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Dietary intake in an urban African population in South Africa, with special reference to the nutrition transition

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dc.contributor.author Bourne LT en
dc.date.accessioned 2016-09-22T09:12:37Z
dc.date.available 2016-09-22T09:12:37Z
dc.date.submitted 1996 en
dc.identifier.uri http://hdl.handle.net/20.500.11892/47742
dc.description.abstract An assessment of the nutritional status of a representative sample of an urban African population has not previously been conducted, nor the extent to which the traditional diet has been abandoned for a western diet. To meet this end, a cross-sectional analytic study was carried out on a representative sample (N=1 146) of the urban African population, aged 3 - 64 years in 1990. Particular attention was paid to specific at-risk groups viz. pre-schoolers (aged 3 - 6 years; N=163), adolescents (aged 15 - 18 years; N=119) and adults (19 - 44 years; N=649). The interrelationships of dietary intake with socio-economic status, demographic indicators as well as measures of urban exposure were also examined. A further aim was to determine the extent to which this rapidly urbanising population's macronutrient profile had shifted from a traditional towards a western atherogenic dietary pattern. This analytic study was nested in a community-based descriptive survey on risk factors for cardiovascular disease. A multi-staged, proportional sampling strategy was used. Quotas were used in the final stage of sampling, based on the age/sex distribution of a 1988 census conducted by the local authorities. Dietary data were collected by means of the 24-hour recall method, by Xhosa-speaking registered nurses who had received intensive training. Anthropometric measurements were taken, and blood samples were drawn according to standard procedures. Socio-demographic questions elicited information on the physical environment and facilities, educational level and employment status. Information was also elicited regarding urban exposure relating to lifetime migration history, thus incorporating retrospective temporality into the study design. From these data, an index of urban exposure was established by calculating the percentage of life spent in an urban environment. Univariate analyses of dietary, anthropometric and biochemical vitamin status were used for the descriptive components of the study of the three specific at-risk age categories. Bivariate analyses examined the effects of selected proxies of socio-economic status, and urban exposure on dietary intake. Finally, multiple linear regressions were performed on the pre-schoolers (N=163) and adult sample, aged 15 - 64 years (N=983) incorporating additional indicators of socio-economic status as predictors, and dietary intake data as outcome measures. Correspondence analysis further explored the relationships between dietary atherogenicity (using the Keys score) and other risk factors for degenerative disease. The results of the 24-hour dietary recall data reflected a population consuming a diet meeting prudent dietary guidelines in all the three age categories (i.e. 3 - 6, 15 - 18 and 19 - 44 years). However, 50 % or more subjects in all subgroups reported intakes <67% of the Recommended Dietary Allowance (RDA) for the following micronutrients: vitamin A, ascorbic acid, thiamin, riboflavin, niacin, vitamin B6, iron, zinc and copper. Among adults low micronutrient intakes were supported by biochemical serum vitamin analyses, conducted on a sub-sample. Of the three age categories, the adolescent age group reflected the highest proportion of respondents reporting micronutrient deficient diets. Women of childbearing age were also particularly micronutrient deficient. Examination of reported median food group intakes in terms of generally accepted guidelines, revealed that the diets in all age groupings were deficient in dairy intakes (<0.5 portions) and fruits and vegetables (<2 portions). The evening meal emerged as the main meal of the day in all age categories, with a considerable proportion of nutrients being consumed during "snacking" periods distributed throughout the day. A particularly disturbing finding was that on the day of recall, only 45 % of pre-schoolers consumed three meals. A complex picture of under- and overnutrition emerged from examinations of the anthropometric data in all subgroups. In 3 - 6-year-olds, 27.6 % were stunted (z-score <-2 height-for-age), 7.9 % were wasted (z-score <-2 weight-for-height) and 7.7 % were underweight (z-score <-2 weight-for-age) while 20.1 % reflected a z-score >+2 weight-for-height, reflecting a substantial proportion of obese children. Gender disparities in anthropometric status were apparent in 15 - 18-year-old adolescents. In young men, 39.7 % were underweight (vs. 4.8 % in women), while 30.6 % of female adolescents were overweight (vs. 10.4 % in men). Anthropometric differences between the genders were particularly striking in men and women aged 19 - 44 years, where 31.2 % of women were obese (body mass index >30) as opposed to 5.6 % of men. In bivariate analyses, higher socio-economic status was associated with diets of better micronutrient quality, particularly in pre-schoolers and adult women. However, a general finding was that higher socio-economic status was also associated with significantly higher dietary atherogenicity. Also consistent with the literature, it was found that dietary intakes became significantly more western in macronutrient composition with increasing urban exposure. Intakes of fats and animal protein increased significantly, while consumption of carbohydrates, plant protein and fibre decreased significantly. The Keys score also reflected these findings by increasing significantly with increasing urban exposure. Regression analyses corroborated these shifts. However, the relatively low R2 values did not permit accurate predictive modelling of dietary data. The correspondence analysis again confirmed an association of high urban exposure and formal housing with higher dietary atherogenicity, while the more prudent scores were associated with low urban exposure, low educational status and informal housing. The study shows that diets of urban Africans are becoming increasingly westernised, and the data suggest that this occurs within a lifetime. It was concluded that with continuing urbanisation and improvements in socio-economic status, dietary intake will contribute to an accelerating, increased risk of degenerative disease in this population. The diet remained micronutrient deficient (expressed in terms of <67 % RDA) at all levels of urban exposure. Comparison of the macronutrient data reported in this study with other local studies on urban Africans over time, indicates the occurrence of a nutrition transition. en
dc.language English en
dc.subject Medical sciences: Health promotion en
dc.subject Dietetics, Nutritional Counselling en
dc.title Dietary intake in an urban African population in South Africa, with special reference to the nutrition transition en
dc.type Doctoral degree en
dc.description.degree PhD en

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