AMERICAN JOURNAL OF CLINICAL PATHOLOGY
Vol. 31, No. 2, February, 1959, pp. 155-159
Printed in U.S.A.
T H E EFFECT OF EATING ON SOME OF THE CLINICALLY IMPORTANT
CHEMICAL CONSTITUENTS OF T H E BLOOD
JOSEPH S. ANNINO AND ARNOLD S. RELMAN, M.D.
Clinical Chemistry Laboratory and the Evans Memorial Department of Clinical Research and Preventive
Medicine, Massachusetts Memorial Hospitals, and the Department of Medicine, Boston University
School of Medicine, Boston, Massachusetts
At the present time it is routine hospital
practice to require that blood specimens for
most diagnostic chemical analyses be drawn
from patients in the fasting state, usually
before breakfast. There is, however, little
published information to justify the inconvenience for both patients and hospital personnel that this custom so often entails. A
review of the literature reveals no comprehensive studies of the effects of ordinary
meals on the concentrations of the clinically
important chemical components of the blood.
There are, of course, numerous observations
on the effects of ingesting large amounts of
certain substances, e.g., glucose, lipids, electrolytes, and others, on their respective blood
concentrations, but such information is of
scant practical value in estimating the usual
effects of eating.
The study described in this paper was performed in order to provide some useful data
about this question. Fifteen of the most frequently used chemical determinations were
performed on the blood of each of 32 apparently normal persons before and after ingesting a standard, average-sized breakfast.
The results would suggest that, with the
exception of glucose, these analyses are not
significantly affected by eating such a meal.
METHODS AND MATERIALS
Thirty-two persons, mostly hospital personnel, participated in the study. Although
the persons were not examined in detail,
they all believed themselves to be in. good
health. They were equally divided into a
"young" group (19 to 35 years) and an
Received, June 19, 1958; revision received,
September 12; accepted for publication October 2.
Mr. Annino is Clinical Chemist, Massachusetts
Memorial Hospitals; and Dr. Relman is Visiting
Physician, Massachusetts Memorial Hospitals,
and Associate Professor of Medicine, Boston University School of Medicine.
lf5
"older" group (50 to 67 years). There were 8
men and 8 women in each age group. The
following procedure was used: A sample of
peripheral venous blood was obtained in the
morning in the fasting state. The patient
then ate breakfast and another blood sample
was obtained, in one-half the patients at 45
min. (Group A), and in the other half at 2 hr.
(Group B) after completion of the meal. These
2 time groups were also equally divided with
respect to age and sex. The breakfast for all
persons consisted of 4 ounces of fruit juice,
1 egg, 2 slices of buttered toast, a cup of
coffee with cream and sugar, and 4 ounces of
milk. Estimated from standard tables, this
meal contains 15 Gm. of protein, 25 Gm. of
fat, 56 Gm. of carbohydrate, 16 mEq. of
sodium, 13 mEq. of potassium, 11 mEq. of
calcium, 324 mg. of phosphorus, and 509
calories.
The chemical analyses performed on each
blood sample were for blood urea nitrogen
and glucose, serum CO2 content, chloride,
sodium, potassium, calcium, phosphorus,
total protein, albumin, globulin, creatinine^
uric acid, total cholesterol, and cholesterol
esters. The blood samples were drawn with
an oiled syringe, and the portion used for the
determination of CO2 content, chloride,
sodium, and potassium analyses was kept
under oil. Potassium oxalate was used as an
anticoagulant for blood urea nitrogen and
glucose analyses. Glucose and C0 2 determinations were performed as soon as possible
after bleeding.
With few exceptions, all of the analyses
were performed by 1 person. Standard
analytical methods were used, 2 ' 4 " 10 ' 12 " 16 or
minor modifications thereof.1
Statistical difference between mean values
was calculated by the Fisher t test.
RESULTS
The data from the 32 fasting samples are
summarized in Table 1. The normal values
156
Vol. SI
ANNINO AND KELMAN
TABLE 1
FASTING VALUES IN 32 NORMAL PERSONS*
Analysis
Reference Citation
for Method
Mean
14
1, 12
1, 2
1. 2
1, -7
10
9
8
15
15
13
13
4
5
6
29.10
103.8
140.8
4.29
15.2
84.3
0.76
7.48
4.33
3.15
230.5
74.5
4.76
3.43
4.34
C0 2 content (mEq. per 1.)
Chloride (mEq. per 1.)
Sodium (mEq. per 1.)
Potassium (mEq. per 1.)
Blood urea nitrogen (rag. per 100 ml.)
Glucose (mg. per 100 ml.)
Creatinine (mg. per 100 ml.)
Total protein (Gm. per 100 ml.)
Albumin (Gm. per 100 ml.)
Globulin (Gm. per 100 ml.)
Cholesterol (mg. per 100 ml.)
Cholesterol esters (per cent of total)
Calcium (mEq. per 1.)
Phosphorus (mg. per 100 ml.)
Uric acid (mg. per 100 ml.)
Standard Deviation
±
1.91
2.7
2.0
0.33
3.7
8.0
0.18
0.37
0.30
0.35
51.5
2.3
0.20
0.46
0.87
* All determinations were performed with serum, except those for blood urea nitrogen and glucose,
which were performed on whole blood.
TABLE 2
DIFFERENCES BETWEEN FASTING AND POSTPRANDIAL VALUES*
Group A—16 Persons
(45 Min. after Eating)
Analysis
Mean
difference
Standard
deviation
+0.65
+0.19
1.41
1.28
0.70
0.47
1.51
21.78
0.081
0.25
0.16
0.23
11.07
1.75
0.09
0.38
0.28
Group B—16 Persons
(2 Hr. after Eating)
Mean
difference
Standard
deviation
+0.3S
+0.3S
+0.50
1.72
2.25
1.32
0.36
1.39
10.17
0.085
0.22
0.24
0.26
10.74
1.54
0.15
0.56
0.31
±
CO2 content (mEq. per 1.)
Chloride (mEq. per 1.)
Sodium (mEq. per 1.)
Potassium (mEq. per 1.)
Blood urea nitrogen (mg. per 100 ml.)
Glucose (mg. per 100 ml.)
Creatinine (mg. per 100 ml.)
Total protein (Gm. per 100 ml.)
Albumin (Gm. per 100 ml.)
Globulin (Gm. per 100 ml.)
Cholesterol (mg. per 100 ml.)
Cholesterol esters (per cent of total)
Calcium (mEq. per 1.)
Phosphorus (mg. per 100 ml.)
Uric acid (mg. per 100 ml.)
+0.69
-0.21
+0.44
+7.S8
+0.006
-0.11
-0.08
+0.02
-4.13
-0.44
+0.03
-0.25
-0.13
±
+0.09
+0.06
-1.13
+0.006
-0.03
-0.05
-0.03
-3.06
-0.31
+0.02
+0.08
-0.16
* Differences calculated as postprandial value minus fasting value, with due regard to sign.
are expressed in terms of means and standard
deviations. Inasmuch as 95 per cent of a
normally distributed population should be
within ± 2 standard deviations from the
mean, this method of presentation may be
used as a working definition of "normal." As
emphasized by Bodansky and Bodansky, 3
such a statistical definition is preferable over
the traditional practice of simply stating the
"normal range." In general, the mean fasting
Feb. 1959
EATING AND CHEMICAL ANALYSIS OF BLOOD
values in Table 1 agree with similar data in
the literature.
The fasting data were tested for statistical
differences between the "young" and "older"
groups, and between the men and the
women. The only significant differences
resulting from age or sex were those in the
concentrations of cholesterol, creatinine, and
uric acid. For the "young" group the mean
cholesterol value was 197.3 ± 37.4 mg. per
100 ml.; the mean value for the "older"
group was 264.3 ± 41.6 mg. per 100 ml. The
difference between these was significant at
the 1 per cent level (p < 0.01). The mean
creatinine value for the male group was
0.83 ± 0.20 mg. per 100 ml., and for the
female group 0.69 ± 0.12 mg. per 100 ml.
The difference between these values was
significant at the 5 per cent level (p < 0.05).
The mean uric acid value for the male group
was 4.77 ± 0.75 mg. per 100 ml., and for the
women 3.92 ± 0.80 mg. per 100 ml., and
this difference was significant at the 5 per
cent level (p < 0.01).
The means of the individual differences
(with regard to sign) between the levels before and after eating, and the standard
deviations of these means, are given in Table
2. The difference in each instance was calculated as the postprandial value minus the
fasting value, so that a "plus" value for the
mean difference means an increase in the
level after eating. None of the differences
was significant at the 5 per cent level, with
the exception of the 45 min. values for
sodium and phosphorus. There seemed to be
a very small rise in sodium and a small reduction in phosphorus. The mean changes in
these concentrations were probably within
the range of analytical error for the determination, but the statistical significance of the
changes derives from the fact that the direction of individual change was quite consistent. The mean glucose difference • at 45
min. was not significantly different from
zero, but the relatively large standard deviation indicates that in a few individual
instances the postprandial values were significantly above or below the fasting level.
There were no significant differences in the
effects of eating between the men and the
women, or between the 2 age groups.
157
In a few instances there was a noticeable
lipemic turbidity of the serum at 45 min. or
2 hr. In no instance, however, was this of
sufficient intensity to interfere with the
analytical procedures.
DISCUSSION
The data given here seem to indicate that
in normal persons an average breakfast is
without significant effect on the plasma concentration of the chemical constituents
measured in this study, with the probable
exception of glucose, and possibly sodium
and phosphorus.
The observed change in sodium 45 min.
after eating is so small as to be of dubious
physiologic significance, despite its apparent statistical validity. There are no confirmatory data in the literature, nor is there
any apparent a priori reason to expect a rise
in concentration following a meal. The slight
reduction in phosphorus 45 min. after eating
is to be anticipated, in view' of the wellknown relation between the level of serum
inorganic phosphate and the utilization of
glucose.11
There was, on the average, a rise in blood
glucose at 45 min., but, because of the large
standard deviation, the mean increase was
not of statistical significance. It should not
be concluded, however, that the standard
breakfast was without significant effect on
the blood glucose. In a few instances the 45
min. level was unequivocally elevated above
the fasting, but these data were balanced by
other persons in whom glucose concentrations were below the control. This variation
is probably explained by the relatively small
load of glucose administered and by large
individual differences in the rate of absorption, the magnitude of the subsequent rise,
and the rate at which the hypoglycemic
phase appears. A more consistent effect of
eating might have been demonstrated if
blood samples had been obtained at more
frequent intervals.
This latter consideration might apply in
theory to any of the other analyses which
were apparently unchanged at 45 min. and
2 hr., inasmuch as the time intervals chosen
were quite arbitrary. With the other analyses, however, unlike the glucose data, there
158
ANNINO AND RELMAN
were no large changes in any individual
instances. This suggests that significant
changes would probably not have been observed even if different time intervals had
been selected. Further study will be required
to settle this point definitely.
Finally, it should be remembered that the
persons in this study were all in apparent
good health. No conclusions may be drawn
from these data about the effects of eating in
states of disease or malnutrition. The present
study does suggest, however, that for general
screening purposes it is unnecessary to have
patients in the fasting state when blood is
drawn for any of the 15 analyses reported
here, with the exception of glucose and phosphorus. Any abnormalities in postprandial
specimens probably could not be attributed
solely to eating, but would more likely be
explained either by some pre-existing abnormality in the fasting blood or by an abnormal response to food. This conclusion
must be qualified by the reminder that the
effects of large variations of food intake and
time intervals were not studied.
SUMMARY AND CONCLUSIONS
Blood obtained from 32 apparently normal subjects, before and after a standard
breakfast, was analyzed for blood urea
nitrogen, glucose, CO2, chloride, sodium,
potassium, creatinine, proteins, cholesterol,
calcium, phosphorus, and uric acid. At 45
min. after the meal there was a small but
significant drop in phosphorus, and a very
small rise in sodium. Glucose levels varied
considerably, but the mean rise was not
significant. Breakfast had no detectable
effects on the other analyses, at 45 min. or
2 hr. I t is concluded that in apparently
normal persons an average breakfast probably will not affect any of the clinically
significant blood constituents studied here,
with the exception of glucose, and perhaps
phosphorus. For screening or diagnostic
purposes, therefore, it does not seem necessary for patients to be fasting when blood is
drawn for these analyses.
SUMMARIO IN INTERLINGUA
Sanguine obtenite ab 32 apparentemente
normal subjectos, ante e post un jentaculo
Vol. 31
standard, esseva analysate con respecto a
nitrogeno del urea sanguinee, glucosa, C0 2 )
chloruro, natrium, kalium, creatinina, proteinas, cholesterol, calcium, phosphoro, e
acido uric. Quaranta-cinque minutas post le
repasto, un micre sed significative reduction
del phosphoro esseva notate e un micrissime
augmento del natrium. Le nivellos de glucosa
variava considerabilemente, sed le augmento
medie non esseva significative. Le repasto
habeva nulle detegibile effecto super le altere
valores, tanto 45 minutas como etiam 2
horas post le ingestion. Le conclusion es que
in apparentemente normal subjectos, un
jentaculo standard remane probabilemente
sin effecto super le clinicamente importante
constituentes chimic del sanguine hie studiate, con le exception de glucosa e forsan de
phosphoro. Pro objectivos detectori o diagnostic, per consequente, il pare innecessari
que le patientes remane jejun ante le obtention de specimens de sanguine pro le supralistate analyses.
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