As obesity escalates at an alarming rate worldwide, it is increasingly recognised that a healthy body weight is important for optimal health and wellbeing. Obesity is associated with a significant increase in morbidity and mortality and costs the nation millions each year. In fact, the World Health Organisation has estimated obesity to cost around 2-7% of the annual health budget; which in New Zealand equates to around $303 million1.
What is obesity?
For adults, the most commonly used measurement of obesity is body mass index (BMI). Although this is a crude measurement it gives a good indication of the proportion of the population who are obese. However it doesn’t distinguish between muscle weight and fat, or indicate where the fat is distributed.
To calculate body mass index, divide weight (in kg) by height (in meters squared). The World Health Organisation classifies a BMI of less than 18.5 as underweight, a BMI of 18.5 to 25 as ideal, 25 to 30 as overweight and over 30 as obese. In New Zealand, however, a BMI of over 32 has been used to define obesity in Maori and Pacific people, as studies have shown that a slightly higher BMI cut-off provides a more accurate indication of fatness amongst these ethnic groups.
For children in New Zealand, anthropometric measurements (height, weight, circumferences and skin folds) are used as indicators of health status and to provide a description of size and shape 2. The BMI cut-off that defines adult obesity is not able to be used in children because they are still growing.
How common is obesity in New Zealand?
Latest figures show that although obesity prevalence increased between 1997 and 2006/7, the rate of increase appears to be slowing. Figures from 2006/7 show that one in three adults is overweight (36.1%) and a further one in four is obese (26.5%) 3.
Most New Zealand children aged 2-14 have a weight within the normal range, however one in five children is overweight (20.9%) and a further one in twelve is obese (8.3%).3
What is the health risk associated with being obese?
The effects of increased body mass index were estimated to account for 11.5% of premature deaths in 19974. The number of obesity-related premature deaths today is likely to be even higher as the burden of obesity continues to increase.
Obesity is a major health risk for a number of chronic diseases, including type 2 diabetes, gallbladder disease, dyslipidaemia, insulin resistance, breathlessness and sleep apnoea. Obesity also increases the risk of heart disease, hypertension, osteoarthritis and gout. In addition, some types of cancer (for example breast cancer in post-menopausal women, endometrial cancer and colon cancer) are associated with obesity, as are reproductive hormone abnormalities, polycystic ovary syndrome and impaired fertility.
Excess abdominal fat in particular is associated with increased risk of diabetes and heart disease. For men, a waist circumference of over 102cm (40 inches) and for women a waist circumference of over 88cm (35 inches) is associated with a substantial increase in health risk.
Cause of Obesity
In simple terms, obesity results from an energy intake (measured in calories or kilojoules) that is in excess of requirements over an extended period of time. Factors such as ethnicity, gender, age, genetics and hormonal factors may influence body weight; however the massive increase in obesity that has occurred in recent years points to the environment as the key influencing factor.
The modern environment has been described as ‘obesogenic’5. Today there is an overabundance of energy dense foods; and, increasing urbanization, modernization and changing occupational structures have resulted in reduced energy expenditure through physical activity.
Maintaining a healthy body weight requires constant effort, to alter dietary patterns and make time for physical activity.
To adequately address obesity, changes are required at an environmental and an individual level. Public health interventions need to target both food consumption and physical activity.
Important settings for public health interventions include the food industry, the media, the primary care settings, schools, workplaces, and sports facilities.
Interventions for treating obesity in individuals include dietary modification, increasing physical activity, cognitive behavioural therapy and, in some cases, surgical options may be required.
Some sectors of the New Zealand population have been identified as being at increased risk of obesity6, including children who have at least one obese parent, Maori and Pacific peoples, women in low socio-economic groups, people with disabilities and/or mental illness, ex-smokers, women post-pregnancy, physically inactive people and people who have previously been obese. Any interventions aimed at preventing and treating obesity should pay special attention to these high-risk groups.
The Ministry of Health’s Food and Nutrition Guidelines for Healthy Adults6 suggest that most New Zealanders would benefit from a better balance between energy intake and energy expenditure. To reduce energy intake, it is recommended that we cut down on foods such as cakes, chips, biscuits, sweets, soft drinks and alcohol. It is important not to reduce foods that make an important nutritional contribution to the diet, for example, vegetables, fruit, wholegrain cereals, pulses, lean meat, poultry, seafood, eggs and lower-fat milk and milk products.
Increasing physical activity is associated with significant health benefits, not only in terms of reducing obesity but also the risk of heart disease, hypertension, stroke, some cancers, diabetes, depression and osteoporosis. It is recommended that we all take at least 30 minutes of moderate-intensity physical activity on most days of the week (for example brisk walking or cycling). Additional benefits can be achieved by taking some vigorous activity as well.
- Ministry of Health (Accessed July 2008) www.moh.govt.nz/obesity
- Ministry of Health (2003) NZ Food NZ Children: Key Results of the 2002 National Children’s Nutrition Survey. Wellington: Ministry of Health.
- Ministry of Health. 2008. A Portrait of Health. Key Results of the 2006/7 New Zealand Health Survey. Wellington. Ministry of Health.
- Ministry of Health (Accessed July 2008) www.moh.govt.nz/moh.nsf/indexmh/obesity-key-facts
- Stanton RA (2006) Nutrition Problems in an obesogenic environment. Medical Journal of Australia, 184 (2): 76-79.
- Ministry of Health (2003) Food and Nutrition Guidelines for Healthy Adults: A background paper. Wellington: Ministry of Health.
This Science Byte was peer-reviewed by Jane Elmslie, PhD, NZRD (Canterbury District Health Board and University of Otago, Christchurch).