Causes of overweight and obesity

While many factors may influence your weight, overweight and obesity occur mainly because of an imbalance between energy intake from the diet and energy expenditure (through physical activities and bodily functions). Genetic and environmental factors also play a role. Attention to diet and physical activity is important to help ensure a healthy body weight.

Energy intake

The total amount of food that your body needs depends on your age, sex, body size, level of physical activity and whether you are pregnant or breastfeeding. Your body converts the protein, fat and carbohydrate in food to energy. Fat is the most concentrated source of energy. Visit to calculate your individual energy requirements.

Energy intake from food varies greatly between individuals. For example, in 2011–12, intake ranged from about 6,000 kilojoules for children aged 2–3 to about 9,000 kilojoules for adolescents aged 14–18. For adults aged 19 and over, the average intake for men was about 10,000 kilojoules and for women was about 7,500 kilojoules [1].

Energy expenditure

The human body expends energy in 3 ways:

  • basal metabolism (the energy used to maintain vital body processes)
  • thermic processes (the energy taken to digest and absorb food)
  • physical activity (the energy used to move around).

Physical activity is the most variable component of energy expenditure, and the main component a person has control over. For a normally active person, physical activity contributes about 20% to daily energy expenditure.

The balance

Healthy eating and physical activity are important for a healthy active life. Maintaining your weight means balancing the energy going into your body (as food and drink) and the energy being used for growth and repair, for physical activity, and to keep your bodily functions working. An excess energy intake, even a small amount over a long period, will cause weight gain. Children and adolescents need enough nutritious food to grow and develop normally. Older people need to keep physically active and eat nutritious foods to help maintain muscle strength and a healthy weight.

The Australian Guide to Healthy Eating is a food selection guide that visually represents the proportion of the five food groups recommended for consumption each day. Following these recommendations and limiting the number of energy-dense, nutrient-poor discretionary foods and drinks is the best way to maintain a healthy weight. Being physically active and eating healthily throughout life helps to promote health and wellbeing and prevent chronic disease.


  1. Australian Bureau of Statistics 2014. Australian Health Survey: Nutrition first results—foods and nutrients, 2011–12. ABS cat. no. 4364.0.55.007. Canberra: ABS.