Norman J. Temple

Antioxidants and disease: more questions than answers

Abstract Reactive oxygen species are widely believed to be involved in the etiology of many diseases as indicated by the signs of oxidative stress seen in those diseases. Conversely, antioxidants are believed to be protective. An important part of the supporting evidence is the consistently-seen inverse association between, on the one hand, intake of β-carotene and vitamin C and of fruit and vegetables, and, on the other hand, risk of cancer and coronary heart disease (CHD). However, the failure of supplemental β-carotene to prevent these diseases in intervention trials suggests that the associations for that nutrient reflect confounding rather than cause and effect. With respect to other antioxidants there is inconsistent evidence that supplements of vitamin E may have some ability to prevent cancer and CHD while selenium may prevent cancer. Overall, the role of oxidative stress in disease, especially cancer and CHD, has probably been overstated; other components of the diet (other nutrients, phytochemicals and dietary fiber) likely play a significantly greater role. The possible benefits of supplements are discussed.

Diet, nutrition and the prevention of type 2 diabetes

OBJECTIVES The overall objective of this study was to evaluate and provide evidence and recommendations on current published literature about diet and lifestyle in the prevention of type 2 diabetes. DESIGN Epidemiological and experimental studies, focusing on nutritional intervention in the prevention of type 2 diabetes are used to make disease-specific recommendations. Long-term cohort studies are given the most weight as to strength of evidence available. SETTING AND SUBJECTS Numerous clinical trials and cohort studies in low, middle and high income countries are evaluated regarding recommendations for dietary prevention of type 2 diabetes. These include, among others, the Finnish Diabetes Prevention Study, US Diabetes Prevention Program, Da Qing Study; Pima Indian Study; Iowa Womens Health Study; and the study of the US Male Physicians. RESULTS There is convincing evidence for a decreased risk of diabetes in adults who are physically active and maintain a normal body mass index (BMI) throughout adulthood, and in overweight adults with impaired glucose tolerance who lose weight voluntarily. An increased risk for developing type 2 diabetes is associated with overweight and obesity; abdominal obesity; physical inactivity; and maternal diabetes. It is probable that a high intake of saturated fats and intrauterine growth retardation also contribute to an increased risk, while non-starch polysaccharides are likely to be associated with a decreased risk. From existing evidence it is also possible that omega-3 fatty acids, low glycaemic index foods and exclusive breastfeeding may play a protective role, and that total fat intake and trans fatty acids may contribute to the risk. However, insufficient evidence is currently available to provide convincing proof. CONCLUSIONS Based on the strength of available evidence regarding diet and lifestyle in the prevention of type 2 diabetes, it is recommended that a normal weight status in the lower BMI range (BMI 21-23) and regular physical activity be maintained throughout adulthood; abdominal obesity be prevented; and saturated fat intake be less than 7% of the total energy intake.

Vegetarian diets, low-meat diets and health: a review

OBJECTIVE To review the epidemiological evidence for vegetarian diets, low-meat dietary patterns and their association with health status in adults. DESIGN Published literature review focusing primarily on prospective studies and meta-analyses examining the association between vegetarian diets and health outcomes. RESULTS Both vegetarian diets and prudent diets allowing small amounts of red meat are associated with reduced risk of diseases, particularly CHD and type 2 diabetes. There is limited evidence of an association between vegetarian diets and cancer prevention. Evidence linking red meat intake, particularly processed meat, and increased risk of CHD, cancer and type 2 diabetes is convincing and provides indirect support for consumption of a plant-based diet. CONCLUSIONS The health benefits of vegetarian diets are not unique. Prudent plant-based dietary patterns which also allow small intakes of red meat, fish and dairy products have demonstrated significant improvements in health status as well. At this time an optimal dietary intake for health status is unknown. Plant-based diets contain a host of food and nutrients known to have independent health benefits. While vegetarian diets have not shown any adverse effects on health, restrictive and monotonous vegetarian diets may result in nutrient deficiencies with deleterious effects on health. For this reason, appropriate advice is important to ensure a vegetarian diet is nutritionally adequate especially for vulnerable groups.

Dietary intake and barriers to dietary compliance in black type 2 diabetic patients attending primary health-care services.

OBJECTIVE To determine the dietary intake, practices, knowledge and barriers to dietary compliance of black South African type 2 diabetic patients attending primary health-care services in urban and rural areas. DESIGN A cross-sectional survey. Dietary intake was assessed by three 24-hour recalls, and knowledge and practices by means of a structured questionnaire (n = 133 men, 155 women). In-depth interviews were then conducted with 25 of the patients to explore their underlying beliefs and feelings with respect to their disease. Trained interviewers measured weight, height and blood pressure. A fasting venous blood sample was collected from each participant in order to evaluate glycaemic control. SETTING An urban area (Sheshego) and rural areas near Pietersburg in the Northern Province of South Africa. SUBJECTS The sample comprised 59 men and 75 women from urban areas and 74 men and 80 women from rural areas. All were over 40 years of age, diagnosed with type 2 diabetes for at least one year, and attended primary health-care services in the study area over a 3-month period in 1998. RESULTS Reported dietary results indicate that mean energy intakes were low (< 70% of Recommended Dietary Allowance), 8086-8450 kJ day(-1) and 6967-7382 kJ day(-1) in men and women, respectively. Urban subjects had higher (P < 0.05) intakes of animal protein and lower ratios of polyunsaturated fat to saturated fat than rural subjects. The energy distribution of macronutrients was in line with the recommendations for a prudent diet, with fat intake less than 30%, saturated fat less than 10% and carbohydrate intake greater than 55% of total energy intake. In most respects, nutrient intakes resembled a traditional African diet, although fibre intake was low in terms of the recommended 3-6 g/1000 kJ. More than 90% of patients ate three meals a day, yet only 32-47% had a morning snack and 19-27% had a late evening snack. The majority of patients indicated that they followed a special diet, which had been given to them by a doctor or a nurse. Only 3.4-6.1% were treated by diet alone. Poor glycaemic control was found in both urban and rural participants, with more than half of subjects having fasting plasma glucose above 8 mmol l(-1) and more than 35% having plasma glycosylated haemoglobin level above 8.6%. High triglyceride levels were found in 24 to 25% of men and in 17 to 18% of women. Obesity (body mass index > or = 30 kg m(-2)) was prevalent in 15 to 16% of men compared with 35 to 47% of women; elevated blood pressure (> or = 160/95 mmHg) was least prevalent in rural women (25.9%) and most prevalent in urban men (42.4%). CONCLUSIONS The majority of black, type 2 diabetic patients studied showed poor glycaemic control. Additionally, many had dyslipidaemia, were obese and/or had an elevated blood pressure. Quantitative and qualitative findings indicated that these patients frequently received incorrect and inappropriate dietary advice from health educators.

Price and availability of healthy food: A study in rural South Africa

OBJECTIVE We investigated the availability of healthier food choices and whether a healthier diet costs more than a diet commonly eaten by low-income families in South Africa. METHODS We visited 21 food stores in 14 rural towns of the Western Cape province of South Africa. We recorded the price and availability of 66 food items, including both commonly consumed foods as well as healthy options. RESULTS Healthier food choices are available in supermarkets. However, many towns only have small food stores with a limited selection of healthy foods. We compared the prices of six commonly consumed foods with healthier versions of those foods (e.g., whole-wheat bread in place of white bread). Healthier foods typically cost between 10% and 60% more when compared on a weight basis (Rand per 100 g), and between 30% and 110% more when compared based on the cost of food energy (Rand per 100 kJ). Next, we compared the extra cost of a healthier diet compared to a typical South African menu. On average, for an adult male, the healthier diet costs Rand 10.2 (US

DOES BETA-CAROTENE PREVENT CANCER? A CRITICAL APPRAISAL

1.22) per day more (69% more). For a household with five occupants, the increased expenditure on food by eating a healthier diet is approximately Rand 1090 per month (US

The cost of a healthy diet: a South African perspective

140); this represents a high proportion (>30%) of the total household income for most of the population. CONCLUSION Healthier food choices are, in general, considerably more expensive than commonly consumed foods. As a result, a healthy diet is unaffordable for the large majority of the population.

SURVEY OF NUTRITION KNOWLEDGE OF CANADIAN PHYSICIANS

Abstract The possible role of beta-carotene as a protective nutrient against cancer is reviewed. Human prospective and retrospective studies strongly indicate that beta-carotene protects against lung cancer and probably against stomach cancer. It may also be protective against cancer of the ovary, cervix, breast and other cancers, but not the colon or rectum. The protective factor appears to be beta-carotene itself, rather than total vitamin A. Experiments using a variety of animal models also show that beta-carotene is anticarcinogenic and appears to act at several stages of the process. Possible mechanisms of action are discussed, namely that it must first be converted to vitamin A, that it alters carcinogen metabolism, that it is an anti-oxidant and that it enhances the immune defenses.

Cabbage and vitamin E: Their effect on colon tumor formation in mice

Energy-dense foods are relatively cheap sources of energy but typically have a low nutrient density. People with a low income may therefore select a relatively less healthy diet. The high energy density of such diets helps explain the association between obesity and low socioeconomic status. Most studies have been carried out in highly developed countries. We have extended this research to South Africa. Some foods, such as oats, beans, carrots, and apples, are moderately priced sources of energy and are healthy (i.e., they have a low energy density and are nutrient dense). However, such foods are likely to be less desired than many other foods, such as candy, cookies, jam, and chocolate, that have a similar cost (in terms of food energy) but are less healthy. We compared the cost of a typical South African diet with a healthier one. On average, the healthier diet costs 69% more, but this estimate is greatly affected by food choices. For a family whose household income is exceeded by one-third of the population, this increased expenditure represents about 30% of total household income. This could be decreased to about 10% to 15% if a healthy diet is carefully designed. Overall, a healthy diet is unaffordable for most South Africans. This shows the importance of not only educating people in developing countries to the importance of a healthy diet but also explaining how to make such a diet affordable. A more effective strategy is government intervention that manipulates food prices.

Food Synergy: The Key to Balancing the Nutrition Research Effort

OBJECTIVES Previous reports have indicated that physicians generally have little training in nutrition and a poor knowledge of the subject. A survey was carried out to determine the nutrition knowledge of physicians working in general practice. METHODS A questionnaire with multiple-choice questions was mailed to 248 physicians working in Alberta, Canada, mainly in Edmonton and Calgary. Non-respondents received a second questionnaire and a phone call. RESULTS Completed questionnaires were received from 36.1% (84 of 233 eligible physicians). The average correct response was 63.1%. The results indicate that physicians are generally aware of information which has been publicized in the medical press: which nutrients are antioxidants; the nutrient associated with the prevention of neural tube defects (folate); the preventive action of fruit and vegetables against cancer; the energy value of fat (9 kcals/g); and the recommended fat intake (under 30% of energy). By contrast they have a poor knowledge of other important topics in nutrition: the typical salt intake of Canadians; the association between excess protein intake and calcium loss; the type of dietary fiber helpful in lowering the blood cholesterol level (soluble fiber); and the nutrient which helps prevent thrombosis (omega-3 fat). CONCLUSIONS These results support other data that physicians need more training in nutrition.