Context Little prospective long-term information is available on the effect
of a ketogenic diet on plasma lipoproteins in children with difficult-to-control
seizures.
Objective To determine the effect in children with intractable seizures of a high-fat
ketogenic diet on plasma levels of the major apolipoprotein B (apoB)–containing
lipoproteins, low-density lipoprotein (LDL) and very LDL (VLDL); and the major
apolipoprotein A-I (apoA-I)–containing lipoprotein, high-density lipoprotein
(HDL).
Design, Setting, and Patients A 6-month prospective cohort study of 141 children (mean [SD] age, 5.2
[3.8] years for 70 boys and 6.1 [4.4] years for 71 girls) with difficult-to-treat
seizures who were hospitalized for initiation of a high-fat ketogenic diet
and followed up as outpatients. This cohort constituted a subgroup of the
371 patients accepted into the ketogenic diet program between 1994 and 2001.
A subset of the cohort was also studied after 12 (n = 59) and 24 (n = 27)
months.
Intervention A ketogenic diet consisting of a high ratio of fat to carbohydrate and
protein combined (4:1 [n = 102], 3.5:1 [n = 7], or 3:1 [n = 32]). After diet
initiation, the calories and ratio were adjusted to maintain ideal body weight
for height and maximal urinary ketosis for seizure control.
Main Outcome Measures Differences at baseline and 6-month follow-up for levels of total, VLDL,
LDL, HDL, and non-HDL cholesterol; triglycerides; total apoB; and apoA-I.
Results At 6 months, the high-fat ketogenic diet significantly increased the
mean plasma levels of total (58 mg/dL [1.50 mmol/L]), LDL (50 mg/dL [1.30
mmol/L]), VLDL (8 mg/dL [0.21 mmol/L]), and non-HDL cholesterol (63 mg/dL
[1.63 mmol/L]) (P<.001 vs baseline for each);
triglycerides (58 mg/dL [0.66 mmol/L]) (P<.001);
and total apoB (49 mg/dL) (P<.001). Mean HDL cholesterol
decreased significantly (P<.001), although apoA-I
increased (4 mg/dL) (P = .23). Significant but less
marked changes persisted in children observed after 12 and 24 months.
Conclusions A high-fat ketogenic diet produced significant increases in the atherogenic
apoB–containing lipoproteins and a decrease in the antiatherogenic HDL
cholesterol. Further studies are necessary to determine if such a diet adversely
affects endothelial vascular function and promotes inflammation and formation
of atherosclerotic lesions.
The ketogenic diet is a high-fat low-carbohydrate adequate protein diet
first developed 8 decades ago for the management of difficult-to-control seizures
in children.1 Recent studies have documented
the short-term and long-term benefits of this diet in improving seizure control.2-4 An evaluation by the
Blue Cross/Blue Shield Technology Center reported5 "
. . . the diet's effectiveness in providing seizure control for children with
difficult-to-control seizures has remained as good, or better than any of
the newer medications." Although the mechanisms by which the diet decreases
seizures remain unknown,6,7 the
level of ketosis produced by the incomplete oxidation of fats when carbohydrates
are in short supply appears to play a critical role in the effectiveness of
this diet.1
The classic ketogenic diet consists of a 4:1 ratio of fat to carbohydrate
and protein combined.3 Because there are 9
calories/g of fat compared with 4 calories/g of either carbohydrate or protein,
the fat content of such a ketogenic diet provides 90% of the child's calorie
intake. Carbohydrates are severely restricted and are usually less than 10
g/d. Younger rapidly growing children and adolescents are often started in
treatment by receiving a less stringent 3:1 ratio of fat to carbohydrate plus
protein to allow sufficient protein (1-1.5 g/kg per day) for growth. Growth
while receiving the ketogenic diet remains within the normal range.8 Calories are calculated at about 80% of estimated
dietary requirements. After diet initiation, the calories and ratio are adjusted
to maintain the child's ideal body weight for height and maximal urinary ketosis
for seizure control.9
Some10,11 but not all12,13 previous studies indicated that a
ketogenic diet produced significant increases in the plasma levels of total
cholesterol and triglycerides. Few data are available concerning the effects
of a ketogenic diet on the plasma levels of the major apolipoprotein B (apoB)–containing
lipoproteins, low-density lipoprotein (LDL) and very LDL (VLDL); and the major
apolipoprotein A-I (apoA-I)–containing lipoprotein, high-density lipoprotein
(HDL). In 1 report, no significant effect on the plasma VLDL, LDL, and HDL
cholesterol levels was found in 24 children treated with the classic 4:1 ketogenic
diet for 3 weeks.12 Whether a very high-fat
diet can induce elevated levels of the triglyceride-rich VLDL and the cholesterol-rich
LDL but lower levels of HDL cholesterol is an important question, because
each of these effects predicts the development of early atherosclerotic lesions,
fatty streaks, and fibrous plaques in the aorta and coronary arteries in adolescents
and young adults.14,15
This prospective study evaluated the effects of a ketogenic diet on
plasma lipoproteins in children treated with a ketogenic diet for intractable
seizures. The objectives were to determine the effect of a ketogenic diet
on the plasma levels of VLDL, LDL, and HDL cholesterol, and their major apolipoproteins,
apoB and apoA-I; and the proportion of children who developed either elevated
total and LDL cholesterol or increased triglyceride levels, or low HDL cholesterol
by using guidelines from the National Cholesterol Education Program (NCEP)
Report of the Expert Panel on Blood Cholesterol Levels in Children and Adolescents.16
A cohort of 371 patients who initiated the ketogenic diet in an attempt
to control their seizures between 1994 and 2001 comprised the study population.2 Of the 230 patients not in this study, 86 discontinued
the ketogenic diet because of ineffective seizure control (n = 37), intercurrent
illness (n = 12), diet too restrictive (n = 25), planned discontinuation (n
= 4), and other (n = 8). An additional 144 patients were not included because
of missing samples at baseline or at 6 months (plus or minus 1 month). Thus,
141 (38%) of 371 patients were included in this study. There were no other
sources of potential bias in the selection among the patients receiving a
ketogenic diet.
The 141 children (boys, n = 70; girls, n = 71) were between the ages
of 4 months and 20 years (Table 1)
and met the following criteria for entry into this study: (1) satisfied the
requirements for inpatient admission to the Johns Hopkins ketogenic diet program,
as previously published2 (briefly, infants,
children, or adolescents had to have a minimum of 2 seizures per week and
must have not responded to at least 2 medications); (2) admitted to the Johns
Hopkins Hospital for initiation of the ketogenic diet and managed according
to a preset protocol2; and (3) a blood sample
obtained after an overnight fast for a lipid and lipoprotein profile, both
at the time of initiation in the ketogenic diet, and 6 months (plus or minus
1 month) after starting the diet. The mean (SD) age was 5.2 (3.8) years for
the 70 boys and 6.1 (4.4) years for the 71 girls.
Of the 141 patients who met the above criteria, follow-up fasting blood
specimens were also obtained for 59 patients at 1 year of follow-up (12 months
plus or minus 1 month) and for 27 patients at 2 years of follow-up (24 months
plus or minus 1 month). The Johns Hopkins Joint Committee on Clinical Investigation
approved the project. Parents of all children who initiated the ketogenic
diet program signed an approved informed consent to collect, analyze, and
report the data.
The patients fasted for 48 hours and then the diet was introduced with
one third of the calculated diet as eggnog for 3 meals, followed up by two
thirds of the calories as eggnog for the next 3 meals. The full calculated
diet was then begun, and the child was discharged to home. At the onset of
the diet, 102 of the patients received a 4:1 ratio of fat to carbohydrate
plus protein, 7 received a 3.5:1 ratio, and 32 received a 3:1 ratio (Table 1). Patients were followed up by
telephone and the diet adjusted depending on the level of ketosis and the
degree of seizure control. The caloric intake was adjusted based on the child's
weight gain or loss to achieve and maintain an ideal body weight for height.
Dietary compliance was assessed by using a standardized Ketogenic Diet Nutrition
Consult form developed by the Johns Hopkins Pediatric Epilepsy Center. This
was used to monitor medical/nutritional status and seizure control, and to
adjust the diet appropriately.
Measurement of Plasma Lipids, Lipoproteins, and Apolipoproteins
Plasma cholesterol and triglyceride levels were measured by enzymatic/colorimetric
methods as previously described.17 The plasma
level of HDL cholesterol was determined in the supernatant following precipitation
of the apoB-containing lipoproteins with heparin manganese.17 The
LDL cholesterol level was calculated by using the Friedewald equation18 in samples with a triglyceride level of less than
400 mg/dL (<4.52 mmol/L). The VLDL cholesterol level was calculated by
dividing the total triglyceride level by 5.18 The
non-HDL cholesterol level was calculated by subtracting the HDL cholesterol
from the total cholesterol. Plasma levels of total apoB and apoA-I were measured
by using immunoturbimetric methods as previously described.19 The
procedures used to ensure laboratory quality control have been reported previously
in detail.19
Differences between baseline and the 6-month follow-up were assessed
by using a general linear model to fit each outcome variable as a function
of the independent variable. This regression technique uses the general estimating
equation method developed to account for multiple observations from the same
subject.20 Through an adjustment of the variance-covariance
matrix, the correlation that is inherent among repeated measures is controlled.21 The analytic plan focused on first modeling changes
in plasma levels of lipids, lipoproteins, and apolipoproteins by using a univariate
approach whereby the individual contributions of each independent variable
could be assessed. In accomplishing this step, the most parsimonious model
could be constructed to account for the contribution of each factor. Given
the exploratory nature of this step in the analysis, overall type I error
was not adjusted for multiple comparisons; however, within each independent
variable, comparisons across strata and time were adjusted by using Bonferonni
correction to account for multiple comparisons.
The independent variables included in the univariate analysis were sex,
age (4 months to 3 years, >3 years to 7 years, >7 years to 10 years, and >10
years), weight (by age- and sex-specific percentiles: <50th, 50th, and
>50th), and the ratio of fat to protein plus carbohydrate in the ketogenic
diet (3:1, 3.5:1, and 4:1). The dependent variables included the plasma levels
of total cholesterol, VLDL cholesterol, LDL cholesterol, HDL cholesterol,
non-HDL cholesterol, triglycerides, total apoB, apoA-I, and the ratios of
total cholesterol to HDL cholesterol, LDL to HDL cholesterol, LDL cholesterol
to apoB, HDL cholesterol to apoA-l, and apoB to apoA-l.
Once the influence of each independent variable was ascertained, the
second step of the analytic plan focused on the construction of a multivariate
model that could best explain changes in plasma measures from baseline to
6 months of receiving the ketogenic diet. To accomplish this, the general
linear model was then extended to a multivariate model where the effect of
multiple independent variables on the outcome variable of interest was assessed
simultaneously. The use of multivariate regression techniques allows for an
experiment-wise type I error level of .05. The outcome of interest was the
change between these 2 points (baseline and 6 months receiving the diet) with
adjustment made for the baseline plasma measure. The distributions of all
dependent variables were assessed for normality based on tests of the coefficient
of skewness and of kurtosis.22 When appropriate,
data transformations were made to approximate normality. Ratio data, such
as total cholesterol and HDL cholesterol, were transformed by using log-transformation
to approximate normality.
Statistical analyses were performed by using SAS version 8.02 (SAS Institute,
Cary, NC). Estimates of statistical power based on the available sample size
were made by using PASS 2002 (NCSS Statistical Software, Kaysville, Utah). P<.05 was considered statistically significant.
Characteristics of the Study Population
The clinical characteristics of the study population are summarized
in Table 1. The patients ranged
in age from 4 months to 20 years. The number of boys and girls was almost
identical (n = 70 and n = 71, respectively). Sixty-six percent of the study
population was 4 months to 7 years of age. The percentages of those patients
below, at, or above the median weight for age were as expected.
The percentage distribution of the ratios of fat to carbohydrate plus
protein in the ketogenic diet in the study population is also summarized in Table 1. Most patients (72.3%) received
a treatment ratio of 4:1. The infant/children and adolescent groups had the
greatest numbers receiving a 3:1 or 3.5:1 treatment ratio, consistent with
the requirements of more protein during these periods of more rapid growth.
The seizure types at the onset of the ketogenic diet were myoclonic/atonic
or infantile spasms (n = 68), absence/atypical absence (n = 23), tonic/clonic/tonic-clonic
(n = 22), complex/simple partial (n = 21), unclassified (n = 4), and no seizures
at diet onset (n = 3). After 6 months of receiving a ketogenic diet, 93 patients
(66%) were at least 50% improved with 17 seizure-free, 39 were less than 50%
improved, and 9 patients were missing the seizure control data.
Influence of Independent Variables on Dependent Variables
There were no significant differences at baseline or 6-month follow-up
for sex, age, weight for age, or ratio of fat to carbohydrate plus protein
in the 3 dietary groups for the plasma levels of total cholesterol, LDL cholesterol,
non-HDL cholesterol, or total apoB.
There were no significant differences at baseline for VLDL cholesterol
level between the various age, sex, weight, and dietary groups. However, at
follow-up, the mean (SE) VLDL cholesterol level was significantly higher in
the 0- to 3-year-old age group than among children older than 10 years (29.98
[1.76] mg/dL [0.78 {0.05} mmol/L] vs 19.02 [1.30] mg/dL [0.49 {0.03} mmol/L], P = .007), and in those with a weight of more than 50th
percentile (24.75 [1.53] mg/dL [0.64 {0.04} mmol/L] vs 18.62 [0.98] mg/dL
[0.48 {0.03} mmol/L], P = .02) compared with children
in the 50th percentile or less. There was a small significant effect of age
and weight on the plasma triglyceride levels at baseline but not at the 6-month
follow-up.
For HDL cholesterol, the mean (SE) levels were significantly higher
at baseline in the boys than in the girls (58.19 [2.07] mg/dL [1.51 {0.05}
mmol/L] vs 52.88 [1.66] mg/dL [1.37 {0.04} mmol/L], P =
.04), in the 3- to 7-year-old and 7- to 10-year-old age groups (59.63 [2.30]
mg/dL [1.54 {0.06} mmol/L], P = .046 and 60.28 [2.86]
mg/dL [1.56 {0.07} mmol/L], P = .047 vs 47.73 [2.11]
mg/dL [1.24 {0.05} mmol/L], respectively) vs those children less than 3 years,
and in those receiving a 4:1 ketogenic diet (57.81 [2.11] mg/dL [1.50 {0.05}
mmol/L] vs 50.50 [2.27] mg/dL [1.31 {0.06} mmol/L], P =
.007) vs those receiving a 3.5:1 or 3:1 diet. These differences at baseline
in HDL cholesterol level were no longer significant after 6 months with the
patients receiving the ketogenic diet. However, at 6 months, the mean HDL
cholesterol level was significantly lower (40.61 [1.62] mg/dL [1.05 {0.04}
mmol/L], P = .008) in the 0- to 3-year-old age group
than in the older age groups. The mean plasma level of apoA-I, the major protein
of HDL, was significantly higher at both baseline (152.14 [3.30] mg/dL, P = .001) and 6-month follow-up (156.5 [3.39] mg/dL, P = .03) in those patients receiving a 4:1 ketogenic diet
compared with those receiving a 3.5:1 or 3:1 diet.
There were no significant differences between the various age, sex,
weight, and ketogenic diet groups at baseline or 6-month follow-up for the
ratios of total cholesterol to HDL cholesterol or LDL to HDL cholesterol,
except that at baseline those patients in the 4:1 ketogenic diet group had
a higher ratio of LDL to HDL cholesterol (2.19 [0.22] vs 1.82 [0.07], P = .008) than those patients in a 3.5:1 or 3:1 diet group.
The ratio of LDL cholesterol to apoB was significantly higher at baseline
in the 7- to 10-year-old age group (1.22 [0.04] vs 1.09 [0.03], P = .03) than those children in the less than 3-year-old group but
this difference was not present at the 6-month follow-up. At baseline, the
ratio of HDL cholesterol to apoA-I was significantly higher in the 3- to 7-year-old
age group (0.39 [0.01] vs 0.36 [0.01], P = .03) vs
the less than 3-year-old group but significantly lower in those patients with
a weight of more than 50th percentile (0.37 [0.01] vs 0.41 [0.02], P = .03) vs those with a weight of 50th percentile or less; neither
of these differences was present at the 6-month follow-up. At the 6-month
follow-up, the youngest group had a significantly lower ratio of HDL cholesterol
to apoA-I (0.28 [0.01] vs 0.32 [0.01], P = .007)
than in the 10-year-old or higher group. The ratio of apoB to apoA-I was significantly
higher at baseline in the girls than in the boys (0.65 [0.02] vs 0.57 [0.02], P = .01) but was significantly lower in the 7- to 10-year-old
group (0.55 [0.03] vs 0.69 [0.03], P = .049) vs the
less than 3-year-old group. These differences were not present after 6 months
of the ketogenic diet.
Baseline Levels of Plasma Lipid, Lipoprotein, and Apolipoprotein Levels
The baseline levels of plasma lipids, lipoproteins, and apolipoproteins
for the study population are shown in Table
2. The mean baseline levels of LDL and HDL cholesterol are similar
to the mean values for this age group in the Lipid Research Clinics population.23 However, the mean baseline triglyceride level was
higher than the healthy population mean of approximately 50 to 60 mg/dL (0.57
to 0.58 mmol/L), and the mean was close to the 95th percentile of 100 mg/dL
(1.13 mmol/L) in the 1- to 10-year-old healthy population. This was accompanied
by a higher mean level of VLDL cholesterol at baseline, leading to a borderline
elevated level of total cholesterol. ApoB, the major protein of VLDL and LDL,
had a higher mean at baseline in this study population compared with the National
Health and Nutrition Examination Survey pediatric population.19 At
baseline, the mean value for non-HDL cholesterol was similar to the pediatric
population based on values available from the Bogalusa Heart Study.24 The mean level of apoA-I was somewhat higher than
that found in the healthy National Health and Nutrition Examination Survey
population.19
The baseline mean levels for the ratios of total cholesterol to HDL
cholesterol, LDL to HDL cholesterol, LDL cholesterol to apoB, HDL cholesterol
to apoA-I, and apoB to apoA-I are shown in Table 3. These ratios are similar to those reported in healthy pediatric
populations, with the exception of the mean ratio of LDL cholesterol to apoB,
which was lower at baseline in this study population than in the reference
populations.25,26 A low ratio
of LDL cholesterol to apoB suggests the presence of small dense LDL particles,
a finding consistent with the higher baseline triglyceride and VLDL cholesterol
levels in this study population.
Effect of a Ketogenic Diet on the Plasma Levels of Lipids, Lipoproteins,
and Apolipoproteins
After 6 months of receiving the ketogenic diet, the mean LDL cholesterol
level increased 50 mg/dL (1.30 mmol/L), reflecting a mean shift of almost
2 SDs (Table 2). The mean LDL
cholesterol level of 148 mg/dL (3.83 mmol/L) after the ketogenic diet reflects
a value that is considerably higher than the 95th percentile (130 mg/dL [3.37
mmol/L]) for this age group. The mean total cholesterol level also increased
markedly to 232 mg/dL (6.01 mmol/L), 2 SDs higher than the mean for a reference
healthy population, and notably higher than the 95th percentile of approximately
200 mg/dL (5.18 mmol/L), a level considered to be high by the NCEP pediatric
panel.16
The difference in the mean triglyceride level after 6 months of receiving
the ketogenic diet was also significantly higher compared with baseline. The
mean value of 154 mg/dL (1.74 mmol/L) well exceeded the approximate 95th percentile
for triglycerides in the first decade (100 mg/dL [1.13 mmol/L]) and the second
decade (130 mg/dL [1.47 mmol/L]) of life. The mean difference between the
baseline and follow-up VLDL levels was also significant and in proportion
to that expected by the increase in the triglyceride levels. Measuring the
non-HDL cholesterol and the apoB levels also assessed the change in the apoB-containing
lipoproteins. Both of these parameters also increased significantly to mean
levels that exceeded the 95th percentiles reported in reference healthy pediatric
populations.19,24 A sizable proportion
of the study population was now both hypertriglyceridemic and hypercholesterolemic.
The difference in the mean level of HDL cholesterol between baseline
and 6 months in patients receiving the ketogenic diet was –7 mg/dL (–0.18
mmol/L) (Table 2). This significant
shift toward lower HDL cholesterol values increased notably the number of
children with low (<35 mg/dL [0.91 mmol/L]) or borderline low (35 to 45
mg/dL [0.91 to 1.17 mmol/L]) levels. However, apoA-I, the major protein of
HDL cholesterol, did not change significantly between baseline and after 6
months, indicating that the number of HDL particles did not decrease on the
ketogenic diet but that the composition of HDL had, containing less cholesterol
in its core.
Effect of a Ketogenic Diet on Lipid Ratios
Compared with baseline, the ratios of total to HDL cholesterol, LDL
to HDL cholesterol, and apoB to apoA-I all increased significantly after 6
months of receiving a ketogenic diet (Table
3). Each of these ratios provides an assessment of the relative
amounts of the apoB-containing lipoproteins to the apoA-I–containing
lipoproteins. The greatest increase occurred in the ratio of apoB to apoA-I,
which increased 2 SDs from the mean at baseline. The increases in the ratios
of total to HDL cholesterol and LDL to HDL cholesterol were between 1 and
2 SDs higher than the means at baseline. Conversely, the ratio of HDL cholesterol
to apoA-I decreased significantly, indicating that the HDL particles contained
less cholesterol relative to apoA-I, a change that is likely to reflect an
exchange of cholesteryl esters from the core of HDL cholesterol for triglycerides
from VLDL cholesterol. The ratio of LDL cholesterol to apoB did not change
significantly after receiving the ketogenic diet; this might reflect the already
low ratio present at baseline.
Effect of Ketogenic Diet on the Development of Dyslipidemia in Children
We next determined the proportion of patients who developed high or
borderline high levels of total cholesterol and LDL cholesterol (Figure 1), total triglyceride levels (Figure 2), or low or borderline low levels
of HDL cholesterol (Figure 1) after
6 months by using the definitions of the NCEP pediatric panel.16
At baseline, 75% of the children had acceptable levels of LDL cholesterol
(<110 mg/dL [<2.85 mmol/L]), a proportion similar to a reference healthy
population (Figure 1). However,
11% had borderline elevated LDL cholesterol levels (110 to 129 mg/dL [2.85
to 3.34 mmol/L]) and 14% had elevated levels; therefore, a higher proportion
had elevated levels at baseline compared with approximately 5% that were expected
to be elevated in a healthy pediatric population. After 6 months of receiving
the ketogenic diet, 53% had elevated LDL cholesterol levels and only 28% were
in the acceptable range.
For total cholesterol, 22% had elevated levels (≥200 mg/dL [≥5.18
mmol/L]) at baseline, 27% had borderline elevated levels (170-199 mg/dL [4.40-5.15
mmol/L]), and only 51% were in the acceptable range (Figure 1). The greater shift toward higher total cholesterol levels
than LDL cholesterol levels at baseline was because of the higher levels of
VLDL cholesterol. After 6 months of the ketogenic diet, 61% of the study population
had high cholesterol levels, 17% were borderline high, and only 22% remained
in the acceptable range.
At baseline, 75% of the study population had acceptable (>45 mg/dL [>1.17
mmol/L]) HDL cholesterol levels, a proportion similar to that found in reference
populations23; 18% had borderline low (35-45
mg/dL [0.91-1.17 mmol/L]) levels, and approximately 6% had low (<35 mg/dL
[<0.91 mmol/L]) HDL cholesterol levels16 (Figure 1). After 6 months receiving a ketogenic
diet, 16% developed low HDL cholesterol levels, 33% were borderline low, and
only 51% were in the acceptable range.
The cut points for total triglyceride levels recommended by the NCEP
pediatric panel differ between the first and second decades (Figure 2).16 For the younger children,
21% had high (≥100 mg/dL [1.13 mmol/L]) triglyceride levels at baseline,
33% had borderline high levels, and 46% had acceptable levels. After 6 months
of the ketogenic diet, 65% were hypertriglyceridemic, 21% had borderline high
triglyceride levels, and only 14% had acceptable levels. In the older children
aged 10 to 19 years, 22% had elevated (≥130 mg/dL [1.47 mmol/L]) triglyceride
levels at baseline, a proportion similar to the younger children. However,
a higher proportion (62%) of the older children had acceptable levels at baseline,
and fewer (16%) had borderline high elevated levels. There was only a small
increase in the number of older children with hypertriglyceridemia, but the
proportion (27%) of those with borderline high levels increased, while those
(46%) with acceptable levels decreased.
Long-term Effect of the Ketogenic Diet on Plasma Lipid and Lipoprotein
Levels
We next examined whether the effects of the ketogenic diet persisted
on follow-up of the patients receiving this diet for up to 24 months (Figure 3). The significantly higher mean
plasma levels of total cholesterol and LDL cholesterol observed after 6 months
remained significantly higher at both 12 and 24 months of follow-up. The mean
levels of total and LDL cholesterol were lower after 12 and 24 months of the
ketogenic diet than after 6 months but remained higher than the cut points
used for high values. A similar pattern was observed for plasma triglyceride
levels, although the higher value at 24 months compared with baseline was
not statistically significant. The lower mean level of HDL cholesterol observed
after 6 months remained significantly lower at both 12 and 24 months of follow-up.
The major finding of this study was the marked increase in the apoB-containing
lipoproteins, VLDL and LDL cholesterol, after 6 months of the ketogenic diet.
This was accompanied by both hypercholesterolemia and hypertriglyceridemia,
which were so extensive that only about 1 in 6 of the study population had
either a cholesterol or triglyceride level in the acceptable range for a pediatric
population. Although the influence of age, sex, weight, and ratio of fat to
carbohydrate plus protein in the diet was controlled for in the analyses,
the results of this study cannot be extrapolated to the general pediatric
population.
Our study group was also receiving a number of medications for seizure
control so diverse that it is not possible to determine the influence of each
drug and dosage combination with the baseline levels of plasma lipids, lipoproteins,
and apolipoproteins. Although it is possible that these seizure medications
may have produced higher baseline VLDL cholesterol and triglyceride levels
in this population, the mean LDL cholesterol level was similar to that found
in reference healthy populations.23 Also, the
liver function tests in this study population had no relationship to the baseline
lipid and lipoprotein levels (data not shown). The effect of the ketogenic
diet on the LDL cholesterol level (and other lipid and lipoprotein parameters)
was so marked that it is highly unlikely that such an effect is simply explained
by the special nature of this study population.
The magnitude of the changes also considerably exceeds those that might
be expected to occur with any laboratory drift with time. The elevation in
the LDL cholesterol level in response to the ketogenic diet was a general
characteristic of this study population and occurred independently of the
baseline LDL cholesterol level or of the degree of seizure control (data not
shown). Only 10 boys and 15 girls did not manifest any increase in their LDL
cholesterol levels. The dramatic increase in the mean total cholesterol level
found empirically was close to that of 57.1 mg/dL (1.48 mmol/L), predicted
from a computer analysis by using Keys' and Hegsted's formulas of healthy
adults on a high-fat low-carbohydrate weight-maintaining energy intake.27
The ketogenic diet also had a marked effect on the HDL cholesterol level
in this population. At baseline, the distribution of the HDL cholesterol level
was similar to that expected for a pediatric population. After 6 months of
the ketogenic diet, only about half the study group had an HDL cholesterol
level in the acceptable range. It is not unusual for the HDL cholesterol level
to decrease when accompanied by an increase in VLDL and triglyceride levels,
an effect often related to an enhanced exchange of triglyceride from VLDL
cholesterol for cholesterol esters on HDL cholesterol by the cholesterol ester
transfer protein.28,29 The resultant
HDL particles and its apoA-I component appear to be removed more avidly by
the kidney, resulting in lower plasma levels of both HDL cholesterol and apoA-I,
and a decreased number of HDL particles.28,29 However,
we found that the apoA-I levels did not decrease with the ketogenic diet,
suggesting another effect of this diet on HDL cholesterol metabolism. For
example, the ketogenic diet may have increased the biosynthesis of apoA-I
or decreased the catabolism of the HDL particle, by mechanisms that are not
completely understood at this time.
The ratios of total to HDL cholesterol, LDL to HDL cholesterol, and
apoB to apoA-I have been used to assess the relative proportions of the apoB-containing
and apoA-I–containing lipoproteins. Higher ratios indicate an increase
in the risk of developing coronary artery disease in adults,28,29 of
early lesions of atherosclerosis in children and young adults,14,15 and
of parental history of myocardial infarction.30 Each
of these ratios increased significantly after the ketogenic diet primarily
because of the marked increase in the apoB-containing lipoproteins, a conclusion
further supported by the significant increase in the non-HDL cholesterol,
another indicator of the concentrations of the apoB-containing lipoproteins.
We used the ratio of LDL cholesterol to apoB to estimate the particle
composition of LDL. The increase in the apoB-containing particles observed
after the ketogenic diet might be because of increased hepatic biosynthesis
and secretion of VLDL cholesterol, leading to an enhanced exchange of triglycerides
in VLDL cholesterol for cholesteryl esters in the core of LDL cholesterol
by cholesterol ester transfer protein, followed up by hydrolysis of triglyceride
in LDL cholesterol by hepatic lipase and lipoprotein lipase, which produces
a cholesterol-depleted small dense LDL cholesterol.28,29 This
may be related to the known effect of ketone bodies to stimulate the biosynthesis
of fatty acids and triglycerides in the liver.1 Overproduction
of VLDL cholesterol and consequently of small dense LDL cholesterol is thus
accompanied by a low ratio of LDL cholesterol to apoB.
After 6 months of the ketogenic diet, the ratio of LDL cholesterol to
apoB did not change significantly. There are several possible explanations
for this observation. First, small dense LDL, as judged by a lower mean ratio
(1.1) of LDL cholesterol to apoB than that (1.2) found in healthy pediatric
populations,25,26 was present
at baseline consistent with the higher than average baseline VLDL cholesterol
and triglyceride levels. Second, it is possible that the ketogenic diet influenced
the activity of cholesterol ester transfer protein or of lipoprotein lipase
and/or hepatic lipase, impeding the formation of the small dense LDL particles.
Further studies of both the complete chemical composition of the apoB-containing
lipoproteins and of their metabolism will be necessary to understand the mechanisms
of action of the ketogenic diet in this population.
Our findings of the induction of marked dyslipidemia in children treated
with a ketogenic diet cannot be directly extrapolated to the use of a ketogenic
diet in children or adults for the purposes of weight reduction. In fact,
a major difference in our pediatric population is that the ketogenic diet
was designed to have sufficient calories to promote healthy growth and development.
Measurement of lipids and lipoproteins in healthy adults receiving a ketogenic
diet has usually been obtained while the patients are actively losing weight,31 and more information is needed to determine what
effect such a diet might have in adults who are consuming sufficient calories
to maintain their weight.27,32 A
high-protein but low-fat ketogenic diet has been used to treat adolescents
with morbid obesity.33 Such children lose weight
successfully during which time the plasma cholesterol, LDL cholesterol, and
HDL cholesterol levels fall significantly. Thus, it appears possible to use
a high-protein diet that is also low in fat to induce weight reduction. Further
studies are clearly indicated in both children and adults on the influence
of both high-fat and low-fat ketogenic diets on lipoprotein metabolism. Finally,
it is possible to use a high-fat ketogenic diet to treat intractable seizures
that uses medium-chain triglycerides rather than the classical long-chain
triglycerides.1,12,34 The
use of medium-chain triglycerides as the source of fat in such a ketogenic
diet appears to produce less of a dyslipidemia than the classic ketogenic
diet.1,12,34
Few serious complications because of the classic or modified ketogenic
diet have been reported. During the initial hospitalizations, short-term complications
include hypoglycemia, vomiting, diarrhea, dehydration, and refusal to eat.
Longer-term complications include irritability, lethargy, kidney stones, acidosis,
hyperuricemia, hypocalcemia, decreased amino acids, growth, and hypercholesterolemia.1-4,8 In
this study, we did not assess the influence of the ketogenic diet on the development
of early lesions of atherosclerosis in this population. It remains to be determined
whether such a ketogenic diet might induce thickening of the intima of the
carotid arteries or endothelial dysfunction, both of which appear to be accentuated
in young populations with elevated LDL cholesterol levels.35,36 The
marked dyslipidemia such as that induced by the ketogenic diet might also
produce an inflammatory response, as judged by highly sensitive C-reactive
protein, IL-8, and other inflammatory markers.37
Even if the ketogenic diet in this group is inflammatory and atherogenic,
this will most likely not preclude its use in intractable seizures in children.
Such treatment is highly effective and its anti-epileptic action may persist
long after the diet is discontinued. Most patients have stopped the ketogenic
diet after 2 years and the temporary use in childhood is unlikely to be associated
with a long-term increase in risk for coronary artery disease in adulthood.
Conversely, prolonged use of a hypercholesterolemic diet throughout childhood
and adolescence is likely to be atherogenic. For example, healthy young men
aged 20 to 25 years who had a cholesterol level of more than 210 mg/dL (5.44
mmol/L) had 5 times the rate of coronary artery disease 30 to 40 years later
than those who had a cholesterol level of less than 170 mg/dL (4.40 mmol/L).38
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