5.1 Energy Balance in the Development of Obesity
5. CAUSES OF OBESITY
Obesity can result from a minor energy imbalance, which lead to a gradual but persistent weight gain over a considerable period. Some researchers have hypothesized that energy imbalance is the result of inherited metabolic characteristics; whereas others believe it is caused by poor eating and lifestyle habits, that is “gluttony and sloth”. Positive energy balance occurs when energy intake is greater than energy expenditure and promotes weight gain (Figure 4). Conversely, negative energy balance promotes decrease in body fat stores and weight loss. Body weight is regulated by a series of physiological processes, which have the capacity to maintain weight within a relatively narrow range (stable weight). It is thought that the body exerts a stronger defence against undernutrition and weight loss than it does against over-consumption and weight gain.
Figure 4 also suggests that positive energy balance and weight gains are influenced by powerful societal and environmental forces which may overwhelm the physiological regulatory mechanisms that operate to keep weight stable. These include increasing automation, lack of recreational facilities and opportunities, increase in food variety and availability. Moreover, the susceptibility of individuals to these influences is affected by genetic and other biological factors such as sex, age and hormonal activities, over which they have little or no control (WHO 1998). Dietary intake and physical activity are important contributing factors in the development of obesity. If calorie intake is in excess of requirement it will be stored mainly as body fat (Figure 4). If the stored body fat is not utilised over time, it will lead to overweight or obesity.
Inter-individual variations in energy intake, basal metabolic rate, spontaneous physical activity, the relative rates of carbohydrate-to-fat oxidation, and the degree of insulin sensitivity seem to be closely involved in energy balance and in determining body weight in some individuals (Ravussin 1993).
Strategy for the Prevention of Obesity - Malaysia
ENVIRONMENTAL & SOCIETAL INFLUENCES Individual / Biological Susceptibility
Dietary & Physical Activity Patterns ENERGY REGULATION
INTAKE FAT CHO PROTEIN GAIN STABLE WEIGHT LOSS
EXPENDITUR ACTIVIT TEF* BMR
BODY FAT STORES
Figure 4: The fundamental principles of energy balance and regulation
* TEF = thermic effect of food; BMR = basal metabolic rate; CHO = carbohydrate. Source: WHO (1998)
5.1.1 Factors that promote or protect against weight gain
Causes of Obesity
WHO (2003) examined the various aetiological factors that could lead to unhealthy weight gain. These factors were categorised based on strength of evidence, namely convincing, probable, possible and insufficient as shown in Table 8. Table 8: Summary of strength of evidence on factors that might promote or protect against weight gain and obesity Decreased risk Regular physical activity. High dietary non-starch polysaccharide (fiber) intake Home and school environments that support healthy food choices for children No relationship Protein content of the diet Increased risk
Evidence Convincing Probable
High intake of energy-dense nutrientpoor foods. Sedentary lifestyles Heavy marketing of energy-dense foods and fast-food outlets. Adverse social and economic condition (in developed countries, especially in women). Sugar sweetened soft drinks and fruit juices. Large portion sizes. High proportion of food prepared outside the home (western countries) “Rigid restraint / periodic disinhibition” eating patterns Alcohol
Low glycaemic index foods
Source : WHO (2003)
Increasing eating frequency
5.2.1 Food consumption pattern
Dietary patterns of Malaysians have changed markedly, as evidenced from an analysis of food...