Patients are at risk of malnutrition as there are not enough nurses to ensure they are properly fed, a poll says.
Elderly people are most at risk
Nearly half of the 2,193 nurses quizzed by the Royal College of Nursing said there were not enough staff to help patients.
And 42% said they do not have enough time to make sure patients eat and drink properly.
Age Concern said the findings were "shocking", but the government said it had made improvements.
A report last year from Age Concern revealed that 60% of older patients - who occupy two thirds of general hospital beds - were at risk of becoming malnourished or seeing their health get worse.
The charity blames poor practice in the NHS with regard to hospital mealtimes.
The Healthcare Commission is also investigating around 25 NHS trusts over their care of elderly patients, including whether patients' nutritional needs are met.
The RCN survey, unveiled at its annual conference in Harrogate, also revealed problems with feeding patients outside designated mealtimes.
Some 49% said inadequate availability of food outside mealtimes was a factor in poor nutrition.
Research shows that malnourished patients stay in hospital for longer, are three times as likely to develop complications during surgery and have a higher mortality rate.
It is estimated malnutrition costs the NHS £7.3bn a year.
Professor Alison Kitson, the RCN's executive director for nursing, said: "Nurses really do care deeply about this but to ensure that good patient nutrition happens, it needs to be a priority for everybody in the system from the catering staff through to chief executives.
"Only then will nurses be able to break through the obstacles and get the time and resources to ensure better patient care."
The RCN has launched its Nutrition Now campaign to raise awareness of the problem by calling on nurses to fill in incident forms when they are unable to help feed patients.
Gordon Lishman, director general of Age Concern, said the findings were "shocking".
"Food and help with eating should be a top priority for all ward staff, and they should be given time to perform this task."
Liberal Democrat health spokesman Norman Lamb said: "When frontline nursing staff are overstretched, patients suffer.
"All too often you hear of elderly and frail patients who have had food placed in front of them with no-one to help them eat it."
Shadow health secretary Andrew Lansley said: "I would urge hospitals to look at new innovations in hospital catering services."
But the Department of Health said a series of measures had been introduced under the Better Hospital Food programme.
A spokesman said: "These include protected meal times, when all non-urgent clinical activity stops, and the introduction of 24-hour catering so patients can now ask a nurse or housekeeper for food, snacks and drinks at any time of the day or night."