By Fergus Walsh
Medical correspondent, BBC News
Obesity has now overtaken alcohol as the number one cause of liver disease.
In some cases the damage is so severe it means patients require a liver transplant.
Doctors say the rise in obesity means the problem will get even worse in years to come.
The warning comes from liver experts at King's College Hospital in south London, one of the UK's leading liver transplant centres.
Dr Varuna Aluvihare, a consultant hepatologist at King's, said says fat induced liver disease has overtaken alcohol and viral infections as the commonest cause of liver disease in Europe and North America.
"If we extrapolate from the US experience its quite likely unless we change things soon in the next 20 or 30 years obesity will be the commonest cause of cirrhosis - that's irreversible scarring, and may be the commonest cause of indication for transplantation," he said.
That will present real problems for transplant units like King's.
Already there is a waiting list for liver transplantation - the rise in fatty liver disease means this is likely to get even longer.
Liver problems have damaged Mr Alderton's legs
Many of Dr Aluvihare's patients are surprised when told that obesity has caused their liver problems.
David Alderton is among them. He has never been a drinker, but he is now being assessed for a liver transplant. His liver is permanently scarred.
Mr Alderton's vital statistics tell their own tale. He is 66 years old and 6' 1" but weighs around 24 stone (152kg).
His Body Mass Index (BMI) is over 40 (a BMI of 30+ is regarded as obese).
David acknowledges that a lifetime of poor diet has led him here.
"I was doing driving seven days a week and that led to irregularly eating all the wrong foods", he said.
"I was normally about 17 stone (108kg) and it increased there onwards.
"I knew it was doing me no favours but the fact that I didn't feel ill, at that time, I carried on the bad habit. I have left it too late."
Often too late
That is one of the problems with liver disease.
By the time symptoms emerge, the damage can be irreversible.
The liver is the body's largest internal organ.
It has hundreds of functions, from breaking down food to convert it to energy, to ridding the body of excess fluids and fighting infection.
When someone becomes overweight the liver often can't cope with the fat levels and it starts to store fat.
This can lead to the liver becoming enlarged. In serious cases the organ can be permanently scarred - cirrhosis.
Although David needs a new liver, his heart and general health may not be up to the rigours of such a big operation, so for now he is not able to get on the waiting list for a transplant.
And it's not just elderly patients who are vulnerable to fat-induced liver disease.
Young people at risk
The rise in childhood obesity means that patients are getting younger and younger.
Obesity can cause extensive liver damage (Picture: King's College Hospital)
Dr Aluvihare says it was virtually unheard of 15 years ago but they are now seeing a handful of children each year presenting with abnormal liver functions tests because of fat deposits.
And it is only going to get worse.
There are things patients can do if fatty liver disease is caught early enough.
Valerie Hillman walks for 30 minutes a day and has a healthier diet since being told she had liver damage.
Like David Alderton she was very surprised to hear that excess body weight can cause serious liver problems. Valerie is 5' 0" and weighs nearly 11 stone (70kg).
Her body mass index is just below 30, but she certainly doesn't look obese.
But her excess weight is enough to have given the 61-year-old diabetes and fatty liver disease.
"Unfortunately it can creep up on you once you are into your 40s," she said.
"I do think people should be aware of this at a lot earlier age so that they can do something about it rather than when they have put on the weight and its too difficult to get rid of."
Being overweight or obese carries with it a huge number of potential health risks, among them heart disease, diabetes, cancer and arthritis. Now add to that liver disease.
It's yet one more reason to try to achieve a healthy body weight, based on a balanced diet and exercise. It's easier said than done.