Children from poor families are easily identified because they tend to be fat, the public health minister has said.
Anna Soubry said when she was at school pupils from deprived backgrounds tended to be "skinny runts".
But cheap and easily available junk food meant the situation had reversed, she added.
Anna Soubry, Conservative MP and Health Minister
The comments, in an interview with the Daily Telegraph, came after she threatened food manufacturers with legislation unless they cut the amount of fat, sugar and salt in products.
Miss Soubry told the newspaper that the culture of "TV dinners" had eroded traditional structures of family life and led some homes to dispense with a dining table entirely.
The Tory MP said it was "heartbreaking" that the poorest in the country were among the most at risk of obesity.
"A third of our children leave primary school overweight or obese," she said.
"When I was at school you could tell the demography of children by how thin they were. You could see by looking at their eyes."
They would be described as "the skinny runts" because they were not getting the right food, she went on.
"When I go to my constituency, in fact when I walk around, you can almost now tell somebody's background by their weight," Miss Soubry said.
"Obviously, not everybody who is overweight comes from deprived backgrounds but that's where the propensity lies."
She added: "It is a heartbreaking fact that people who are some of the most deprived in our society are living on an inadequate diet. But this time it's an abundance of bad food."
The minister suggested some parents thought cheap junk food was the only way to feed their children.
She said on her way to work at Westminster she saw parents buying their children unhealthy "breakfast buns" from fast food shops.