Why is weight loss important

There can be little doubt that obesity has become a major public health and economic problem of global significance. According to World Health Organization (WHO) estimates, approximately 1 billion people throughout the world were overweight in 2002 and more than 300 million of these were obese. Prevalence rates continue to rise rapidly in all areas of the world, including low-income countries, and obesity associated illness are now so common that they are replacing the more traditional public health concerns, such as undernutrition and infectious disease, as the most significant contributors to global ill health.

The health impact of obesity is considerable, and obesity impacts on both quality and length of life. Overweight and obesity are associated with a wide range of chronic conditions, such as diabetes, hypertension, cardiovascular disease, and certain cancers, as well as non life threatening but painful conditions, such as arthritis, back pain, and breathlessness. Obesity also places enormous financial burdens on governments and individuals and accounts for a significant proportion of total health care expenditure in developed countries. Analyses suggest that obesity is fast approaching cigarette smoking as the major preventable cause of mortality.

In recent years, our understanding of the epidemiology and causation of obesity has improved dramatically and there is an acceptance that urgent action is required to address the problem. However, there are very few examples of successful, large-scale obesity prevention initiatives from any area of the world. Despite these limitations, sufficient understanding has been gained from smaller scale obesity prevention initiatives together with experiences from the management of other epidemics of non-communicable diseases to allow effective planning and implementation of obesity prevention programs to proceed.

Overweight and obesity problems

There are a number of reasons why prevention is likely to be the only effective way of tackling the problem of overweight and obesity. First, obesity develops over time, and once it has done so, it is very difficult to treat. A number of analyses have identified the limited success of obesity treatments to achieve long-term weight loss. Second, the health consequences associated with obesity result from the cumulative metabolic and physical stress of excess weight over a long period of time and may not be fully reversible by weight loss. Third, the proportion of the population that is either overweight or obese in many countries is now so large that there are no longer sufficient health care resources to offer treatment to all. It can be argued, therefore, that the prevention of weight gain (or the reversal of small gains) and the maintenance of a healthy weight would be easier, less expensive, and potentially more effective than to treat obesity after it has fully developed.

Objectives of obesity prevention

There remains a great deal of confusion regarding the appropriate objectives of an obesity prevention program. It is often assumed that to be effective, any intervention to address the problem of excess weight in the community should result in a reduction in the prevalence of overweight and obesity. However, such an objective is unrealistic and may be counterproductive. Most communities are experiencing significant increases in the average weight of the population as a result of a sizeable energy surplus resulting from reduced energy expenditure combined with an increased energy intake. This is leading to rapidly escalating rates of overweight and obesity. To reverse this trend will require not only the removal of this energy surplus but also the creation of a negative energy balance that will need to be maintained by the whole population for a significant period of time. Few interventions are capable of reducing energy intake, or increasing energy expenditure sufficiently, or are sustained long enough and with sufficient reach to achieve this effect. More appropriate objectives would relate to a reduction in the level of weight gain or the maintenance of weight stability in adults and the achievement of appropriate growth and development in children. The achievement of these objectives would result in a slowing in the rate of increase, followed by stabilization and then an eventual decline in the level of overweight and obesity in the community.

However, even the goal of weight stability within a population may be difficult to achieve in the short term because it would require the maintenance or reestablishment of energy balance in time of significant energy surplus. Therefore, it may be necessary to identify more sensitive short- and medium-term outcomes to evaluate obesity prevention programs. Such process outcomes may relate to the achievement of appropriate changes in energy intakes or outputs, food or physical activity behaviors, or changes to the environment that are significant enough to positively impact upon the achievement of energy balance.

Importance of weight gain prevention

There are a number of important reasons why it is preferable to focus on weight gain prevention as the key individual and population objective of obesity prevention initiatives in adults. The association between elevated body mass index (BMI) and increased risk of ill health is clear and consistent. However, research has demonstrated that weight gain per se is also associated with increased health risk, and that this risk is independent of absolute BMI (provided a person is not underweight). A number of studies have shown strong relationships between weight gain and increasing levels of diabetes, hypertension, gall bladder disease, and coronary heart disease. Therefore, a large weight gain in a lean individual may carry equivalent risk to maintaining a stable but slightly elevated BMI in an overweight individual. The combination of an elevated BMI and ongoing weight gain, however, leads to greatly magnified levels of risk.