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School of Dietetics and Human Nutrition, Macdonald Campus of McGill University, Ste-Anne-de-Bellevue, Québec, Canada H9X 3V9;
*
Medlantic Research Institute, Washington, DC 20010–2933; and
Department of Medicine, University of Maryland, Baltimore, MD 21201–1524
2To whom correspondence should be addressed.
 |
ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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KEY WORDS: • weight loss • energy restriction • cholesterol • deuterium • humans
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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). Elevated circulating cholesterol concentrations, which
are also associated with risk of CVD (Gotto et al. 1990
,
Ulbricht and Southgate 1991
), are reduced by
weight loss (Dattilo and Kris-Etherton 1992
).
However, the mechanism through which weight loss reduces circulating
lipid levels remains to be identified.
Although body cholesterol pools receive up to two thirds of their input
from de novo synthesis (Rudney and Sexton 1986
),
cholesterogenesis has been largely overlooked as a potential factor in
CVD development in the context of obesity. The few studies focusing on
cholesterol metabolism have consistently observed cholesterol synthesis
rates in obese subjects to be greater than those in nonobese subjects
(Miettinen 1971
, Nestel et al. 1973
,
Ståhlberg et al. 1997
). Furthermore, energy restriction
decreases human endogenous cholesterol synthesis (Bennion and Grundy 1975
, Jones et al. 1988
,
Kudchodkar et al. 1977
). However, none of these studies
were of sufficient length to induce body weight decline.
Kudchodkar et al. (1977)
credited the decline in
synthesis to the lower metabolic state associated with energy
restriction, rather than to body weight reduction because the changes
observed in synthesis occurred before any significant shift in body
weight. To date, the effects of long-term weight loss on
whole-body endogenous cholesterol synthesis have not been
specifically investigated in humans.
Therefore, this prospective controlled study was conducted to evaluate the effects of weight loss, as achieved through energy restriction, on in vivo circulating cholesterol concentrations and synthesis in a cohort of middle-aged men exhibiting mildly elevated plasma cholesterol concentrations. It was hypothesized that circulating lipoprotein cholesterol concentrations and synthesis rates would decrease after 6 mo of modest weight loss.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Six moderately obese men (76.4–104.8 kg, 64–77 y old) were recruited from the Baltimore, MD area. All subjects were screened for mildly elevated LDL-cholesterol (LDL-C) concentrations (3.36–4.91 mmol/L). Subjects were asked to complete a general health questionnaire before the start of the study; they were excluded from participation if they were smokers, exercised more than three times per week, consuming more than three alcoholic drinks per day or had undergone any oral hypolipidemic therapy within 3 mo before the study. None of the subjects reported a history of CVD. The study was approved by the Institutional Review Board of the University of Maryland at Baltimore. All subjects gave written informed consent before the start of the study, and all procedures conducted were in accordance with research guidelines of the Institutional Review Board of the University of Maryland at Baltimore.
Protocol and procedures.
Subjects were enrolled in a 9-mo, two-phase sequential study.
Subjects in phase 1 consumed an American Heart Association (AHA) Step I
diet (AHA 1988
) for 3 mo with no change in regular
energy intake. Target intakes for this diet were 30, 55 and 15% of
energy as fat, carbohydrate and protein, respectively, with the fat
consumed in the form of 8, 10 and 12% energy as saturated,
polyunsaturated and monounsaturated fatty acids, respectively. Dietary
cholesterol intakes were targeted not to exceed 300 mg/d. A registered
dietitian provided assistance in adhering to the AHA Step I diet.
During this period, subjects were asked not to exercise more than three
times per week and not to engage in activity exceeding 1674 kJ (400
kcal) per occasion. Assignments, including an activity log and 3-d food
records, were collected weekly to monitor compliance with the protocol.
Body weights were measured weekly to determine whether subjects
remained weight stable throughout the first phase. The percentage of
body fat was measured by dual emission X-ray absorptiometry (DEXA)
during pre- and postweight loss periods. To determine whether the
subjects changed their level of cardiovascular fitness during the
study, maximal aerobic capacity [VO2max, mL/(kg · min)]
was determined during the pre- and postweight loss periods by using the
Balke protocol (Bruce and Horsten 1969
).
Immediately after phase 1, subjects commenced a 6-mo energy-restricted AHA Step 1 diet (phase 2). Subjects were instructed to reduce their mean targeted energy intake from 12 to 11 MJ/d to achieve a total weight loss goal of 8 kg over the 6-mo period. A registered dietitian was available at the research center to instruct subjects on how to make simple food substitutions or alterations to food preparation that would result in a 1000 kJ/d reduction in energy intake without selectively reducing intake of specific macronutrients. Compliance was monitored using 3-d food records and body weight measurements taken weekly, as during phase 1. During the final 5 d of each phase, a fasting blood sample was taken from each subject in the morning to determine plasma lipid levels and baseline body water and cholesterol deuterium enrichments. Subjects then received a bolus oral dose of 1.2 g/kg body water of deuterium oxide (D2O, 99.9% deuterium; Isotech, Miamisburg, OH). A second fasting blood sample was obtained 24 h later for measurement of lipid levels, and body water and cholesterol deuterium enrichments. Erythrocytes were separated from plasma by centrifugation (1000 x g for 20 min), and both fractions were stored at -70°C.
Plasma lipid analysis.
Plasma lipid concentrations were determined using enzymatic techniques
validated by the NIH Lipid Research Clinics (University of Maryland,
Baltimore VA Medical Center, Division of Gerontology). HDL-C levels
were determined after treatment of plasma with dextran sulfate and
Mg++ using a Hitachi 717 autoanalyzer (Boehringer Mannheim,
Indianapolis, IN). Plasma LDL-C concentrations were calculated from
plasma total cholesterol (TC), triglyceride (TG) and HDL-C
concentrations by using the equation formulated by Friedewald et al. (1972)
.
Cholesterol biosynthesis measurement.
Cholesterol FSR were determined at the end of each phase as the rate of
incorporation of deuterium into erythrocyte membrane free cholesterol
over 24 h (Jones et al. 1993b
). Total erythrocyte
lipids were extracted using a modified Folch extraction procedure
(Folch et al. 1957
) and dried under nitrogen. Free
cholesterol was isolated by TLC on silica gel against a free
cholesterol standard. Cholesterol bands were scraped from the TLC
plates, and the cholesterol was eluted from silica with a
hexane/chloroform/diethyl ether solution (5:2:1 v/v//v). The
cholesterol was transferred to Pyrex combustion tubes containing CuO
and silver wire. Tubes were subsequently flame-sealed under vacuum,
and cholesterol was combusted to CO2 and
H2/D2O at 520°C for 4 h. Water resulting
from the combustion was cryogenically separated from CO2 by
distillation into Pyrex tubes containing 50 mg zinc under vacuum. Tubes
were flame-sealed under vacuum, and the water was reduced at
520°C for 30 min to obtain H2/D2 gas.
Deuterium enrichment of the resultant gas was measured on a
dual-inlet isotope ratio mass spectrometer (VG Isogas 903D,
Cheshire, UK). Plasma water enrichment was measured after dilution of
0- and 24-h plasma samples with water of known isotopic abundance to
bring the enrichment into the working range of the International Atomic
Energy Agency mass spectrometer calibration standards.
Erythrocyte membrane free cholesterol deuterium enrichment values at 0
and 24 h were expressed relative to the corresponding mean plasma
water sample enrichment after correcting for the deuterium-protium
ratio in cholesterol to yield fractional synthesis rates (FSR, in %/d)
for the free-cholesterol pool. The FSR index represents that
fraction of the free portion of the rapidly turning over central
cholesterol pool that is synthesized in 24 h according to the
formula (Jones et al. 1993a
):
 | (1) |
where 
refers to deuterium enrichment above baseline over
24 h. The factor 0.478 represents
Dmax, the maximum number of deuterium
atoms incorporated per molecule of cholesterol over periods up to
48 h (Jones et al. 1993a
).
Absolute synthesis rate (ASR) was calculated according to the formula:
 | (2) |
M1 = 0.287 x body weight (kg)
+ 0.0358 x TC concentration (mmol/L) - 2.40 x TGGP where
M1 represents the size of the
M1 pool, and TGGP is a variable equal
to 1, 2 or 3, depending on the plasma triglyceride concentration
(<2.72, 2.72–3.41 or >3.41 mmol/L) (Goodman et al. 1980
).
Statistical analysis.
Paired t tests and Wilcoxon Signed-Rank tests were used to compare FSR and plasma lipoprotein cholesterol concentrations measured at the end of each phase using SAS statistical software (SAS Institute, Cary, NC). Differences were considered significant at P < 0.05.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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). Individual weight losses ranged from 3 to 8 kg. Body mass index (BMI)
and percentage of body fat also decreased (P < 0.05)
from phase 1 to phase 2.
|
). Levels of LDL-C and TG decreased (P < 0.05).
whereas HDL-C levels did not change from phase 1 to phase 2.
Neither TC:HDL (4.83 ± 1.06 to 4.46 ± 1.07), nor LDL:HDL
(3.15 ± 0.86 to 2.84 ± 0.93) ratios differed significantly
between phases. The CV for TC and LDL-C measurements averaged
1.2%, whereas the CV for TG and HDL-C measurements averaged 1.5
and 4.3%, respectively.
|
). The CV for the FSR measurement averaged 3.29%. A decline
(P < 0.05) in ASR was also observed between phase 1
[1.66 ± 0.84 g/(kg · d)] and phase 2 [0.59 ± 0.38
g/(kg · d)].
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|
DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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,
Nestel et al. 1973
). More recently, Ståhlberg et al. (1997)
demonstrated marked elevations in both activity and
mRNA expression of 3-hydroxy-3-methyl glutaryl coenzyme A (HMG CoA)
reductase in biopsied liver obtained from obese vs. nonobese patients.
However, these studies failed to demonstrate whether cholesterol
synthesis normalizes in obese individuals after weight loss. Our
findings show for the first time that weight loss achieved through diet
alone results in modest lipid level reductions accompanied by a
substantial decrease in fractional and absolute cholesterol synthesis.
The findings are consistent with data showing that hospitalized obese
subjects maintained on very-low-energy diets (~1000 kJ/d) for a
period of 3–5 mo secreted more cholesterol in bile after weight loss;
however, the reported changes in synthesis were not significant
(Bennion and Grundy 1975
). Other studies revealed that
acute energy restriction without weight loss similarly suppresses human
cholesterol synthesis (Jones et al. 1988 and 1993b
,
Kudchodkar et al. 1977
). The extent of weight loss
observed in this study is similar to that seen in other trials
evaluating the effects of weight loss through diet alone on various
outcomes (Dengel et al. 1995
, Thompson et al. 1979
, Wood et al. 1988
). Our data suggest that
moderate energy restriction is a potent inhibitor of cholesterol
biosynthesis in humans.
The changes in circulating TC, LDL and TG concentrations observed after
weight loss in this study were similar to those obtained in the
meta-analysis of other studies examining the influence of weight
loss on circulating lipid concentrations in older subjects
(Dattilo and Kris-Etherton 1992
). Lipid level change
with weight loss is not invariably observed, however. Wing et al. (1987)
observed significant changes only in TG
concentrations after a 2.4–6.8 kg weight loss over a 1-y period. A
recent study by Nicklas et al. (1997)
showed that weight
loss has no effect on TC and LDL-C concentrations in postmenopausal
women who initially consumed an isoenergetic AHA Step I diet. However,
these authors (Nicklas et al. 1997
) concluded that
combined diet modification and weight loss led to substantial
improvements in the lipid profiles of their subjects. It is likely that
methodological factors might explain the failure of these studies to
observe a significant effect of weight loss on circulatory lipid
levels.
Independent of the lowering of circulatory lipid level, decreasing
cholesterol biosynthesis may exert other beneficial effects in the
prevention of CVD. For instance, synthesis may reduce levels of
isoprenoid metabolites that are formed during cholesterol biosynthesis
and putatively play a role in atherosclerosis development
(Corsini et al. 1996
, Hughes 1996
). Furthermore, when synthesis of these metabolites is
arrested by administration of HMG CoA reductase inhibitors, smooth
muscle cell migration and proliferation, which have been implicated in
atherogenesis, are also decreased. Suppression of production of these
intermediates through weight loss may thus contribute to the lowering
of CVD risk.
HDL-C levels were not influenced by weight loss in this study.
Wing et al. (1987)
demonstrated in humans that
diet-induced changes in body weight of 5% significantly reduced TG
but did not change HDL-C concentrations. Lack of effect of weight
loss on HDL-C levels has also been observed by Wood et al. (1991)
. Thompson et al. (1979)
did observe
HDL-C levels decline in women undergoing weight loss through energy
restriction and concluded that the decrease was a product of negative
energy balance.
In summary, these findings add strength to the reported position that
weight loss of 5–15% initial body weight is beneficial for the
reduction of CVD risk factors (Van Gaal et al. 1997
).
Moderate weight loss induced by mild energy restriction results in a
disproportionately greater reduction in cholesterol synthetic rates.
Thus, it is concluded that depression of biosynthesis at least
partially explains the lowering of circulatory cholesterol level
associated with weight loss.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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3 Abbreviations used: AHA, American Heart
Association; ASR, absolute synthesis rate; BMI, body mass index; CVD,
cardiovascular disease; DEXA, dual emission X-ray absorptiometry;
FSR, fractional synthesis rate; HDL-C, HDL cholesterol; HMG CoA,
3-hydroxy-3-methylglutaryl coenzyme A; LDL-C, LDL cholesterol; TC,
total cholesterol; TG, triglyceride; VO2max, maximal
aerobic capacity.
Manuscript received December 28, 1998. Initial review completed February 12, 1999. Revision accepted April 28, 1999.
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REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
1. American Heart Association Dietary guidelines for healthy American adults: a statement for physicians and health professionals by the Nutrition Committee, American Heart Association. Circulation 1988;77:721A-724A
2. Ashley F. W., Kannel W. B. Relation of weight change to changes in atherogenic traits: the Framingham study. J. Chronic Dis. 1974;27:103-114[Medline]
3. Bennion L. J., Grundy S. M. Effects of obesity and caloric intake on biliary lipid metabolism in man. J. Clin. Investig. 1975;56:996-1011
4. Bruce R. A., Horsten T. R. Exercise testing in the evaluation of patients with ischemic heart disease. Prog. Cardiovasc. Dis. 1969;11:371-390[Medline]
5. Corsini A., Bernini F., Quarato P., Donetti E., Bellosta S., Fumagalli R., Paoletti R., Soma V. M. Non-lipid-related effects of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors. Cardiology 1996;87:458-468[Medline]
6.
Dattilo A. M., Kris-Etherton P. M. Effects of weight reduction on blood lipids: a meta-analysis. Am. J. Clin. Nutr. 1992;56:320-328
7.
Dengel J. L., Katzel L. I., Goldberg A. P. Effect of an AHA diet, with or without weight loss, on lipids in obese middle aged and older men. Am. J. Clin. Nutr. 1995;62:715-721
8.
Folch J., Lees M., Sloane-Stanley G. H. A simple method for the extraction and purification of total lipids from animal tissues. J. Biol. Chem. 1957;226:497-509
9. Friedewald W. T., Levy R. I., Frederickson D. S. Estimation of the concentration of low density lipoprotein without the use of preparative ultracentrifuge. Clin. Chem. 1972;18:499-502[Abstract]
10. Goodman D. S., Rees Smith F., Seplowitz A. H., Ramakrishnan R., Dell R. B. Prediction of the parameters of whole body cholesterol metabolism in humans. J. Lipid Res. 1980;21:699-713[Abstract]
11.
Gotto A. M., La Rosa J. C., Hunninghake D., Grundy S. M., Wilson P., Clarkson B., Hay J. W., Goodman D. S. The cholesterol facts. Circulation 1990;81:1721-1733
12. Hughes A. D. The role of isoprenoids in vascular smooth muscle: potential benefits of statins unrelated to cholesterol lowering. J. Hum. Hypertens. 1996;10:387-390[Medline]
13.
Jones P.J.H., Leitch C. A., Li Z.-C. Human cholesterol synthesis measurement using deuterated water: theoretical and practical considerations. Arterioscler. Thromb. 1993;13:247-253
14.
Jones P.J.H., Leitch C. A., Pederson R. A. Meal-frequency effects on plasma hormone concentrations and cholesterol synthesis in humans. Am. J. Clin. Nutr. 1993;57:868-874
15. Jones P.J.H., Scanu A. M., Schoeller D. A. Plasma cholesterol synthesis using deuterated water in humans: effects of short term food restriction. J. Clin. Investig. 1988;11:627-633
16.
Kudchodkar R. J., Sodhi H. S., Mason D. T., Borhani N. O. Effects of acute caloric restriction on cholesterol metabolism in man. Am. J. Clin. Nutr. 1977;30:1135-1146
17.
Miettinen T. A. Cholesterol production in obesity. Circulation 1971;44:842-850
18. Nestel P. J., Schreibman P. H., Ahrens E. H. Cholesterol metabolism in obesity. J. Clin. Investig. 1973;52:2389-2397
19.
Nicklas B. J., Katzel L. I., Bunyard L. B., Dennis K. E., Goldberg A. P. Effects of an American Heart Association diet and weight loss on lipoprotein lipids in obese, postmenopausal women. Am. J. Clin. Nutr. 1997;66:853-859
20. Rudney H., Sexton R. C. Regulation of cholesterol biosynthesis. Annu. Rev. Nutr. 1986;6:245-272[Medline]
21. Ståhlberg D., Rudling M., Angelin B., Björkhem I., Forsell P., Nilsell K., Einarsson K. Hepatic cholesterol metabolism in human obesity. Hepatology 1997;25:1447-1450[Medline]
22.
Thompson P. D., Jeffrey R. W., Wing R. R., Wood P. D. Unexpected decrease in plasma high density lipoprotein cholesterol with weight loss. Am. J. Clin. Nutr. 1979;32:2016-2021
23. Ulbricht T.L.V., Southgate D.A.T. Coronary heart disease: seven dietary factors. Lancet 1991;338:985-992[Medline]
24. Van Gaal L. F., Wauters M. A., De Leeuw I. H. The beneficial effects of modest weight loss on cardiovascular risk factors. Int. J. Obes. (suppl.) 1997;21:S5-S9
25. Wing R. R., Koeske R., Epstein L. H., Nowalk M. D., Gooding W., Becker D. Long-term effects of modest weight loss in type II diabetic patients. Arch. Intern. Med. 1987;147:1749-1753[Abstract]
26. Wood P. D., Stefanick M. L., Dreon D. M., Frey-Hewitt B., Garay S. C., Williams P. T., Superko H. R., Fortmann S. P., Albers J. J., Vranizan K. M., Ellsworth N. M., Terry R. B., Haskell W. L. Changes in plasma lipids and lipoproteins in overweight men during weight loss through dieting as compared with exercise. N. Engl. J. Med. 1988;319:1173-1179[Abstract]
27. Wood P., Stefanick M. L., Williams P. T., Haskell W. L. The effects on plasma lipoproteins of a prudent weight-reducing diet, with or without exercise, in overweight men and women. N. Engl. J. Med. 1991;325:461-466[Abstract]
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