How to prevent weight gain

Weight gain and obesity develop when the energy intake from food and drink exceeds energy expenditure from physical activity and other metabolic processes. It is often assumed that the prevention of weight gain should focus solely on attempting to alter these behaviors within individuals and communities. However, research has consistently shown that numerous and diverse factors, including environmental and social factors, influence the behaviors that lead to excessive weight gain. Addressing aspects of the obesogenic (obesity-promoting) environment, as well as individuals' eating and physical activity patterns, is considered to be critical to the success of any obesity prevention program.

The 2003 WHO report on diet, nutrition, and the prevention of chronic disease undertook a detailed review of the literature and identified a range of key factors that either increase or decrease the risk of weight gain and the development of obesity. These factors were rated on the quality of evidence available to support their contributory role. This analysis serves as a very useful guide as to the focus of weight gain prevention initiatives.

Diet and physical activity behaviors

The WHO analysis identified a number of key dietary and physical activity behaviors, amenable to change, that could conceivably influence energy balance sufficiently to contribute to the prevention of weight gain and obesity. Behaviors that reduced the risk of obesity included regular physical activity, high dietary fiber intake, low glycemic index diets and possibly breast feeding. Behaviors that increased the risk of obesity included a high intake of energy-dense foods, a high intake of sugar-sweetened drinks and juices, time spent in sedentary behaviors, and possibly large portion sizes, a high intake of fast foods, and a restrained eating pattern.

The area of dietary and physical activity antecedents to weight gain and obesity is still poorly understood and new research findings, which help clarify our understanding, are being presented on a regular basis. In addition, different behaviors are more prevalent or pronounced in different regions of the world. It is therefore difficult to give definitive recommendations on the most important and useful behaviors to target in obesity prevention strategies. However, strong evidence exists to support the inclusion of some key behaviors.

Reducing energy intake

• Reducing the intake of high energy-dense foods (high in fat/sugar):
  There is a high level of agreement that the over-consumption of energy-dense foods is a major contributor to excess energy intake and weight gain and that restriction of energy-dense food items is a useful strategy for the prevention of weight gain. However, discussion continues as to whether fat or refined carbohydrate is the major contributor to energy density in the modern diet and thus should be the target of programs to control weight. The debate is being fuelled by dietary data from many developed countries that show that dietary fat intakes have leveled out or declined slightly and intakes of carbohydrates have increased dramatically. However, research has shown that dietary fat (along with water and fiber) is a major contributor to the energy density of foods and that ad libitum low-fat diet plans are an effective dietary approach to weight gain prevention or moderate weight loss. There is also strong evidence that excess carbohydrate, particularly high glycemic index carbohydrate, contributes to weight gain and its restriction aids weight loss and improves cardiovascular risk factor profiles.
• Increasing the intake of high-fiber, energy-dilute foods (vegetables and fruits):
  There is less evidence on the effectiveness of increasing the intake of energy-dilute foods such as vegetables and some fruits in the diet. Such a strategy would assist weight gain prevention only if the inclusion of such foods leads to a reduction in the intake of more energy-dense alternatives and thus creates a reduction in energy intake. Few studies have addressed this issue in a comprehensive manner, but the additional health benefits of these foods makes such a strategy low risk in nutritional terms.
• Reducing the consumption of sugar-sweetened soft drinks and juices:
  Evidence is accumulating from a variety of studies that energy consumed as sweetened drinks is less well compensated for than energy consumed as solid food. Longitudinal studies have also indicated that sweetened drinks (soft drinks or sodas) are associated with weight gain in both children and adults. Recent work has also demonstrated that the simple strategy of reducing the intake of sweetened drinks can be effective in preventing or limiting inappropriate weight gain.
• Reducing the level of food prepared outside of the home:
  The proportion of food purchased and consumed at food outlets outside of the home has increased dramatically in recent decades in both developed and developing nations. In the United States, approximately 40% of the household food budget is spent on food eaten away from home, and much of this is spent at fast-food outlets. A number of analyses have linked increased consumption of fast food with increased risk of obesity. Although few studies have evaluated the effect of reducing the consumption of fast food, it would seem to be a valuable strategy with few nutritional negatives.
• Reducing portion sizes:
  The portion size of packaged foods and snacks, as well as restaurant serving sizes, has increased rapidly in recent times and has been identified as an important factor in the consumption of excess energy. Evidence suggests that people will consume the portion of food they are provided rather than respond to satiety signals to stop eating and leave food. Also, as the serving size increases, the ability of consumers to estimate accurately how much they have consumed decreases. Reducing portion sizes is a simple but immediately effective mechanism for reducing energy intake.

Increasing energy expenditure

Although it is difficult to obtain accurate assessments of physical activity, there is little doubt that energy expenditure from activity has decreased in the past 50 years in most countries throughout the world. In contrast to popular belief, participation rates in organized leisure-time physical activity have increased in recent times in many countries. This supports the contention that the greatest contributor to this reduction in energy expenditure is associated with substantial changes in occupational and incidental physical activity. Changes in employment patterns and work practices together with a reliance on motorized transport and the removal of almost all manual labor from our daily lives have led to a dramatic reduction in daily physical exertion.

Studies that have examined the association between physical activity and weight gain and the impact of increasing physical activity on weight gain prevention have been limited by the ability to accurately measure physical activity and to engage people in sufficient levels of physical activity to prevent weight gain. However, there is sufficient evidence to support an important role for increasing physical activity in any weight gain prevention strategy, although questions remain about how much exercise is necessary and what type of exercise is appropriate to promote. The issue of the amount of extra time that people should spend in moderate physical activity to prevent weight gain remains hotly debated, but it is clearly substantially more than the 30 minutes on 5 or more days each week recommended by experts to reduce cardiovascular disease risk. The type of exercise that should be the focus of weight gain prevention strategies is also under review. It has been suggested that the most effective ways to include regular physical activity in daily living are through increased incidental activity, increased participation in active recreation, and increased use of active transport.

Changes in societal structures and improvements in technology have allowed a reduction in time spent at work or on domestic chores, leaving a greater proportion of the day for leisure. At the same time, most of the entertainment options developed to fill this time, such as watching television, playing video games, and using computers, are sedentary activities that require very little energy expenditure. These forms of entertainment, which initially complemented other forms of leisure activity, are occupying more hours of the day and are displacing more active pursuits and games. As a consequence, a number of studies have identified clear links between time spent in this sedentary behavior and weight gain. However, it is important to make a distinction between a lack of physical activity and sedentary behavior because their mechanisms for impacting on body weight may be different and a person with a high level of physical activity can also have a high level of sedentary behavior. Although the precise pathway by which sedentariness influences weight gain is not known, it is believed to involved both a reduction in physical activity and an increase in dietary energy intake through inappropriate food intake that is often stimulated by and accompanies sedentary activities.

Some studies in children have shown that programs that seek to reduce time spent in sedentary behaviors are more effective in controlling weight than programs that aim to increase physical activity alone. In some cases, a simple program to reduce the amount of time spent watching television was sufficient to significantly limit inappropriate weight gain in children.