Diet and Nutrition Prevention of Chronic Diseases

5. Excess weight gain and obesity

• 5.1 Is obesity a growing problem?
• 5.2 How can diet and physical activity affect obesity?
• 5.3 What factors are known to affect obesity?
• 5.4 How could obesity be prevented?

5.1 Is obesity a growing problem?

While obesity is most common in developed countries, almost all countries are now affected by this worldwide epidemic, as diets are becoming richer and people more inactive. The increase in the number of cases of excessive weight gain and obesity has been paralleled by an increase in some chronic diseases such as cardiovascular disease and diabetes. In the United States obesity and physical inactivity alone accounted for about 9% of total health care costs in 1995. Obesity also entails social and economic costs in terms of lost workdays, visits to the doctor and premature deaths.

Within a country, the occurrence of obesity tends to vary between certain age groups and socioeconomic classes. For example, in the most affluent countries, obesity is now affecting not only middle aged people, but also increasingly young adults and children.

Population education strategies supported by substantial policy changes could be effective in eventually reversing these trends.

This text is a summary of: WHO/FAO Diet, Nutrition and the prevention of chronic diseases
5.2.1 Background – 5.2.1 Trends 

5.2 How can diet and physical activity affect obesity?

Certain types of foods and eating habits have been linked to weight gain and obesity, for instance snacking, binge-eating, and eating out.

Physical activity and physical fitness are important factors in reducing the risk of unhealthy weight gain and related illnesses, such as heart diseases, and moderate to high fitness entails health benefits (independently of body weight).

With increasing overweight, as measured by the Body Mass Index (BMI), there is an increase in mortality rates and in the proportion of people with additional health conditions. In one study in the USA, over half of all deaths in women with a BMI greater than 29 kg/m² could be directly attributed to their obesity.

This text is a summary of: WHO/FAO Diet, Nutrition and the prevention of chronic diseases
Section 5.2.3 Diet, physical activity and excess weight gain and obesity 

5.3 What factors are known to affect obesity?

convincing evidence shows that weight gain can result from low physical activity, while regular exercise can help to maintain a healthy body weight.

There is convincing evidence that regular physical activity helps prevent unhealthy weight gain whereas sedentary lifestyles, particularly sedentary occupations and inactive recreational activities such as watching television, promote it. Between 45 and 60 minutes of moderate-intensity physical activity on most days or every day are recommended to prevent unhealthy weight gain. Preventing weight gain after substantial weight loss may require about 60-90 minutes of physical activity per day.

A high intake of dietary fibre has been shown to promote weight loss. Contrastingly, weight gain is promoted by a high intake of energy-dense foods that contain a lot of fat or sugar and few nutrients.

The long-term effectiveness of most dietary strategies for weight loss, including low-fat diets, remains uncertain unless these strategies are accompanied by changes in physical activity and food behaviours. Weight-loss diets that lack evidence from trials of long-term effectiveness and nutritional adequacy cannot be recommended for populations.

Table 7: Summary of strength of evidence on factors that might promote or protect against weight gain and obesity

Advertisements are constantly promoting foods that are fried and high in fat and sugar. The fact that children can be exposed to such ads through television,might explain the strong relationships found between television viewing and obesity in children . High sugar drinks probably contribute to weight gain as well. Just one extra glass of soda or fruit drinks per day can increase a child’s risk of becoming obese by 60%. This evidence makes a strong case for limiting the amount of high sugar drinks consumed by children.

Several large studies showed that breastfeeding probably protects the baby against unhealthy weight gain while providing many other benefits as well. The attitude of children towards food and exercise is largely dependent on their experiences in the home and school environments. Introduction to healthy foods in the home and appropriate teaching in schools can help children make healthy choices regarding food and exercise.

Studies have also shown possible links between food portion sizes and weight gain. People may overestimate appropriate portion sizes and therefore eat more than they should. Eating out may also contribute to excess weight gain because food prepared outside the home is typically higher in fat and cholesterol than home-made meals. In contrast, eating foods that breakdown slowly, releasing glucose over a long time (low-glycaemic foods) could possibly protect against unhealthy weight gain.

Certain psychological factors may influence eating patterns and therefore increase the risk of obesity. A "rigid restraint" all-or-nothing approach to eating, dieting, and weight control is probably associated with a higher risk of obesity. The risk is lower for a "flexible restraint" eating pattern with a more gradual approach to dieting in which "fattening" foods are eaten in limited quantities without feelings of guilt.

Other possible factors have been studied, but evidence of an effect on weight gain or obesity is insufficient. For example, there is insufficient evidence that alcohol intake increases the risk of obesity.

This text is a summary of: WHO/FAO Diet, Nutrition and the prevention of chronic diseases
Section 5.2.4 Strength of evidence 

5.4 How could obesity be prevented?

Obesity can be prevented by encouraging healthy habits early in life.

During infancy, parents should ensure that the child is receiving nutritious food in appropriate quantities. This can initially best be achieved through breastfeeding. If, however, a milk formula is used, it should not contain added starch or sugars. Parents should accept the child’s ability to regulate energy intake rather than feeding until the plate is empty.

During childhood and adolescence, parents should encourage physical activity and a diet which contains plenty of fruits and vegetables. Excessive television viewing and the consumption of energy-dense foods and drinks with added sugars should be discouraged and, where possible, replaced by family activities and home-made meals.

In developing countries, programmes designed to address undernutrition should take into consideration both stature and weight to avoid overfeeding.

In countries in economic transition, as populations become more sedentary and able to access energy-dense foods, there is a need to maintain the healthy components of traditional diets and to educate mothers and poor communities about nutrition and obesity.

Individuals can reduce the overall risk of obesity by:

• Maintaining a BMI (Body Mass Index) of 18.5-24.9 kg/m². BMI is an indicator of the prevalence of obesity within a population and the median for the adult population should be in the range of 21-23 kg/m².
  
  Table 8: Classification of overweight in adults according to BMI
• Controlling waist circumference. Waist measurements give an indication of abdominal fat mass and total body fat. Above a certain waist measurement, there is an increased risk of metabolic complications (102 cm for men, and 88 cm for women) which can in turn increase the risk of developing chronic diseases.
• Engaging in one hour of moderate physical activity per day (for instance walking).
• Controlling total energy intake by consuming less energy-dense foods and drinks, and more fruits, vegetables and fibre.

This text is a summary of: WHO/FAO Diet, Nutrition and the prevention of chronic diseases
Section 5.2 Recommendations for preventing excess weight gain and obesity