Collecting Dietary Intake Data with Different Tools

  1. 3.1. Assessing Intake on Specific Days to Assess Nutrients and Energy Intakes
  2. 3.1.1. 24-H Recall. The 24-h recall helps the patient to remember his/her food intake on the previous day and to quantitate it (46-52). The interviewer needs to be trained to recall the patient's exact food intake. Accurate quantification is essential. Providing food models, bowls, and plate and picture charts are helpful for collecting accurate intake data. This tool assesses the actual intake of the patient. However, the 24-h recall is not sufficient to describe the patient's usual dietary pattern because it covers a short time. The recall usually takes 20-30 min to complete, but it may take longer if many different foods, ethnic foods, or mixed dishes with various ingredients are consumed. The 24-h recall is the most commonly used dietary tool in the United States, and it is used in the National Health and Nutrition Examination Survey (NHANES) (48-49) and the Nationwide Food Consumption Surveys of Food Intake by Individuals. The interviewer can conduct a 24-h recall on random days via telephone although accurate quantification of food intake is more difficult unless the patient is instructed on portion size in advance of the interview (50-52).

The strengths of the 24-h recall include that it does not require literacy and it does not require the patient to change his or her dietary habits because the data collection is done after the patient eats. Use of dietary supplements can be easily included; these are important sources of nutrients in many CKD patients. Also, all foods can be included as choices are not confined to a food list. Serial 24-h recalls are helpful in getting an idea of patterns of intakes and the ebbs and flows of intake.

The limitations include the need for reliance on memory, need for accurate quantification of portion size, and need for a highly trained interviewer. In addition, underreporting is extremely common, and therefore, quantitative estimates need to be combined with other indices such as weight or weight change, hydration status, and so on to get a true picture of the patient's condition.

3.3.1.2. Food Records. This method provides qualitative and quantitative data on food intake. Food records are usually collected for an average of 3 days including 2 week days and 1 weekend day (46,47,52,53). For dialysis patients, the record should contain dialysis and non-dialysis days and 1 weekend day because the eating pattern changes based on the dialysis treatment itself and also on appetite changes related to it. A 2-day diet diary can be used for HD patients to monitor variation in food intakes between dialysis days and non-dialysis days (Table 5) (30). Instruction on time of eating, foods, beverages, portion size, snacks, methods of preparation, food ingested, and special recipes should be included to collect accurate intake data. Food models and household measuring cups and spoons are useful to estimate portion size (46,54-56). If a patient participates in a research study, provision of measuring instruments or even a household scale for measuring food will help the patient record accurate data. Food records should be carefully reviewed by a dietitian immediately after completion to ensure that the detailed description of the foods and recipes is accurate as it is difficult to code the foods for later analysis if this is not done.

The major strengths of the food record are that it does not depend as much on the individual's memory, and the portion size estimates may be more accurate because the records are ideally filled at the same time of eating. Use of dietary supplements and medications containing nutrients can be included.

Common limitations include under-reporting, mistakes in conversion of weight and volume, alterations of eating habits during recording periods, and the heavy burden it puts on patients (57-61). Patients must be literate to collect and record their intakes. Nutrient intakes are calculated using an up-to-date database and computerized dietary analysis system.

  1. 3.2. Dietary Patterns
  2. 3.2.1. Dietary History. The diet history is used to estimate the patient's usual food intake and meal pattern over a long period of time. The components of the dietary history include usual eating pattern, a crosscheck of frequency of consumption of specific food items, and a 3-day food record. However, the 3-day food record is usually omitted and the time periods covered by the diet history vary. A shorter time frame (less than 1 month) produces better validity, and obtaining of a dietary history for a period over 1 year is unrealistic (46,47).

The major strength of the dietary history is that it provides a detailed picture of the eating pattern (58,59,62-65). The weakness of the dietary history is that it requires a highly skilled interviewer. It takes 40-60 min to complete, is difficult to quantify, and is ill-suited for later data entry into a computer. Therefore, it is rarely used today for clinical and research purposes.

3.3.2.2. "Usual Intake": Semi-Quantitative Food Frequency Questionnaire. The Semi-Quantitative Food Frequency Questionnaire (SFFQ) is used to assess the frequency of consumption of food items and groups of foods during a specific reference time period, which may or may not be the period the patient actually bases his/her recalls on (46,47,66). The SFFQ provides the information of usual food consumption patterns. The SFFQ evaluates usual intake of the foods rather than food intake of specific days. The SFFQ has two components, food list and frequency of consumption; seasonal variation of specific foods can be also included in it. The SFFQ is most commonly used for epidemiological studies because usual food intake patterns appear to affect the outcomes of some diseases.

The advantages of the SFFQ are that it is relatively quick to administer. It can be administered by interviewers, by telephone, via mail, or self-administered. Processing the SFFQ is inexpensive, and self-administered versions are available from some processing centers.

Limitations of the SFFQ include the fact that in CKD there often is no usual intake; intakes rise and fall from day to day as the disease waxes and wanes, so that it is impossible for the patient to identify a pattern. Also, the SFFQ portion size descriptions may be unclear, and analysis of quantities of specific nutrients can be inaccurate. The instrument is ill-suited for making estimates of total intakes; it is really designed to distinguish between groups of patients. The SFFQ should be validated and tested for reproducibility for use in minority groups (67-73).

The most common SFFQs are Willett's "Harvard" SFFQ and the "Block" (National Cancer Institute) SFFQ in various forms (66,71,72). These SFFQs come in different versions, and all of them are validated by concurrent comparison with another method rather than against a "gold standard" that represents actual intake. The SFFQs are not used often to assess dietary intake in patients with CKD because the multiple dietary restrictions that are involved in this population make the assumptions about commonly eaten food groups invalid (74). The items on vitamin and mineral supplements are not appropriate for the types of dietary supplements common in CKD or among dialysis patients, and oral nutritional supplements are not included on usual SFFQs. The modification of these SFFQs for use in kidney disease can perhaps someday be a useful tool to assess dietary intake for

CKD patients in future studies. At present, simple food frequency questionnaires can be used which take less time. However, it is difficult to translate data from these questionnaires into quantitative estimates of patients' daily nutrient intakes.

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