Medical reasons are at the root in one in five cases of severe obesity in children, according to a joint research project between Erasmus and Amsterdam university teaching hospitals.

Although an unhealthy lifestyle – a bad diet and lack of exercise – is usually blamed for obesity in children, around 20% of cases have other causes, the researchers found.

Some 16% of children and teenagers in the Netherlands are overweight and 3% are considered to be obese. Of them, 18,000 children are seriously obese, and 300 of these children were the focus of this research.

‘We looked into the precise cause of obesity in each child, ranging from dna tests and hormone measurements to their physical condition and how fast they burned calories,’ research doctor Ozair Abawi said.

In 20% of cases, the researchers found an underlying health problem, much higher than the 5% quoted in medical literature.

In some cases, obesity was inherited, in others medicine the children used were behind their overweight. Most underlying causes were found in pre-school children.

‘It is important that doctors try to determine why a child is obese… so you can target treatment,’ research doctor Lotte Kleinendorst said. ‘Such a diagnosis can  support both parents and children.’