Validation of a dietary record system for the estimation of daily cholesterol intake in individual outpatients13

Transcription

1 Validation of a dietary record system for the estimation of daily cholesterol intake in individual outpatients13 Edith C. White, M.A., Donald J. McNamar Ph.D., and E. H. Ahrens, Jr., M.D. Introduction ABSTRACT In order to develop a reliable system for measuring daily cholesterol intake in individual outpatients, studies were undertaken to establish the shortest time period (in days) for which it is necessary to obtain daily food intake records. Three volunteers were trained in dietary record-keeping and portion-size assessment, and instructed to self-select a low-cholesterol diet for 2 days. During the study period they maintained daily dietary records and collected dummy diets. Comparisons of cholesterol intake calculated from the dietary records (mean 144 mg/day, SD ± 13, n = 6) to the values from chemical analysis (118 ± 28 mg/day) demonstrated that the calculated values were higher (mean 19%). More importantly, it was found that a minimum of 9 days records of dummy diet analyses were required in order to reach an estimate of daily cholesterol intake that varied by less than 1% from the mean of the 2-days values. In 1 outpatients trained to adhere to a moderately low-cholesterol intake and who maintained sequential dietary records for 9 days, it was found that the mean daily intake was 251 mg/day but that individual patients exhibited substantial daily variations in cholesterol intake (average coefficient of variation = 54%, range = 8.5 to 121.2%). These results demonstrate that, under conditions of training in dietary record-keeping and portion-size assessment, adherence to a low-cholesterol diet, and with collection of at least 9 days of dietary records, a reliable quantitative estimate of daily dietary cholesterol intake can be obtained in free-hiving outpatient populations. Am. I. Clin. Nutr. 34: , KEY WORDS Dietary records, daily cholesterol intake, outpatient study, gas-liquid chromatography, dummy diet analysis Any attempt to quantify the key parameters of cholesterol metabolism in man requires precise measurements of dietary cholesterol intake, cholesterol absorption by the intestinal tract, the rate of synthesis in body tissues, pool size estimates, and excretion rates. These values are now attainable in patients studied under metabolic ward conditions where dietary intakes can be controlled and all sterol excretions can be carefully monitored. However, in outpatients the direct measurement of these descriptors of cholesterol homeostasis has proven elusive. A recent study by Samuel et a!. (1) has validated the use in man of an isotope-ratio method for measuring cholesterol absorption that requires only one blood sample and no stool collections; we have concluded that this method is suitable for measurements of percentage cholesterol absorption in an out-patient population. However, in order to estimate dietary cholesterol absorption in absolute terms (mg/day), methods must be available for accurately estimating the mean daily cholesterol intake as well as the day-to-day variations in intake. The difficulties encountered in attempting to quantify the daily intakes of macro- and From the Rockefeller University, New York, New York Supportod in part by United States Public Health Service Grants HL 6222 and HL from the National Heart, Lung, and Blood Institute, by FR-12 from the General Clinical Research Centers Branch, Division of Research Resources, by a Grant-in-Aid from the National Dairy Council, grants from the Herman Goldman Foundation, The New York Heart Association and Weight Watchers Foundation, Inc., and by a Career Scientist Award to D.J.M. from the Irma T. Hirsch! Charitable Trust. reprint requests to: Dr. E. H. Ahrens, Jr., The Rockefeller University, 123 York Ave., New York, NY 121. Downloaded from ajcn.nutrition.org by guest on April 8, 216 The American Journal of Clinical Nutrition 34: FEBRUARY 1981, pp Printed in U.S.A American Society for Clinical Nutrition 199

2 2 WHITE ET AL. micronutrients from dietary records or 24-h recalls are well known and have recently been critically analyzed (2, 3). The present study was undertaken to test the conclusion of Liu et a!. (3) that for any one patient the analysis of daily food intake records will yield a reasonably precise estimate of mean daily intake of cholesterol if reliable records are kept for a long enough period of time, but that at some point, due to the rule of diminishing returns, continued record-keeping becomes pointless. It was thus our goal to establish the number of daily records required to establish an estimate of daily cholesterol intake that varied by less than 1% from the mean of all days records analyzed. It seemed obvious that this number would be minimized if patients were trained to adhere to restricted intakes of cholesterol-containing foods, since in any experimental situation in which highcholesterol intakes are to be compared to low intakes it would be simple and precise to add any desired number of large or extra large whole eggs (which each contain 25 mg of cholesterol, SD ± 2, n = 4) to the low-cholesterol diet to which the patients had first been adapted. In the course of these studies we also tested the closeness of fit of cholesterol intake data calculated from standard food tables with those obtained by chemical analysis of dummy diets. These experiments have shown that in trained patients the collection and analysis of nine consecutive daily food records leads to an estimate of daily cholesterol intake that varies less than 1% from the mean, provided the patients ingest low-cholesterol foods: and that food table estimates were higher than chemical analyses of dummy diets by a mean of 19%, range -6 to +52%. Materials and methods Subjects The studies were performed in two groups of subjects: three healthy young university students (two male, one female) and 1 hyperlipidemic male outpatients from the Center for Prevention of Premature Arteriosclerosis at The Rockefeller University Hospital.! Student volunteers were instructed by a dietician in portion-size estimation using Nasco food models. Evaluation of the effectiveness of this instruction was carried out by a second trained dietician who quizzed the volunteers in portion-size estimates of meal trays as they passed the cashier at the University cafeteria. Each volunteer also was instructed how to maintain a low-cholesterol (<3 mg/day) diet ofwhich approximately 35% of the calories were composed of fat with a P/S ratio of 2. Each volunteer was asked to keep daily dietary records for 2 consecutive weekdays and to collect identical dummy diets for all meals in 1-day pools. II In a second study of the same students conducted 1 yr after study I, the volunteers were retrained in dietary record-keeping and portion-size assessment, but new dietary guidelines were introduced in order to reduce still further the mean cholesterol intake by excluding organ meats from the diet. Dietary records and dummy diets were collected as previously described for 1 consecutive weekdays. I!! One hundred hyperlipidemic outpatients were instructed to eat a low-cholesterol diet (<3 mg/day), of which 35% of the calories were composed of fat with a P/S ratio of 2. Each patient had been trained over a 3- to 6-month period in dietary record-keeping, portionsize assessment, and adherence to the dietary guidelines in a series of at least four visits with several trained dieticians. Each patient kept dietary records for 9 days; no dummy diets were collected. Dietary records A list was compiled of commonly eaten cholesterolcontaining foods in which (for convenience in training and in record-keeping) food items with similar cholesterol contents were grouped together. This checklist was made up of five categories of food items: meats, fish, shellfish, dairy products, and oils. Portion-size training was based on 1) 3-oz portion sizes where this was applicable (meats, fish, some shellfish); 2) an item basis (six shrimps, clams, oysters, etc.) or 3) a volume basis (dairy products and oils). The cholesterol contents of these food items were obtained in Tables of Food Composition (4). Chemical analysis Dummy diets were analyzed for cholesterol content according to the method validated by Miettinen et al. (5). In brief, 1-g ahiquots of the homogenate of each dummy diet were analyzed in duplicate. Samples were refluxed for 1 h with 2 ml of N NaOH in 9% ethanol and extracted three times with 5 ml of petroleum ether. The neutral sterol fractions were dried, transferred to I- dram vials, and the trimethysilyl ether derivatives were analyzed by gas-liquid chromatography on DC-56 columns. Coprostanol was added to the homogenate ahiquote as an internal standard to correct for recoveries during the procedure, and quantification of dietary sterols was calculated in relation to 5a-cholestane added in known amounts before derivatization. Results I The data presented in Table 1 demonstrate the large day-to-day variations in dietary cho- Downloaded from ajcn.nutrition.org by guest on April 8, 216

3 QUANTITATION OF DIETARY CHOLESTEROL 21 TABLE 1 Daily dietary cholesterol intake: comparison of daily food records and chemical analysis of dummy diets Subject No. days Cholest erol intake (mg/day) Chemical analysis Dietary records Error of records.f ± SD (cv)? I 1 2 9±48 (53.3) 137 ±59(43.1) ± 1 (68.) 159 ± 163 (12.5) ±42(35.6) 135 ±35(25.9) II ± 79(54.1) 177 ± 81(45.8) ± 36(28.1) 121 ± 35(28.99) ± 58 (69.9) 95 ± 45 (47.4) lesterol intake, whether the data were derived by chemical analysis or from food table data (average coefficient of variation 55%). Comparison of the chemically determined values with the calculations based on dietary records shows that the values for cholesterol intake derived from food tables were higher than the analytical results in all three subjects (mean = +25%). II Upon retraining the same volunteers to maintain a lower cholesterol intake, the calculated values for cholesterol intakes showed similar day-to-day variations (mean coefficient of variation 51%) but a closer fit between the chemical and food table analysis (mean error of the dietary record data = + 1%). In study I subject 2 showed a large day-today variations in cholesterol intake, due mainly to periodic intakes of organ meats, and in study II this variation was considerably reduced. (The very large difference between the two sets of analytical data in the first study of subject I (52.2%) were presumably due to errors in portion-size evaluation as judged by inspection of the dummy diets.) The variations in the day-to-day intake of cholesterol are shown graphically in Figure 1, where the cholesterol intake for each subject is expressed as a percentage of the mean daily intake over the entire test period and also as the cumulative mean daily cholesterol intake expressed as percentage of the mean daily intake over the entire period. The number of food records required to achieve an average daily cholesterol intake within ± 1% of the final mean ranged from 5 to 11 days in study I and 3 to 6 days in study II. Similar data (not shown) were obtained when the results of the chemical analysis of the dummy diets were plotted. III To d...lermine further the individual variability in daily cietary cholesterol intake, 1 trained outpatients recorded daily dietary intakes for 9 consecutive days. Analysis of their daily records demonstrated that individual patients varied considerably in terms of the constancy of their daily cholesterol intakes. As shown in Figure 2, 2% of the population attained a constant mean cholesterol intake by 3 days and 55% of the population by 6 days, yet 8% of the group had failed to attain a constant intake even by day 8 of the 9-day collection period. The average daily dietary cholesterol intake in this population ranged from 93 to 467 mg/day (mean 247 ± 8; coefficient of variation 32.3%), whereas the individual coefficient of variation for the 9- day period averaged ± 54%. Discussion The present study was undertaken to determine how many daily food records are required in order to obtain a reasonably accurate estimate of daily dietary cholesterol intake. In the course of answering this question we also compared the cholesterol intake data calculated from food tables with those obtained by chemical analyses of dummy diets. The fmdings suggest that a reasonably valid estimate of dietary cholesterol intake can be obtained from 9 to 1 days food Downloaded from ajcn.nutrition.org by guest on April 8, 216

4 22 WHITE ET AL. Inc o >, V a., c. >.. Ec C I C E I a Subject 3 I II A k V #{176} /w ( FIG. 1. Variations of daily cholesterol intake in three trained volunteers. Daily cholesterol intake was determined from daily food records gathered continuously for 19 to 2 days (test I) and for 7 to 1 days (test II). U: daily cholesterol intake as percentage of the mean values for n days and #{149}: cumulative mean daily cholesterol intake as percentage of the mean values for n days. The arrow indicates the number of days records required to achieve a daily value of cholesterol intake within ±1% of the final means of all data. records, provided that the patients have been adequately trained in portion-size assessment and in dietary record-keeping, and provided that the diet prescribed is moderately or very low in cholesterol-containing foods. The comparability of data obtained from food tables and those derived from chemical analysis of dummy diets was acceptably close- 1% in the case of study 11(118 mg/day, Days 5 Days FIG. 2. Days required to attain a constant (± 1%) cholesterol intake in 1 trained out-patients by analysis of nine consecutive daily food records. Results are presented as the number of patients attaining a constant daily mean cholesterol intake after 1 to 9 days of diet records (cross-hatched columns) and as the cumulative number of patients attaining a constant daily mean intake curve. average intake). Thus, while it may be psychologically beneficial to require an individual patient to maintain constant dietary records over the entire course of a study, quantitative reliability can be achieved by the analysis of 9 days of records. The number of consecutive days records required for reliable estimates of daily cholesterol intake in individual patients depends both on the intake level and on intraindividual variations of intake. Thus, Marr (6; personal communication 1979) reported that for men on ad libitum diets as many as 2 days are needed to properly classify 8% of the individual into the correct upper and lower tertiles of the distribution; Liu et al. (3), also working with the food records of free-living men on ad libitum diets, noted that 7 days records were adequate to separate the first and fifth quintiles... Borgstrom et al. (7) also reported wide intraindividual variations in the Dalby study of 2 individuals. However, it is to be expected that the more restricted the dietary intake of cholesterol (by omission of eggs and organ meats, for instance), the lower the daily intraindividual variation, and, vice vers the fewer the restrictions, the longer the record-keeping period that is required. Thus, our laboratory s objectives are best served by training our Downloaded from ajcn.nutrition.org by guest on April 8, 216

5 QUANTITATION OF DIETARY CHOLESTEROL 23 patients not only in accurate record-keeping and portion-size assessment, but also on as low an intake of cholesterol as is feasible in a free-living situation. The ground has now been laid for performing cholesterol absorption studies in large numbers of outpatients, where the isotoperatio method (1) is used to determine percentage absorption of ingested cholesterol and where the limiting factor may be the requisite training of patients in portion-size assessment by trained dieticians. We believe that the present study demonstrates that very low-cholesterol diets are achievable in outpatients. The addition to that diet of any desired amount of cholesterol can be achieved by adding whole eggs to the basal diet. Thus, to a basal diet containing 125 mg/ day of cholesterol, the addition of 2 large or extra large whole eggs will raise the daily intake by 5 mg/day to a total of 625 mg/ day; this results in daily variation limits even lower than 1%. Testing mean daily cholesterol absorption in mg/day at 125 and at 625 mg intake levels will allow the accurate assessment, for the first time, of the precision of feedback control of cholesterol synthesis as a function of cholesterol intake in individual patients, where daily synthesis is measured either by sterol balance methods (8), by compartmental or input-output analysis (9, 1) of cholesterol kinetics, or by measurement of the fractional conversion of labeled mevalonate to cholesterol(ll). U References 1. Samuel P, Crouse JR, Ahrens EH, Jr. Evaluation of an isotope ratio method for measurement of cholesterol absorption in man. J Lipid Res 1978:19: Garn SM, Larkin FA, Cole PE. The problem with one-day dietary intakes. Ecol Food Nutr 1976;5: Liu K, Stamler J, Doyer A, McKeever J, McKeever P. Statistical methods to assess and minimize the role of intra-individual variability in obscuring the relationship between dietary lipids and serum cholesterol. J Chron Dis 1978;31: Adams CF. Nutritive value of American foods in common use. Agriculture Handbook no Washington, D.C.: United States Department of Agriculture, Miettinen TA, Ahrens EH, Jr, Grundy SM. Quantitative isolation and gas-liquid chromatographic analysis of total dietary and fecal neutral steroids. J Lipid Res 1967 : Marr, JW. Surveys: aims and methods. Nutrition (Lond) 1973;27: Borgstrom B, Norden A, Akesson B, Jagerstad M. A study of food consumption by the duplicate portion technique in a sample of the Dalby population. Scand J Soc Med (suppl 1): Grundy SM, Ahrens EH, Jr. Measurements of cholesterol turnover, synthesis, and absorption in man carried out by isotope kinetics and sterol balance methods. J Lipid Res 1969;lO: Goodman DS, Noble RP, Dell RB. Three-pool model of the long-term turnover of plasma cholesterol in man. J Lipid Res l973;l4: Samuel P, Lieberman S. Improved estimation of body masses and turnover of cholesterol by computerized input-output analysis. J Lipid Res 1973; 14: McNamara DJ, Ahrens EH, Jr, Samuel P, Crouse, JR. Measurement of daily cholesterol synthesis rates in man by assay of the fractional conversion of mevalonic acid to cholesterol. Proc Nail Acad Sci USA 1977;74: Downloaded from ajcn.nutrition.org by guest on April 8, 216