University of Melbourne professor of medicine Joseph Proietto said recent research showed that while obese people who made the effort could shed weight in the short term, after four to five years the lost weight was almost completely regained.

Far from being due to laziness, this appeared to be caused by hormonal changes as the body sought to return to what it considered its benchmark weight…

Professor Proietto wrote that while genetic factors were known to cause a predisposition to obesity, genetic mutations could not have happened fast enough to explain the surge in obesity rates in recent decades.

Instead, he said epigenetic changes — in which genes are switched on or off in response to environmental exposures in the womb or early infancy — were now thought to be responsible.