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Rural/urban nutrition-related differentials among adult population groups in South Africa, with special emphasis on the black population
Lesley T Bourne, BSc (Diet), MSc (Med), PhD
National Urbanisation and Health Programme, Medical Research Council, Tygerberg, W Cape
Medical Research Council, PO Box 19070, Tygerberg, 7505, W Cape.
Krisela Steyn, MSc, NED, MD
Chronic Diseases of Lifestyle Programme, Medical Research Council, Tygerberg W Cape

S A J Clin Nutr 2000 February Vol. 13 No 1.

Abstract
In South Africa the adult population includes blacks, ranging from those living near-traditional lifestyles to urban sophisticates, immigrant Indians, coloureds (of European, black, Malay, Khoi and San descent), and whites. Shifts in dietary intake to a less prudent pattern are occurring with apparent increasing momentum, particularly among blacks who constitute by far the bulk of the population. Macronutrient dietary intake profiles among adults range from prudent among blacks, to Western in other groups However, data have shown that among urban blacks fat intakes have increased by 63%, while carbohydrate intakes have fallen by 14% in the past 50 years. Shifts towards the Western diet are apparent among rural African dwellers as well. Other risk factor profiles for chronic diseases, such as heart disease, reflect differences among cultural groups. Rural/urban differentials of risk factors among blacks continue to deserve attention from policymakers and health education professionals. Superimposed on the increasing onset of chronic diseases of lifestyle among South African adults is the HIV/AIDS epidemic, which is rapidly gaining momentum and could become the most common cause of morbidity and mortality.

In South Africa the black population predominates by far over other population subgroups (representing 77.4% of the population)1 and is the most impoverished of all groups. While the majority of blacks reside in ‘non-urban’ areas (56.7%), the urban proportion (currently 43.3%) is steadily increasing, with many living in informal housing on the fringes of cities

Consequently, over time most studies on nutritional status and dietary intake have focused on blacks. However, these studies have primarily focused on preschool children (particularly in rural areas) since they represent the most vulnerable age sector. Nevertheless, it could be argued that since adults determine intakes of very young children, examination of their diets and nutritional status is warranted.

Dietary transition
Diet, and the excessive intake of fats in particular, has long been recognised as a risk factor for the development of heart and other degenerative diseases in Western countries. 2,3 Epidemiological research has shown that increases in fat intake and decreases in carbohydrate consumption have come to be associated with increasing rates of cardiovascular disease.4-6 For example, fat intake increased by 34% over 70 years in the USA, while carbohydrate intake decreased by 22% in that period.7 Similarly, in Ireland over a period of 42 years fat intake increased by 24% while carbohydrate intake decreased by 17%.8 These dietary changes were accompanied by rapid industrialisation and economic growth, particularly in the USA.9 From studies of some 85 countries, Perisse et al.10 Showed that as either national or personal income rises, the proportion of animal products, fat, and sugar in the food supply increases, and the proportion of cereal grains and starches decreases. This type of transition has occurred in most Western European countries and in Canada, Australia, New Zealand and the USA. More recently, such dietary shifts have been observed in low-income countries.11

Dietary transition in the South African black population
One of the hypotheses supported by rural/urban comparisons of African populations has been that with urban exposure the traditional diet is abandoned for a Western diet, typified by decreases in carbohydrate and fibre and increases in fat. The traditional diet is associated with a low prevalence of degenerative diseases, whereas the Western diet is associated with an increased prevalence.12,13

Examinations of macronutrient intakes over time from various studies done on blacks are therefore pertinent, representing both urban and rural studies.14-23 Despite the variety of methodologies employed and the incompleteness of much of the data (e.g. in many cases no standard deviations are provided and sampling procedures are not well described), the available data serve to illustrate certain trends, namely that: (i) there is little variation in the proportion of protein intake over time, and between rural and urban areas; (ii) fat intakes show an overall upward trend over time in both rural and urban areas; and (iii) conversely, the proportion of energy derived from carbohydrate decreases in both urban and The collective evidence from these data, therefore, illustrates that although there is much evidence of diets meeting primary prudent guidelines, there has been a slow shift in the direction of a Western diet over time.

Manning et al.18 reported that such atherogenic changes were already evident in Cape Peninsula blacks during the early 1970s, and Rossouw24 found urban black 11-year-old children from Cape Town to have higher levels of atherosclerotic risk factors than their rural counterparts. Since there was an absence of dietary data of a representative sample of adult blacks in South Africa, a study 25 was conducted in 1990 on a sample of 983 men and women aged 15 - 64 years in Cape Town. Years of urban exposure were determined from a migration history and this was used to calculate the pecentage of life spent in a city for each individual. A breakdown of the macronutrient distribution stratified by urban exposure on a subset of adults aged 19 - 44 years (where women were of childbearing age) revealed that reported fat intake (expressed as % energy (%E)) increased significantly (P < 0.01), while carbohydrate intake decreased significantly (P < 0.01). Although significance was not reached for total protein, animal protein increased significantly (P < 0.01), while the %E plant protein decreased significantly (P < 0.01, data not shown). In other words, as urban exposure increased, so did the atherogenicity of the diet

Mean nutrient intakes are reported in detail elsewhere.26 The results of the evaluation of macronutrient intake (60% energy from carbohydrate and 26% energy from fat) revealed that the diet of this study population meets the requirements of the South African Diet Consensus Panel, 27 which are in line with the American Heart Association’s recommendations. 28 However, it represents a transitional phase between the ‘traditional’ diet (> 60% energy from carbohydrate, < 25% energy from fat) and a ‘Western’ eating pattern (< 50% energy from carbohydrate, > 35% energy from fats). Large percentages of individuals fell below two-thirds of the RDA 29 for several vitamins and minerals, reflecting a nutritionally depleted diet. 26

An evaluation of the dietary pattern revealed a diet confined to a relatively narrow range of foods. 30 Insufficient intake of dairy products and vegetables and fruits was striking, although requirements for intakes of cereals and components of the meat and fat groups were met. This pattern has also been found among other population groups in South Africa, as reflected in the SANNS Report.31

Analyses of food group intake by urban exposure illustrate the backdrop of shifts in food choices behind these macronutrient trends. Table I presents data from the 19 - 44-year-old age category (in which women are of childbearing age). It can be noted that dairy and cereal intake fell with increasing urban exposure, while intakes from other food groups rose.25

The low intakes of vitamins and minerals in this sample have been supported by serum biochemical vitamin analyses (Professor D Labadarios – personal communication). Moreover, a high prevalence of anaemia, particularly in women (20.8%) as opposed to men (6.3%), reflects the pattern of lower iron intakes by women, 32 and in particular the high proportion of women with an iron intake below the RDA. The low vitamin and mineral status not only places many individuals at risk for developing deficiency syndromes, but also compromises their immunity to infections. There are also obvious implications for pregnant and lactating women.

Somewhat paradoxically, the atherogenic diets of the more urbanised individuals place them at risk for the development of degenerative diseases. Diet-related anthropometric and physiological outcomes reported from the present study and other studies in Cape Town, 33 simultaneously reflect a profile of growth retardation and wasting in children (who consume adult-prepared foods), including risk factors associated with degenerative diseases, such as obesity and hypertensiion among adults.34 The coexistence of under- and over-nutrition presents a complex picture for health workers and policy-makers.

A comparison of fat and carbohydrate proportions of energy intake from these data with those of adults in 1940, 14 shows a 14% reduction in carbohydrate intake and 63% increase in fat intake over this 50-year period. These changes are more dramatic than has been observed in Western countries undergoing rapid industrialisation over longer period of time.

Further analyses 35 have revealed that the ‘newer arrvals’ to the city are associated with low educational status, informal housing and diets with low atherogenicity but of particularly low nutrient quality. In juxtaposition, the more urbanised individuals with higher educational status living in formal housing consumed diets somewhat richer in nutrients, but with significantly higher atherogenicity. This suggests that improvement in socio-economic status does not necessarily lead to improved nutritional status, but is associated with a shift to another inappropriate nutritional pattern that predisposes to the development of atherosclerosis. Many factors impact on food choices and methods of food preparation. Poverty, lack of knowledge and social instability in the black population militate against healthy eating being a priority in the minds of township dwellers. The long commuting distances of employed city dwellers frequently result in their choosing easy-to-prepare foods and snaacks which are generally refined and high in fat content. Conversely, the more traditionally orientated individuals are frequently the under-employed ‘newer arrivals’, who may have the time to prepare relatively low-cost maize and legume based dishes, which have slow cooking times. Dietary interventions have to take these and other factors into account.

Table I. The influence of increasing urban exposure on energy contribution of food groups (19 - 44-year-olds, N = 649, men and women combined – the BRISK study 25

The black population in relation to other population groups
Fig. 1, which illustrates the macronutrient profiles of all population groups,36-38 shows that only the mean macronutrient profile of blacks conforms to the Prudent Dietary Guidelines. 27,28 However, in the light of the evidence presented above this is changing rapidly, despite the poverty still inherent in this group.

Fig. 1. Current dietary profiles of population subgroups.

Diet-related outcomes in South African adult population groups
In 1972 Walker 39 predicted that increasing urbanisation and a rise in socio-economic status in developing populations would increase their proneness to obesity, hypertension, diabetes and strokes. These predictions have largely been borne out in the African population.

Obesity
Table II presents the prevalence of obesity (BMI > 30) in the various South African groups, among men and women respectively. 40-45 It can be seen that the prevalence of obesity in women in urban and rural black communities is higher than that found in any of the other studies. All of these studies utilised the same methodology, with the exception of the USA study (shown for comparative purposes), and included largesamples. The early anthropometric studies of African samples were either purely verbally descriptive (i.e. ‘good’, ‘sturdy’ or 'poor' physiques’), or used measures not comparable with those in use today. Moreover, the majority of studies were performed on mineworkers and children. However, more recent work shows that obesity (BMI > 30) is more prevalent in African women (above all other ethnic groups) than in men (Table II). noted in the comparison with Afro-Americans, local prevalence rates are approaching those in developed Western populations.

Table II. Comparison of body mass index (BMI) > 30 for inter-ethnic South African men and women
Ethnic group

Hypertension and dyslipidaemia
The prevalences of hypertension and dyslipidaemia reported from five cross-sectional studies46 are presented in Table III These studies utilised standardised methodology and included the coloured community of the Cape Peninsula (976 urban coloureds),47 the Indian community in Durban (753 urbban Indians), 43 the black community of the Cape Peninsula (986 urban blacks),34 the black community of QwaQwa (853 rural blacks)44 and the white community of the south-western Cape from three small towns (7 188 rural whites).48 Comparisons were made after age-standardisation of the prevalences in each study against a world population standard.

The urban coloured group, 47 including both men (23%) and women (25%), had the highest prevalences of hypertension (blood pressure ³ 160/90 mmHg). The lowest rates among med were for the urban blacks (11%),34 while among women the lowest rates were found in rural whites in 1991 (12%).48 Hypercholesterolaemia in men was most common among rural whites (28%, pre-intervention baseline study, 1979)48 and urban coloureds (15%).47 Among women, rural whites from the 1979 study also reflected the highest percentages of hyper -cholesterolaemia (34%),48 again followed by urban coloureds (15%).47 A low high-density lipoprotein cholesterol/total cholesterol ratio (HDLC/TC) was most frequently observed in Indian men (45%)43 and white men (46%).48

Of particular interest was the fact that the overall adverse risk profile among blacks was found in the rural sample as opposed to their urban counterparts. However, it has been argued that QwaQwa has many features of urban life.44

Table III. Prevalence (%) of hypertension and dyslipidaemia in men and women (15 - 64 years) in South Africa, age-standardised against a world population.46

Diabetes
Prevalences of diabetes among the different population groups in South Africa vary and there is little doubt that this can in part be attributed to differences in diet and lifestyle.

In the past when blacks followed a traditional lifestyle, diabetes was virtually absent, as it still is in Tanzania.49 Early studies dating from 1960 to determine the prevalence of diabetes were entirely hospital-based. In a Cape Town study 50 the crude prevalence was 3% (with no age or sex standardisation against the population being calculated).

More recent community-based studies using the 1985 World Health Organisation(WHO) criteria for diabetes indicate that the prevalence is considerably higher in African subjects than it was approximately 25 years ago, ranging from 5% in Gauteng 51 to 8.0% in Cape Town. 52 However, the true extent of this change may be confounded by differences in methodology.

Importantly, the Cape Town survey 52 identified the following factors as independent risk factors: age, upper segment body fat distribution, urbanisation (i.e. more than 40% of life spent in an urban area) and obesity.

The late Professor Jackson’s group studied the prevalence of diabetes in 968 coloured subjects ‘representative’ of the urban Cape coloured community. 53 The age-adjusted prevalence of diabetes in those over the age of 15 was found to be 9%.

The only survey describing the prevalence among white South Africans was reported by Jackson and co-workers in 1969.54 The crude as well as age-adjusted prevalence in subjects 15 years and older was 37%.

In recent studies among Indians the prevalence of diabetes Ranges from 1% to 13% (age adjusted data). A comprehensive review of South African studies has been conducted by Levitt and Mollentze.55

Conclusion
While South Africa needs to deal with the increasing onset of chronic diseases of lifestyle, there is still an unfinished process of reducing infections and growth retardation. Superimposed on these is the HIV/AIDS epidemic, which is rapidly gaining momentum to become the most important cause of morbidity and mortality. Resource allocation between these competing demands poses extremely difficult public health policy options

The authors thank Jean Fourie for her diligent attention to detail in editing this article.

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