A mother called her obese child a "doughnut", stopped them exercising and fed them takeaways before they died from a heart condition at 13, a report has found.
The teenager was consuming more than 2,000 calories before lunch, prior to their death in April 2015.
A serious case review also found the mother "put obstacles in the way" to prevent them from taking part in PE.
Manchester Safeguarding Board said it was reviewing its neglect strategy.
The details of the review, which concluded last year, came to light at a meeting of Manchester City Council's children and young people's scrutiny committee, as reported by the Local Democracy Reporting Service.
'Missed health appointments'
It found the Greater Manchester teenager, who has not been named, was not provided with a PE kit by their mother despite enjoying classes.
The mother blamed the child for not losing weight, called them "lazy" and falsely claimed they could not take part because of health problems and disabilities, it said.
"[The school] found it difficult to challenge [the] mother about putting obstacles in the way of [the teenager] from taking part in something they enjoyed and which was beneficial for their wellbeing," the report added.
The teenager, who asked teachers to keep their attendance at exercise classes a secret from their mother, also missed health appointments.
The review also found the child weighed more than 30kg (4st 10lb) at the age of three and as a teenager would consume a takeaway as a second breakfast.
During the teenager's final weeks, the mother also took takeaway food to the hospital for her child to eat, the report said.
It added the child's weight "contributed" to their cardiomyopathy condition.
The review said "professional paralysis" amongst authorities meant they were hesitant about considering childhood obesity as an indicator of neglect and abuse.
Manchester Safeguarding Board said its neglect strategy was now being "refreshed" to include identifying factors such as obesity.
Chair Julia Stephens-Row said "it's not an easy conversation to be talking to parents about their child's weight and also potentially their own weight" but added it was about "empowering those professionals to have those different conversations".
Criminal inquiries were started following the teenager's death but no action was taken.