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NHANES 3, conducted from 198894 by the National Center for Health Statistics, US Department of Health and Human Services, included five major components: a household questionnaire, medical history questionnaire, dietary questionnaire, physical examination and clinical tests. The survey sample was designed and recruited using multi-stage area probability sampling procedures. Parts of the survey were conducted in the home, the rest in specially designed mobile examination centers (MECs), where the dietary and clinical procedures were conducted.

NHANES 3 dietary components consisted of a 24-hour recall, a food frequency questionnaire, and questions about special diets, medications and nutritional supplements. Recall data were collected for over 25 000 people. These data may be analyzed to characterize consumption of chocolate confectionery for various population groups. The major limitation of NHANES 3 data is that only one 24-hour recall is obtained for each person, so intra-individual variation cannot be estimated.

Third National Health and Nutrition Examination Survey (NHANES 3).

In the 199496 CSFII, respondents provided recall data on each of 2 days, approximately 1 week apart. These data were obtained for about 15 000 individuals of all ages. The survey sample was designed and recruited using multi-stage area probability sampling procedures.

CSFII data on age, sex, race, region, season and other variables allow estimation of consumption of foods, including chocolate confectionery, for a wide variety of population subgroups. Results can be reported based on consumption per day or on 2-day averages.

199496 US Department of Agriculture Continuing Survey of Intakes by Individuals (CSFII).

allow an estimation of amounts consumed by asking subjects if their usual portion size is small, medium or large compared to a stated 'medium' portion. The size of the medium portion is usually based on mean intakes of large populations but may be standardized for various age/sex groups.

The diet history is used to obtain information from individuals about the usual pattern of eating over an extended period of time (12, 13). Used primarily in epidemiological research, the diet history is a more in-depth and time-consuming procedure than the recall, record and FFQ methods. A recall or FFQ may be included as a diet history component.

In prospective food consumption studies, survey participants are asked to record information on foods and beverages as the foods are consumed during a specific period. Quantities of foods and beverages consumed are entered in the record usually after weighing or measuring the amounts served and subtracting leftover amounts.

The Dietary and Nutritional Survey of British Adults (NDS) (14) and the

Prospective

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German Nationale Verzehrsstudie (NVS) (15) are examples of surveys conducted using diary/record methods (Figs 20.3 and 20.4). British national surveys using methodology similar to that used in the NDS for adults have been conducted to assess dietary intakes of infants (16), toddlers (17) and school-aged children (18).

The Dietary and Nutritional Survey of British Adults was carried out between October 1986 and August 1987 by the Ministry of Agriculture, Fisheries and Food (MAFF). The survey sample was recruited using a multi-stage random probability design, with the goal of obtaining a nationally representative sample of non-institutionalized adults ages 16 to 64.

Approximately 2200 survey respondents completed 7-day dietary records. The results can be analyzed to estimate chocolate confectionery intakes by population subgroups per day or per week; percentages of populations consuming chocolate confectionery on a particular day; or percentages of populations consuming chocolate confectionery on at least 1 day of the survey period.

The Dietary and Nutritional Survey of British Adults.

The German NVS was conducted from October 1985 to January 1989. Over 20 000 individuals completed 7-day weighed food records and 7-day activity records. Basic socio-demographic data were collected on all individuals; one 'target individual' 18 years or older in each household also provided information on food frequency, health history, lifestyle and nutrition knowledge and attitudes.

As with the British survey data, NVS data can be analyzed to estimate chocolate confectionery intakes by population subgroups per day or per week; percentages of populations consuming chocolate confectionery on a particular day; or percentages of populations consuming chocolate confectionery on at least 1 day of the survey period.

The Nationale Verzehrsstudie.

In general, data from short-term recalls and from food diaries are the most accurate and flexible data to use in estimating food consumption by individuals. Data from these surveys can be used to calculate distributions of intake, and estimates can be calculated for subpopulations based on age, sex, ethnic background, socio-economic status and other demographic variables, provided that such information is collected for each individual.

It must be recognized that, although data on foods consumed by individuals in general provide a better picture of intake patterns than do food supply data or household budget data, the validity and reliability of the methods and the potential for error in data collection must be considered.

Methods for assessing food consumption by individuals have been validated by surreptitious observation and by using biological markers, but the validity of one survey method for use in obtaining accurate food consumption data generally is tested using another common survey method. Method reliability the extent to which a method yields reproducible results depends somewhat on the number

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of days of dietary intake data collected for each individual in the population. The number of days of food consumption data required for reliable estimation of population intakes is related to each subject's day-to-day variation in diet (intra-individual variation) and the degree to which subjects differ from each other in their diets (inter-individual variation) (19, 20). When intra-individual variation is small relative to inter-individual variation, population intakes can be reliably estimated with consumption data from a smaller number of days than should be obtained if both types of variation are large. The number of intake days required for reliable estimation of consumption is smaller for a frequently consumed food (e.g. milk) than for an infrequently consumed food (e.g. organ meats).

Potential sources of error in individual food consumption surveys include chance and measurement factors. The size of error due to chance depends somewhat on the extent to which the sample population reflects the actual population. Error due to chance may also arise from data collection at different times of the day, on different days of the week, or at different seasons of the year. The survey instrument may introduce measurement error if questions are not clear, if standard probes lead the subject to a desired answer, if questions are culture specific, or if questions do not follow a logical sequence. Interviewer bias may contribute to measurement error if the interviewer is judgmental or uses nonstandard probes to obtain data.

Respondents may contribute to measurement error if they omit reporting foods actually consumed, misrepresent the quantity of foods consumed, or report consumption of foods which were not actually consumed. Foods that are not staples in the diet or that might be viewed as luxury items such as chocolate are more likely to be under-reported by some populations than are staple foods such as wheat, rice or potatoes. Dietary under-reporting by obese individuals has been documented in a number of studies (2123). Heitmann and Lissner (22) identified snack-type foods as the category most likely to be omitted from dietary reports.

Consumption Patterns for Chocolate Confectionery Availability of Chocolate Confectionery in the USA

Chocolate confectionery shipment data compiled by the DOC (5) indicate that from 199296, per capita availability of these products increased by 13%, from 12.8 g/day to 14.5 g/day (Table 20.1). DOC data show that enrobed and molded chocolate confectionery with candy, fruit, nut or granola centers were most popular and accounted for nearly half of all types of chocolate confectionery available to Americans. Data compiled by the IOCCC (4) show similar increases in per capita availability of chocolate confectionery in recent years, from 12.6 g/day in 1991 to 14.5 g/day in 1996 (Fig. 20.5).

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