According to a new study, many parents are afflicted with "weight blindness," and are unable to recognize when their children are obese. The study, pubished today in the British Journal of General Practice, found that 31 percent of parents underestimated their child's body mass index (BMI).

In fact, just 1 percent of parents classified their child as obese, and fewer than 1 percent overestimated their child's BMI. However, the team of researchers did find that there was an 80 percent chance that parents would classify their child as obese if the child was in the 95th percentile.

Researchers suggest that if parents are unable to identify that their child is overweight, it calls into question the effectiveness of many of the public health campaigns that are designed to address the growing problem of obesity in the home. The team says that the research could help evaluate how effective public health interventions really are, and also help narrow the focus to help children in different groups of the population.

Senior author Dr Sanjay Kinra, of the London School of Hygiene & Tropical Medicine, said, "If parents are unable to accurately classify their own child's weight, they may not be willing or motivated to enact the changes to the child's environment that promote healthy weight maintenance."

Co-author Professor Russell Viner, of the UCL institute of Child Health, said, "Measures that decrease the gap between parental perceptions of child weight status and obesity scales used by medical professionals may now be needed in order to help parents better understand the health risks associated with overweight and increase uptake of healthier lifestyles."

"By encouraging children to eat healthily, maintain a healthy weight, and be regularly physically active, parents can help children develop healthy habits and protect against health problems later in life. We know that obesity is linked to a range of health risks later in life - including increased cancer risk - so it's vital that parents are aware of their child's Body Mass Index (BMI), and can spot if their youngster is starting to become overweight," director of the World Cancer Research Fund, Amanda McLean says.

"But we also need to acknowledge that more can, and should, be done to encourage healthy eating and greater physical activity in our society. We need targeted policies that help people lead healthy lives - from clearer nutritional labeling to a focus on health education in schools. By encouraging good habits we can help future generations lead happy, healthy, lives."