Dietary Intake of Patients With Chronic Kidney Disease Entering the LORD Trial: Adjusting for Underreporting
Article Outline
Objective
The study objective was to determine the dietary intake of patients with chronic kidney disease before and after filtering for suspected underreporters and to investigate the impact of underreporting on the interpretation of diet data.
Design
This was a cross-sectional study.
Setting
The study included outpatients from hospitals and clinics in Northern Tasmania, Australia.
Patients
Data from 113 patients enrolled in the Lipid Lowering and Onset of Renal Disease trial were used in this study. Patients with serum creatinine greater than 120 mmol/L were included, and those taking lipid-lowering medication were excluded.
Methods
Patients completed a 4-day self-report diet diary, and FoodWorks software was used to determine their daily intake of energy, macronutrients, and specific micronutrients. Diet diaries were assessed for likely underreporting using the Goldberg cutoff approach with a ratio of energy intake to estimated resting energy expenditure of 1.27. Nutrient intakes were compared with current National Kidney Foundation’s Kidney Disease Outcomes Quality Initiative guidelines, World Health Organization recommendations, recommended daily allowances, and daily values adjusted for energy intake.
Results
Demographics of the patients were as follows: male/female, 71/42; age (mean ± standard deviation), 60 ± 15 years; body mass index, 28.6 ± 6.0 kg/m2, and serum creatinine, 223.4 ± 110.0 mmol/L. According to the criteria, 80 patients (70.8%) were underreporting their energy intake. Underreporters were more likely to be female and younger, and have a higher body mass index and elevated serum creatinine. In all patients, daily energy intake (89.6 ± 32.4 kJ/kg) was lower than recommended (125-145 kJ/kg); however, this was not the case for valid reporters (128.3 ± 23.7 kJ/kg). Protein intake was higher (0.9 ± 0.3 g/kg) than recommended (0.75 g/kg) in all patients and even higher (1.2 ± 0.3 g/kg) in valid reporters. Mean calcium, zinc, and dietary fiber intakes were all below recommendations in all patients, but these differences were not apparent in valid reporters.
Conclusion
Interpreting self-report diet diary data from patients with chronic kidney disease without attempting to exclude underreporters will lead to erroneous conclusions, especially in respect to energy, protein, dietary fiber, calcium, and zinc intakes.
NUTRITION IS KNOWN to play a major role in the preservation of kidney function, the reduction of cardiac comorbidities, and the overall well-being of patients with chronic kidney disease (CKD), with deterioration in nutritional status known to precede end-stage kidney disease.1 Although it is recommended that regular monitoring of the patient’s nutritional status should be a routine component of predialysis care,1 measuring dietary intake is difficult. A self-report multiday diet diary is acknowledged as one of the best approaches to quantify energy and nutrient intake. However, it is also well recognized that there are considerable sources of error that may effect interpretation of the data.2
The validity of the data from self-report diet diaries can be assessed by determining the ratio of energy intake (EI) with resting energy expenditure (REE), and a joint report organized by the World Health Organization (WHO) determined that a cutoff limit of 1.27 is likely to identify individuals who underreport on diet diaries.3 The frequency of underreporting has been assessed in numerous studies in many subject groups, including children,4 adolescents,5 athletes,6 obese subjects,7 and the general population.8 Estimates vary from as low as 2%9 to 85%,10 with most studies reporting the incidence to be approximately 20%.11 In patients with CKD, a recent study using the 1.27 EI:REE cutoff reported a much greater prevalence of underreporting (72.5%),12 and this was similar to a previous study of patients on hemodialysis (61%).13
In the general population, underreporting has led to erroneous conclusions regarding nutrient intake.14, 15 The aims of this study were to confirm the extent of underreporting in patients with CKD and to assess the impact of underreporting on dietary conclusions.
Methods
Study Population
Data from 113 patients with CKD enrolled in the Lipid lowering and Onset of Renal Disease (LORD) trial were included in this analysis. The trial is a randomized placebo-controlled study investigating the effects of 10 mg of atorvastatin on the progression of kidney disease in patients with CKD.16 The inclusion criterion for the trial is a serum creatinine greater than 120 μmol/L. Exclusion criteria were patients already taking lipid-lowering medication or women with childbirth potential. Patient characteristics are provided in Table 1. All patients were white, and the primary causes of kidney disease, according to the classification system used by the Australian and New Zealand Dialysis Transplant Registry, were hypertension (n = 37), glomerulonephritis (n = 31), reflux nephropathy (n = 10), polycystic kidney disease (n = 9), diabetic nephropathy (n = 8), analgesic nephropathy (n = 1), and miscellaneous (n = 17). The study was approved by the Ethics Committee of the Launceston General Hospital in accordance with the guidelines of the Declaration of Helsinki. Patient recruitment occurred from January 2002 to January 2005.
Table 1. Patient Characteristics (Mean ± Standard Deviation)
| Variable | All N = 113 | Valid Reporters n = 33 | Underreporters n = 80 |
|---|---|---|---|
| Sex (female) | n = 42, 37% | n = 8, 24% | n = 34, 43%† |
| Age (y) | 60 ±15 | 65±10 | 59±16⁎ |
| Body mass (kg) | 81.8±17.3 | 74.5±12.3 | 84.8±18.2† |
| Body mass index (kg/m2) | 28.6±6.0 | 25.4±3.4 | 30.0±6.4† |
| Systolic blood pressure (mm Hg) | 143.4±20.2 | 145.5±24.3 | 142.5±18.3 |
| Diastolic blood pressure (mm Hg) | 81.0±12.9 | 82.1±15.2 | 80.6±11.9 |
| Hemoglobin (g/L) | 130.6±17.0 | 134.8±18.7 | 128.9±16.1 |
| Hematocrit (L/L) | 0.39±0.05 | 0.41±0.1 | 0.39±0.05 |
| Estimated glomerular filtration rate (mL/min/1.73 m2) | 40.3±19.4 | 38.9±14.9 | 40.8±21.0 |
| Urinary protein excretion (g/d) | 1.28±1.94 | 0.74±0.87 | 1.50±2.20 |
| Creatinine clearance (mL/sec) | 0.68±0.32 | 0.77±0.27 | 0.64±0.30⁎ |
| Serum creatinine (μmol/L) | 223.4±110.0 | 187.9±60.4 | 238.0±122.0⁎ |
| Total cholesterol (mmol/L) | 5.6±1.4 | 5.8±1.4 | 5.6±1.4 |
| HDL cholesterol (mmol/L) | 1.2±0.4 | 1.3±0.4 | 1.2±0.3⁎ |
| LDL cholesterol (mmol/L) | 3.5±1.1 | 3.6±1.1 | 3.4±1.1 |
| Total cholesterol/HDL cholesterol ratio | 4.9±1.6 | 4.6±1.7 | 5.0±1.5 |
| Triglycerides (mmol/L) | 2.2±1.4 | 1.9±0.9 | 2.4±1.6 |
| Serum albumin (g/L) | 40.2±4.5 | 41.5±3.8 | 39.6±4.7 |
⁎Significantly different from valid reporters (P < .05). |
†Significantly different from valid reporters (P < .01). |
After informed consent was obtained, patients were provided with a 4-day diet diary as part of baseline measures for the LORD trial. Patients then had a 3-month run-in phase before they started taking either the hydroxymethylglutaryl-coenzyme A reductase inhibitor, atorvastatin (10 mg), or placebo. At the end of the run-in phase, patients provided fasting blood and 24-hour urine samples. Less than 5 days after these samples were obtained, patients attended a routine clinic visit where height and weight were measured and the completed diet diaries were returned. Patients were then provided with the tablets to begin the intervention.
All clinical chemistry measures were completed in public and private pathology laboratories accredited with the National Association of Testing Authorities (Australia). Full blood counts were performed on a Coulter MaxM (Coulter, Luton, UK). Total cholesterol, high-density lipoprotein cholesterol, triglycerides, urinary chemistry, electrolytes, and liver enzymes were measured on an Olympus AU-600 automated analyzer (Olympus Mishima, Shizuoka, Japan). Low-density lipoprotein cholesterol was calculated using the Freidwald formula.17 Estimated glomerular filtration rate was determined using the Cockcroft and Gault equation,18 and creatinine clearance was calculated from the 24-hour urine collection.
Diet Diaries
The 4-day diet diary contained photographs of common foods (e.g., steak, pasta, rice, potatoes) on plates with their corresponding mass. For each food, three different portions were displayed (large, medium, and small). This diary had been previously validated against 7-day weighed records.19 When patients were provided with the diaries, they were given detailed instructions by one of two trained nurses on what was expected, and specific examples were given. They were asked to complete the diary entry at the time of food consumption, with the instruction that the 4 days should be as close to their next pathology visit as possible. This was toward the end of the run-in phase, approximately 3 months after they were given the diary. They were asked to include 3 weekdays and 1 weekend day. The diaries were analyzed using version 4.0 of FoodWorks (Xyris, Brisbane, Australia). Dietary supplements were also entered into the analysis with the specific supplement details obtained at either the baseline or end of run-in visit. Energy and protein intakes were based on actual body weight. It should be noted that this database is not complete for all nutrients in all foods, especially for vitamin and minerals.
Assessing Valid Reporters
The ratio between EI and estimated REE was used to assess the accuracy of each patient’s diet diary. A cutoff value of 1.27 was selected on the basis of a joint report from the Food and Agriculture Organization, WHO, and the United Nations University.3 Estimated energy expenditure was determined using the Schofield equations20 with an adjustment for physical activity levels.21 Physical activity was assessed using the Active Australia Questionnaire.22
Data Analysis
Data are displayed as the mean ± standard deviation (or 95% confidence intervals) and compared with current National Kidney Foundation’s Kidney Disease Outcomes Quality Initiative (K/DOQI) guidelines,1 WHO recommendations,23 recommended daily allowances (RDA), and daily values (DV)23 adjusted for EI. For the determination of normal, overweight, and obese, the recommendations from the WHO were used, with a healthy body mass index (BMI) at 18.5 to 24.9, a BMI greater than 25 indicating overweight, and a BMI greater than 30 indicating obesity.24 T tests were used to compare valid reporters and underreporters. Significance was assumed when P less than .05, and all statistical analyses were performed using Version 8.2 of STATA (Statacorp, College Station, TX).
Results
The mean ± standard deviation EI/resting metabolic rate [RMR] of all patients was 1.08 ± 0.34. After using the Goldberg cutoff approach and an EI/RMR of 1.27, it was calculated that 80 patients (70.8%) were underreporting their usual EIs. Indeed, 53 of all the patients reported their EI to be below their estimated RMR. The estimated EI/RMR of the underreporters was 0.90 ± 0.20. This effectively meant that they reported consuming 30% less than their energy needs.
To allow for the possibility that overweight and obese patients may have been intentionally eating less energy to decrease body weight, additional analyses were carried out using an RMR derived from healthy body weight calculated using a BMI of 25. With this approach, only 9 of the 80 underreporters would have been removed from this list, further supporting the notion that the diet diaries were not being accurately completed.
Characteristics of all patients, valid and underreporters, are shown in Table 1. There were significantly (P < .05) more female (43% vs. 24%) and younger (59 vs. 65 years) underreporters. In addition, underreporters had a greater body mass (85 vs. 75 kg), BMI (30 vs. 25 kg/m2), and serum creatinine (238 vs. 187 μmol/L). There was a trend (P = .058) for higher urinary protein excretion in underreporters (1.5 vs. 0.7 g/day). In regard to BMI, 12% of the valid reporters were obese, 30% were overweight, 55% were of normal weight, and 3% were underweight, and in those underreporting, 39% were obese, 35% were overweight, and 26% were of normal weight.
Figure 1 summarizes the findings from the dietary analyses of all patients (data also in Table 2). From these data it would be concluded that these patients with CKD had energy, total carbohydrate (%), complex carbohydrate, dietary fiber, calcium, and zinc intakes significantly lower (P < .001) than recommendations. In addition, the percentage of energy from fat and total protein intake were significantly higher than recommended by the WHO and K/DOQI, respectively. However, after excluding the underreporters, the only nutrient that was still below a recommended level was grams of complex carbohydrate. Dietary protein and percent fat were still above recommended levels.
Figure 1.
Nutrient intakes as a percentage of recommendations (mean
95% confidence interval). *Complex carbohydrates, fat, saturated fat, and cholesterol are DVs adjusted for EI using the K/DOQI recommendation (125 kJ/d). Protein, fat, saturated fat, and cholesterol intakes are all recommended to be below the indicated 100%, thus the different shading. Box plots show 10th, 25th, 50th, 75th, and 90th percentiles. CHO, carbohydrate; DV, daily value; EI, energy intake; K/DOQI, National Kidney Foundation Kidney Disease Outcomes Quality Initiative.
Table 2. Dietary Intakes of Patients With Chronic Kidney Disease (Mean ± SD)
| Daily Intakes | Recommendation | All Patients | Valid Reporters | ||
|---|---|---|---|---|---|
| Daily Intake (Mean ± SD) | No. of Patients (of 113) Below/exceeding⁎ Recommendation (%) | Daily Intake (Mean ± SD) | No. of Patients (of 33) Below/exceeding⁎ Recommendation (%) | ||
| Energy (kJ/kg) | 125–145 kJ/kg† (K/DOQI) | 89.6±32.4 | 95(84%) | 128.3±23.7 | 16(48%) |
| Protein (%)⁎ | 10%–15% total energy intake (WHO) | 18.2±3.5 | 86(76%) | 16.3±3.3 | 17(57%) |
| Protein (g/kg)⁎ | 0.75 g/kg† (K/DOQI) | 0.9±0.3 | 81(72%) | 1.2±0.3 | 33(100%) |
| Carbohydrate (%) | 50%–75% (WHO) | 46.4±7.0 | 76(67%) | 48.2±6.4 | 19(56%) |
| Complex carbohydrate (g) | Adjusted DV‡ 367 g for All 334 for VR | 111.3±44.9 | 113(100%) | 153.3±40.4 | 33(100%) |
| Fat (%)⁎ | 15%–30% (WHO) | 31.6±6.4 | 69(61%) | 32.5±5.3 | 24(73%) |
| Fat (g)⁎ | Adjusted DV§ 79 g for All 72 g for VR | 58.9±21.7 | 26(23%) | 80.9±19.1 | 24(73%) |
| Saturated fat (g)⁎ | Adjusted DV∥ 24 g for All 22 g for VR | 24.2±10.2 | 50(44%) | 33.1±10.0 | 28(85%) |
| Cholesterol (mg)⁎ | Adjusted DV¶ 367 mg for All 334 mg for VR | 209.4±96.4 | 11(9%) | 254.5±105.5 | 6(18%) |
| Vitamin C (mg) | 30–40 (RDA) | 118.1±88.8 | 0(0%) | 155.1±90.0 | 0(0%) |
| Vitamin A eq. (μg) | 750 (RDA) | 910.7±623.4 | 52(46%) | 1269.1±872.4 | 5(15%) |
| Total folate (μg) | 200 (RDA) | 280.9±108.4 | 25(22%) | 366.8±119.8 | 0(0%) |
| Thiamin (mg) | 0.7–1.1 (RDA) | 1.6±0.7 | 14(12%) | 2.1±0.7 | 0(0%) |
| Riboflavin (mg) | 1.0–1.7 (RDA) | 1.8±0.9 | 27(24%) | 2.3±0.9 | 0(0%) |
| Niacin (mg) | 11–19 (RDA) | 32.5±10.1 | 1(0%) | 23.0±6.8 | 0(0%) |
| Sodium (mg) | Range 920–2300 (RDA) | 2326.7±916.2 | >49 (43%)<4 (4%) | 3112.5±951.4 | >26 (79%)<0 (0%) |
| Calcium (mg) | 800–1000 (RDA) | 703.9±319.4 | >16 (14%)<79 (70%) | 940.9±335.4 | >12 (36%)<14 (42%) |
| Magnesium (mg) | 270–320 (RDA) | 263.7±95.4 | >27 (24%)<69 (61%) | 349.4±104.7 | >18 (55%)<7 (21%) |
| Potassium (mg) | Range 1950–5460 (RDA) | 2725.4±1005.0 | >2 (2%)<23 (20%) | 3508.9±1186.5 | >2 (6%)<0 (0%) |
| Iron (mg) | 7–12 (RDA) | 10.7±4.1 | >32 (28%)<18 (16%) | 14.1±4.8 | >21 (64%)<0 (0%) |
| Zinc (mg) | 12 (RDA) | 9.2±2.6 | 94(83%) | 10.9±2.7 | 23(68%) |
| Phosphorus (mg) | 1000 (RDA) | 1179.3±403.9 | 38(34%) | 1545.9±386.2 | 1(3%) |
| Dietary fiber (g) | Range 27–40 (WHO) | 19.8±8.9 | >5 (4%)<94 (83%) | 28.0±10.2 | >5 (15%)<17 (52%) |
⁎Protein, fat, saturated fat, and cholesterol intakes are all recommended to be at or below recommendations. |
†Recommended intakes for energy and protein intake are based on actual body weight. |
‡DV for complex carbohydrate intake = 300 g/d for a 8368 kJ/d intake. This was adjusted for each individual using the recommended K/DOQI minimum energy intake (125 kJ/d). |
§DV for fat intake is less than 65 g/d for a 8368 kJ/d intake. This was adjusted for each individual using the recommended K/DOQI minimum energy intake (125 kJ/d). |
∥DV for saturated fat intake is less than 20 g/d for a 8368 kJ/d intake. This was adjusted for each individual using the recommended K/DOQI minimum energy intake (125 kJ/d). |
¶DV for cholesterol intake is less than 300 mg/d for a 8368 kJ/d intake. This was adjusted for each individual using the recommended K/DOQI minimum energy intake (125 kJ/d). |
Discussion
The major findings of this study are that a large percentage (70.8%) of the 113 patients with CKD underreported their EI using a 4-day self-report diet diary and that conclusions based on these analyses are likely to be inaccurate.
Our findings are in agreement with Avesani et al.,12 who used the same cutoff of 1.27 EI/REE and found that 72.5% of patients with CKD underreported their EI. The incidence of underreporting seems to be much higher in patients with CKD than in the general population. A review by Hill and Davies11 provides a comprehensive list of studies investigating the validity of self-reported EI, with the majority of studies finding that the incidence of underreporting is approximately 20%.
The percentage of overweight or obese patients underreporting was 74% compared with 42% of the valid reporters. The association between underreporting and increased body mass/BMI is consistent with the literature.12, 25 It may be that the patients were restricting their EI to lose weight. However, when an ideal weight (based on a BMI of 25) was used, and the EI/RMR ratio was recalculated, only 9 of the 80 underreporters would have been removed from the list of underreporters. Furthermore, the EI/RMR ratio of the 80 underreporters was only 0.90. This indicates that the underreporters are either considerably reducing their EI or inaccurately reporting their food intake. On the basis of evidence from numerous other studies and longitudinal data from patients with CKD showing that reporting low EIs is not associated with long-term weight loss,12 it is postulated that the patients are consuming more energy than they are reporting. Potential reasons for underreporting are numerous and a recent review article by Maurer et al.25 discusses the complex psychosocial and behavioral characteristics that may explain underreporting.
Other characteristics of the underreporters in this study were as follows: female, younger age, higher serum creatinine (lower creatinine clearance), and a trend (P = .058) for elevated urinary protein excretion. Attitudes to food provide the most likely explanation for diet-recording behavior26 and the finding that female patients with CKD are more likely to underreport is consistent with the literature from the general population.11, 25, 26 It is believed to be due to increased body and diet consciousness and an associated desire to convey a positive image when completing diet diaries and thereby misrepresenting their intake.
The finding that younger patients were more likely to be underreporting (mean age difference between valid and underreporters was 6 years) is unusual compared with previous studies.11 A possible explanation is that younger patients might now be much busier than older individuals because of differing work commitments and therefore may have been more likely to forget or not devote enough time to accurately completing the diary.
Underreporters had elevated serum creatinine and lower creatinine clearance and a trend (P = .06) for elevated urinary protein excretion. This suggests that patients with less kidney function are more likely to underreport, which may also be related to a desire to relay a more positive image of their food consumption. To our knowledge, there have been no other reports on the relationships between the extent of a disease and the degree of underreporting.
The other major finding of this study was that conclusions based on the analysis of all patients would be false if there is no attempt to determine the accuracy of the reporting. Other studies have also found that dietary conclusions can be significantly altered by the inclusion or exclusion of underreporters.14, 15 The main discrepancy in our study was EI. After the first analysis with all 113 patients, it would have been concluded that this group of patients are energy deficient to the point that they are only obtaining 70% of their energy needs (using the lowest value from the recommended range). Because, on average, the group was overweight, a decrease in EI may be beneficial. However, it is likely that many of these patients are not accurately reporting their food intake. Therefore, an initial conclusion of a potentially beneficial low EI is incorrect.
There is much debate regarding the recommended protein intake for patients with CKD.27 If low-protein diets are beneficial to patients with CKD, then the findings of this study indicate that a greater percentage of patients are consuming more than that recommended by K/DOQI.1 Indeed, when all patients were analyzed, 72% are above the protein recommendation of 0.75 g/kg body mass. However, when underreporters are excluded, all 33 patients (100%) are above this level. Qualitative analysis of the diet diaries showed that a large number of individuals consumed red meat on a regular basis, suggesting that a good strategy to decrease dietary protein intake would be to advise a limitation of red meat consumption. However, additional care must be taken to avoid malnutrition with low protein intakes (<0.6 g/kg body mass).
Mean total carbohydrate (%), complex carbohydrate, dietary fiber, calcium, and zinc intake were lower than recommended in the entire study group. However, when the underreporters were excluded, the only nutrient that was still below a recommended level was grams of complex carbohydrate. Because the percentage total carbohydrate intakes were only slightly below the WHO lower-limit recommendation of 50%, this indicated a high intake of simple sugars. All dietary guidelines recommend low intakes of simple sugars, and dietary advice, such as reading food labels and avoiding foods with sugar, honey, sucrose, dextrose, or corn syrup listed as the first or second ingredient, would be beneficial to these patients.
A number of factors may limit the external validity of our findings. The patients with CKD included in this analysis are from a trial investigating the effects of atorvastatin on kidney function. These individuals were not taking lipid-lowering medication at the time this study was carried out, which may not be representative of all patients with CKD. The use of a 4-day diet diary to collect food information is recognized as having a number of limitations, such as difficulties in estimating food quantities, compliance with regularly recording foods, and the use of unfamiliar terms/foods that makes entry into a software program difficult.28 A number of strategies were used to avoid these potential problems, including providing a diary with portion-size pictures that was previously validated against 7-day weighed records in a non-CKD population19 and asking them to enter foods at the time of consumption and providing them with detailed instructions by a trained individual.
Our estimation of energy expenditure was obtained using the Schofield formulae, and although there are studies to report the validity of these equations in healthy populations, they have not been validated in patients with CKD. However, our incidence of underreporting was strikingly similar to that found by Avesani et al.12 (71% vs. 72.5%), who determined energy expenditure using indirect calorimetry. Finally, the calculation of normalized protein nitrogen appearance would have been a useful addition to investigating the protein status of the patients. Unfortunately, in patients with CKD this requires the additional measure of urinary urea,29 which is not a routine measure in these patients.
Conclusions
These data show that the population sample with CKD studied have a high incidence (71%) of underreporting their dietary intake. Without accounting for underreporting, dietary analysis would lead to erroneous conclusions, especially in respect to energy, protein, dietary fiber, calcium, and zinc intakes. It is, however, of note that there are some real dietary issues, and advice on intake of protein and fat is important.
Acknowledgments
The authors thank Lisa Anderson, Marianne Smith, and Krystal Chugg for their assistance in collecting data.
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This project was supported by a grant from the Clifford Craig Medical Research Trust, C. Prosser Green Trust. Pfizer Pharmaceuticals provided atorvastatin and placebo for the LORD trial.
PII: S1051-2276(07)00096-9
doi:10.1053/j.jrn.2007.04.004
© 2007 National Kidney Foundation, Inc. Published by Elsevier Inc All rights reserved.
