Dozens of cases of malnutrition were seen at the St Helens and Knowsley Hospital Services NHS Trust last year, figures show.
Charities have warned that many households cannot afford a healthy diet, and called for government action to increase access to nutritious food.
Patients were admitted to hospital with malnutrition around 75 times at the St Helens and Knowsley Hospital Services NHS Trust in the 12 months to March 2018, according to NHS Digital data.
This was unchanged from two years ago.
But across England, cases have shot up by 18% over the same period, from 7,855 cases in 2015-16 to 9,307 cases in 2017-18.
Malnutrition is caused by a person's diet containing either not enough, or too much, of the nutrients they need, according to the NHS.
The Joseph Rowntree Foundation, an anti-poverty charity, warned that over 1.5 million households across the country are regularly left struggling to afford essentials such as food.
Chris Goulden, from the organisation, said: "Living in poverty can severely restrict a family’s ability to put food on the table and lead a healthy life.
"The poorest fifth of households spend twice as much of their income on food and fuel compared with those in the richest fifth, meaning those on the lowest incomes are most vulnerable to price rises, inflation and the benefits squeeze."
Public Health England recommends that people follow its Eatwell Guide to make sure they are eating a healthy, balanced diet.
However, a 2018 report by independent think tank the Food Foundation found that more than one in four households would need to spend more than a quarter of their disposable income after housing costs to meet the guide's recommendations.
For parents in the bottom 20% of earners, the cost would be 42% of their income.
The St Helens and Knowsley Hospital Services NHS Trust also saw cases of rickets and scurvy during 2017-18.
Across England, scurvy has increased by 14% since 2015-16, rising to 167 incidents last year, while rickets cases fell by 10% to 474 incidents.
The Food Foundation warned the figures were signs of a "broken food system".
Executive director Anna Taylor said: "Although cases of rickets, scurvy and malnutrition are caused by a complicated range of factors, they are not conditions that we should have to be talking about anymore in a country as wealthy as the UK.
“Nearly 4 million children in the UK live in households for whom a healthy diet is unaffordable.
"We need industry and government to take action now to ensure that everyone has access to enough nutritious food.”
A spokeswoman from the Department of Work and Pensions said there were now fewer households with low incomes.
"We know there’s more to do ensure that every family has access to nutritious, healthy food", she said.
“Malnutrition is a complex issue and most patients diagnosed in England have other serious health and social problems.
"For people that need extra support with their living costs we spend £90 billion a year on working-age benefits and will be spending £28 billion more by 2022 than we do now.”