Sadiq Khan found that one in five London schoolchildren are classed as very overweight by the time they leave primary school.
Whilst in eight boroughs, including Southwark and Westminster, more than a quarter of 11-year-olds are considered obese, while one in ten five-year-olds across London are considered seriously overweight.
The figures, obtained from the Department of Health, revealed that 17,608 (22.4%) 11-year-olds in London were classed as obese in 2013/14, up from 15,817 (21.85%) four years ago.
More than two thirds (24 out of 33) of local authorities have above average numbers of obese five-year-olds, whilst 29 local authorities have higher than average numbers of obese 11-year-olds.
Khan attacked the rise of fast food shops opening close to schools and, if elected, would support local authorities bringing in tighter measures to curb this.
He would also support the introduction of the so-called sugar tax and would work with TfL to bring in signs across the network to encourage walking between stops, perhaps by using the Oyster card system to reward those who chose to walk.
Khan told the Evening Standard: “If we don’t start doing something now to tackle the growing problem of childhood obesity then we’re storing up a whole host of problems down the line.
“We need to do more to discourage fast food shops opening up around schools and colleges and I want to five local authorities the power to put a stop to this.”