Packed lunches are, on average, nutritionally worse than the meals offered by schools, and the amount of essential nutrients in them decreased between 2006 and 2016.
The study, published in the BMJ Open magazine, included 2006 data of 1,148 students in 76 schools in England.
Of these schools, 18 also participated in a 2016 comparison survey, which included a total of 323 students.
He discovered that while the general amount of sugar in packed lunches had decreased, many foods still contained too much sugar, salt or fat, while fruit and vegetable levels had barely changed.
Vitamin C content dropped from 58 mg to 30 mg, and few lunches for children met the recommendations for fiber, vitamin A, iron or zinc.
Compulsory standards governing the nutritional quality of meals served at school were introduced in 2006 in England.
These restrict sweets, salty snacks and sugary drinks, while fruits, vegetables, starch, protein and dairy should be included in each meal.
However, there is no legislation for packed lunches and parents are free to choose what to include in them.
The study found that most of the sandwiches in both surveys were made with white bread and the most frequent filling
It was ham, which according to health experts is related to bowel cancer.
More than half of the lunch boxes in both surveys contained chips or other salty snacks, while about one in three included a chocolate chip cookie.
About four out of 10 lunch boxes also contained sugary pumpkin or a carton of fruit drinks in 2016, although this was less than in 2006.
Three lunches analyzed in the 2016 study contained only a sugary drink, a salty snack and a chocolate bar.
The study, led by the Faculty of Food and Nutrition Sciences at the University of Leeds, concluded: “Packed lunches are still of poor quality with few established standards for school meals.
“Although some children’s packed lunches contain healthy foods, the packed lunches continue to be dominated by sweet and savory snacks and sugary drinks.
“A minority of children eat vegetables or salads and this has not changed in the last 10 years.”
It is believed that about half of the children bring a lunch to take to school, while the other half have school meals.