Obesity is defined as abnormal or excessive fat accumulation that may impair health. In infants and children under 5 years of age obesity is assessed according to the WHO "Child growth standards" (weight-for-length, weight-for-height) and the WHO Reference for 5-19 years (body mass index-for-age).

In adults overweight is defined as the individual’s body mass index (BMI). This is a simple index of weight-for-height, defined as a person's weight in kilograms divided by the square of his or her height in metres (kg/m²). In adults BMI greater than or equal to 25 is overweight; and BMI greater than or equal to 30 is obesity.

Obese infants and children are likely to continue being obese during adulthood and are more likely to develop a variety of health problems as adults. These include:

• Cardiovascular disease
• Insulin resistance (often an early sign of impending diabetes)
• Musculoskeletal disorders (especially osteoarthritis - a highly disabling degenerative disease of the joints)
• Some cancers (endometrial, breast and colon)
• Disability.

Children at risk of becoming overweight or obese include children who:

• consume food and drinks that are high in sugar and fat on a regular basis such as fast food, candy, baked goods, and ESPECIALLY pop and other sugar-sweetened beverages
• are not physically active each day
• watch a lot of TV and play a lot of video games, activities that don’t burn calories (sedentary time)
• live in an environment where healthy eating and physical activity are not encouraged
• eat to help deal with stress or social problems
• come from a family of overweight people where genetics may be a factor, especially if healthy eating and physical activity are not a priority in the family
• come from a low-income family who do not have the resources or time to make healthy eating and active living a priority
• are exposed to the aggressive marketing of energy-dense foods and beverages to children and families
• have a lack of information about sound approaches to nutrition
• have a lack of access, availability and affordability to healthy foods
• have a genetic disease or hormone disorder such as Prader-Willi syndrome or Cushing’s syndrome

Supportive policies, environments, schools and communities are fundamental in shaping parents’ and children’s choices, making the healthier choice of foods and regular physical activity the easiest choice (accessible, available and affordable), thereby preventing obesity.

• Early initiation of breastfeeding within one hour of birth;
• Exclusive breastfeeding for the first 6 months of life; and

The introduction of nutritionally-adequate and safe complementary (solid) foods at 6 months together with continued breastfeeding up to two years of age or beyond

• Limit energy intake from total fats and sugars;
• Increase consumption of fruit and vegetables, as well as legumes, whole grains and nuts;
• Engage in regular physical activity (60 minutes a day).

• Reducing the fat, sugar and salt content of complementary foods and other processed foods;
• Ensuring that healthy and nutritious choices are available and affordable to all consumers;
• Practicing responsible marketing especially those aimed at children and teenagers.