Experts have warned more than three million people in the UK are suffering from or are at risk of malnutrition.
According to the British Association for Parenteral and Enteral Nutrition (Bapen), 90% of the people in danger live in the community rather than in care homes or hospital, but the problem is "under-recognised and under-treated".
The report said malnutrition is taking its toll on individuals, health and social services, with the condition costing an estimated£13 billion a year.
A survey in 2007 found 28% of patients were at risk of being malnourished on admission to hospital, along with 30% of new care home residents and 19% of people admitted to mental health units, but it did not take into account those people living in the community.
Older people recently discharged from hospital and patients with conditions like dementia or cancer are more likely to be affected by malnutrition, and the burden of the condition is expected to grow as Britain's population is ages.
Bapen is urging the Government to reduce the extent and cost of poor nutrition by increasing the number of patients screened for their risk.
It says this could be done by improving staff training, providing more equipment for weighing, and introducing incentives to conduct nutritional screening.