Obesity definition

The definition of obesity is based on risk to health. Body mass index (BMI) is a commonly used measure to assess whether an individual is clinically obese. This is calculated using:

BMI = Weight (kg)/[Height (m) × Height (m)]

Although the BMI ranges are applicable to adult men and women, they are not satisfactory for children, adolescents or elderly people, in whom the proportion of lean body mass is changing. This index is best applied to the age range 19–65 years and a BMI between 20 and 25 is considered desirable in this age range. A BMI in adults of 25–30 indicates that an individual is overweight; a BMI of above 30 indicates that an individual is clinically obese and, as such, the condition constitutes a risk to health. A simpler way of determining health risk in adults is to measure waist circumference. A waist measurement of over 94 cm (37 inches) in men and 80 cm (32 inches) in women is associated with increased risk to health. A waist measurement of over 102 cm (40 inches) in men and 88 cm (35 inches) in women is associated with a substantial risk to health.

Risk associated with Obesity

The fact that obesity is a serious medical condition is being increasingly recognized. Obese people are at increased risk of heart disease, hypertension, type 2 (non-insulin-dependent) diabetes, gallstones, osteoarthritis of weight-bearing joints, sleep apnea, reproductive disorders and some cancers. It is important that obesity is given more prominence as a risk factor for disease.

Myth and facts

The ‘old myth’ that obesity occurs as a result of a low metabolic rate is unfounded. One of the few statements about obesity that can be made with absolute certainty is that obesity can occur only when energy intake remains higher than energy expenditure for an extended period of time. In other words, where there is a chronic displacement of the energy balance equation (‘energy in’ minus ‘energy out’ = change in body energy stores). Environmental changes that have occurred over the last few years, such as a more sedentary lifestyle and the ready availability of energy-dense foods, are the most likely underlying factors in the increasing prevalence of obesity. There are studies that have shown small differences in metabolism between obese subjects and their lean counterparts, but these differences are very subtle and are far outweighed by the impact of environmental influences and behavioral factors. A key strategy in tackling the rising prevalence of obesity must be education about the need for positive lifestyle changes. Health professionals should provide advice both for individuals and at a population level.

Diet and obesity

Predisposition to obesity has often been associated with intakes of high-fat foods. There does seem to be an increased liking for high-fat foods in those predisposed to obesity, e.g. obese people, formerly obese people, non-obese people with a high BMI, children of obese parents and restrained eaters.
There are a wide variety of dietary interventions available for the treatment of obesity, including low-calorie diets, very-low-calorie diets, milk diets and novel diets. Unfortunately, with many diets, long-term follow-up shows that much of the weight lost is regained. For dietetic success, it is important to focus on the patient’s individual needs, to set realistic goals, to instigate small achievable changes rather than large changes, and to focus on weight maintenance (once the desired amount of weight has been lost).

Exercise and Obesity

In terms of prevention, the development of new strategies to promote an environment that is ‘user-friendly’ in terms of activity is important. This will require action from the Government, local authorities and health authorities to provide affordable recreational facilities and safe environments for walking, jogging or cycling.

There are many benefits of exercise, which go far beyond weight control, e.g. exercise can reduce depression, anxiety and stress, enhance mood and self-esteem, and improve sleep quality. Recommendations for obese people, in terms of activity, are: that the amount of time spent in sedentary activities should be reduced; vigorous activity should be avoided, bouts of longer periods of moderate and sustained exercise are more beneficial; and more weight-bearing movement should be encouraged.

Changes need to be promoted both in people and in the environment in which they live. There are four key issues that need to be addressed. These are:

  1. Obesity is now a serious health problem in an increasing proportion of the population; action is now needed to prevent a further increase in prevalence.
  2. Part of the solution involves changing the national diet to include more foods of a low-energy density such as fruit and vegetables.
  3. Another part of the solution is to change the national lifestyle to include more physical activity, particularly opportunistic exercise such as using the stairs, and walking rather than using the car or bus for short distances. Strategies should address the needs of all segments of the population, but especially children.
  4. Strategies are now needed for both prevention and treatment of obesity; one strategy can not be expected to be effective for both objectives.

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