Europe's ageing population means more will die of malnutrition unless urgent action is taken, warns a charity.
The sick and elderly are particularly prone to malnutrition
The European Nutrition for Health Alliance says the problem is already endemic in the community, hospitals and homes for the elderly.
Experts believe up to half of elderly people in hospitals and residential and care homes are malnourished.
With the number of 80-year-olds doubling every decade, the number of malnourished people could also grow.
The ENHA said care providers needed to do more work on identifying and treating those most at risk.
This includes people who are sick with long-standing diseases as well as the elderly.
The alliance's co-chairman Professor Jean-Pierre Baeyens said: "Malnutrition is indeed endemic. Many people are not aware of the problem. If we do not act now it could increase. We are facing a time bomb."
Being malnourished is different to being underweight, although they often go hand in hand. It is possible to be overweight yet malnourished.
Malnutrition means not getting enough of the essential nutrients we need for a healthy life.
Not only does it cause health problems itself, it delays recovery from illness.
Professor Marinos Elia, Professor of Clinical Nutrition at Southampton University, estimates that malnutrition and its associated diseases cost the UK £7 billion a year.
He is due to publish a report on the full healthcare economics of nutrition later this year.
"Hospital expenditure is really quite large. People who are malnourished tend to stay in hospital longer."
He said there was also a great deal of malnutrition in the community, particularly among people with low incomes.
He said there were simple solutions that could help. For example, in Scottish hospitals it is now becoming mandatory to screen patients for malnutrition, he said.
Those who are malnourished may need help with feeding and selecting the right foods or require supplements.
In England, the government has revamped NHS hospital menus in a bid to make them more appetising for patients.
"There is more recognition but it is still not enough," said Professor Elia.
Professor Peter Kopelman of the Royal College of Physicians said he would like to see malnutrition checks become mandatory in English hospitals.
He said there had been an improvement in the quality of hospital food in recent years but that there were still malnourished patients in hospitals.
He said training healthcare professionals about nutrition was key.
Jonathan Ellis of Help the Aged said many older people needed help to eat meals, yet received no assistance.
"Malnutrition in these cases can so easily be prevented by delivering basic standards of care. To deny such basic care in the 21st century is simply unacceptable."