Scrapping free school meals for infants would be "short-sighted" because the scheme could help alleviate the obesity crisis, a group of leading doctors has warned.
The claim, made in a letter to the Sunday Times, comes amid reports the Government is considering dropping the policy, which was introduced last September by the coalition.
Professor Baroness Hollins, a former president of the British Medical Association, and Dr Nigel Carter, chief executive of the British Dental Health Foundation, are among 40 leading figures calling for the meals to be protected from cuts.
The letter, which is also signed by representatives of charities Diabetes UK and the National Obesity Forum, said: "With one in three children leaving primary school overweight or obese, ensuring a nutritionally balanced school lunch has never been so important.
"A free school meals policy could end up paying for itself many times over and reduce the spiralling costs to the NHS of treating obesity and other diet-related illnesses. It would surely be short-sighted to cut the funding in November's spending review.
"We see the provision of a free healthy school lunch for infants as the bedrock of a transformative childhood obesity strategy - a strategy that also tackles the marketing and pricing of less healthy food and drink and boosts' schools' teaching of food education."
Only 1% of packed lunches meet nutritional standards for schools, the letter said, adding children who were overweight face health risks such as asthma, early signs of heart disease and poor mental health.
The Government has not confirmed if it is looking into whether to continue the scheme, which is available to all children in England in the first three years of school.
The news met with criticism from the Liberal Democrats, who introduced the policy, as well as celebrity chef and healthy eating campaigner Jamie Oliver, who said scrapping free meals would be "a disaster".
A Government spokesman said: "We believe that every child, regardless of their background, should have the same opportunities.
"That is at the heart of what we are doing with school food - no child should be hindered because they are not eating a nutritious meal at lunchtime."