3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item The impact of dietary habits and practices during adolescence on the risk of obesity: the birth to twenty cohort(2013-04-29) Feeley, Alison Bridget BernadetteBackground: South Africa is not exempt from the obesity epidemic and latest figures show that a third of adult men and two-thirds of adult women are either overweight or obese. Concomitant are changes in dietary habits and practices which have been implicated in the risk of obesity. Concern is that obesity and related non-communicable diseases (NCDs) manifest at younger ages. Adolescence, as well as being a stage during the life course when eating attitudes and behaviours are formed, is a particular time when the aetiology of NCDs becomes evident. Little is known about the dietary patterns during adolescence in South Africa, and if policymakers are to attempt to reduce the burgeoning statistics relating to obesity then it is important to understand adolescent dietary habits and eating practices. Aims: To describe adolescent dietary habits and practices among South African adolescents and how they might influence obesity risk. Methods: This study used a mixed methods study design, using both historical and prospective data and included four study components in both an urban (components 1-3) and a rural setting (component 4). Firstly, a cross-sectional assessment of fast-food intake of urban 17-year-olds from the Birth to Twenty Cohort (Bt20); secondly, a longitudinal descriptive analysis of dietary habits and practices of the Bt20 participants over a five-year period, between ages 13 – 17 years followed; thirdly a longitudinal assessment of the relationship between dietary habits, change in socio-economic status (SES) and obesity in the Bt20 adolescents was conducted; and finally, an exploratory survey assessing the availability of fast foods in a rural area. Results: The cross-sectional analysis showed that mean fast food intake was 8.1 (4.6) items and 7.2 (4.7) items/week for males and females respectively. Furthermore, the kota (or quarter) was the most popular fast food item and on average it provided 5 370 kJ, 51 g fat (of which 13 g Saturate fatty acids (SFA)). The longitudinal analysis showed that poor dietary habits and practices were embedded by the age of 13 years and were characterised by: high fast food consumption with at least five items/week consumed from the age of 13 years. Breakfast (weekday and weekend) consumption declined for both genders and females ate breakfast less regularly than males. Snacking while watching television increased with age: with females consuming more (4.0 (4.8) - 7.3 (5.9)) snacks per week than males (3.3 (4.5) - 6.0 (5.8). Two-thirds of participants ate their main meal with their family but among girls there was a trend towards eating this meal less regularly with increasing age. Confectionery consumption remained the same, around nine items/week for males and 10 items/week for females. Lunch box usage declined with age, conversely the number of tuck shop purchases increased with age. The prevalence of combined overweight and obesity was (8.1%) and (27%) in 17-year-old males and females respectively. In males only, soft drink consumption was associated with obesity denoted by BMI z-score and fat mass (p<0.05). In the final multivariate model, soft drink consumption remained positively and significantly associated with both outcomes and „acquiring‟ a fridge over the 12-year period remained negatively associated with both BMI z-score and fat mass (p<0.001). Among females, no associations were found. Thus further data on other lifestyle variables are needed to understand better the exposures related to obesity risk in females. In the rural setting fast food was found to be available albeit a limited variety; two-thirds of the collected samples were either vetkoek (fried dough balls) or fried chips (yielding between 943 kJ – 5 552 kJ and 11 g – 64 g fat). Compared to the kotas available in Soweto, the samples obtained in the rural setting contained more energy and fat (6 300 kJ, 60 g fat vs. 5 369 kJ, 51.5 g fat). Conclusions: This research highlights that poor dietary habits and practices prevail in adolescence which may be implicated in negative health outcomes in later life. Of concern is the finding that poor dietary habits were embedded by the age of 13 years which suggests that interventions need to target families and children prior to adolescence in order to reduce the pervasiveness of these habits in the older child. The prevalence of combined overweight and obesity is higher than the national statistics for both boys and girls at the age of 17-years. This research confirms that some dietary behaviours are associated with obesity risk namely soft drink consumption – but in males only. However soft drink consumption may be a marker for other lifestyle behaviours associated with obesity. Other dietary habits were not shown to be associated with obesity in neither males nor females, which highlights the difficulty in the measurement of exposures relating to diet. This study also showed in males at least, that socio-economic factors are important when considering obesity risk. The availability of fast foods in a relatively impoverished rural area is concerning as it may indicate that this community is undergoing nutritional changes such as those seen in urban environments. With urbanisation and economic transition, households experience a change in SES and these changes drive behaviour which can either enable or disable health outcomes. In this study SES improvement, e.g. fridge ownership seems to enable certain behaviours which can be obesogenic. However we cannot halt development in this context but we must devise ways to improve lifestyle choices which will promote health rather than impede it.Item Exploring the paradox: double burden of malnutrition in rural South Africa(2011-03-09) Kimani, Elizabeth WambuiBackground: In low- to middle-income countries, rising levels of overweight and obesity are a result of multiple transitions, in particular, a nutrition transition. Consequently, in these countries, metabolic diseases are contributing increasingly to disease burden, despite the persisting burden of undernutrition and infectious diseases. Understanding the patterns and factors associated with persistent undernutrition and emerging obesity in children and adolescents, and concomitant risk for metabolic disease, is therefore of criticial importance. This should contribute to public health policy on interventions to prevent adult disease. Aims: To better understand the double burden of malnutrition in a poor, high HIV prevalent, transitional society in a middle-income country; In so doing, to inform policies and interventions to address the double burden of malnutrition. Methods: A cross-sectional growth survey was conducted in 2007 targeting 4000 children and adolescents 1-20 years of age living in rural South Africa. The survey was nested within the ongoing Agincourt Health and Socio-demographic Surveillance System, which acted as the sampling frame and also provided data for explanatory variables. Anthropometric measurements were performed on all participants using standard procedures. In addition, HIV testing was done on children aged 1 to 5 years and Tanner pubertal assessment was conducted among adolescents 9-20 years. A one-year follow-up of HIV positive children included a matched control group of HIV negative counterparts. Data collection involved both quantitative and qualitative methods. Growth z-scores were used to determine stunting, underweight and wasting and were generated using the 2006 WHO growth standards for children up to five years and the 1977 NCHS/WHO reference for older children. Overweight and obesity were determined using the International Obesity Task Force cut-offs for BMI for children aged up to 17 years and adult cut offs of BMI =25 and =30 kg/m2 for overweight and obesity respectively for adolescents 18 to 20 years. Waist circumference cut-offs of =94cm for males and =80cm for females, and waist-to-height ratio of 0.5 for both sexes, were used to determine central obesity and hence metabolic disease risk in ix adolescents. Descriptive analysis described patterns of nutritional status by age, sex, pubertal stage and HIV status. Linear and logistic regression was done to determine predictors of nutrional outcomes. A p-value of <0.05 was considered statistically significant. Results: Prevalence of undernutrition, particularly stunting, was substantial: 18% among children aged 1-4 years, with a peak of 32% in children at one year of age. Stunting and underweight were also substantial in adolescent boys, with underweight reaching a peak of 19% at 14 years of age. Concurrently, the prevalence of combined overweight and obesity, almost non-existent in boys, was prominent among adolescent girls, increasing with age, and reaching a peak of 25% at 18 years. Risk for metabolic disease using waist circumference cut-offs was substantial among adolescents, particularly girls, increasing with sexual maturation, and reaching a peak of 35% at Tanner stage 5. Prevalence of HIV in children aged 1-4 years was 4.4%. HIV positive children had poorer nutritional outcomes than that of HIV negative children in 2007. The impact of paediatric HIV on nutritional status at community level was, however, not significant. Significant predictors of undernutrition in children aged 1-4 years, documented at child, maternal, household and community levels, included child’s HIV status, age and birth weight; maternal age; age of household head; and area of residence. Significant predictors of overweight/obesity and risk for metabolic disease in adolescents aged 10-20 years, documented at individual/child and household levels included child’s age, sex and pubertal development; and household-level food security, socio-economic status, and household head’s highest education level. There was a high acceptance rate for the HIV test (95%). One year following the test, almost all caregivers had accepted and valued knowing their child’s HIV status, indicating that it enhanced their competency in caregiving. Additionally, nutritional status of HIV positive children had improved significantly within a year of follow-up. Conclusions: The study describes co-existing child stunting and adolescent overweight/obesity and risk for metabolic disease in a society undergoing nutrition transition. While likely that this profile reflects changes in nutrition and diet, variation in infectious disease burden, physical activity patterns, and social influences need to be investigated. The findings are critical in the wake of the rising public health importance of metabolic diseases in low- to middle-income countries, despite the unfinished agenda of undernutrition and infectious diseases. Clearly, policies and interventions to address malnutrition in this and other transitional societies need to be double-pronged. In addition, gender-biased nutritional patterns call for gender-sensitive policies and interventions. The study further documents a significant role of paediatric HIV on nutritional status, and the potential for community-based paediatic HIV testing to ameliorate this. Targeted early paediatric HIV testing of exposed or at risk children, followed by appropriate health care for infected children, may improve their nutritional status and survival.Item Impact of obesity on the susceptibility of the myocardium to hypertensive and adrenergic-induced apoptosis(2010-04-15T09:44:07Z) Vengethasamy, LeandaExcess adiposity may increase the risk of heart failure through interactions with conventional risk factors. As cardiomyocyte apoptosis may be an important mechanism responsible for the development of heart failure the aim of the present study was to determine whether obesity enhances a) the increased cardiomyocyte apoptosis that accompanies pressure-overload hypertrophy and b) sympathetic-induced cardiomyocyte apoptosis. The impact of dietary-induced obesity on cardiomyocyte apoptosis was studied in elderly spontaneously hypertensive rats (SHR) and age-matched (8-9 months of age at the beginning of the study) Wistar Kyoto rats (WKY) after a 5 month feeding period and in young WKY rats (1 month of age at the beginning of the study) receiving either isoproterenol (ISO) or the vehicle (saline) for 5 days at the end of the feeding period. To induce obesity rats were fed a diet that promotes hyperphagia. At the end of the feeding period echocardiography was performed. Cardiac myocyte apoptosis was assessed using a TUNEL staining technique. Rats receiving the obesity-inducing diet had increases in body weight and visceral fat content. No further changes in systolic blood pressure were observed in rats during the feeding period. SHRs on the obesity-inducing diet had an increased left ventricular end-diastolic diameter and a decreased endocardial fractional shortening. As compared to lean rats, dietary-induced obesity resulted in an increase in the percentage of cardiomyocytes that were apoptotic in SHRs (3.4±0.5%, p<0.005 vs all other groups) and in WKYs receiving ISO (0.35±0.05%, p<0.05 vs Control-ISO and p<0.01 vs Control-saline and Diet-saline groups). In conclusion, obesity was associated with cardiomyocyte apoptosis through an interaction with pressure-overload hypertrophy v and excessive sympathetic activation. These findings provide insights into the potential mechanisms through which obesity may promote the development of heart failure.Item What obese and non-insulin dependent diabetes mellitus patients experience and expect from their primary care doctors concerning weight-loss management(2009-11-03T10:27:47Z) Bham, Zuneid AhmedWorldwide, obesity prevalence is rapidly rising. Doctors have poor understanding of what patients experience and expect from them regarding weight-loss management. This qualitative study explored what obese patients with Non-insulin Dependent Diabetes Mellitus experience and expect from their primary care doctors concerning weight-loss management. Free attitude interviews were conducted with eight participating patients. The findings showed that doctors encouraged and counselled patients regarding weight-loss, mainly giving dietary advice, but did not routinely weigh them. Patients accepted responsibility for losing weight, trusted their doctors, valued their advice highly and did not want referrals to gymnasiums or dieticians. They expected doctors to advise them practically about exercise, diet and weight-loss goals, weigh them regularly and communicate effectively. They believed that doctor-patient relationships and interaction are important in weight-loss management, patients should be treated on an individual basis and the process should be empowering. Medical intervention costs were not problematic for this group. Generally patients were satisfied with their doctors but there were areas concerning patients’ expectations that primary care doctors should take cognisance of.Item Impact of excess adiposity on blood pressure and cardiovascular target organ damage(2009-10-19T10:40:25Z) Majane, Olebogeng Harold IsaiaEpidemiological trends suggest that obesity is becoming a major public health problem. Although obesity contributes toward cardiovascular risk by promoting the development of hypertension, dyslipidaemia and diabetes mellitus (conventional risk factors), there is increasing evidence to suggest that excess adiposity may increase risk through effects on cardiovascular target organs that are independent of conventional risk factors. These obesity-induced effects may be produced by mediating damage and dysfunction of large vessels and the heart, and by promoting the development of cardiac hypertrophy. However, the independent effect of excess adiposity on large vessels has not been confirmed in all studies. Moreover, whether the impact of excess adiposity on cardiac hypertrophy or cardiac damage and dysfunction is dependent on an interaction with blood pressure (BP) is uncertain. In the present thesis I addressed these questions. Before evaluating these questions I first identified the preferred clinical index of adiposity when predicting BP. In this regard, some, but not all studies support the notion that indexes of central adiposity (waist circumference or waist-to-hip ratio) are the preferred predictors of conventional BP over indexes of general (body mass index) or subcutaneous (skin-fold thickness) adiposity. Moreover, to my knowledge no study has been conducted in a large study sample to evaluate whether indexes of central adiposity are the preferred predictors of ambulatory BP, a measure of BP that is more closely associated with cardiovascular events than conventional BP. In the first study conducted in a relatively large, randomly selected population sample (n=300) with a high prevalence of excess adiposity (65%), I demonstrated that waist circumference is the only clinical index of adiposity that is associated with an increased conventional and ambulatory systolic and diastolic BP, independent of other indexes of adiposity. With regards to the effects of excess adiposity on large arteries, there is inconsistency in the reports demonstrating relations between indexes of adiposity and large artery dysfunction (arterial stiffness) independent of factors such as BP, heart rate and diabetes mellitus. As convincing independent relations between clinical indexes of adiposity and arterial stiffness have been noted in older, but not in younger populations, I hypothesized that age may determine whether excess adiposity promotes increases in arterial stiffness independent of confounders. Indeed, in 508 randomly selected persons from a population sample with a high prevalence of excess adiposity (~63% overweight or obese), I was able to show that age markedly influenced the independent relationship between indexes of central adiposity and an index of large artery stiffness in women but not in men after adjusting for confounders. The adjusted effect of indexes of central obesity on arterial stiffness was ~5-fold higher in older than in younger women. With respect to the impact of excess adiposity on cardiac growth, although severe obesity is associated with an enhanced impact of BP on left ventricular mass (LVM), there is uncertainty as to whether the same effects occur in milder forms of excess adiposity, data confounded by the high prevalence of participants receiving antihypertensive therapy in previous studies. In the present thesis I demonstrated in a randomly recruited population sample of 398 participants with a high prevalence of mild-to-moderate obesity and hypertension (~41%), but in whom antihypertensive use was limited (~17%), that adiposity is indeed associated with an enhanced impact of conventional and ambulatory BP or arterial stiffness on LVM index and wall thickness independent of additional conventional risk factors. With regards to the impact of obesity on cardiac function, although obesity is a risk factor for heart failure independent of other conventional cardiovascular risk factors, whether this effect occurs through changes in cardiac systolic chamber function is uncertain. In the present thesis I provide the first evidence to show in an animal model of genetic iv hypertension and dietary-induced obesity, that dietary-induced obesity promotes the progression from compensated cardiac hypertrophy to cardiac pump dysfunction without promoting hyperglycaemia. This effect was attributed to alterations in both intrinsic myocardial systolic dysfunction and cardiac dilatation, effects that were associated with excessive cardiomyocyte apoptosis and activation of enzymes that promote myocardial collagen degradation. Therefore in the present thesis I provide evidence to support the notion that waist circumference should hypertension and dietary-induced obesity, that dietary-induced obesity promotes the progression from compensated cardiac hypertrophy to cardiac pump dysfunction without promoting hyperglycaemia. This effect was attributed to alterations in both intrinsic myocardial systolic dysfunction and cardiac dilatation, effects that were associated with excessive cardiomyocyte apoptosis and activation of enzymes that promote myocardial collagen degradation. Therefore in the present thesis I provide evidence to support the notion that waist circumference should be measured when predicting BP changes, that excess adiposity does indeed decrease large vessel function independent of conventional risk factors, but that this effect is age-dependent, and that the deleterious effects of excess adiposity on cardiac hypertrophy and cardiac pump function are indeed dependent on an interaction with BP, but not other confounders.