Overeating, poor diet and lack of exercise explain most of the increase in childhood obesity. Genetics also plays a role, as genes help determine a child’s body type and how the body stores and burns fat. Obesity is more common in Hispanics and black Americans than in some other racial and ethnic groups. Poverty may play a role as well because sweets and sodas are often cheaper than fresh fruits and vegetables.

Overweight parents are more likely to have an overweight child, and children who are heavy are more likely to grow up to be obese adults. The probability of an obese child remaining obese into adulthood is 20 percent for obese 4-year-olds and 80 percent for those who are obese in adolescence, according to the American Academy of Pediatrics.

Obese children face a higher risk of metabolic syndrome. This condition includes controllable risk factors for heart disease, many of which are also risk factors for diabetes, including excess blood fats (hyperlipidemia), high blood glucose, high blood pressure and excess body weight. The American Heart Association (AHA) reports that about 1 million American children between 12 and 19 years old, or about 4.2 percent, have metabolic syndrome. About 73 percent of the 1 million children were classified as overweight, and the remaining had all the risk factors for becoming overweight.

Many of the factors behind childhood obesity involve eating habits, such as:

• Increased portion sizes
• Diet high in cholesterol and saturated fats
• Diet high in processed starches and sugars
• Diet low in fiber, fruit and vegetables
• Increased consumption of soft drinks
• Increased consumption of fast food
• Consuming more fats, sugars and soft drinks while in school

Children are also exercising less today than in years past. Computers, video games and television have replaced outdoor play for millions of children. Several studies have shown that fewer than half of the nation's schoolchildren participate in daily physical activity. The American Dietetic Association suggests parents involve children in meal planning, portion control and also become a positive role model for good nutrition and exercise.

Other factors associated with obesity include:

• Lack of muscle mass. Muscle burns calories at a higher rate than other tissues, which helps manage weight. The sedentary lifestyle of many children is a major contributing factor for a lack of muscle mass.
  
  
• Medications. Some medications, such as certain antidepressants and antihistamines, may cause a child to gain unintended weight.
  
  
• Psychological factors. Some children eat out of boredom, sadness, stress or anger.
  
  
• Chronic diseases. Disorders including insulin resistance, hypothyroidism, polycystic ovary syndrome and Cushing's syndrome have been shown to contribute to obesity.
  
  
• Vitamin deficiencies. Filling up on non-nutritious foods not only adds extra calories that can promote weight gain, it also puts children at risk for vitamin deficiencies.
  
  
• Inadequate sleep. Studies in recent years have increasingly indicated that insufficient sleep may promote obesity in children and adults, perhaps by altering hormones in a way that leads to overeating.