A stunning diet test every parent should read: This family put Joe Wicks’s theory that ultra-processed food causes bad behaviour to the test. The effect on eight-year-old Isobel’s tantrums was remarkable

For the past three years, peace has been in short supply for Kate and Mike Rawlings as the behaviour of their older child has spiralled out of control.

Isobel, now eight, would routinely turn meal times at their Northampton home into a battlefield, repeatedly getting up and down from the table…