Malnourishment costs £13bn a year in health costs
People suffering from malnutrition - or at risk of it - in the UK stands at three million, experts believe.
It is the clearest idea yet of the scale of the problem after those in the community as well as hospitals and care homes were included in the count.
The British Association for Parenteral and Enteral Nutrition said the problem was costing £13bn a year to treat and urged GPs to do more.
But GPs said that it was already being taken seriously.
BAPEN's report looked at previous research on the extent of malnutrition in a range of settings from hospitals and mental health units to sheltered housing and care homes.
Researchers estimated that of the three million either malnourished or at risk of malnutrition, 93% were living at home or in sheltered accommodation, 5% were in care homes and 3% in hospitals and other NHS settings.
They said elderly people, particularly those with long-term conditions, were most at risk, although isolation and poverty also played key roles.
The association, together with a range of charities, have been campaigning about nutrition for years.
The pressure has resulted in a number of improvements, including more screening and better food in hospitals and care homes.
But BAPEN said it was now time for GPs to do more.
Under guidelines, they are meant to use the official malnutrition screening checklist, which measures weight, height and any recent weight loss to give a malnutrition risk score, when they believe someone might be at risk.
But the association said this was still not being done routinely and urged ministers to include more incentives in the GP contract.
The report said the health cost of the problem was also likely to be in the region of £13bn - twice as high as some previous estimates.
Malnourished people stay in hospital longer, succumb to infection more often and visit their GP more frequently.
Professor Marinos Elia, one of the lead authors of the report and a former chair of BAPEN, said: "The evidence is clear and the time is right.
"The emphasis must now be on prevention and that means spotting it in the community."
As well as GPs, he said pharmacists could get involved in community screening, while transport planners could do more to ensure people had good links to supermarkets.
Pamela Holmes, of Help the Aged, said: "Malnutrition in the community is drastically overlooked.
"Social workers, community nurses, GPs and other health professionals need to be educated and trained to spot and treat the signs of malnutrition."
Professor Steve Field, of the Royal College of GPs, said: "It is a very important issue, but I think it is something GPs are already taking seriously.
"We routinely weigh and measure patients so I don't think it is necessary to change the GP contract."
But the Department of Health in England said despite the problems being reported overall people were getting healthier.
A spokeswoman said: "The Department recognises that good diet and nutrition are important for everyone.
"Sustained investment in tackling health inequalities has paid off. Life expectancy in England is the highest it has ever been, including in disadvantaged areas.
"We are committed to reducing health inequalities further, and have put in place the most comprehensive programme ever in this country to address them."
She also pointed out the Nutrition Action Plan published in Autumn 2007 specifically aimed to address the issue of malnutrition in care homes and hospitals by encouraging screening and staff training as well as issuing guidance.