The latter approach was adopted to avoid overesti-

mates of unabsonbed isotope in the feces; overestimates that

probably reflect endogenous excretion of isotope that was

absorbed and rapidly excreted (within the first 2 d).

The apparent isotope absorption results, based on determi-

nation of isotopic tracer excreted in feces, were lower than the

whole-body counting results by ‘�‘8% (Table 2), an indication

of the extent of error caused by the endogenous fecal excretion

of absorbed tracer. However, the apparent isotope absorption

method still correlated well with the serial whole-body count-

ing method (r = 0.79, P < 0.0001; n = 41) and yielded

proportional differences between dietary treatments with only

slightly increased variability (Table 2). The elemental apparent

absorption (balance) method was much more variable, yielding

differences between dietary treatments consistent with the

other absorption methods for the amount of zinc absorbed, but

not consistent with the other methods for percent absorption

(Table 2). The apparent elemental absorption method did not

correlate with the serial whole-body counting method when

results were expressed as percent absorption, but the correla-

tion was significant when the results were expressed as

milligrams zinc absorbed (r = 0.64, P < 0.0001; n = 42)

(Figure 1). Zinc absorption (in mg) by the serial whole-body

counting method also correlated with zinc balance (r = 0.62,

P < 0.0001; n = 42) and urinary zinc excretion (r = 0.43,

P < 0.01; n = 42).

3.0

� 2.0

0.

0

� 1.0

Ii:2 3 4

Zinc Absorption by Whole Body Counting (mg/d)

FIGURE 1. Correlation between zinc absorption determined by whole-

body counting (serial method) and apparent zinc absorption determined by

the elemental balance method (n = 42). The symbols H, L, and S refer to

the high-meat, low-meat, and low-meat, supplemented diets, respectively.

Zinc absorption, balance, and related clinical indexes

The efficiency of zinc absorption (as measured by serial

whole-body counting) was similar (28-30%) for both the high-

and low-meat diets, but was significantly reduced by supple-

menting the low-meat diet with minerals (18%) (Table 2).

Because the high-meat diet contained twice as much zinc as the

low-meat diet, the amount of zinc absorbed from the high-meat

diet (3.6 mg/d) was significantly more than from the low-meat

diet (2.0 mg/d) on the low-meat diet supplemented with

minerals (2. 1 mg/d) (Table 2).

Differences in zinc excretion did not fully compensate for

the additional 1.6 mg absorbed from the high-meat compared

with the low-meat diet. Slightly more zinc (0.07 mg) was

excreted in the urine during the high-meat diet (Table 3).

Endogenous fecal zinc excretion, estimated from the differ-

ences in absorption between serial whole-body counting and

apparent absorption measurements, was #{176}‘#{176}0.9,0.4, and 0.7 ±

0.5 mg (� ± pooled SD), (P < 0.05 for the difference between

the high- and low-meat diets) using isotope apparent absorption

Effect of dietary treatments on zinc absorption as determined by whole-body counting and fecal recovery methods’

.

AbsorptIon methodHi

(13.0 ±

gh meat

� mg Zn/d)Low meat

(6.7 ± 0.8 mg Zn/d)

Low mea(1 1.6 ±

t, supplemented

1.3 mg Zn/d)

Pooled

SD ‘#{176}

Whole-body counting (serial)

(% absorption) 28#{176} 30#{176} 18k’ 4.6 0.0001

(mg absorbed/d) 3.6” 20h21h 0.5 0.0001

Whole-body counting [A.rvidsson et al (50)](% absorption) 29#{176} 310 l8�’ 4.6 0.0001

(mg absorbed/d) 370 21b 21b 0.4 0.0001Isotope apparent absorption [(diet-stool)/diet]

(% absorption) 21#{176} 22#{176} 12b 5.2 0.0001(mg absorbed/d) 2.7’ 15h

14h 0�5 0.0001

Elemental apparent absorption [(diet-stool)/diet]

(% absorption) 16#{176} 3l� 8�’ 8.6 0.002(mg absorbed/d) 2.1’ o2b 09b i.o 0.0002

626 HUNT ET AL

TABLE 3Diet effects on nitrogen, mineral, and trace element balances’

High meat Low meat Low meat, supplemented Pooled SD P

CalciumDiet (mg/d) 789 ± 100 728 ± 101 771 ± 105

Urine

(mg/d) 187� 18P 143b 25 0.0002

(% of diet) 24� 25C 18b 3.9 0.0003

Feces

(mg/d) 546 554 591 64 NS

(% of diet) 7#{216}� 76� 77� 7 0.05

Balance(mg/d) 57 -6 36 78 NS(% of diet) 7 - 1 5 10 NS

Copper

Diet (mg/d) 1.49 ± 0.12 1.41 ± 0.20 1.56 ± 0.30

Feces(mg/d) 1.55a 140b 0.14 0.03

(% of diet) 105k 100ab ioBalance

(mg/d) _0.07a 001ab 012b 0.16 0.02

(% of diet) 5a �jab 7b io 0.03

IronDiet (mg/d) 12.1 ± 1.2 8.8 ± 1.1 12.3 ± 1.5

Feces(mg/d) 9.1a 6#{149}5b 9.2a 0.91 0.0001

(% of diet) 75 74 75 7.1 NSBalance

(mg/d) 3.la 2.3a 3.la 0.88 0.04

(% of diet) 25 26 25 7.1 NS

Magnesium

Diet (mg/d) 268 ± 26 214 ± 23 257 ± 32

Urine

(mg/d) 89.9a 812ab 80#{149}8b 9 0.02

(% of diet) 34� 38b 3P 3.9 0.0005

Feces

(mg/d) 230k 174b 218k 22 0.0001

(% of diet) 86 81 85 7.6 NS

Balance(mg/d) -52 -40 -42 21 NS(% of diet) -20 -19 -17 8.9 NS

Manganese

Diet (mg/d) 3.66 ± 0.40 3.48 ± 0.41 3.63 ± 0.48

Feces(mg/d) 3.55 3.45 3.46 0.36 NS

(% of diet) 98 99 95 9.8 NS

Balance

(mg/d) 0.11 0.04 0.17 0.34 NS

(% of diet) 2 1 5 9.8 NS

Nitrogen

Diet (g/d) 16.60 ± 1.26 8.84 ± 1.07 8.84 ± 1.17

Urine

(g/d) 14.44a 682b 675b 0.74 0.0001

(% of diet) 87C 78b 77b 7.6 0.002

Feces(g/d) 1.44a 122b 128b 0.13 0.0003

(% of diet) 9C 14b 14b 1.4 0.0001Balance

(g/d) 0.73 0.80 0.80 0.99 NS

(% of diet) 4 9 8 8.0 NS

PhosphorusDiet (mg/d) 1712 ± 198 1030 ± 127 1530 ± 193

Urine(mg/d) 885k 491b 819C 93 0.0001(% of diet) 52 48 53 7.0 NS

MEAT, Zn ABSORPTION, MINERAL AND N BALANCE 627

TABLE 3 Continued

High meat Low meat Low meat, supplemented Pooled SD P

Feces(mg/d) 569a 452b 582#{176} 66 0.0001

(% of diet) 34C44b 38C 3.5 0.0001

Balance

(mg/d) 258� 87b129b 136 0.008

(% of diet) 14 8 8 8.8 NS

Zinc

Diet (mg/d) 13.0 ± 1.5 6.7 ± 0.8 11.6 ± 1.3

Urine

(mg/d) 0.33”026b o26b 0.04 0.0001

(% of diet) 2.5a 38b 2.2a 0.6 0.0001

Feces(mg/d) lo.9a 65b 10.7” 0.93 0.0001

(% of diet) 84� 97t� 92b 8.6 0.002Balance

(mg/d) 1.8a o66h 1.02 0.0003

(% of diet) 13C 1b 6ab 8.8 0.0001

‘ Dietary data are X ± SD. ANOVA was not conducted for dietary data because of the limited number of independent samples. Diet variability reflectsindividual differences in energy intake as well as analytical variability. Means with the same superscript letter are not significantly different.

measurements, and 1.5, 1.8, and 1.2 ± 1.0 mg (NS) using

apparent elemental absorption measurements. The biological

half-life of 65Zn, estimated for the limited observation period of

14-35 d after administration, was highly variable, and did not

differ significantly between diets. Although the low-meat and

low-meat, supplemented diets were associated with lower zinc

retention compared with the high-meat diet, plasma zinc was

not affected by diet and did not correlate with zinc absorption

or urinary zinc excretion.

Nitrogen balance and related indexes

Consistent with adequate nitrogen intake and body weight

maintenance, the twofold difference in nitrogen consump-

tion was accompanied by proportional differences in nitro-

gen excretion, producing similar positive nitrogen balances

on all diets (Table 3). If a conversion factor of 6.25 g

protein/g N is used, then mean protein intakes for the 14

volunteers were 1.56 ± 0.18, 0.83 ± 0.10, and 0.83 ± 0.11

g/kg body wt, from the high-meat, low-meat, and low-meat,

supplemented diets, respectively. After subtracting esti-

mated miscellaneous losses of 8 mg N/kg (52), nitrogen

balances during these diets were 0.018 ± 0.12, 0.022 ±

0.08, and 0.025 ± 0.08 glkg, respectively, and did not differ

from zero (equilibrium).

The high-meat diet resulted in significantly higher blood

urea nitrogen and uric acid, without differences in serum

creatinine, albumin, transferrin, or retinol-binding protein

(Table 4). Serum total protein was slightly, but not signifi-cantly greater for the high-meat compared with the other two

diets (Table 4). Although serum creatinine was unaffected by

diet, urinary creatinine excretion was greater for the high-meat,

compared with the low-meat or low-meat, supplemented diets

TABLE 4Diet effects on blood indexes related to protein and mineral nutriture’

High meat Low meat Low meat, supplemented Pooled SD P

Total protein (g/L) 68.5 67.6 66.7 2.0 NSUrea nitrogen (mmolIL) 6.7a 38b 40b 0.5 0.0001

Uric acid (�molIL) 25? 235L� 233b 23 0.02

Alkaline phosphatase Qikat/L) 1.56a 166b i.64� 0.09 0.02Ferritin (,�,/J�)2 74� 82b 82b 7 0.01

Iron-binding capacity (MmolIL) 58� 53b 53b 4 0.002Transferrmn saturation (%) 27.2” 314b 309ab 4 0.03

Monoamine oxidase (nkat/L)3 4.09a 438ab 444b 0.36 0.03Plasma zinc (pmol/L) 11.6 11.4 11.5 0.5 NS

‘ n = 14. Means with the same superscript letter are not significantly different. The following blood variables were not significantly affected by diet:

glucose, creatinine, total cholesterol, LDL cholesterol, albumin, transferrmn, retinol-binding protein, total protein, Cu, Ca, Fe, K, Na, Mg, P, Zn, ionizedcalcium, percent ionized calcium, hematocrit, hemoglobin, zinc protoporphyrin, transferrmn, red blood cells, red cell distribution width, total triiodo-

thyronine, free triiodothyronine, total thyroxine, free thyroxine, thyroid stimulating hormone, acid phosphatase, parathyroid hormone, calcitonin,

osteocalcin, estradiol, 25-dihydroxycholecalciferol.

2 � 13; We omitted results for one volunteer that were unusually variable, without apparent explanation. Inclusion of this volunteer increased dietarydifferences, but reduced statistical power: ferritin values for the high-meat, low-meat, and low-meat, supplemented diets became, respectively, 74a, 83ab

and 85b (pooled SD = 10, P < 0.01, n 14).3 To obtain nkatfL the clinical units/0.6 mL were multiplied by 0.09259.

628 HUNT ET AL

(9.6 compared with 8.0 and 7.9 mmol/d, pooled SD 0.5,

P < 0.0001).

Calcium balance and related clinical indexes

Urinary calcium was not affected by high dietary protein

from meat (Table 3). Supplementation with some of the mm-

erals found in meat reduced urinary calcium excretion by �‘40

mg/d (Table 3). Calcium balance was not adversely affected by

meat consumption. Compared with the other diets, the high-

meat diet resulted in lower serum alkaline phosphatase values

(Table 4), without differences in acid phosphatase, calcium,

ionized calcium, parathyroid hormone, calcitonin, osteocalcin,

estradiol, 25-hydroxycholecalciferol, or urinary hydroxypro-

line, pynidinium, or deoxypynidinium. Bone mineral content

and density were not affected by diet within these relatively

short treatment periods.

Iron balance and related clinical indexes

The retention of iron reflected the lower dietary iron content

of the low-meat diet, but was not different (25-26%) for the

three diets when expressed as a proportion of dietary intake

(Table 3). Unexpectedly, two independent clinical measure-

ments-ferritin and iron-binding capacity-suggested reduced

iron status (within the normal range) with the high-meat diet

(Table 4). Transfenrin saturation, calculated from iron-binding

capacity and serum iron, was also significantly reduced with

the high-meat diet. The order of dietary treatments was ran-

domized to prevent confounding of diet effects by time and

phlebotomy. Measures of iron status not affected by diet in-

eluded hemoglobin, hematocnit, zinc protophorphynin, trans-

ferrin, serum iron, and red cell distribution width. Monoamine

oxidase activity, reported to be reduced in platelets of patients

with iron-deficiency anemia (53), was lower in plasma when

volunteers consumed the high-meat diet than when they con-

sumed the low-meat, supplemented diet (Table 4). We tested in

vitro whether the effects of macronutnients on urea, uric acid,

and/or albumin could account for increased iron-binding ca-

pacity, but found no influence on iron-binding capacity when

these constituents were added to a clinical chemistry control

serum (SeraChem, Instrumentation Laboratory Co, Lexington,

MA) in amounts that reflected the mean differences associated

with meat intake in this study.

Copper, magnesium, manganese, and phosphorus balance

Copper retention appeared to be slightly reduced as a result

of the high-meat diet, with fecal copper significantly higher

than with the low-meat diet and copper balance significantly

more negative than with the low-meat, supplemented diet (Ta-

ble 3). Magnesium retention was negative with intakes of

210-270 mg/d (Table 3), and did not differ between diets.

Urinary excretion of magnesium was greater for the high-meat

diet, significant only in comparison with the low-meat, supple-

mented diet (Table 3). Manganese intakes of �‘3.5 mg/d ne-

suited in a manganese balance that did not differ from zero

(equilibrium; without adjusting for integumental losses). Man-

ganese balance was unaffected by diet (Table 3). Phosphorus

retention and excretion were roughly proportional to phospho-

rus intake, which was lower with the low-meat diet (Table 3).

DISCUSSION

Zinc absorption methods

The zinc absorption results indicate that relative differences

in zinc absorption corresponding to diet treatment can be

effectively determined by whole-body counting or by fecal

excretion of a single isotopic tracer (apparent isotope absorp-

tion, Table 2). However, the latter method underestimated

absolute zinc absorption by 8%, indicating the extent of error

attributable to endogenous fecal excretion.

All isotopic methods used in this study assume that a tracer

extrinsically added in the final stages of food preparation forms

a common pool with the dietary zinc before absorption, an

assumption that has been generally (54-56), but not completely

supported (57).

The apparent elemental absorption (balance) method is muchless sensitive than isotopic methods, but it has the advantages

of relying on zinc intrinsic to the food (in contrast with assum-

ing extrinsic tracer validity) and of extending the results of a

controlled feeding study to information about other elements (it

may not be technically or economically feasible to use isotopic

tracers for several elements concurrently). The extensive van-

ability in fecal excretion data substantially reduces the sensi-

tivity and power of the balance method, especially for elements

such as zinc for which body retention is controlled to a con-

siderable degree by endogenous fecal excretion. Percentage of

zinc absorption from high- and low-meat diets differed signif-icantly by the apparent elemental absorption method, but not

by the isotopic methods. This probably reflects an error in

estimating the percentage of apparent elemental absorption,

especially from diets with different zinc contents, which are

likely to differ in the fraction of fecal zinc from endogenous

excretion. However, despite the reduced sensitivity of elemen-

tal balance measurements, the present results indicate that

apparent elemental absorption, zinc balance, and urinary zinc

measurements can be of some value in detecting differences

between diets, and that these measures correlate with more

sensitive determinations of zinc absorbed (Figure 1). Presum-

ably, the balance method yielded similarly useful information

for other elements that were not labeled with radiotracers.

Endogenous zinc excretion was not measured directly in this

experiment. Rough estimates of endogenous excretion of zinc

in the feces can be derived from the difference between the

whole-body counting results and apparent absorption results

for either the isotope or elemental methods. Because of lower

variability, use of the apparent isotope absorption data to

estimate endogenous excretion provided greater statistical

power to detect dietary treatment differences, in contrast with

the endogenous excretion estimates using the much more van-

able apparent elemental absorption data. Greaten endogenous

excretion with greater zinc absorption is consistent with the

results of animal studies (58).

Zinc retention from a high-meat diet

The present results indicate greater zinc absorption from ahigh-meat diet, roughly in proportion to the amount of addi-

tional zinc provided by the meat. Zinc absorption is enhanced

by the addition of protein to a meal when the zinc content

remains constant (13-16). In animal models, more protein is

needed to achieve this enhancement when there is more zinc in

the meal (59). However, percentage zinc absorption is reduced

MEAT, Zn ABSORPTION, MINERAL AND N BALANCE 629

(and the amount of total zinc absorbed is increased) by small

increments (1-3 mg) in the zinc content of a meal (14, 15). Of

course, meat provides both protein and zinc, as well as other

minerals. The similar efficiency of zinc absorption with the

high- and low-meat diets, together with the reduced efficiency

of zinc absorption from the low-meat diet supplemented with

minerals (Table 2), suggest that any enhancing effect of added

meat protein on zinc absorption (13, 14, 16) was offset by a

reduction in percentage zinc absorption associated with the

minerals in meat, including zinc.

The efficiency of zinc absorption from the high- and low-

protein diets in the present study was similar to the 29 ± 8%

zinc absorption by younger women consuming an experimental

diet based on the US Food and Drug Administration total diet

study (60). There have been limited controlled studies of the

effect of protein on zinc absorption from whole diets. The

present results contrast with preliminary reports from Spencer

et al (61) and Spencer and Samachson (62), suggesting that

high protein intake reduces zinc absorption. Spencer et al (61,

62) reported reduced plasma 65Zn and increased fecal excretionof orally administered �5Zn when dietary protein was in-

creased; however, these early reports did not indicate the

source of protein or whether dietary zinc was controlled for. In

another report dietary protein and phosphorus interacted to

affect zinc retention, such that zinc retention (balance method)

was increased by dietary protein (isolated protein sources) only

when phosphorus intake was moderate, and not increased with

protein intake (17). Although the present study did not test the

effects of isolated protein on phosphorus as controlled van-

ables, they suggest that no net enhancement or inhibition of

zinc absorptive efficiency occurred with common protein

sources rich in phosphorus (meat from a combination of beef,

pork, chicken, and fish) and that more total zinc was retained

by consuming these foods that are rich in zinc.

Percent zinc absorption was reduced when the low-meat diet

was supplemented with zinc and other minerals in quantities

supplied by the additional meat in the high-meat diet (Table 2).

As a practical consequence, it cannot be assumed that equimo-

lan zinc fortification or supplementation of diets with minerals

will compensate for reduced dietary zinc associated with

low-meat diets.

Greater urinary zinc excretion with increased dietary protein

was reported previously (5, 17-19). The results from the

present study suggest that such increases in urinary zinc may be

explained by increased amounts of zinc absorbed. Urinary zinc

excretion has been positively associated with differences in

dietary zinc content (63, 64).

The analyzed zinc contents of the experimental diets (Table

2), which were within 10% of values calculated from US

Department of Agriculture food-composition data (38), empha-

size the high concentration of zinc in meat. In the present study,

meat was substituted for carbohydrate and fat sources with

minimal zinc content. Persons reducing meat intake for health

reasons would probably substitute vegetable protein sources

and other foods that provide additional zinc, as well as other

factors that may reduce zinc bioavailability, such as phytic acid

and fiber. Based on studies with single meals, Sandstr#{246}m (65)

estimated 30% absorption of = 10-12 mg Zn in diets of typical

industrialized countries, and 15-20% absorption of =8-9 mg

Zn in lactoovovegetanian diets in affluent countries. If theseestimates are accurate, omnivores absorb more than twice the

daily zinc that vegetarians absorb. Such comparisons were

supported by reduced zinc retention (balance method) from a

vegetarian diet, compared with diets with a similar zinc con-

tent, containing varying amounts of beef (66), and by reduced

plasma, hair, and urinary zinc in persons following a vegetarian

diet for 3-12 mo (67).

Assuming integumental zinc losses of 0.5-0.8 mg/d (63, 68),

the low-meat diet resulted in negative zinc balance in the

present study. Unfortunately, there are no sensitive, functional

indicators of marginal zinc status to further evaluate the effects

of this negative balance.

Nitrogen balance and protein requirements ofolder women

The similar nitrogen balances observed during the high- and

low-meat diets confirm the current recommended dietary al-

lowance of 0.8 g protein/kg body wt for women aged > 51 y

(69). These results are in contrast with those of a recent report

by Campbell et al (70) of nitrogen balance in 12 men and

women aged 56-80 y, which used lactoovovegetanian diets that

provided protein in amounts (0.8 and 1.6 g protein/kg body wt)

similar to those of the present study. Campbell Ct al (70)

concluded that 0.8 g protein/kg body wt was inadequate, and

that 1.0 g protein/kg was required to achieve nitrogen equilib-

nium in elderly adults. Volunteers in the present study were

similar to those of Campbell et al in age and body mass index.

The variability in body mass index was greater in the present

study; however, the body mass index did not correlate with

nitrogen balance. In contrast with the study by Campbell et al,

the present study was not blinded with a partial formula diet,

had longer equilibration and balance periods, included com-

parisons between different diets in the same individuals, and

used meat as a protein source. Perhaps most important to

nitrogen balance determinations, the diets of the volunteers in

the present study provided more energy per kilogram body

weight (137.7 ± 15.1 compared with 127.7 ± 10.0 kJ/kg, P

0.06 by t test) than did the diets in the study of Campbell et al

(70). Because protein requirements for nitrogen equilibrium

were met by both the high- and low-meat diets in the present

study, the data could not be used to estimate protein require-

ments, except to conclude that these requirements did not

exceed 0.8 g/kg body wt.

Calcium retention from a high-meat diet

The present results support the work of Spencer et al (8, 9),indicating no adverse effect of meat protein on urinary calcium

excretion or calcium retention. The reduction in alkaline phos-

phatase associated with the high-meat diet in the present study

is difficult to interpret; increased alkaline phosphatase activity

is commonly associated with increased osteoblastic activity,

and elevated activities occur with physiological bone growth,

as well as healing of bone fractures, rickets, osteomalacia,

hypenparathyroidism, and other bone diseases, but activities are

generally normal in osteoporosis (71). The data from the

present study indicate that a diet high in meat protein does not

adversely affect calcium balance or metabolic markers associ-

ated with calcium metabolism. In view of this and other (8, 9)

controlled experimental trials showing no effect of meat pro-

tein on calcium retention, associations between dietary protein

and the risk of osteoporosis, using multiple-regression analysis

630 HUNT ET AL

and/or isolated protein sources, should not be used as a basis

for public advice to reduce meat intake.

Iron retention from a high-meat diet

Because meat is considered a highly bioavailable source of

iron (20-25), the reduced iron status suggested by decreased

ferritin and increased iron-binding capacity with the high-meat

diet was unexpected. Fenritin measurements have been genen-

ally unchanged in clinical trials on the influence of iron ab-

sorption with calcium or ascorbic acid supplementation (31,

34-37), and ferritin measurements are commonly confounded

by phlebotomy in nutrition studies. However, the present study

indicates that fernitin values can be influenced by diet, albeit in

an unexpected direction, within a 7-wk period.

Although the iron-balance measurements did not indicate

poorer iron retention with the high-meat diet than with the

low-meat diet supplemented with ferrous gluconate, neither

did they suggest enhanced iron retention associated with

meat intake. Because iron balance results are relatively

insensitive, it would be helpful to repeat the experiment with

radiolabeled heme and nonheme iron to determine whether

absorption of these types of iron was enhanced by the

high-meat diet despite clinical indicators of reduced iron

status. The isoenergetic substitution of vegetable fats and

simple sugars for meat may have introduced dietary van-

ables besides meat that influence iron absorption. In addi-

tion, it is possible that reducing dietary protein may have

enhanced iron bioavailability. Observations that nonheme

iron was better absorbed with meat were originally based on

meals in which meat was substituted for egg white (25),

which inhibits iron absorption (72), rather than compared

with a protein-free meal. Under conditions of constant non-

heme-iron content, added beef enhanced nonheme-iron ab-

sorption from a meal of corn meal by threefold, but had no

effect on iron absorption from a meal of flat, yeast-leavened

wheat bread (73). Even if the efficiency of iron absorption

was not enhanced by meat in these diets, less total iron was

retained from the low-meat diet because of its lower iron

content, presenting a paradox related to the ferritin and

iron-binding-capacity measurements.

The increased iron-binding capacity may have resulted from

an unidentified serum iron-binding protein other than trans-

ferrin. Increased iron binding by a protein other than transferrin

is supported by the observation that transfernin measured by

radialimmunodiffusion was not affected by diet in the present

study. The protein is unlikely to be albumin, because albumin

concentrations were unaffected by diet, and our in vitro testing

suggested that albumin, in amounts equivalent to the nonsig-

nificant increase in serum total protein, could not account for

the increased iron-binding capacity. Iron-binding-capacity

measurements do not completely correlate with transfennin

measurements (74), and may overestimate the latter by 16-

20% because not all iron is bound to transferrin (75)

Although it is impossible to rule out other dietary variables

beside iron that may have affected iron-binding capacity in this

study, iron-binding capacity and ferritin are generally regarded

as good clinical indicators of iron status. There is great interest

in the hypothesis that high iron concentrations in the body mayincrease the physiological availability of free iron to participate

in damaging oxidative reactions, and both of these indexes of

iron status have been reported as possible risk factors for

chronic diseases such as myocardial infarction and cancer (32,

76-78). Causality is far from clear. These indexes of body iron

pools may not be sensitive indicators of iron ingestion. The

results of the present study suggest the need for further eval-

uation of these iron-status indexes as markers of iron stones,

iron ingestion, and possibly other dietary variables.

Retention of copper

The results of the present study suggest that copper retention

was reduced during the high-meat diet. Cohn et al (19) reported

that copper retention was unaffected by dietary protein (from

common foods including meat) and zinc (from foods and zinc

sulfate), whereas Greger and Snedeker (17) found enhanced

apparent copper absorption associated with protein from iso-

lated sources. More information is needed concerning dietary

interactions affecting copper absorption and retention in

humans.

Retention of magnesium

The negative magnesium balance observed in the present

study was unexpected. The recommended dietary allowance

for magnesium of 280 mg/d was based in part on balance

studies indicating adequate magnesium balance with intakes as

low as 3.0- 4.5 mg/kg body wt in healthy men, and common

dietary intakes of 207 mg/d for adult women (69). Possible

reasons for negative magnesium balances in the present study

may include sex, age, and unidentified dietary characteristics.

Summary and conclusions

In comparison with a low-meat diet or a low-meat diet

supplemented with minerals and trace elements provided by

meat, a high-meat diet increased zinc retention, with a slight

increase in urinary zinc excretion. Addition of minerals and

trace elements including zinc did not compensate for the zinc

provided by meat. Reduction of meat intake, even if replaced

by plant-food sources of zinc, is likely to reduce zinc intake

and retention; however, it is not known whether such a reduc-

tion in zinc retention would have long-term functional conse-

quences. Nitrogen balance was similarly maintained by these

51-70-y-old women consuming the high- and low-meat diets,

providing 1.6 and 0.8 g protein/kg body wt, respectively, which

confirms the current recommended dietary allowance for pro-

tein in older women. The high-meat diet did not increase

urinary calcium excretion on impair calcium balance on indexes

of bone metabolism, and therefore impaired calcium balanceshould not be used as a rationale for reducing meat intake.

Although iron balance was not different with high- and low-

meat diets with similar iron content, the high-meat diet was

associated with changes in two independent measures, serum

iron-binding capacity and fernitin, suggesting reduced iron sta-

tus within a normal range. Further research is needed to

determine how dietary factors, including but not limited to

dietary iron, affect serum fernitin and other clinical indexes of

iron status. UWe are grateful for the assistance of the professional and technical staff

supporting metabolic studies at the Grand Forks Human Nutrition Research

Center. We especially acknowledge H Lukaski for bone mass measure-ments, B Hoverson for dietary services, D Milne for supervising clinical

chemistry and balance analyses, B Vetter for volunteer services and su-

pervision, C Zito for in vitro work with iron-binding capacity, and B

MEAT, Zn ABSORPTION, MINERAL AND N BALANCE 631

Momcilovic for discussions related to whole-body counting. We also thank

the dedicated volunteers who made this project possible.

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