The composition and level of dietary intake in China

In China, the standard approach to collecting accurate dietary data was the three-day household inventory to measure household food consumption and nutrient intake. Measuring individual food consumption was regarded as less accurate and was thought to be unacceptable before the 1980s. A multiple-day household inventory method is time-consuming and expensive, as it requires a high-quality, durable scale and trained field workers. Moreover, the method provides only nutrient intake and food consumption data at the household level. It neither differentiates the intake of guests from

usual household members nor measures food eaten away from home (AFH). For these reasons, it is very difficult to assess nutrition status and conduct a range of studies at the individual level with the inventory method. Nevertheless, nutritionists in China and elsewhere in Asia believe the increased cost and effort are justified by the increased quality of measurement.

Since the 1980s, several large-scale nutrition surveys have been completed to observe the impact of socioeconomic changes on food consumption and chronic diseases in China. However, there has been no systematic analysis of the quality of 24-hour dietary recall, and little work has been done to consider ways to improve these dietary-assessment methods. Although more and more studies and discussions have focused on such methods in the world, minimal research has assessed the reliability of 24-hour dietary recall, and little attention has been paid to improving the quality of the dietary surveys in China.

Surprisingly little work has been undertaken to validate dietary intake methods in Asia, and many gaps hamper our understanding of the probity of the data they generate around the world. No established clear standards and no biochemical or other biological markers provide the necessary details to validate a dietary method. When scales are calibrated properly, weighing (household inventory) is precise. As is standard practice for a wide range of dietary intake-validation studies, the more detailed household inventory is assumed to be the gold standard. For this reason, the accuracy (repeatability and validity) of 24-hour recall is measured by comparison with it. Comparison is undertaken mainly by determining the absolute and relative differences in the results of the two methods. The same Chinese food composition tables are used for both sets of results. In other words, no biochemical or other biological markers are used to validate these methods.

We compared the household diet inventory with individual dietary recall using data from the China Health and Nutrition Survey (CHNS). Detailed data were collected for the same three consecutive days from all respondents. The study also evaluated the methodology whereby the quality of the 24-hour recall was enhanced by use of a household measure of cooking oil consumed.

There are clear reasons for collecting 24-hour dietary intake data. China has conquered the problems of food scarcity at the national level and has undergone a remarkable transition in the structure of food consumption. This has gone hand in hand with marked changes in eating behaviour. For instance, AFH food consumption has increased in response to the dynamic changes in real disposable income and market labour force patterns. Within-household variations in food intake and eating patterns appear to be expanding. Food and nutrition policy is focusing less on food security needs and more on the health-related needs of selected age and gender groups. As this occurs, data on individual dietary intake become more valuable.

Of course, the major disadvantage of 24-hour recall is its reliance on respondents' ability to remember not only each food consumed but also the quantity of each item eaten during the previous day. The accuracy and precision of this method vary, therefore, depending on the population, types of foods consumed, and dietary practices. In China, an additional problem is related to the measurement of cooking oil and other condiments used in food preparation, since the Chinese food composition table is based on items as purchased and not as cooked. For this reason, measuring cooking oil would have been omitted from the traditional 24-hour recall.

The traditional Chinese eating pattern is to prepare and serve a limited number of complex dishes and have each individual place various portions of each dish on his or her plate or bowl. Group consumption from common plates increases the difficulty of obtaining accurate measurement of individual consumption. People are not accustomed to estimating portion sizes. In addition, snacks and food eaten away from home depend on a respondent's memory. Estimating individual quantities is difficult, in particular for children under the age of 11 years, whose intake has to be recalled by mothers or other adults. These limitations are crucial in de creasing the validity and precision of the individual 24-hour recall method.

During the past decade, significant changes have taken place in the composition and level of dietary intake in China. Two sets of large-scale nutrition surveys were conducted, both of which employed household inventories to assess dietary intake at the national and provincial levels. The longitudinal study of the CHNS and the 1992 China Third Nationwide Nutrition Survey (CNNS III) combined household inventory and individual recall to assess individual consumption. In this study, we used the CHNS 1991 survey data to compare dietary intake by 24-hour recall for the individuals with data from changes in household food inventories made during the same survey period. This analysis not only examines basic differences but uses multivariate methods to try to explain some of the reasons for differences in the results of the two methods.

In Western countries, dietary fat intake is calculated directly from food composition tables that incorporate recipes or processed foods. China has not measured and edited the nutrient contents of recipes. The available food composition tables consist of raw food items. Thus, individual fat intake determined by 24-hour recall appears to be underestimated if the amount of household cooking oil used is ignored. For this reason, a method.