Almost 50,000 people could be dying with malnutrition in English hospitals, the Tories have claimed.
A new Government report suggests the number of people thought to have malnutrition in hospital is an underestimate.
Many such patients are already malnourished before they enter hospital although they can deteriorate on the wards.
Campaigners say there is a lack of help with eating in hospitals alongside a failure to recognise the severity of the problem.
The inquiry report into Mid Staffordshire NHS Foundation Trust noted some patients were left without food and water for days at a time.
Around half of families questioned said there were issues with obtaining meals and drinks.
The latest end-of-year report from the Nutrition Action Plan Delivery Board said 239 patients died because of malnutrition in English hospitals in 2007.
Overall, 2,656 were reported to have died from malnutrition in hospitals and care homes since 1997, it added.
The report’s authors said: “However, we believe that these statistics can be very misleading.
“They represent less than 0.5% of the number who died in hospital with malnutrition.
“We know that malnutrition predisposes to disease, it delays recovery from illness and it increases mortality.
“It follows that the effect of malnutrition on mortality rates is substantially greater than the number reported to have died because of malnutrition.”
Extrapolation by the Tories suggests this means 47,800 people died in hospital with malnutrition in 2007.
The report was delivered to the Government in August 2009 but has only just been released.
Shadow health minister Stephen O’Brien said: “It is horrific that so many patients are dying with malnutrition.
“We have raised this issue many times but Labour ministers have dragged their feet and are doing very little about it.
“The Government has sat on this devastating report since last summer - it is tragic to think that many more lives might have been saved if they hadn’t deliberately delayed publishing it because of the embarrassment it causes them.
“The Government urgently needs to take this report and its recommendations seriously.
“And it needs to free doctors and nurses from a culture of box-ticking and bureaucracy so that every patient can get the care they need in hospital.”
More than seven million people in the UK are vulnerable to malnourishment - around 150,000 people in hospitals, 600,000 people in care homes, 700,000 people in sheltered accommodation and six million who are dependent on others for their food and water needs, the report said.
However, Phil Hope MP, Labour’s Care Services Minister, insisted the figure of 50,000 was totally untrue.
He said: ““The figures used by the Conservatives are wholly misleading because, sadly, malnutrition is often a side effect linked to many long-term conditions, especially with terminal illnesses or with cancer. It does not necessarily contribute to or is a cause of an individual’s death.
“To suggest otherwise is irresponsible and shows an acute lack of understanding of the NHS and of the complex issues that can lead to malnourishment.
“It completely misleads the public to compare the number of patients dying as a result of malnutrition, which is 239, with the number of people who have some degree of malnourishment, often as a result of ill health.
“Once again, the Conservatives have failed to properly describe complex statistics and are presenting totally inaccurate figures.”