Being too heavy or too light at birth and gaining weight before height as a child could lead to a life of obesity, according to a new report.

Childhood obesity is such a critical public health issue it could reverse gains made over the last 50 years in reducing heart disease and death, health experts say.

“Childhood obesity is increasing worldwide,” said Marie Francoise Rolland-Cachera, of the National Institute of Health and Medical Research in Paris.

“Being obese as a child increases the risk of being an obese adult,” she told the 14th European Congress on Obesity.

Studies show babies with a high birth weight have a higher risk of suffering from Obesity later in life. Infants who do not weigh much at birth but who catch up rapidly could also be more likely to grow into obese adults.

Gaining weight before height - or adiposity rebound - and how fat is deposited on the body during adolescence are also thought to have an impact on the risk of adult obesity and related illnesses like diabetes and cardiovascular disease.

“This is a time bomb waiting to happen,” Dr William Dietz, of the Centers for Disease Control in the United States, told the meeting.

At least 155 million school-age children worldwide are overweight and about 35-40 million of that figure are obese, according to the International Obesity Task Force (IOTF).

A lack of exercise, changing diets and bigger meals have been blamed for the rise in childhood obesity.

“The trend is continuing rapidly upwards because we are not tackling some of the big public health issues,” said Dr Tim Lobstein, the childhood obesity coordinator at the IOTF.

Making sure women are properly nourished during pregnancy will help to ensure babies are born at the optimal weight and breast feeding will give the baby the right nutrients for normal development, he added.

Schools should improve nutrition and exercise facilities for children, he said.