Up to a quarter of children aged four or five in the North are overweight or obese, the chief medical officer said today.
Dr Michael McBride said levels were rocketing to unacceptably high levels. He was publishing his annual report today and said the increasing use of fast food and television watching was responsible for the epidemic.
"Obesity levels are rising at an alarming rate, particularly among children," he said. "We all know the importance of a healthy diet and taking more exercise. "We must act now to avoid a future where our children face significant health problems."
Diabetes and heart disease are among the perils facing those seriously overweight. Levels among five-year-olds have risen from 17 per cent in 1997 to 23 per cent in 2004. In 2004, the most recent year available, one in four girls and one in five boys aged five were obese or overweight.
Obesity causes around 450 deaths every year. Factors behind the rise include the overuse of high calorie, convenience food, the relative cost of healthy options and inadequate cooking skills among parents.
There has also been a growth in watching television and computer and other sedentary activities and a reluctance to allow young children outside for safety reasons. Dr McBride added: "We are living longer, healthier lives but what about our children? "There are no guarantees that they will share that good health most of us enjoy as parents.
"Next to smoking, poor diet is the biggest single cause of Northern Ireland's poor health record." The 2006 annual report also said the number of cases of sexually transmitted diseases had doubled in the last 10 years.
In 2005 there were just under 13,000 diagnoses.
Almost 50 new cases of syphilis are being uncovered every year, compared to one or two in the 1990's. The dossier highlighted rising levels of diabetes.
There are around 60,000 sufferers, many linked to obesity. It also said men in deprived areas were living seven years less than the most affluent.