Anne-Marie gorges on fast food and doesn't exercise yet stays slim. So scientists studied every detail of her life to find out why. Could her case help you?

Anne-Marie Martin is one of those women we love to hate — someone who tells you, while stuffing down a McDonald’s meal, that she can eat what she likes without putting on weight.

Her eating habits are, even she admits, downright shameful. She tells me that she has been known to visit McDonald’s three or four times in one week, albeit only, she says, ‘If it’s a very busy week when I’m rushing around with no time to cook’...........

This is a woman who not only has a passion for pasties, but goes out of her way to make them even more unhealthy. She routinely prises up the top so she can fill up the air space inside with lashings of calorie-rich salad cream. ‘Delicious,’ she says.