Liver diseases, including cirrhosis, are increasingly being seen in overweight teenagers, experts report.
An unhealthy diet can contribute to liver damage
Cirrhosis, irreparable liver damage, is commonly linked with alcohol misuse, but can also be caused by a fatty diet.
Dr Giorgina Mieli-Vergani, a specialist at King's College Hospital in London, warned teenagers with liver problems may need transplants in later life.
Obesity experts said the warnings gave added weight to the argument that children need to eat well.
Dr Mieli-Vergani said she had seen one 15-year-old who was very overweight and suffering from cirrhosis and other liver problems linked to obesity.
Professor Roger Williams, the liver specialist who treated George Best at the Cromwell Hospital in London, said he too had recently treated a teenager who was in the stage before the full onset of cirrhosis.
He described the case, and the health concerns it raised for obese teenagers, as "frightening".
In cirrhosis, which occurs during the late stages of various liver disorders, normal tissue is destroyed and replaced by fibrous scar tissue.
This permanent damage prevents the liver from performing its normal functions.
However, Dr Mieli-Vergani said this was the severe end of the spectrum, and the more common problem she saw was non-alcoholic steato-hepatitis (NASH).
She said that 10 years ago, she saw around one child every two years with NASH. However, it has now risen to between six and 10.
NASH increases the risk of having further liver problems.
Both cirrhosis and NASH could increase the risk an affected teenager could require a liver transplant later in life - if they do not change their habits, Dr Mieli-Vergani said.
She told the BBC News website: "There's no doubt whatsoever that there has been an increase in NASH over the last 10 years, which is partly due to diet."
Dr Mieli-Vergani said the US was seeing the most cases of NASH, but warned the UK was probably the "worst country in Europe".
She said this was largely because of the high-fat, high sugar diet many children ate.
Excess fat in liver cells can cause them to expand, leading to inflammation and scarring.
Dr David Haslam, clinical director of the National Obesity Forum, said: "There really isn't an organ in the body that is safe from the effects of obesity - and the liver is a vital organ."
Catherine Arkley, chief executive of the Children┐s Liver Disease Foundation said: "We have seen an enormous rise in the number of children with fatty liver disease."
But she added:"We still know remarkably little about NASH in young people and this highlights the need for more research so informed guidelines can be given."