In May 2022, food inflation was at a record 19%. The research found 2.3 million low-income households on Universal Credit had to change the kind of food they buy to afford it.
Rachelle Earwaker, senior economist for the Joseph Rowntree Foundation, said the figures reflect a pattern of worsening poverty in the UK.
“Over the past year people have been telling us about being unable to afford hot meals, shampoo or a warm shower. We are seeing these levels of hardship persist and it has become a horrendous new normal.”
More on poverty:
Low-income households live on less than 60% of the median income and include working households.
Around two thirds (68%) of working-age adults in poverty live in a household where at least one adult is in work, according to JRF.
Katherine Chapman, director of wage campaign the Living Wage Foundation, said the figures should push employers to support employees on low incomes.
Speaking to HR magazine, she said: "Higher prices combined with stagnant wages have baked significant levels of hardship into our society.
“These findings from the JRF paint a disturbing picture of life below the real living wage today and of poorer health and wellbeing for those impacted in the future too.
"It is critical that action be taken to support those on the lowest incomes through this cost of living crisis. “
The number going without items such as food, heating or basic toiletries (63%) has remained around 7 million for more than a year.
Sam Balch, director of campaigns and content at responsible business network Business in the Community, said low-income households are experiencing the worst of the cost of living crisis.
Speaking to HR magazine, he said: “Research shows that those from low-income households spend higher proportions of their income on essential items such as food and other household products.
“With the rate of inflation on these items currently at more than 19%, the cost of living crisis is impacting low-income households more than others.”
The figures are published as a separate study from the CIPD Scotland found one in five working Scots losing sleep due to money worries.
Nearly a third (32%) said their employer is not doing enough to support their financial wellbeing.
Balch said businesses should review wages and benefits to ensure they are financially supporting their employees.
He said: “While this is also a difficult time for businesses, they must consider how they are supporting their employees and customers as prices continue to remain high.
“Paying the real living wage, for example, and providing products and services that are genuinely affordable are small steps businesses can take that can have a real impact on those who are struggling to make ends meet.”