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3 Department of Food Economics and Consumption Studies, Christian-Albrechts-University of Kiel, D-24098 Kiel, Germany and 4 Robert Koch-Institute, D-13353 Berlin, Germany
* To whom correspondence should be addressed. E-mail: sthiele{at}food-econ.uni-kiel.de.
| ABSTRACT |
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| Introduction |
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Second, count measures do not account for the distribution of individual food quantities. An individual with equal shares of food products has a greater food diversity than an individual who consumes 90% of 1 product and 10% of the others. A food diversity index must reflect this. Altogether, a healthy food diversity index must consider 3 aspects simultaneously: number, distribution, and health value of a consumed food basket. All aspects are emphasized in newer recommendations for healthy eating. The German diversity guideline, for example, underlines: "Enjoy the great variety of food. There is no healthy, unhealthy or even forbidden food. It is the quantity, selection, and combination of food that matters" (10).
Particularly in economic studies, there is a growing application of distribution measures that consider number as well as distribution of different (food) products to quantify diversity (11,12). We wanted to determine whether these indices are suitable measures of healthy food diversity. This answers the demand of many nutritionists for a more precise definition of food diversity and to develop a suitable indicator (13,14,8,15).
| Materials and Methods |
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A measure to evaluate diversity in terms of number as well as distribution of different food items is the Berry-Index. This index was applied mainly in economic food diversity studies (11,12,1719). Recently, the Berry-Index, which is also known as the Simpson-Index, has been applied in a nutritional study by Katanoda et al. (20) to measure dietary diversity and its annual changes in Japan. The Berry-Index (BI) is defined as:
(21), where si is the share of product i in the total amount of food consumed. The index is bounded between 0 and 11/n, whose limit value approximates 1 if the number of foods (n) increases. BI = 0 indicates that an individual consumes only 1 food product, BI = 11/n refers to a situation where the individual consumes equal shares of all products considered.
From a nutritional perspective, the latter assumption is not desired. According to food guide recommendations, healthy foods should be consumed in higher shares than unhealthy ones. Hence, the highest index value has to be assigned to a situation where an individual consumes recommended food group shares. The basic idea of the new healthy food diversity indicator was to modify the Berry-Index so that the index rises if the distribution of foods moves in favor of healthier products. Therefore, we incorporated a component into the Berry-Index that is able to reflect the health value of consumed foods. In this analysis, we derived health values from actual food guidelines of the German Nutrition Society (DGE),3 but other food guidelines can also be used as a basis for the modification of the Berry-Index.
The visual representation of the DGE food guidelines are illustrated by a nutrition circle and a food pyramid. The nutrition circle (Fig. 1) illustrates the shares of food groups that should be consumed in terms of weight. These shares are calculated on the basis of the DGE reference values for nutrient intake. Exemplary diets are constructed with the aim that the reference values for nutrient intake are achieved on average over a 7-d period (22). In accordance with the sides of the food pyramid, these shares can be summed up in 3 groups: 73% plant foods, 25% animal foods, 2% fats and oils. [The pyramid also includes a 4th dimension that refers to beverages. Because we are primarily interested in caloric foods, we exclude all noncaloric beverages such as mineral water, coffee, and tea, whereas caloric beverages are assigned to other food groups. For example, 100% juices are assigned to fruits and vegetables, sugar-containing beverages (e.g. lemonades) are assigned to sweets, etc.]
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. The maximum health value that can be achieved is 0.26. Thus, division of hv by its maximum ensures that hv is bounded between 1 and nearly 0.
The final construction of the healthy food diversity index was achieved by combining health value (hv) and diversity of the food basket
. The resulting Healthy Food Diversity (HFD)-Index is defined as
. Multiplication of the Berry-Index with the health value ensures that neither a high hv nor a high BI alone yield a high HFD-Index. The HFD-Index, which is bounded between 0 and 11/n, has the following desired properties: 1) If the distribution between hf groups of the pyramid does not change, it increases with the growing number of food items; it increases the more equally the food items are distributed within the hf-groups; and 2) If distribution between hf groups of the pyramid does change in favor of healthy (unhealthy) food groups, it increases (decreases).
Therefore, the HFD-Index is able to differentiate between healthy and unhealthy food diversity over all food groups based on real observable diets without omitting unhealthy foods.
Data and statistical analyses. To verify if the developed HFD-Index was able to reflect a healthy diet, we conducted Pearson's correlation analyses, where individuals' HFD were correlated with nutrient supply and biochemical parameters. All statistical analyses were conducted using SPSS version 12.0. The significance level was set at 0.05 in all analyses.
The empirical analyses were based on data from the German Nutrition Survey (GeNuS) of 1998, which is representative for noninstitutional German adults (23). (GeNuS was part of the German National Health Interview and Examination Survey 1998. The survey was approved by the Federal Data Protection officials. Survey participants were informed in detail about the study goals, interview, and examination procedures as well as anonymous data record keeping and analyses. They were able to refuse any part of the examination program. Participants provided written informed consent prior to the interview and examination.) A number of 4030 participants were comprehensively interviewed concerning their diet of the preceding 4 wk by trained nutritionists using a validated computerized dietary history method (24). The participants reported 2678 different foods that were aggregated for this analysis into 133 different food categories (see Supplemental Table 1). In addition to food data, the GeNuS provides information for >30 micro- and macronutrients and for several blood serum parameters such as blood serum cholesterol and homocysteine.
The serum was frozen immediately and stored for analysis at 40°C. Time between blood sampling and analysis never exceeded 7 d, except for homocysteine. Blood lipids were analyzed on an automatic analyzer type MEGA (Merck Darmstadt). Total serum cholesterol was assayed using the enzymatic CHOD-PAP method (Merck Darmstadt). HDL cholesterol was determined with an immunoseparation-based homogenous assay from WAKO. Triacylglycerol was measured with the GPO-PAP method (Merck Darmstadt). Homocysteine was analyzed with a commercially available HPLC kit (Immundiagnostik Bensheim) by using a Shimadzu chromatography system with fluorescence detection within 1 y after storage at 40°C.
To measure the nutrient supply of the participants of the GeNuS, we used the nutrient adequacy ratio (NAR), which is defined as the ratio of a certain nutrient intake to its recommended dietary allowance (25). The NAR was truncated at 100%; hence, if a person reaches >100% of the recommendation, no further credit was given (13). In this analysis, NAR for 30 nutrients were used for validation of the HFD-Index. As the empirical database refers to German individuals, the guidelines of the DGE were used as a reference for nutrient intake (26). The mean values of the calculated NAR ranged from 99.99 for vitamin K to 0.84 for sodium (Table 2 for descriptive statistics of all variables used in the empirical analyses).
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| Results and Discussion |
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In the case of vitamin B-12, the correlation coefficient for the HFD-Index was not significant (P = 0.11), i.e. higher healthy food diversity was not associated with vitamin B-12 supply. This finding can be explained by the positioning of foods in the German food pyramid. The main suppliers of vitamin B-12 are meat and dairy products. Because of their comparatively high fat and cholesterol concentrations, these food items received a low valuation in the German pyramid. Therefore, a diet rich in meat and dairy products resulted in a lower HFD-Index. Hence, the HFD-Index was not able to reflect nutrients mainly occurring in animal-based food products. Also, thiamin, riboflavin, and niacin mainly occur in animal-based foods and thus had low correlation with the HFD-Index. It can be expected that taking American food guidelines (MyPyramid) as a basis for HFD-Index would yield better results (e.g. vitamin B-12 supply), because these guidelines give more weight to fat-reduced dairy products.
A comparison of the HFD-Index with the Berry-Index and Count-Index for selected nutrients with notable risk of deficient supply (Fig. 3) revealed that nearly all of them were more strongly correlated with the HFD-Index than with other food diversity indices. Only the supply of nutrients mainly occurring in animal-based foods (thiamin, riboflavin, and calcium) was better reflected in the Berry-Index and Count-Index. Again, this reflects the low valuation of animal-based foods in the German food guidelines and hence in the HFD-Index.
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To gain further insight into the HFD-Index and its ability to indicate a high diet quality, correlations between variety and some serum biochemical variables were calculated (Table 4). The HFD-Index showed for all considered biochemical parameters plausible and significant signs. A higher HFD-Index was associated with an increased serum HDL cholesterol concentration, which indicates good protection against vascular fat sediments (29). In the case of serum triacylglycerol, uric acid, and homocysteine, significant negative correlations with HFD-Index were found. This is plausible, because increased values of these serum parameters indicate an unfavorable diet. For instance, a high serum homocysteine value is associated with a low supply of folic acid, thiamin, and riboflavin. These vitamins protect against cardiovascular as well as neuropsychological diseases (30). The other variety indices, the Berry-Index and the Count-Index (Table 4), also had expected signs, but correlation coefficients were predominantly smaller and they were not always significant.
Altogether, the HFD-Index showed for both the supply with nutrients and serum biochemical variables predominantly better correlation results and hence was more suitable for measuring healthy food diversity compared with the Count- and Berry-Index. The inclusion of both diversity and health recommendation aspects seems to be an important advantage of the HFD-Index. However, the development of a healthy food diversity indicator is dependent on nutritional guidelines for optimal food distribution. The unequal assessment of animal-based foods in different guidelines (e.g. American vs. German) reveals the demand for future research on the valuation of foods.
The call for improved healthy food diversity indicators stated in previous studies (15,8,14,13) provided the impetus to develop a new index that considered 3 important aspects of a varied diet simultaneously: number, distribution, and health value of foods. The health value was derived from the recently published German food pyramid. The incorporation of this value into an existing diversity indicator, the Berry-Index, was implemented. The correlation results showed that this new HFD-Index was able to reflect a healthy diet. Nutrient supply variables as well as serum biochemical parameters were significantly correlated with the HFD-Index and the signs were as expected. The comparison with previous indices, the Count-Index and the Berry-Index, showed that the HFD-Index was the most suitable indicator to measure healthy food diversity. Particularly, nutrients with notable risk of deficient supply such as folate, fluoride, dietary fiber, vitamin E, and iodine were better reflected in the new HFD-Index than in traditional variety indices. The highest correlation was detected for folate, which can be found in small amounts in numerous foods. Nutrients mainly (exclusively) occurring in animal foods were not adequately reflected in the HFD-Index. This was explained by the low valuation of animal foods in the German food guidelines.
Taking other food guidelines as a basis for the HFD-Index for analyzing the association between healthy food diversity and nutrient supply is a promising area of future research. The HFD-Index seems to be a suitable foundation to review the performance of different food guidelines in terms of achieving nutrient intake recommendations.
| FOOTNOTES |
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2 Supplemental Table 1 and Supplemental Figures 1 and 2 are available with the online posting of this paper at jn.nutrition.org. ![]()
3 Abbreviations used: DGE, German Nutrition Society; GeNuS, German Nutrition Survey; HFD, healthy food diversity; NAR, nutrient adequacy ratio. ![]()
Manuscript received 14 July 2006. Initial review completed 16 August 2006. Revision accepted 14 December 2006.
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