with wild type drives the wild type p53 protein into the mutant conformation. .... (Life Technologies, ..... dude: purely mechanical effects on the gut such as bulk-.
4 Breesac B, Galvin 1CM, Liang TJ, Isselbacher
KJ, Wands JR, Ozturk M. Abnormal structure and expression of p53 gene in human hepatocellular carcinoma Pruc Nati Acad Sd USA 1990;87:1973-7. 5. Masuda H, Miller C, Koeffler HP, Battifora H, Clime MJ. Rearrangement of the p53 gene in human osteogenic sarcomas. Proc Natl Acad Sci USA 1987;84:7716-.9. 6. Milier CW, Also A, Tsay C, Slamon D, Ishizaki K, Toguchida J, et al. Frequency and structure of p53 rearrangements in human osteoearcoma. Cancer Rca 1990;50:7950-4. 7. Vogelstein B, Kinzler KW. p53 function and dysfunction. Cell
1992;70:523-6. 8. Hollatein M, Sidranaky D, Vogeistein B, Harris CC. p53 mutation in human cancers. Science 1991;253:49-53. 9. Yamada Y, Yoshida T, Hayashi K, Sekiya T, Yokota J, Hirohasbi S, et aLp53 gene mutations in gastric cancer metastasis and in gastric cancer cell lines derived from metastases. Cancer Rca 1991;51:5800.-5.
10. Nigro JM, Baker SJ, Preisinger AC, Jeasup JM, Hostetter R, Cleary K, et al. Mutations in the p53 gene occur in diverse human tumor types. Nature 1989;342:705-8. 11. Takahashi T, Nau MM, Chiba I, Birrer M,J, Rosenberg RK, Vinocour M, et al. p53: a frequent target for genetic abnormalities in lung cancer. Science 1989;246:491-.4. 12. Bos JL. The i-as gene family and human carcinogenesis. Mutation Rca 1988;195:255-71. 13. Yokosuka 0, Omata M, Imazeki F, Okuda K. Active and inactive replication of hepatitis B virus deoxyribonucleic acid in chronic liver disease. Gastroenterology 1985;89:610-6. 14. Liu TC, Lin SF, Chen TP, Chsng JG. Ras genes in myelocytic leukemia. J Formosan Med Assoc 1991;90:825-30. 15. Haliassos A, Chomel JC, Tesson L, Baudis M, Kruh J, Kaplan JC, Kitzis A. Modification of enzymatically amplified DNA for the detection of point mutation. Nucleic Acids Rea 1989;17:3606. 16. ChangJG, Chiou SS, Perng LI, Chen TC, Lin TC, Lee IS, et al. Molecular characterization of G-6-PD deficiency by natural and amplification created restriction sites: five mutations account for most G-6-PD deficiency cases in Taiwan. Blood 1992;80:1079-82. 17. Lindeman R, Hu SP, Volpato F, Trent JR. Polymerase chain
reaction
mutagenesis
enabling
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detection
of
common p-thalassemia mutations in Mediterraneans. Br J Haematol 1991;78:100-4. 18. Eiken HG, Odland B, Boman H, Skjelkvale L, Engebretsen LF, Apold J. Application of natural and amplification created restriction sites for the diagnosis of P1(13 mutations. Nucleic Acids Rca 1991;19:1427-30. 19. Kwok S, Kellogg DE, McKinney N, Spasic D, Goda L, Levenson C, Sninaky JJ. Effects of primer-template mismatches on the polymerase chain reaction: human immunodeficiency virus type I model studies. Nucleic Acids Res 1990;18:999-1005. 20. Ehien T, Dubeau L. Detection of i-as point mutations by polymerase chain reaction using mutation-specific, inosine-contaming oligonucleotide primers. Biochem Biophy Rca Commun
1989;160:441-7. 21. Nasri M, Thomas D. Relaxation of recognition sequence of specific endonuclease Hindffl. Nucleic Acids Rca 1986;14:811-21. 22. linazeki F, Omata M, Nose H, Ohto M, Isono K. p53 gene mutations in gastric and esophageal cancers. Gastroenterology 1992;103:892-6. 23. Baker SJ, Preisinger AC, Jessup JM, Paraskeva C, Markowitz S, Wilson JK, et al.p53 gene mutations occur in combination with l7p alleic deletions as late events in colorectal tumorigenesis. Cancer Rca 1990;50:7717-22. 24. Rodrigues NR, Rowan A, Smith MEF, Kerr IB, Bodmen WF, Gannon JV, Lane DP. p53 mutations in colorectal cancer. Proc Nati Acad Sci USA 1990;87:7555-9. 25. Baker SJ, Fearon ER. Deletions and p53 gene mutations in colorectal carcinoma. Science 1989;244:217-21. 26. Milner J, Medcalf BA. Cotranslation of activated mutant p53 with wild type drives the wild type p53 protein into the mutant conformation. Cell 1991;65:765-74. 27. Kern SE, Pietenpol JA, Thiagalingam 5, Seymour A, Kinzler WK, Vogelstein B. Oncogenic forms of p53 inhibit p53-regulated gene expression. Science 1992;256:827-30. 28. Ozturk M, Bressac B, Puisieux A, Kew M, Volkmann M, Bozcall 5, et al. p53 mutation in hepatocellular carcinoma after aflatoxin exposure. Lancet 1991;338:1356-9.
CLIN. CHEM. 39/10, 2191-2198 (1993)
Dietary Nutrient Intakes and Slight Albuminuria in People at Least 40 Years Old Patricia
A. MetcaIf,1’
John K. Baker,3 Robert K. K. Scragg,’
Evan Dryson,4
Alastair
J. Scott,2
and Chris J. Wild2 We studied the relation between diet and slight albuminutia in 5416 people, ages 40 years and over, who participated in a health screening survey of a local worktorce. Degree of albuminuna showed log-linear univariate relations with dietazy protein, cholesterol, and sodium intakes, and negative loglinear unrvariate relations with dietary fiber and polyunsaturated to saturated fat (P/S) ratio. After adjusting for age, Departments of 1Community Health and 2Mathematics and Statistics, University of Auckland, Private Bag 92019, Auckland 1, New Zealand. 3Department of Clinical Biochemistry, National Women’s Hospital, Private Bag, Auckland 3, New Zealand. 4Penrose Occupational Health Centre, P.O. Box 12056, Auckland 6, New Zealand. 5Address correspondence to this author at: Department of Biostatistics, CB#8030, School of Public Health, The University of North Carolina, Chapel Hill, NC 27599-8030. Fax 919-962-3265. Received December 11, 1992; accepted April 23, 1993.
gender, and ethnicity, the relative risk (95% confidence intervaU for slight albuminuria was significantly increased in people reporting dietaiy cholesterol consumption >226 mg/day compared with people reporting consumption 226 mg/day [1.32(1.02, 1.70)], and significantly reduced in people reporting dietary fiber consumption >26 g/day compared with people reporting consumption 26 g/day [0.74 (0.58, 0.95)]. There was no significant effect of dietary protein, P/S ratio, or salt intake. We condude that risk of slight albuminuna is increased by consumption of dietary cholesterol and reduced by consumption of dietary fiber. Indexing Terms: cholesterol
.
flr
.
protein
-
salt
The increased excretion of small amounts of albumin in the urine (slight albununuria or microalbuminuria) is associated with incipient diabetic nephropathy (1, 2), CUNICAL CHEMISTRY, Vol. 39, No. 10, 1993
2191
coronary heart disease (3), and premature death in people with diabetes meffitus (1, 4). Similai- associations, such as increased cardiovascular mortality (5) and increased prevalence of progressive renal disease (6), have been described in the elderly general population. We previously reported associations between slight albuncinuria and body mass index, hypertension, and hyperlipidemia in 5429 Albustix-negative subjects who participated in a New Zealand workforce survey (7). Moreover, we found significant associations between slight albuminuria and cigarette smoking and heavy alcohol consumption, renewing speculation that the presence of slight albuminuria might represent a marker of cardiovascular risk (8). Other factors that influence urinary albumin excretion include overnutrition (9, 10), dietary protein intake (11), dietary fat (9, 12), and dietary phosphate (13). The aim of this study was to investigate the relation between slight albuminuria and dietary nutrient intakes in a middle-aged population. Subjects and Methods Study Population The study population comprised 5670 individuals (4106 men and 1564 women), ages 40-78 years (median 49 years), who participated in a health screening survey of a New Zealand workforce (14). Participants were 78.8% European, 7.7% Maori, 11.7% Pacific Islander, and 1.8% Asian, distributed among 46 companies in Auckland and Tokoroa. Participants gave informed consent, and procedures followed were in accordance with the Ethical Committee of Auckland University. Participants fasted from 2200 the evening before the interview and collected on the day of interview a firstvoided urine sample into a sterile container for albumin estimation and bacterial culture (Life Technologies, Grand Island, NY). Urine samples were refrigerated at 4#{176}C within 3 h of arrival at the laboratory and analyzed on the same or following day. Of the 5616 participants who completed the food frequency questionnaire, 5416 were included in the current study (79.2% European, 7.6% Maori, 11.4% Pacific Islander, and 1.8% Asian), after excluding 200 participants who tested positive for urinary tract infection. Usual dietary intake over the past 3 months was estimated by the Wfflett food frequency questionnaire, which was modified to include food items eaten by New Zealand Maori and Pacific Islanders. Nutrient intakes were calculated from published food serving sizes (15) and published food tables (16), with New Zealand data being used as necessary. Mjustment of variables for dietary cholesterol intake were calculated by the method of Willett (17). We confirmed that this dietary instrument was valid for Europeans and non-Europeans in a subsample of 176 individuals (67.0% European, 10.2% Maori, 19.3% Pacific Islander, and 3.4% Asian) (unpublished observations). After participants rested 15 mm, we measured their blood pressure twice while they were in the sitting p02192
CUNICAL CHEMISTRY,Vol. 39, No. 10, 1993
sition, with a Hawksley random zero sphygmomanometer, and used the disappearance of Korotkoff sounds to determine phase V diastolic pressure. Their weight and height were measured after they removed shoes and heavy clothing. All participants were subjected to a 75-g oral glucose tolerance test with blood samples collected after an overnight fast and 2 h after the glucose load.
Analytical Techniques Urinary albumin concentrations were determined by immunoturbidixnetric assay (Cambridge Life Sciences, Cambridge,
UK). The urinary
albumin
method
was lin-
ear from 0 to 165 mgfL and sensitive to 2 mgfL. Imprecision was 8.4% for normal and 7.4% for abnormal control samples. Total serum cholesterol and triglyceride concentrations were measured on a Chem I analyzer (Technicon, Tarrytown, NY), and glucose concentrations were measured on a centrifugal analyzer (Boehringer, Mannheim, Germany), as was serum high-density lipoprotein (HDL) cholesterol after precipitation of apolipoprotein B-containing lipoproteins with magnesium phosphotungstate (18). Interbatch CVs were as follows: cholesterol 3.6%, triglyceride 5.4%, glucose 2.1%, and HDL cholesterol 3.4%.
Diagnostic Criteria Participants were assigned to groups as follows: normal albuminuria (men 28 mg/L, women 29 mgiL); slight albuminuria (men 29-299 mg/L, women 30-299 mgfL); and clinical albuminuria (300 mgfL) (7). Bacteriuria was diagnosed in samples with a colony count >1 x i0 organisms/L and (or) leukocyte count >100 000/L. Hypertension was defined as systolic blood pressure 160 mmHg and (or) diastolic blood pressure 95 mmHg (19). Hypertension was present in 3.3% of participants with normal albuminuria, 11.2% of participants with slight albuminuria, and 46.7% of participants with clinical albuminuria. Diabetes meffitus was diagnosed as a 2-h plasma glucose concentration of 11.1 mmolJL, according to World Health Organization criteria for epidemiological surveys (20). Diabetes mellitus was present in 2.6% of participants with normal albuminuria, 14.9% of participants with slight albuminuria, and 13.6% of participants with clinical albuminuria Statistical Methods Because of the positively skewed frequency distribution of urinary albumin concentrations, these were converted to log, values for calculations; the results are presented as geometric means (the exponential of the mean of the log-transformed data) and associated 95% confidence intervals. Multiple linear regression analysis was used to assess the joint effects of variables associated with urinary albumin concentrations. Relative risks controlledfor possible confounding effects, and as‘Nonstandard abbreviations: HDL, high-density lipoprotein; P/S. polyunsaturated to saturated fat; LDL, low-density lipoprotein.
sociated 95% confidence intervals were determined by the Mantel-Haenszel method. These statistical analyses were performed with SAS (Research Triangle Park, NC) statistical software. Piecewise linear models were fitted to log-transformed urinary albumin concentrations, dietary salt intakes, and the ratio of polyunsaturated to saturated fat (P/S) to obtain estimates of the point at which a significant change of slope occurred and its associated 95% confidence interval (21). The 22 people with clinical albuminuria (including 3 with diabetes mellitus, 1 with a past history of pyelonephritis, and another with a past history of renal calculi) were excluded from regression analyses and figures because their numbers were small and their urinary albumin concentrations highly influential. Study numbers vary for different analyses because of missing information. We calculated bivariate curves by robust locally weighted regression (22), using 75% of the data for smoothing each x value. Confidence intervals were obtained by using the bootstrap technique (23) as follows: After randomly sampling the study population of 5394 people with replacement and calculating the weighted regression line 1000 times, we calculated an approxi-
mate 95% confidence interval as the 2.5th and 97.5th of the 1000 bootstrapped regression esti-
percentiles mates. Results
Mean dietary nutrients in people with normal, slight, and clinical albuminuria are shown in Table 1. People with clinical albuminuria or slight albuminuria consumed significantly more protein and cholesterol and significantly less fiber than did nonalbuminuric individuals. The dietary P/S ratio was significantly reduced and there was a trend toward increased salt consumption in people with slight albuminuria and clinical albuminuria. Expressing results as their percentage contribution to total energy intake still showed highly significant dif-
ferences in protein, fiber, and cholesterol intake between the groups (Table 2). There was also a trend in dietary intake from normal to clinically albuminuric individuals, such that people with slight albuminuria and clinical albuminuria tended to consume less carbohydrate as fiber and starch, more protein, and more fat as saturated fat and cholesterol. The relations between degree of albuminuria and dietary protein and dietary cholesterol consumption were linear (Figure 1), whereas the relation with dietary sodium intake was piecewise linear (Figure 2) with a significant increase in slope corresponding to a dietary
sodium intake (95% confidence interval) of 2.4(2.0, 2.8) g/day. There was a negative linear relation between degree of albuminuria and dietary fiber intake, and a negative piecewise linear relation between degree of albuminuria and the P/S ratio, with a significant change in slope corresponding to a P/S ratio (95% confidence interval) of 0.38(0.36,0.40) g/day (Figure 3). The exclusion of diabetic subjects did not alter any of the above relations. After a4justing for age, gender, and ethnicity, the relative risk of slight albuminuria was significantly increased among people consuming >226 mg/day of cholesterol (Table 3). Similarly, there was a reduced relative risk of slight albuminuria among people consuming >26 g/day of dietary fiber. In contrast, there was no significant risk associated with dietary protein, P/S ratio, or salt intake, or with percentage contribution of saturated fat to total energy intake (Table 3). To determine whether the source of dietary cholesterol, i.e., beef, organ meats such as liver or kidney, or eggs, was an important determinant of the degree of albuminuria, we eamined urinary albumin concentrations in the different subgroups.After adjusting for age, gender, and ethnicity, urinary albumin concentrations (mean; 95% confidence interval) were slightlyhigher in 5242 beef eaters (5.1 mgfL; 4.98, 5.30) than in 174 nonbeef eaters (4.3 mg’L; 3.59,5.08) (P = 0.0398), but there was no significant difference between 359 organ meat
Table 1. Age- and Gender-Adjusted Daily Nutrient Normal
5126
Energy,MJ Carbohydrate, g Starch, g Sucrose, g Fiber, g
Protein,g Protein/weight,g/kg Fat, g P, g
S, g Cholesterol, mg Salt, g
8.5
224 70 43 26 74 1.02 81 12.1 34
223
(8.41,8.58)
(221.8, 226.6) (68.6, 70.8) (42.2, 44.2) (25.8, 26.5) (73.3, 74.7) (1.01, 1.03) (79.7,81.7) (11.9,12.3)
(33.9, 34.9) (220.5, 226.1)
2.08 (2.05, 2.10)
lntakesa
Slight albumlnurla
Clinical albumlnurta
268 8.7 (8.24, 9.00) 213 59 41 22
22 9.7
(203.3, 223.9) (54.9, 62.7)*** (36.9, 45.1) (20.8,
237 66
49 23 95
22.6)’”
78 (75.1,82.0)* 1.01 (0.96, 1.06)
83
(8.31,11.27)
(200.3, 280.8) (52.3, 83.3)
(34.8,69.9) (18.6, 28.0) (81.4,110.3)”
1.21 (1.10, 1.37)
(78.9, 88.1)
93
11.7 (10.9,12.6) 36 (34.3,38.7) 252 (238.4, 265.8)*** 2.12 (2.00, 2.24)
(76.3, 112.3)
11.3 (8.8, 14.5) 41 (33.4, 50.6) 304 (251.3, 367.4)” 2.56(2.11,
3.10)’
Values br dieta,y nutilents are geometlic means (and assocIated 95% confidence Intervals). Statistically significant at p 94 g/day, P/S ratio >0.36, salt >2.4 g/day, and S >14%. b EthnIcgroups were European and Asian vs Maorland Pacific Islander. SA. slight albuminuna (n = 268); NA, normal albuminutla(n = 5126); S, saturated fat (percentagecontributionto total energy intake).
Multivanate Analysis When all variables were entered into a multiple-regression model, we found significant regression coefficients for age, male gender, body mass index, diastolic blood pressure, serum triglycerides, dietary fiber, and dietary cholesterol (Table 4). If all other variables remain constant, this model predicts that a 100 mg/day increase in dietary cholesterol intake will increase urinary albumin concentrations by 5.1% (95% confidence interval: 5.09-5.17%) and a 25 g/day increase in dietary fiber intake will reduce urinary albumin concentrations by 9.5% (9.3-9.7%). The net contribution of these variables accounted for 13.9% of the variation of urinary
albumin concentrations. Dietary protein and the P/S ratio were each no longer significant when dietary cholesterol was included in the regression model. Salt intake was no longer significant
Table 4. Muftlpie-Regresslon Model of Variables Associated with Urinary Albumin Concentratlon
Intercept Age Male gender Ethnlcityb Body mass index (BMI) (BMI)2
Gender x BMI Diastolicbloodpressure (Diastolicblood pressure)2 Serumtriglycerides
Dietarycholesterol
Param.t.r estimata 1.4349 -0.0080
0.3066 0.3704 0.0014 0.0026 0.0253 0.0084
SE
f
0.0307 46.688 0.0021 -3.880
0.0309 0.0380
0.0051 0.0004 0.0053
0.0003
0.0014 0.0001
0.0556 0.0005
00002
9.919 9.759
P 0.0001 0.0001 0.0001 0.0001
0.266 0.7906 6.753 0.0001 4.392
0.0001
6.080 0.0001 0.0001 3919
0001
-0.0040
Energy’
0.0000 -0.0001
00011 00000 00003
-0.0590
0.0338
07076 1:747 0:0807
0.0000
0.460
Proteinc P/S ratio
Salt”
0.0000
-3775 -0022
00002
Fiber
09822
-0375
0.6459
‘Data are converted: Iog(urlnary albumin + 1); multipler2 = 0.139, n = 5384. b Ethnicity was coded as Maorl and Pacific Islanders = 1; Europeans and Asians = 0. c Adjusted for dietary cholesterol intakes. Explanatory variables are centered by subtracting their average values as follows: age -48.8 years; body mass index -27.3 kg/rn2; diastolic blood pressure -76.8 mmHg;serum triglycendes -1.65 mmol/L; fiber -29 g/day; cholesterol -248 mg/day; P/S ratio -0.39.
after body mass index and age were included in the model. Because the correlations between dietary cholesterol and total energy (r = 0.73), dietary protein (r = 0.78), and dietary salt intakes (r = 0.59) were high,
these nondietary cholesterol variables were adjusted for dietary cholesterol intakes. Discussion questionnaire. Many different methods, such as a 7-day food diary, 24-h recall, weighed foods, and food questionnaires, have been used in assessing diet. In studying large populations, the food frequency questionnaire has become the primary method for measuring dietary intake in epidemiologic studies because it offers the advantages of convenience, ease of administration, and low cost (24). These questionnaires are designed to estimate average diet over an extended period. Although they may yield higher values than 7-day records (25), they do allow an approximate ranking of individuals by nutrient intake and are suitable for comparison of groups (26). Choke of urine specimen. The fasted early-morning urine sample was chosen because of its reportedly less biological variation than random (untimed) samples or timed collections (27). To avoid the confounding effect of urinary creatinine concentrations and additional sources of biological variation, and because of criticisms concerning the use of ratios in medicine (Kronmall RA. Spurious correlation and “the fallacy of the per ratio standard” revisited. Presented at the October meeting of the Modical Section of the Royal Statistical Association, 1991), Food freque,uy
we investigated the associations of urinary albumin concentrations rather than of the albumin: creatinine ratio. Although repeat determinations were not carried out in people with increased urinary albumin concentrations, there is no reason to believe that the probability of a false positive is different from the probability of a false negative. Therefore, misclassification errors will be nondiiferential and tend to attenuate rather than accentuate associations (28). For some comparison with other studies, an albumin excretion of 20-200 zg/min is approximately equivalent to 30-300 mg/24 h, or 3-30 mg/mmol creatinine (27). Protein. Feeding excess protein to animals with ex-
perimental renal disease can induce progressive renal CLINICAL CHEMISTRY, Vol. 39, No. 10, 1993
2195
insufficiency. For example, Chanutin and Ludewig varied the dietary protein of partially nephrectomized rats by increasing the dried meat content of the diet from 10% to 80% and found that degree of proteinuria, severity of renal insufficiency, and mortality increased progressively (29). Conversely, feeding a low-protein diet to rats with remnant kidneys prevented the striking increases in glomerular plasma flow and capillary pressures that lead to hyperfiltration (30). Moreover, the accompanying proteinuria and structural alterations of epithelial cells were less severe (31). We observed a significant increase in protein consumption among individuals with slight albuininuria and clinical albuminuria (Table 1), although protein was eliminated as a significant factor by dietary cholesterol when nutrients were entered in a stepwise manner into a multivariate model (Table 4). This observation is consistent with the findings of Jameel et al. (32), who found that dietary protein intake did not correlate with the development of clinical proteinuria in 376 non-insulin-dependent diabetic subjects after adjusting for age, sex, ethnicity, systolic blood pressure, and 2-h blood glucose. Watts et al. (12) studied a group of insulindependent diabetics and also observed no significant difference of dietary protein intake in 15 patients with slight albuminuria and 15 patients with normal albu-
miii excretion. Cholesterol. Several reports have suggested a role for dietary lipids in the progression of renal disease. Gbmerular sclerosis developed in guinea pigs fed a 1% cholesterol diet (33), and rats maintained on a 4% cholesterol/1% cholic acid diet showed a significant increase in urinary protein excretion, a decline in glomerular filtration rate, and features of focal segmented glomerulosclerosis (34). A high intake of dietary fat has previously been incriminated in gbomerulopathy in nondiabetic patients (10), insulin-dependent diabetic patients (12), and experimental animals (9). The mechanism by which dietary cholesterol might influence the progression of albuminuria is not clear. There was a significant interaction between dietary cholesterol and plasma triglyceride in the current study (not shown), suggesting that the hypertriglyceridemia may be part of the mechanism that contributes to renal damage. By reverse cholesterol transport, hypertriglyceridemia causes both reduced HDL cholesterol and increased low-density lipoprotein (LDL) cholesterol concentrations (35). Some workers have suggested that LDL cholesterol might be the primary endothelial damaging agent in glomerulosclerosis, such as occurs in the pathogenesis of atherosclerosis (36). Mesangial cells possess normal LDL receptors, and histological evanilnation of glomeruli from the kidneys of people with the nephrotic syndrome often reveals massive accumulation of lipid in mesangial cells (36). Moreover, abnormalities of lipoprotein metabolism, ineluding lecithin:cholesterol acyltransferase deficiency and apolipoprotein E gbomerulopathy, have been associated with proteinuria and progressive renal disease (37, 38). 2196
CUNICAI.. CHEMISTRY, Vol. 39, No. 10, 1993
The association between dietary cholesterol and degree of albuminuria was independent of HDL and LDL cholesterol concentrations. There were also no significant interactions between dietary cholesterol and HDL
or LDL cholesterol concentrations with degree of albuminuria (not shown). We previously reported (7) that HDL cholesterol concentrations were significantly related to urinary albumin concentrations, but that this association was no longer significant after serum triglyceride concentrations and body mass index were included in the regression model predicting urinary albu-
min concentrations. In contrast, there was no significant relation between LDL cholesterol concentrations and degree of albuminuria after adjusting for gender (P = 0.1844). However, this lack of a significant relation should be interpreted with caution. LDL cholesterol was calculated by the Friedewald formula, with total cholesterol and HDL cholesterol concentrations measured on different instruments. Therefore, it is possible that the
combination of interbatch and interinstrument measurement errors and the different methods of measuring total cholesterol and HDL cholesterol may have masked a significant relation. The program used in the current study did not provide dietary cholesterol concentrations by source of cholesterol. However, when participants were divided into beef eaters, organ meat eaters, or egg eaters, the lower urinary albumin concentrations observed in nonbeef eaters than in beef eaters suggested that dietary cholesterol of meat origin was the most important. In contrast, dietary cholesterol from organ meats or eggs did not appear to significantly influence the degree of albuminuria
Increased intake of dietary cholesterol was previously reported to be associated with an increased risk of death from ischemic heart disease, from other cardiovascular diseases combined, and from all cardiovascular diseases combined (39). It is possible that the previously observed association between degree of albuminuria and coronary heart disease (3) might be mediated, at least in part, by dietary cholesterol. Fiber. Dietary fiber intake has been related to a number of diseases, including large bowel cancer, varicose
veins, deep vein thrombosis, hemorrhoids, appendicitis, diverticular disease of the colon, hiatus hernia, ischemic heart disease, and diabetes mellitus (40). However, there have been no previous reports of an association between dietary fiber and degree of albuminuria. Postulated mechanisms of action of dietary fiber indude: purely mechanical effects on the gut such as bulkiness, reduced energy density, reduced gastric emptying, and intestinal transit; hormonal effects such as altered secretion of the gut hormones enteroglucagon, gastroinhibitory polypeptide, and somatostatin; binding of bile acids, which interferes with intestinal micelle formation and reduces fat absorption; fermentation by enteric bacteria, forming fiber acetate, propionate, and butyrate, which may have hypolipidemic and hypoglycemic effects; and antioxidant functions, which may reduce the in vivo oxidation of dietary fat (41). It is pos-
sible that the effect of dietary fiber on degree of albuminuria may be mediated by its lipid-lowering effect (42). However, the association between dietary fiber and urinary albumin concentrations observed in the current study was independent of the effect of serum triglyceride concentrations, and there was no significant interaction. Salt. Dietary sodium intake influences arterial blood pressure in -20-50% of hypertensive individuals (43), and albuminuria is a common finding in essential hypertension. Salt susceptibility is associated with demographic characteristics such as ethnicity, obesity, and old age (44). The correlation between dietary salt and albumunuria in the current study was weak (Figure 3) and became nonsignificant after adjusting for age, gender, and ethnicity (Table 3). This could be due to interindividual variation in the hypertensive effect of salt loading. Clinical implications. Because slight albuminuria is interpreted as a marker of incipient nephropathy in people with diabetes meffitus, dietary protein restriction of 0.6-0.8 g/kg body weight has been recommended as part of routine management (45). This recommendation is based on the beneficial effects of such a diet in people with progressive diabetic nephropathy. However, no attempts have been made to identify which particular nutrients are nephrotoxic. Slight albuminuria has been proposed as a risk factor for coronary artery disease (3, 5). The general population is urged to adopt a Mediterranean-type diet high in monounsaturated fat (olive oil), low in cholesterol and saturated fat, and rich in unprocessed vegetable foods because this diet is associated with reduced cardiovascular morbidity and an improved patient compliance profile (46). If slight albuminuria is a marker of risk for cardiovascular disease, our findings would tend to support the recommendation of a Mediterranean diet. In a study of healthy individuals, Wiseman et a!. found significantly lower gbomerular filtration rate, diastolic blood pressure, and urinary albumin excretion in strict vegetarians compared with lactovegetarians and omnivores (47). Although omnivores consumed 35% more protein than vegans, this difference was considered unlikely to account for the marked differences observed.
We conclude that diet has an important effect on renal function in normal healthy individuals and that increased consumption of cholesterol-rich food, such as beef, increases the risk of slight albuininuria. In contrast, increased consumption of fiber, found in high concentrations in fruit, vegetables, and cereals, appears to be protective in reducing the risk of slight albuminuria. These results support a role of diet in the etiology of slight albuminuria. Majorfundingfor the Workforce Diabetes Study was provided by the New Zealand Health Research Council and the Medical Research Council Diabetes Task Force. Supplementary funds were received from Lotteries Medical Research. PAM. was jointly funded by the Health Research Council of New Zealand and the
National Kidney Foundation of New Zealand. We thank John Birkbeck for providing the computerized dietary nutrient table, and Lynn Gillanders and Kerry Maher for advice regarding typical serving sizes.
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