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There are a host of influences contributing to the development of overweight and obesity, including genetic, metabolic, environmental, behavioural, socioeconomic and cultural factors [1]. Weight gain is caused by consumption of macronutrients in excess of the body’s requirements creating a situation of positive energy balance. An energy imbalance over a sustained period of time leads to a person becoming overweight [2].
Body mass index (BMI) - calculated by dividing weight (in kilograms) by height (in metres) squared - is commonly used to categorise people in terms of appropriateness of weight (Table 1).
| Classification | BMI | Risk of co-morbidity |
|---|---|---|
| Source: WHO Consultation on Obesity (2000) [3] | ||
| Underweight | <18.50 | Low |
| Normal | 18.50-24.99 | Average |
| Overweight | 25.00-29.99 | Increased |
| Obese | 30.00+ | Further increased |
A complementary measure to BMI is waist circumference, as excess fat carried in the abdominal area is associated with increased risk of ill health. A waist circumference of 94 cm or more in men and 80 cm or more in women indicates increased risk of ill health and a waist circumference of 102 cm or more in men and 88 cm or more in women indicates substantially increased risk [4]. (This and the BMI classification may not be suitable for people aged 18 years or below and the cut-off points may not be suitable for all population sub-groups.)
A combination of macro and micronutrients are required to provide energy and to maintain normal metabolic function, growth and repair. The National Health and Medical Research Council’s Nutrient Reference Values provides information on recommendations for daily energy and nutrient intakes for children and adults based on the latest scientific evidence [5]. The NHMRC recommends a dietary intake of different types of foods, where all nutrients can be obtained within energy requirements and energy-dense, nutrient-poor foods are replaced with plenty of vegetables, fruits, wholegrain cereals, moderate amounts of lean meats, fish, and poultry, and small amounts of polyunsaturated or monosaturated fats and oils, and plain water. By increasing levels of activity, dietary choices become more flexible and have the benefits of assisting the maintenance of normal bodyweight and reducing the risk of a range of chronic diseases.
The actual energy requirements needed to maintain current body size and level of physical activity may be different to the desirable energy requirements needed to maintain a body size and levels of physical activity consistent with good health [5]. For people who are overweight or obese, desirable energy requirements may be lower than actual requirements. For people who are both overweight or obese and physically inactive, the difference between actual and desirable will depend on the balance between degree of overweightness and level of inactivity.
Overweight and obesity are associated with a range of debilitating and life-threatening conditions, such as cardiovascular disease, type 2 diabetes, high blood pressure, certain cancers, sleep apnoea, osteoarthritis, psychological disorders and social problems [2].
In terms of the association of overweight and obesity with specific health outcomes, there is good evidence of the association with:
and moderate evidence of the association with:
Obesity is a significant risk factor for the development of type 2 diabetes, a metabolic disease characterised by hyperglycaemia (high blood glucose levels) [7]. The chronic hyperglycaemia of diabetes is associated with long-term damage, dysfunction and failure of body organs, especially the heart and blood vessels, eyes, kidneys and nerves. The Australian Diabetes, Obesity and Lifestyle Study found that people who were obese were six times more likely to develop metabolic disorders than those of normal weight [7]. Physically inactive people are also at increased risk of developing such disorders.
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Strategies for dealing with overweight and obesity include psychological interventions and changes to nutrition and/or physical activity. Intensive, individually-tailored interventions have been shown to provide some success for overweight and obese people, and those at high risk of weight-related chronic disease . Obesity, however, is not just an individual problem: it is a population problem, and the World Health Organization recommends that it needs to be tackled as such [3]. In terms of interventions to address overweight and obesity in adults and older Australians there is plenty of evidence of the efficacy of interventions for those who are already obese, but there is less evidence for interventions that aim to prevent weight gain at a population level .
