Three overweight elephants at a Swiss circus will have to diet and work out in order to shed between 50 and 300 kilogrammes (110-660 pounds), Swiss newspaper Tages Anzeiger reported Wednesday.

To help them lose weight, Circus Knie is not only putting them on a special and low-sugar diet but also making them work for their food.

Hay barrels will now be suspended above the elephants' heads, forcing them to make an effort to reach their food.

Sabu, weighing in at 4.3 tonnes, will have the toughest regime, as it needs to shed 300 kilogrammes.

Circus Knie's vet Hanspeter Steinmetz says he has a foolproof way of detecting if an elephant is overweight, by observing the animal's hips.

If the hip bones are hidden or only slightly visible, the elephant is overweight. If they stand out, the elephant is too thin.