Sources of error and bias in the assessment of dietary intake : 24-hour recalls and food records

The first aim of this dissertation was to validate the 24-hour recall method of dietary assessment and to identify possible sources of error and bias in a cross-cultural sample of South African women. The second aim of this dissertation was to determine the source and extent of inter-researcher variability associated with the interpretation of food intake records. The first study was designed to consider whether reporting error is dependent on individual subject characteristics such as ethnicity, body mass, body fatness, age and education, or whether it is due to the dietary assessment tool (i.e., the 24-hour recall). In this study 118 women (25-55 years old) representing different ethnic and language groups (51 Xhosa-speaking, 31 Afrikaans-speaking, 36 English-speaking), different job types ( 25 unemployed, 25 general assistants, 52 medics and para-medics and 16 administrative personnel) and different levels of education (5 with 6-7 years of schooling, 35 with 8-10 years of formal schooling, 43 with 11-12 years of formal schooling and 35 with post high school diploma or degree) consumed a meal that was based on what they reported to habitually eat. All food and beverages consumed were covertly weighed and this was compared to a 24- hour dietary recall performed on the following day. Results of this study showed that the overall variance in reporting error was low. The error was, however, nutrient specific and was related to certain subject characteristics. Under-reporting was greater for subjects with a higher percentage body fat mass and a greater body mass index. Subjects with a lower level of education were more likely to under-report absolute carbohydrate (g) intake, whereas subjects with a higher level of education tended to under-report dietary fat. Subjects with a greater knowledge of food and nutrition were more likely to under-estimate protein intake and overestimate carbohydrate intake. 'Seasonality' (fluctuations in food purchases due to income) affected body mass, socio-economic status and dietary reporting error. Under-reporting of fat intake (g) was greatest in subjects that experienced the most fluctuations in income. In the second study of this dissertation, three post graduate students in dietetics independently assessed and analyzed ten, 3-day food records. The specific areas of variability that were studied related to (i) the selecting of food names/codes on the computer dietary analysis program, (ii) the keying of data from the written dietary records (clerical errors) to the data storage file and, (iii) the conversion of food consumption quantities to gram weights (judgment errors). There were no systematic differences in the variability amongst dietitians in interpreting and analyzing dietary data in this study. The mean coefficient of variation for added sugar was 14.8 ± 12.6 (g) and for fat 7.1± 5.2 (g). In one subject, the range of difference in fat (kJ) intake assessed by the dietitians was as high as 1313 kJ. Conclusions: 1) Adiposity is a universal predictor for under-reporting of dietary intake. 2) Inaccuracies in dietary reporting are nutrient specific and may be influenced by social desirability bias (through education or knowledge of food), language, familiarity with certain foods and 'seasonality' in food purchases. 3) These same factors influence the choices of food and beverages that subjects make in a 'test meal' that is used to validate dietary intake 4) The variations in interpretation of the quality and quantity of reported food intake by the measurer is a source of experimental error that cannot be ignored and which may account, at least partially, for the difference between true and reported intake

Development and validation of instruments measuring body image and body weight dissatisfaction in South African mothers and their daughters

Objective We sought to validate questionnaires concerning body image perception, body size dissatisfaction and weight-related beliefs in multi-ethnic South African mothers and their daughters. Settings and subjects: Girls attending primary school (ages 9-12 years, n = 333) and their mothers (n = 204) were interviewed regarding their demographics and body image. Weight, height and skinfold thicknesses were measured. Body image questions and body mass index (BMI) were compared with silhouettes adapted from the Pathways Study for girls and Stunkard\u27s body image figures for mothers. A Feel-Ideal Difference (FID) index score was created by subtracting the score of the silhouette selected by the participants as \u27Ideal\u27 from the one selected as most closely representing their current appearance or \u27Feel\u27. We hypothesised that a higher FID index score would be associated with greater body size dissatisfaction. Results BMI percentiles in girls (r = 0.46, P \u3c 0.05) and BMI in mothers (r = 0.68, P \u3c 0.05) were positively correlated with the selected silhouettes based on size. Participants who reported feelings of being \u27fat\u27 and those who perceived that their family and friends were more dissatisfied with their body size had significantly higher FID index scores. Scores were lower in black than white girls (all P \u3c 0.05). No differences were found in FID index scores between ethnic groups of mothers. Internal reliability of the \u27thin\u27 and \u27fat\u27 belief constructs for girls was demonstrated by standardised Cronbach\u27s α values ≥ 0.7. Conclusion Silhouettes, FID index, \u27fat\u27 and \u27thin\u27 belief constructs (in girls) are age-appropriate, culturally sensitive and can be used in further intervention studies to understand body image

Conjugated linoleic acid versus high-oleic acid sunflower oil: effects on energy metabolism, glucose tolerance, blood lipids, appetite and body composition in regularly exercising individuals

The aim of this study was to measure the effects of 12 weeks of conjugated linoleic acid (CLA) supplementation on body composition, RER, RMR, blood lipid profiles, insulin sensitivity and appetite in exercising, normal-weight persons. In this double-blind, randomised, controlled trial, sixty-two non-obese subjects (twenty-five men, thirty-seven women) received either 3.9 g/d CLA or 3.9 g high-oleic acid sunflower oil for 12 weeks. Prior to and after 12 weeks of supplementation, oral glucose tolerance, blood lipid concentrations, body composition (dual-energy X-ray absorptiometry and computerised tomography scans), RMR, resting and exercising RER and appetite were measured. There were no significant effects of CLA on body composition or distribution, RMR, RER or appetite. During the oral glucose tolerance tests, mean plasma insulin concentrations (0, 30, 120 min) were significantly lower (P= 0.04) in women who supplemented with CLA (24.3 (SD 9.7) to 20.4 (SD 8.5) microU/ml) compared to high-oleic acid sunflower oil control (23.7 (SD 9.8) to 26.0 (SD 8.8) microU/ml). Serum NEFA levels in response to oral glucose were attenuated in both men and women in the CLA (P=0.001) compared to control group. However, serum total cholesterol and LDL-cholesterol concentrations decreased in both groups and HDL-cholesterol concentrations decreased in women over 12 weeks (P=0.001, P=0.02, P=0.02, respectively). In conclusion, mixed-isomer CLA supplementation had a favourable effect on serum insulin and NEFA response to oral glucose in non-obese, regularly exercising women, but there were no CLA-specific effects on body composition, energy expenditure or appetite

Food purchasing characteristics and perceptions of neighborhood food environment of South Africans living in low-, middle- and high-socioeconomic neighborhoods

Using intercept surveys, we explored demographic and socioeconomic factors associated with food purchasing characteristics of supermarket shoppers and the perceptions of their neighborhood food environment in urban Cape Town. Shoppers (N = 422) aged ≥18 years, categorized by their residential socioeconomic areas (SEAs), participated in a survey after shopping in supermarkets located in different SEAs. A subpopulation, out-shoppers (persons shopping outside their residential SEA), and in-shoppers (persons residing and shopping in the same residential area) were also explored. Fruits and vegetables (F&V) were more likely to be perceived to be of poor quality and healthy food not too expensive by shoppers from low- (OR = 6.36, 95% CI = 2.69, 15.03, p < 0.0001), middle-SEAs (OR = 3.42, 95% CI = 1.45, 8.04, p < 0.001) compared to the high-SEA shoppers. Low SEA shoppers bought F&V less frequently than high- and middle-SEA shoppers. Purchase of sugar-sweetened beverages (SSBs) and snacks were frequent and similar across SEAs. Food quality was important to out-shoppers who were less likely to walk to shop, more likely to be employed and perceived the quality of F&V in their neighborhood to be poor. Food purchasing characteristics are influenced by SEAs, with lack of mobility and food choice key issues for low-SEA shoppers

A practical guide to the use of nutritional supplements in South Africa

Sportspersons should ensure that the decision to use a dietary supplement is a safe one. Unlike medicines, which are regulated by the Medicines Control Council, there is no governing body to control and regulate the supplement industry in South Africa. As a result many supplements may contain banned substances and there is a chance that not all the ingredients are accurately listed on the label of a supplement product. National and international sporting bodies place the responsibility of using supplements on the sportsperson. The legal clause ‘strict liability’ means that the sportsperson is responsible for any and all substances appearing in their urine and blood

Dietary supplement use in younger and older men exercising at gyms in Cape Town

Objective: Compare dietary supplement use and associated factors between younger and older men exercising at gyms (Cape Town). Design: Cross-sectional comparative study (self-administered questionnaire). Setting: Younger (21–31 years) and older (≥ 45) men exercising at gyms (Cape Town). Subjects: 210 younger and 91 older men. Outcome measures: Supplement use (frequency, reason, effectiveness, information sources, label use) and gym exercise profile and goals. Results: 80.6% younger and 81.3% older men had used supplements in the past 6 months. Younger men were more likely to use energy drinks (50% vs. 29.7%; p = 0.014), protein bars (18.1% vs. 7.7%; p = 0.038), protein powders (50% vs. 8.8%; p < 0.001), amino acids (15.2% vs. 2.2%; p = 0.004), weight gainers (10.9 vs. 1.1%; p = 0.011), recovery drinks (13.8 vs. 6.6%; p = 0.026), creatine (34.3 vs. 4.4%; p < 0.001), glutamine (22.4 vs. 7.7%; p = 0.004), arginine (8.6 vs. 0%; p = 0.016), pre-train (11.9 vs. 3.3%; p = 0.04) and fat burner (11.4 vs. 0%; p = 0.004). Multi-vitamins, vitamin C and B vitamins were consumed by both groups. Younger men spent more hours/week exercising in a gym (6.1 ± 4.0 vs. 4.0 ± 1.7; p < 0.001) and doing strength exercises (4.0 ± 2.9 vs. 1.6 ± 1.2; p < 0.001). The main exercising goal was building muscle/strength (38.8%), to stay fit (21.8%) or to look good (15.5%) for younger men and to stay fit (41.6%) or healthy (41.6%) for older men (p < 0.001). Conclusions: Younger and older men exercising in select gyms in Cape Town use a variety of supplements. Supplement use and exercising by younger men seem to focus on muscle building/strength and fitness; that of older men on improvement of fitness and health

Sleep in Children With Autism Spectrum Disorders: How Are Measures of Parent Report and Actigraphy Related and Affected by Sleep Education?

Sleep disturbance is common in children with autism, resulting in a great need for effective treatments. To evaluate treatments for sleep disturbance in this population, it is critical to understand the relationship between measures of sleep captured by parent report and objective measures. The Children’s Sleep Habits Questionnaire (CSHQ) and actigraphy-measured data from 80 children with autism and sleep onset delay were evaluated. Reported problems with sleep onset delay were concurrent with sleep duration problems in 66% of children, night wakings in 72% of children, and bedtime resistance in 66% of children; 38% of children were reported to have problems with all CSHQ insomnia domains. Actigraphy-measured sleep duration was correlated with estimates using CSHQ-reported bed and wake times