A project to raise awareness of malnutrition among elderly people is being launched with government backing.
Nearly a million over-65s in England suffer from untreated malnutrition, says charity Age UK - almost all of whom are in the community.
The project will aim to identify individuals in this group and support those who need help to eat properly.
Age UK, which is leading the work, said it wanted to ensure people did not "slip through the net".
More hospital admissions
The Malnutrition Prevention Project will begin in five pilot areas, including Lambeth, in south London and Salford, in Greater Manchester, in January.
There are two strands to the project - one is raising awareness of malnutrition among professionals such as hospitals, care homes and GP surgeries, and the other is through volunteers who might encourage older people to be aware of malnutrition, and for instance to cook for themselves or other people, or to attend lunch clubs.
The project will target people with low body mass index [that is, people who are underweight] and those who appear to be losing weight without trying - signs that are often wrongly seen as a normal part of ageing.
It is part of the government's response to the Francis report into events at Stafford Hospital - which found patients, many of them elderly, had not been able to eat or drink properly and that nutrition was not treated as a priority.
However, research has shown that 93% of malnourished older people are in the community.
Being malnourished can mean medication is less effective if it should be taken on a full stomach - and this makes it harder to recover from illness.
Compared with well-nourished people, those who are malnourished see their GP twice as often, have three times the number of hospital admissions and stay in hospital more than three days longer, the experts behind the project say.
Eating social activity
Dianne Jeffrey, chairman of Age UK, also chairs the Malnutrition Task Force expert group behind the project.
She said eating and drinking properly was "critical to being healthy and remaining independent".
But, she added, malnutrition went untreated and undiagnosed in "nearly one million older people in England".
"We hope that by working closely with hospitals, GP surgeries and care homes, we can tackle this hidden problem and help ensure that older people do not slip through the net."
David McCullough, chief executive of the Royal Voluntary Service, a charity that helps older people stay active, told BBC Radio 5 Live: "This is not a money problem, it is about the sort of changes people go through when they get older.
"A lot of us think that part of getting older is losing weight, but it is not a standard thing and is an indication of people not eating properly.
"Eating on your own is not much fun - eating is something, for most of us, we do with friends and family.
"When people are stuck at home alone they tend to eat less and drink less and that has really quite profound consequences for their health.
"We want to raise awareness and figure out the easy ways of us all identifying this problem so that we can jump in and deal with it."
Health minister Dan Poulter said: "Many people think of malnutrition as a problem that only affects the third world.
"But the reality is that over three million people in the UK have the potential to become malnourished - many of whom are frail and elderly."
He said action was needed. "Carers and NHS staff will be better equipped to identify, tackle and prevent malnutrition - so older people get better care and receive more support in their own homes and communities."