Indian
J Physiol Pharmacol 2002;46 (4);
The Effect of Ingestion of Egg on Serum Lipid Profile
in Healthy Young Free-Living Subjects
GAYATRI CHAKRABARTY, R. L. BIJLANI*, S. C. MAHAPATRA,
NALIN MEHTA, R. LAKSHMY**, SUMAN VASHISHT** AND S. C. MANCHANDA**
Departments of Physiology and **Cardiology,
All India Institute of Medical Sciences,
New Delhi – 110 029
*Corresponding Author (e-mail: rambij@medinst.ernet.in)
(Received on April 22, 2002)
Abstract:
Egg is a major source of dietary cholesterol. Previous studies
on the effect of egg on serum lipid profile have given conflicting
results. Further, the serum lipid response to egg shows marked
individual variation. Since the variation is at least partly genetically
determined, and the response depends partly on the overall diet,
studies on different ethnic groups are important. There is hardly
any study on the subject available on Indians. In the present
investigation, eighteen healthy young volunteers (7 male, 11 female)
on a lacto-vegetarian diet were given one boiled egg per day for
8 wk in a randomized controlled cross-over study. Compared to
the values obtained after 8 wk of egg-free period, the mean serum
total cholesterol, LDL cholesterol, HDL cholesterol, total cholesterol/HDL
ratio, VLDL cholesterol and triglycerides were not significantly
different after 8 wk of egg consumption. However, the serum total
cholesterol after 4 wk of egg consumption was significantly higher
than the control values. Further, seven subjects out of 18 had
an appreciable elevation of serum total cholesterol or LDL cholesterol,
or both, after 8 wk of egg consumption. The study suggests that
in young healthy Indian subjects on a vegetarian diet, consuming
one egg per day raises serum cholesterol levels at 4 wk but in
the majority baseline values are restored by 8 wk. However, some
hyper-responders continue to have elevated serum cholesterol even
at 8 wk but in the majority baseline values are restored by 8
wk. Knowing the response of an individual may be important before
making egg consumption a regular habit.
Key
words: egg,dietary,cholesterol, cholesterol
lipoproteins, atherosclerosis
An
important feature of egg which is of interest to nutritionists
and medical scientists is its high cholesterol content. High dietary
intake of cholesterol has a reasonably predictable effect on serum
cholesterol. Attempts have been made to express the relationship
in quantitative terms in the form of equations (1-3). However,
the body needs cholesterol for metabolic functions, and the requirements
of the body are met by supplementing dietary cholesterol with
endogenous cholesterol synthesis. In view of this, the National
Cholesterol Education Program of the U.S.A. allows up to 300 mg
dietary cholesterol per day in the Step I diet (4). Further, the
endogenous synthesis of cholesterol is regulated to maintain cholesterol
homeostasis (5). That is possibly one reason why the effects of
feeding cholesterol as such, or in the form of egg, have not been
consistent. Although many studies have shown a positive relationship
between dietary and serum cholesterol (5-8), some studies have
shown no cholesterolaemic response to dietary cholesterol (9-11).
Several epidemiological studies have also found no relationship
between egg consumption and serum cholesterol or coronary heart
disease (12-13). In a meta-analysis of 17 studies, Weggemans et
al found that 100 mg of additional dietary cholesterol raises
both serum cholesterol and HDL cholesterol such that there is
an increase in the ratio of total to HDL cholesterol ratio by
0.02. Hence they concluded that the advice to limit the consumption
of eggs is still valid (14). However, it is difficult to describe
the effect to dietary cholesterol in general terms on the basis
of averages because of a marked individual variation in response
(15) which is at least partly genetically determined (16). In
view of this, observations made on one ethnic group cannot be
extrapolated to other groups, who may be genetically different.
We have come across no experimental study on the effect of consumption
of eggs on the Indian population. Studies on Indians are important
not only because we may be genetically different from the Western
populations, on whom most of the previous studies have been done,
but also because of other relevant reasons. Indians have a relatively
high incidence of coronary artery disease (CAD), and the disease
in Indians is premature and extensive (17). The risk factors for
CAD are also somewhat different for Indians because of their predilection
for insulin résistance syndrome (18). Finally, the Indian diet
is typically a vegetarian, high carbohydrate, low fat diet. In
such a diet, the only major potential source of cholesterol is
the egg. The cholesterol content of one egg (about 250 mg) is
within the permissible limit of 300 mg (4). Therefore the effect
of egg consumption needs to be examined against the background
of the genetic and dietary profile of Indians.
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Subjects
The
study was conducted on 18 healthy adult volunteers (7 male, 11
female). The subjects were normolipidaemic, and none of the subjects
smoked or used alcohol.
Experimental design
The
study was conducted in the form of a randomized controlled trial
with a cross-over design. The study started with a lead-in period
of 2 wk, during which the subjects were requested to consume a
relatively constant egg-free lacto-vegetarian diet, to make no
changes in the cooking medium, to avoid baked foods (because they
may contain eggs), and to maintain a relatively constant physical
activity.
After the lead-in period of 2 wk, the
subjects were randomly divided into two groups, group I (n = 8;
4 female; 4 lactovegetarians, 3 lacto-ovo-vegetarians, 1 non-vegetarian)
and Group II (n = 10; 3 male, 7 female; 5 lactovegetarians, 3
lacto-ovo-vegetarian) and Group II (n = 10; 3 male, 7 female;
5 lactovegetarians, 3 lacto-ovo-vegetarians, 2 non-vegetarian).
Group I consumed for 8 wk one boiled egg every day but otherwise
the diet continued to be as during the lead-in period (experimental
treatment). Group II consumed for 8 wk a diet similar to that
during the lead-in period (control). At the end of the 8-wk dietary
period, the two groups crossed over for a period of 8 wk (Fig.
1).
Fig.1
click for full view |
Fasting
blood samples were collected at the beginning of the lead-in-period
(2 wk), the end of the lead-in period (0 wk), 4 wk, 8 wk, 12 wk
and 16 wk.
The
protocol of the study was approved by the Ethics Committee of
the All India Institute of Medical Sciences, and the volunteers
gave their informed written consent for participation in the study.
Diet
When
required by the study, the subjects had the boiled egg at any
meal of the day, usually at lunch. The eggs provided to the subjects
weighted about 50 g each, and their composition was as shown in
Table I. The subjects maintained a report card in which they made
a daily entry regarding taking, or not taking, the egg, and also
recorded any major changes in their diet or physical activity.
TABLE
I: Composition of the eggs used in the study.
|
Constituent
|
Amount
|
|
|
|
|
Protein
(g/100 g egg)
|
10.4
|
|
Carbohydrate
(g/100 g egg)
|
2.76
|
|
Fat
(g/100 g egg)
|
11.62
|
|
Saturated
fatty acids (%)
|
32.62
|
|
Monounsaturated
fatty acids (%)
|
45.70
|
|
n-6
Polyunsaturated fatty acids (%)
|
45.56
|
|
n-3
Polyunsaturated fatty acids (%)
|
0.29
|
|
Cholesterol
(g/100 g egg)
|
600.00
|
|
Energy
(kcal/100 g egg)
|
155.78
|
Measurements
Serum
lipid profile was assessed from the mean of values obtained on
two consecutive days. The measurements included total cholesterol,
total triglycerides, HDL cholesterol and LDL cholesterol, which
were estimated using kits from Randox Laboratories Ltd., Ardmore,
U.K. Briefly, cholesterol or triglycerides in the sample were
oxidized enzymatically releasing hydrogen peroxide. Hydrogen peroxide,
in the presence of peroxidase interacts with 4-cholorophenol and
4-aminoantipyrene to yield quinoneimine, which can be measured
calorimetrically from absorbance at 546 nm. HDL cholesterol was
measured after precipitating LDL and VLDL by addition of phosphototungstic
acid in the presence of magnesium ions. LDL was measured after
precipitating it with heparin at pH 5.04. The inter-assay and
within-assay variations were respectively 6.98% and 3.64% for
cholesterol, 13.85% and 3.02% for triglycerides, 11.77% and 2.74%
for HDL. VLDL cholesterol and total cholesterol: HDL cholesterol
ratio were calculated from the above measurements.
Statistical analysis
The
values of all outcome measures at –2 wk, 0 wk, 4 wk, 8 wk, 12
wk and 16 wk were first tabulated for the two groups separately.
There was no period effect on any of the parameters studies. Therefore
pooling the results from the two groups was considered valid.
Then the 16 wk values of Group I and 8 wk values of Group II were
pooled to get the control (no egg) values. This was considered
appropriate because these were the values based on antecedent
egg-free diet for 8 wk in Group I and for 10 wk in Group II. The
8 wk values of Group I and 16 wk values of Group II were pooled
to get the effect of the egg treatment for 8 wk (fig. 1). The
‘no egg’ values were compared with ‘egg values’ by Student’s t-test
for paired observations. Similar pooling and comparisons were
also done for ‘no egg’ treatment with 4 wk of ‘egg’ treatment
to see the time course of changes, if any. A comparison was also
made to see the changes, if any, during the lead-in period. Since
0 wk values were compared with 4 wk as well as 8 wk values by
Student’s t-test, differences were considered significant if P<0.05/2,
i.e. P<0.025, using Bon Ferroni’s correction (19).
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RESULTS
The characteristics of subjects
are given in Table II. There was no significant difference between
the subjects in the two groups with respect to the characteristics
shown in the Table as well as in terms of the serum lipid profile.
As observed in the table, the cholesterol intake increased by
300 mg/d during the experimental (egg) period as compared to the
control period.
TABLE
II : Characteristics of subjects.
|
|
Group
I
|
Group
II
|
|
|
|
|
|
Age
(years)
|
24.0±5.71
|
23.7±2.26
|
|
Weight
(kg)
|
|
|
|
At
–2 wk
|
57.31±7.95
|
55.70±6.15
|
|
At
16 wk
|
57.38±7.23
|
55.55±6.12
|
|
Height
(m
|
|
|
|
BMI
(kg/m2)
|
|
|
|
At
– 2 wk
|
20.68±1.26
|
20.73±1.81
|
|
At
16 wk
|
20.73±1.23
|
20.06±2.13
|
|
Haemoglobin
(g/100 mL)
|
11.78±1.23
|
12.06±2.13
|
|
Fasting
plasma
|
|
|
|
Glucose
(mg/100 mL)
|
96.61±5.61
|
86.02±9.82
|
|
Cholesterol
intake (mg/d)
|
|
|
|
Control
period
|
50.97±35.42
|
48.95±26.32
|
|
Egg
period
|
350.97±35.42
|
348.95±26.32
|
All
values are mean ± S. D
TABLE
III: Serum lipid profile after control and experimental treatment.
|
Parameter
|
After
control
(egg-free
diet) treatment
|
After
experimental
(egg
consumption) treatment
|
|
|
|
4
wk
|
8
wk
|
|
Total
cholesterol (mg/dL)
|
175.99±29.27
|
186.05±29.28
|
184.77±31.22
|
|
LDL
cholesterol mg/dL)
|
94.18±36.63
|
98.66±24.80
|
100.18±29.77
|
|
HDL
cholesterol (mg/dL)
|
60.63±8.03
|
60.20±5.87
|
57.89±9.09
|
|
Total
cholesterol/HDL cholesterol ratio
|
2.97±0.71
|
3.14±0.74
|
3.28±0.80
|
|
VLDL
cholesterol (mg/dL)
|
24.82±8.02
|
27.78±10.02
|
28.29±7.48
|
|
Triglycerides
(mg/dL)
|
104.99±27.78
|
113.44±32.32
|
114.23±30.54
|
All
values are Mean ± S. D
*P<0.025
Egg
was the major source of dietary cholesterol during the experimental
period, and milk and milk products its only source during the
control period. There was no significant change in body weight
or body mass indeed (BMI) during the course of the study.
Since
there was no period effect on any of the parameters studied, the
results from the two groups were pooled. The lipid profile at
the end of the control (egg-free) dietary period and that after
4 wk and 8 wk of experimental treatment (egg consumption) has
been shown in Table III. Serum total cholesterol after 4 wk of
egg consumption was significantly higher than the control value.
No other value after 4 wk or 8 wk of egg consumption from the
corresponding control value.
Scrutiny
of individual responses revealed that four of the subjects had
a considerable increase in serum total cholesterol, ranging from
+ 19.3% to +34.6% and five of the subjects had a rise in serum
LDL cholesterol ranging from + 13.0% to + 72.8% after 8 wk of
egg consumption. Two subjects were common to these groups. Thus
seven subjects out of 18 (38.9%) had an appreciable rise in total
cholesterol or LDL cholesterol, or both, after 8 wk of egg consumption.
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In
the present study, consumption of one boiled egg per day for 8
wk led to a serum lipid profile not significantly different from
that resulting from consumption of an egg-free diet for 8 wk.
Lack of effect of egg consumption is consistent with several previous
studies on populations with various ethnic backgrounds (9-11).
However, there are also several studies in which an increase in
dietary cholesterol intake through egg consumption or otherwise
has led to an increase in serum cholesterol (6-8). This may be
partly related to the amount of dietary cholesterol. Some of the
studies in which a positive relationship has been observed between
dietary cholesterol and serum cholesterol have given 600-1500
mg dietary cholesterol per day (5, 20). An even more important
factor responsible for the conflicting results from various studies
seems to be the duration of the study. In general, studies based
on 4 wk or less of egg consumption have shown an increase in serum
cholesterol (5-8, 20) whereas longer studies involving 8 wk or
more of egg consumption failed to find any significant rise in
serum cholesterol (9-11). Our dietary period was 8 wk but we studied
serum lipids also at the mid-point of the dietary period. We also
observed a significant rise in total serum cholesterol at 4 wk.
Thus it seems that the homeostatic mechanisms which regulate cholesterol
biosynthesis in response in changes in dietary cholesterol intake
(5) take about 8 wk to be fully effective.
Although
the average serum cholesterol level did not show any significant
change after 8 wk of egg consumption, we observed considerable
individual variation in response. The phenomenon of hypo- and
hyper-responders is well known (15), and seems to have a genetic
basis (16).
Our
study has been done on healthy young volunteers on a vegetarian
diet. Similar studies on Indian populations are required also
on older hyperlipidaemic subjects whose dietary pattern may be
different. Therefore the present study itself cannot be used for
making general recommendations. But it suggests that, like other
populations, Indians also show marked individual variations in
response. Ascertaining the response of an individual to egg consumption
is therefore important before making egg a regular item of the
diet.
ACKNOWLEDGEMENTS
We
could like to thank the Indian Council of Medical Research for
financial support (ID No. 2000-00460). We are grateful to the
volunteers for their cooperation. Ms. Promila Kapoor and Ms. Suman
Thakur provided able technical assistance, and Mr. Satish Sachdeva
provided efficient secretarial assistance.
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