One in seven elderly Britons suffers from malnutrition, even though Britain is one of the world's richest nations, according to a report published on Wednesday.
Illness and lack of services mean many elderly people are not eating properly.
The elderly in northern England and the northwest are most likely to suffer malnutrition, along with people living in residential homes, where up to 20 per cent of people aged 65 and over are thought to be at risk.
Malnutrition among the over 65s costs up to £4bln a year, the report said.
"It is a very serious problem in the elderly and in the long-term ill and a lot of people suffering from malnutrition are not being picked up because there is no routine screening being done,"said Wendy Morris of the Malnutrition Advisory Group (MAG).
The group of academics and health professionals compiled the report to show the extent of the problem and to prod the government into action to overcome it.
"Its aim is to urge the government to do more, to try and make nutrition screening and the management of malnutrition an integral part of care in the National Health Service," Morris added.
"At the moment the government's position is to improve the nutrition of the general population...there are no specific policies to deal with people who are malnourished."
MAG is calling for routine nutritional screening throughout the NHS and the establishment of national standards for the detection and management of malnutrition.
It is also urging the government to include nutrition training in nursing and medical colleges.
Disease is the main cause of malnutrition in the elderly. Elderly people lose their appetite or ability to eat during an illness or are not fit enough to make sure they eat properly.
Apart from causing weakness, fatigue and an increased risk of infections, malnutrition is also linked to psychological problems such as apathy, depression and anxiety.
Studies have shown that up to 40 per cent of adults and 60 per cent of the elderly who are admitted to hospital are malnourished.
"Malnutrition in patients aged 65 years and over probably costs two to four billion pounds annually, mainly as a result of increased rates of hospital admission and length of hospital stay," the report said.