ArabicChineseEnglishFrenchRussianSpanish
WHO home
All WHO This site only
 

Nutrition

  WHO > Programmes and projects > Nutrition > Nutrition health topics
printable version

5. Population nutrient intake goals for preventing diet-related chronic diseases: Previous page | 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27

5.2 Recommendations for preventing excess weight gain and obesity

5.2.1 Background

Almost all countries (high-income and low-income alike) are experiencing an obesity epidemic, although with great variation between and within countries. In low-income countries, obesity is more common in middle-aged women, people of higher socioeconomic status and those living in urban communities. In more affluent countries, obesity is not only common in the middle-aged, but is becoming increasingly prevalent among younger adults and children. Furthermore, it tends to be associated with lower socioeconomic status, especially in women, and the urban-rural differences are diminished or even reversed.

It has been estimated that the direct costs of obesity accounted for 6.8% (or US$ 70 billion) of total health care costs, and physical inactivity for a furtherUS$24 billion, in the United States in 1995. Although direct costs in other industrialized countries are slightly lower, they still consume a sizeable proportion of national health budgets (1). Indirect costs, which are far greater than direct costs, include workdays lost, physician visits, disability pensions and premature mortality. Intangible costs such as impaired quality of life are also enormous. Because the risks of diabetes, cardiovascular disease and hypertension rise continuously with increasing weight, there is much overlap between the prevention of obesity and the prevention of a variety of chronic diseases, especially type 2 diabetes. Population education strategies will need a solid base of policy and environment-based changes to be effective in eventually reversing these trends.

5.2.2 Trends

The increasing industrialization, urbanization and mechanization occurring in most countries around the world is associated with changes in diet and behaviour, in particular, diets are becoming richer in high-fat, high energy foods and lifestyles more sedentary. In many developing countries undergoing economic transition, rising levels of obesity often coexist in the same population (or even the same household) with chronic undernutrition. Increases in obesity over the past 30 years have been paralleled by a dramatic rise in the prevalence of diabetes (2).

5.2.3 Diet, physical activity and excess weight gain and obesity

Mortality rates increase with increasing degrees of overweight, as measured by BMI. As BMI increases, so too does the proportion of people with one or more comorbid conditions. In one study in the USA (3), over half (53%) of all deaths in women with a BMI>29 kg/m2 could be directly attributed to their obesity. Eating behaviours that have been linked to overweight and obesity include snacking/eating frequency, binge-eating patterns, eating out, and (protectively) exclusive breastfeeding. Nutrient factors under investigation include fat, carbohydrate type (including refined carbohydrates such as sugar), the glycaemic index of foods, and fibre. Environmental issues are clearly important, especially as many environments become increasingly “obesogenic” (obesity-promoting).

Physical activity is an important determinant of body weight. In addition, physical activity and physical fitness (which relates to the ability to perform physical activity) are important modifiers of mortality and morbidity related to overweight and obesity. There is firm evidence that moderate to high fitness levels provide a substantially reduced risk of cardiovascular disease and all-cause mortality and that these benefits apply to all BMI levels. Furthermore, high fitness protects against mortality at all BMI levels in men with diabetes. Low cardiovascular fitness is a serious and common comorbidity of obesity, and a sizeable proportion of deaths in overweight and obese populations are probably a result of low levels of cardio-respiratory fitness rather than obesity per se. Fitness is, in turn, influenced strongly by physical activity in addition to genetic factors. These relationships emphasize the role of physical activity in the prevention of overweight and obesity, independently of the effects of physical activity on body weight.

The potential etiological factors related to unhealthy weight gain are listed in Table 7.

5.2.4 Strength of evidence

Convincing etiological factors

Regular physical activity (protective) and sedentary lifestyles (causative). There is convincing evidence that regular physical activity is protective against unhealthy weight gain whereas sedentary lifestyles, particularly sedentary occupations and inactive recreation such as watching television, promote it. Most epidemiological studies show smaller risk of weight gain, overweight and obesity among persons who currently engage regularly in moderate to large amounts of physical activity (4). Studies measuring physical activity at baseline and randomized trials of exercise programmes show more mixed results, probably because of the low adherence to long-term changes. Therefore, it is ongoing physical activity itself rather than previous physical activity or enrolment in an exercise programme that is protective against unhealthy weight gain. The recommendation for individuals to accumulate at least 30 minutes of moderate-intensity physical activity on most days is largely aimed at reducing cardiovascular diseases and overall mortality. The amount needed to prevent unhealthy weight gain is uncertain but is probably significantly greater than this. Preventing weight gain after substantial weight loss probably requires about 60-90 minutes per day. Two meetings recommended by consensus that about 45-60 minutes of moderate-intensity physical activity is needed on most days or every day to prevent unhealthy weight gain (5, 6). Studies aimed at reducing sedentary behaviours have focused primarily on reducing television viewing in children. Reducing viewing times by about 30 minutes a day in children in the United States appears feasible and is associated with reductions in BMI.

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

Evidence

Decreased risk

No relationship

Increased risk

Convincing

Regular physical activity
High dietary intake of NSP (dietary fibre)b


Sedentary lifestyles
High intake of energy-dense micronutrient-poor foodsc

Probable

Home and school environments that support healthy food choices for childrend
Breastfeeding


Heavy marketing of energy-dense foodsd and fast-food outletsd
High intake of sugars-sweetened soft drinks and fruit juices
Adverse socioeconomic conditionsd (in developed countries, especially for women)

Possible

Low glycaemic index foods

Protein content of the diet

Large portion sizes
High proportion of food prepared outside the home (developed countries)
“Rigid restraint/periodic disinhibition” eating patterns

Insufficient

Increased eating frequency


Alcohol

a Strength of evidence: the totality of the evidence was taken into account. The World Cancer Research Fund schema was taken as the starting point but was modified in the following manner: randomized controlled trials were given prominence as the highest ranking study design (randomized controlled trials were not a major source of cancer evidence); associated evidence and expert opinion was also taken into account in relation to environmental determinants (direct trials were usually not available).
b Specific amounts will depend on the analytical methodologies used to measure fibre.
c Energy-dense and micronutrient-poor foods tend to be processed foods that are high in fat and/or sugars. Low energy-dense (or energy-dilute) foods, such as fruit, legumes, vegetables and whole grain cereals, are high in dietary fibre and water.
d Associated evidence and expert opinion included.

5. Population nutrient intake goals for preventing diet-related chronic diseases: 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27 | Next page

[an error occurred while processing this directive]