Particle size of LDL is affected by the National Cholesterol Education
Program (NCEP) step II diet in dyslipidaemic adolescents
Leila Azadbakht, Parvin Mirmiran, Mehdi Hedayati, Ahmad Esmaillzadeh, Nilufar Shiva and
Endocrine Research Center, Shaheed Beheshti University of Medical Sciences, P.O. Box 19395-4763, Tehran, Iran
(Received 6 March 2006 – Revised 8 August 2006 – Accepted 31 August 2006)
The objective was to determine the effects of the National Cholesterol Education Program (NCEP) step II diet on LDL and HDL particle size in
dyslipidaemic adolescents. Forty-four dyslipidaemic adolescents, aged 10–18 years, participated in this case-control study. The control diet was a
diet similar to what most Tehranian adolescents eat. NCEP step II diet was a diet with 30% of energy as total fat, less than 7% saturated fat, less
than 200mg cholesterol/d, less than 15% of energy as MUFA and less than 10% as PUFA. Lipoprotein particle size was the major outcome vari-
able, which was measured after 3 months of intervention. Comparison was made by the repeated measurement ANOVA. The mean BMI was 26·3
(SD 4·2) kg/m2. There were no significant changes in weight or physical activity in the two groups during the study. The NCEP diet resulted in
higher reduction in total cholesterol (213 (SD 4) v. 22 (SD 0·3) mg/dl, P,0·001) and LDL (29 (SD 2) v. 3 (SD 0·6) mg/dl, P,0·01), and higher
increase in size of the LDL (1·7 (SD 0·4) v. 0·1 (SD 0·4) nanometer, P,0·001). HDL particle size did not change significantly. NCEP step II diet
had a favourable effect on the LDL particle size. The related mechanism needs to be studied in future experimental designs.
National Cholesterol Education Program (NCEP): Adolescents: LDL: Lipoprotein particle size
Epidemiological, pathological, clinical and genetic studies
give evidence that atherosclerosis begins during childhood
and the serum lipid profile concentration in childhood is a
useful parameter in predicting adult dyslipoproteinaemia
(Boreham et al. 1993). It has been shown that mean choles-
terol concentrations in children of many countries have
increased in recent years (Plaza et al. 1989), and hypercho-
lesterolaemia in these children is approaching values found
in populations with high incidence of ischemic heart disease
(Akerblom et al. 1984). According to the results of the
Tehran Lipid and Glucose Study (Azizi et al. 2000), 22%
of the Iranian population of children and adolescents had
LDL cholestrol (LDL-C) values between 110 and 129mg/
dl and 17% had values $130mg/dl (Azizi et al. 2001).
Dietary modification to lower LDL-C is the primary strategy
for reducing CVD risk (Sempos et al. 1993). The National
Cholesterol Education Program (NCEP) step II recommends
reducing saturated fat intake to ,7% of energy in the
initial management of individuals with hypercholesterol-
aemia (Sempos et al. 1993). It has been mentioned that
the NCEP step II diet produced a desirable lipoprotein
response (Schaefer et al. 1995; Flynn et al. 1999). Of
course, different responses in other studies may be due to
positive family history of heart disease (Knutsen & Knutsen,
1991; Mietus-Snyder et al. 1993). It has been indicated that
the NCEP step II diet significantly decreases triacylglycerol-
rich lipoprotein and plasma apo AIV concentrations (Sun
et al. 2001). A significant decrease in HDL subfraction 2
cholestrol has also been mentioned in other studies (Wood
et al. 1991; Walden et al. 2000). Circulating LDL-C con-
centrations are a well-stablished risk factor for CHD, but
many individuals with CHD have normal or only slightly
elevated LDL-C (Kannel & Wilson, 1992). A relation
between plasma concentrations of small dense LDL and car-
otid intima media thickness has been shown in adults (Sko-
glund-Andersson et al. 1999) and the association of these
particles and cardiovascular risk factors has also been men-
tioned in children (Kojima et al. 2005). These associations
may be explained by atherogenicity of small dense LDL
due to increased plasma residence time, susceptibility to oxi-
dation and binding affinity for proteoglycans in the sub-
endothelial space (Lamarche et al. 1999). LDL particles
are heterogeneous with respect to size, density composition
and physicochemical properties (Lindgren et al. 1969; Chap-
man et al. 1988). Discrete subspecies of LDL, based on par-
ticle size, were first described over 20 years ago (Krauss &
Burke, 1982), but not enough attention has been given to
the influence of dietary habits of adolescents on the size
of lipoproteins. A significant proportion of the cardioprotec-
tive properties of HDL has been attributed to the largest and
less dense HDL subfraction 2 particles (Lamarche et al.
1997). Therefore, we aim to determine the effects of the
NCEP step II diet on LDL and HDL particle size in dys-
*Corresponding author: Dr Fereidoun Azizi, fax þ98 21 22402463, email Azizi@erc.ac.ir
Abbreviations: LDL-C, LDL cholestrol; NCEP, National Cholesterol Education Program.
British Journal of Nutrition (2007), 98, 134–139
q The Authors 2007
Subjects and methods
The present study includes adolescents aged 10–18 years
recruited from among participants of the Tehran Lipid and
Glucose Study (Azizi et al. 2000), with hypercholesterolaemia
(total cholesterol $170mg/dl and LDL-C $110mg/dl; Krum-
mel, et al. 2004). Each adolescent was asked to complete a
personal health and medical history questionnaire that served
as a screening tool. Patients were excluded if they had psy-
chiatric problems, took any medication affecting nutrient
metabolism, blood lipids and blood pressure, or any vitamin
and mineral supplements and antacids containing magnesium
or calcium. All the adolescents were evaluated for thyroid
function by the measurement of serum thyroid-stimulating
hormone (TSH), triiadothyronine (T3) and tetraiodothyronine
(T4) and those with any liver or renal diseases were excluded.
Sixty adolescents were assessed for eligibility in the study.
Fourteen subjects were ineligible because they did not meet
protocol criteria; forty-six patients were randomly assigned
to the two groups, the control and the NCEP step II diet,
Twenty-three of the assigned received a NCEP step II diet
and the other twenty-three received a control diet. Two adoles-
cents dropped out (one from the NCEP step II and one from
the control group). Other patients completed the study and
were included in the data analysis (forty-four patients). The
nutritionist who prescribed the diets had to be aware of the
group assignment. Laboratory staff were not aware of the
patients’ group assignments. Diets were offered according to
specific individualized programmes at the end of run-in (base-
line). The proposal of the present study was approved by the
research council of the Endocrine Research Center of Shaheed
Beheshti University of Medical Sciences and informed written
consent was obtained from each subject.
random number sequence.
The control group was not given a diet prescription and was
simply instructed to ‘eat as usual’. Their eating patterns
reflected the consumption of macronutrients, fruit, vegetables
and dairy products, typical of what many Tehranians eat
(carbohydrates, 50–60%; proteins, 15–20%; and total fat
,30%; most of fat specified as saturated, using two to
three servings of fruit, three servings of vegetables, one ser-
ving of dairy) (Mirmiran et al. 2005).
National Cholesterol Education Program step II diet
The NCEP step II diet had 30% of energy as total fat, less than
7% saturated fat, less than 200mg cholesterol/d, less than 15%
of energy as MUFAand less than 10% as PUFA.Table 1 shows
the nutrient and food groups consumed during the intervention
We determined the energy needs for each person indivi-
dually according to the equation from the Institute of Medi-
cine, Food & Nutrition Board (2002). Energy was calculated
to maintain the weight and weight loss or weight gain was
prevented. The patients were visited every 2 weeks, each
session for a patient being 45–60min. They were in touch
with the nutritionist by telephone every day; behavioural
and psychological counselling was offered. The nutritionist
explained the benefits of each diet for patients, emphasizing
that if they continued this diet, related metabolic abnormal-
ities could be controlled. The diets were individually pre-
scribed using a calorie count system and an exchange list
was given to each patient for exchanging food items and
counting calories. A nutritionist educated subjects on how
to use the exchange list and write food diaries. Every patient
had to bring his or her 3d diet records every 2 weeks and
the diaries were reviewed by study staff. A 7d menu cycle
with twenty-one meals at six energy levels (5021, 6276,
7531, 8368, 9623, 10460kJ (1200, 1500, 1800, 2000,
2300, 2500kcal)) was developed for each diet.
To maximize treatment fidelity, group discussions were
conducted monthly. In these sessions the food items that
should be eaten in each diet were emphasized and interven-
tion patients received education on reducing dietary energy
and diet compliance; patients were encouraged to follow
their diets. The investigators randomly took part in the
counselling sessions, controlling the messages that the nutri-
tionist was giving to each group and randomly questioning
the patients about their diets. The patients’ compliance
was assessed by analysing the three food record diaries
every 2 weeks and the attendance at meetings and monthly
Table 1. Nutrient content and food group servings of menus for the
control diet and the National Cholesterol Education Program (NCEP)
step II diet
NCEP step II
diet§ (n 22)
Protein (% of energy)
Total fat (% of energy)
Saturated fat (% of energy)
PUFA (% of energy)
MUFA (% of energy)
Carbohydrate (% of energy)
Food groups (servings/d)
Nut seeds and legumes
Poultry and fish
Fat and oils
Mean values were significantly different from those of the control diet: *P,0·04.
†Nutrient contents were calculated according to Nutritionist III version 7.0.
‡Diet similar to what most Tehranian adolescents usually eat.
§Diet contains 30% of energy as total fat, less than 7% saturated fat, less than
200mg cholesterol/d, less than 15% of energy as MUFA and less than 10% as
Diet and lipoproteins particle size135
After the 3 weeks of run-in, the clinical centre followed
patients every 2 weeks for the 3 months duration of interven-
tional feeding. We conducted a run-in to homogenize the con-
measurements were taken every 2 weeks during the 3
months of the study period except for blood tests, which
were repeated every 6 weeks, both in the control and NCEP
Participants were requested not to change their habitual
levels of physical activity for the duration of the study. To
compute intake at baseline and during intervention, 3d records
were used for each month. Nutrients were analysed by Nutri-
tionist III software, version 7.0 (N-Squared computing, Salem,
OR, USA), which was modified for Iranian foods.
and base ofdiets.The
Weight was measured using digital scales and recorded to the
nearest 0·1kg while the subjects were minimally clothed with-
out shoes. Height was measured using a tape measure with
subjects in a standing position, without shoes, while the
shoulders were in a normal state.
Twelve-hour fasting blood samples were collected in tubes
containing 0·1% EDTA and then centrifuged at 48C and 500g
for 10min to separate the plasma. Blood glucose was
measured on the day of blood collection by the enzymatic col-
orimetric method using glucose oxidase. Total cholesterol and
triacylglycerol concentrations were measured by commer-
cially available enzymatic reagents (Pars Azmoon, Tehran,
Iran) adapted to selectra autoanalyser. HDL cholesterol was
measured after precipitation of the apo B-containing lipopro-
teins with phosphotungistic acid. LDL-C was calculated
according to the Friedewald method (Friedewald et al.
1972). Inter- and intra-assay CV were 1·6 and 0·6% for tri-
acylglycerol. Blood pressure was measured twice after the par-
ticipants had sat for 15min (Azizi et al. 2002). Additional
covariate information regarding age, smoking habits (Azizi
et al. 2003), physical activity (Mirmiran et al. 2003), medical
history and current use of medications (Azizi et al. 2003) was
obtained using validated questionnaires, completed during the
screening and every 2 weeks, as mentioned earlier. Physical
activity was assessed by the Lipid Research Clinic question-
naire (Ainsworth et al. 1993).
Lipoprotein particle size was estimated by non-denaturing
polyacrylamide gradient gel electrophoresis using the Krauss
& Burke (1982) method. Briefly, 5ml serum were electrophor-
esed (PS-250; Hybaid, Lexington, KY, USA) for 24h at 125 V
(on 2–16% for LDL and 4–25% for HDL) polyacrylamide
gradient gels (90mmol/l Tris, 80mmol/l boric acid, 3mmol/l
EDTA, pH 8·3). Gels were pre-run at 125 V for 15min
prior to loading samples. The gel was fixed in 50% methanol
containing 10% acetic acid and Coomassie Brilliant Blue R-
250. The lane containing the calibrators (high-molecular
weight standards) was stained with Coomassie Brilliant Blue
R-250 and was destained with 20% methanol plus 9%
acetic acid; for lipid staining, gradient gels were stained
with 0·04% Oil Red 0 (Sigma) in 60% ethanol at 558C and
destained with 10% acetic acid and finally were scanned
using a Helena Gel scanner (Junior 24; Helena, Beaumont,
France). The non-denaturing polyacrylamide gradient gel elec-
trophoresis was done on the basis of the Krauss & Burke
(1982) method, and for calibration, in each run, the gels con-
tained the calibrators (high-molecular weight standards con-
taining thyroglobulin dimer, thyroglobulin and ferritin). So
on the basis of the standard curve the sample lipoprotein
sizes were determined. This method cannot determine the
size of HDL subfractions 3a, 3b and 3c; it can determine
HDL subfraction 2a and the majority of HDL subfraction
2b. It means HDL size relates to HDL subfraction 2b size in
the present study. Inter- and intra-assay CV were 8 and 5%
for LDL size and 6 and 7% for HDL size, respectively.
One-way ANOVA and x2tests were used to determine the sig-
nificance of any baseline differences between groups. We
compared data at base line, after 6 weeks and again after 12
weeks, separately for each diet, by using repeated measure-
ment ANOVA. Comparison between the changes of the two
groups also was assessed by between-group analyses in the
responses were evaluated in different weight status by Stu-
dent’s t test. The outcome measures were the changes in lipo-
protein particle size from the end of the run-in to the end of
the intervention. All analyses were conducted using SPSS ver-
sion 9.0 (SPSS Inc., Chicago, IL, USA).
The mean age and BMI of adolescents were 14·5 (SD 1·2) years
and 26·3 (SD 4·2) kg/m2. Table 2 shows the baseline character-
istics of the subjects. Baseline characteristics of these adoles-
cents did not differ significantly across the NCEP step II and
control diet groups. Table 3 shows the mean changes of the
serum lipids, lipoproteins and size of lipoproteins in the NCEP
step II diet and control diet, after 6 weeks and 12 weeks, com-
pared with baseline evaluations. Significant reductions in total
cholesterol (P,0·03) and LDL-C (P,0·02) were seen among
adolescents who consumed the NCEP step II diet. The NCEP
step II diet significantly increased LDL-C particle size. Fig. 1
shows the mean change (and 95% CI) of total cholesterol,
LDL, HDL, triacylglycerol and size of lipoproteins. The
NCEPstepIIdietresultedinhigher decrease intotalcholesterol
(213(SD 4)v.22(SD 0·3)mg/dl,P,0·001),LDL(29(SD 2)v.
LDL (1·7 (SD 0·4) v. 0·1 (SD 0·4) nm, P,0·001). Weight and
physical activity did not change significantly during the study
The prevalence of hypercholesterolaemia decreased signifi-
cantly (P,0·05) in the NCEP step II group (68% in NCEP
step II v. 100% in the control group) after 3 months. There
was no significant difference in lipid response or lipoprotein
particle size in normal and overweight children.
The results of the present study which was conducted in
hypercholesterolaemic adolescents showed that the NCEP
step II diet had a favourable effect on LDL particle size,
such that the mean diameter of LDL changed from the
L. Azadbakht et al. 136
medium to the large category. Therefore, dietary habit may
influence LDL size distribution. Other factors that are
suggested to explain as much as half of the variation in
LDL size distribution are genetic factors, adiposity and hor-
monal status (Greon et al. 1994; Krauss & Dreon, 1995;
Krauss, 2001). However, the present study discussed the role
of one of the environmental factors, diet. Cross-sectional
and dietary intervention studies reported an increase in small
dense LDL with increasing carbohydrate intake (Kratz et al.
2002) and a slight shift to smaller LDL particle size when
MUFA or PUFA replaced saturated fatty acids in healthy
men (Gill et al. 2003). Of course there were some differences
in the results of interventional and crossover studies, which
might be due to the different designs, or the kind of saturated
fatty acid intake (milk products, meat or poultry, etc.), and
levels of serum cholesterol. Sjogren et al. (2004) showed
that saturated fatty acid intake from milk products was associ-
ated with more favourable change in the LDL size profile.
However, mildly hypercholesterolaemic men responded with
an increase in smaller LDL subfractions when substituting
saturated fatty acids for MUFA. The results of Sjogren et al.
(2004) showed that dietary intervention on hypercholestero-
laemic subjects might be more effective. There are some
trials on the effect of diet on LDL particle size, however,
the present study, according to our knowledge, is the first
study to evaluate the influence of the NCEP step II diet on
lipoprotein size in hypercholesterolaemic adolescents. The
beneficial effects of the NCEP step II diet on lipoprotein
level had previously been shown, but the present study pre-
sents results regarding the size of lipoproteins.
Fibre content of the NCEP step II diet was higher than the
control diet which could explain its beneficial effects on lipid
concentrations and particle size to some extent.
Regarding HDL particle size, significant changes were not
seen after intervention, which may be due to lack of classifi-
cation for HDL and were judged based on only the mean
diameter of the HDL.
Regarding HDL concentration, the NCEP step II diet did not
Table 3. Cardiovascular risk factors of adolescents at baseline, after 6 weeks and after 12 weeks of intervention, by diet groups†
(Mean values and standard deviations)
National Cholesterol Education Program
step II diet
Baseline‡ After 6 weeks
weeks Baseline‡ After 6 weeks
Fasting blood sugar (mg/dl)
Total cholesterol (mg/dl)
LDL-C particle size (nm)
HDL-C particle size (nm)
HDL-C, HDL cholestrol; LDL-C, LDL cholestrol.
†For details of procedures and diets, see p. 000 and Table 1.
‡Baseline values are not significantly different among different diet groups.
§P values are resulted from repeated measurements ANOVA among baseline, after 6 weeks and after 12 weeks.
Table 2. Descriptive data of adolescents at baseline, according to the diet groups†
step II diet (n 22) Control diet (n 22)All (n 44)
Systolic blood pressure (mmHg)
Diastolic blood pressure (mmHg)
Physical activity (%)
Junior high school
†For details of diets, see Table 1.
Diet and lipoproteins particle size137
to some others (Wood et al. 1991; Walden et al. 2000). It seems
that different patterns of LDL size distributions and overall lipo-
results of various studies; of course itshould be kept in mind that
age factors in the present study (adolescence) might be the cause
NCEP step II diet may exert a favourable effect on the LDL par-
ticle size might be dependent on LDL concentrations. This
terolaemic subjects; however, since we were unable to separate
the subfractions of LDL and HDL and reported only the mean
diameter of lipoproteins, this was a limitation of the present
study. Another limitation was the inability to report the amount
of trans-fatty acid intake, in two groups separately, since trans-
fatty acid analysis was not included in the software analysis
sent study, actual foodwas not providedtosubjects and onlydiet
was prescribed. Using an appropriate control group, matched to
the intervention group for confounding variables, is the strength
of the present study.
It is concluded that a NCEP step II diet not only reduces the
serum LDL concentration of hypercholesterolaemic adoles-
cents but also has a favourable effect on the LDL particle
size distribution. The precise related mechanism needs to be
studied in future experimental designs.
We express our gratitude to all participants of the study and
also the staff of Endocrine Research Center for their efforts
in conducting the study.
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Diet and lipoproteins particle size 139