Monkeys at a zoo have been banned from eating bananas - because they are too unhealthy.

Animal nutritionists have likened giving bananas to the primates at Paignton Zoo in Devon to humans eating too much cake and chocolate.

To most people, monkeys and bananas go together like a horse and carriage, but it seems that this cliche is now redundant.

The monkey troop at the zoo have been on a health kick and have been avoiding food that is too sweet and sugary - including bananas.

Amy Plowman, head of conservation and advocacy, said: "People usually try to improve their diet by eating more fruit - but fruit cultivated for humans is much higher in sugar and much lower in protein and fibre than most wild fruit because we like our fruit to be so sweet and juicy.

"Giving this fruit to animals is equivalent to giving them cake and chocolate.

"Compared to the food they would eat in the wild, bananas are much more energy-dense - they have lots of calories - and contain much more sugar that's bad for their teeth and can lead to diabetes and similar conditions.

"It can also cause gastrointestinal problems as their stomachs are mostly adapted to eating fibrous foods with very low digestibility."

Dr Plowman said it had not been too hard to wean the monkeys off bananas and give them vegetables instead.

"We reduced the amounts slowly so they had a long period to get accustomed to their new diet," she said.

"They didn't get a choice but - unlike children - they couldn't complain.

"The alternative is vegetables and lots of them, especially leafy green veg. We still use starchy root veg.

"But we have reduced amounts as it can still be quite high in sugar and other readily-digestible carbohydrate. Leafy green veg is great because it is high in protein, fibre and lots of vitamins and minerals."

A typical monkey diet now features lots of green leafy vegetables, smaller amounts of other vegetables and as much browse - leafy branches - as possible, especially for the leaf-eating monkeys.

A specialist pellet feed gives them the correct balance of nutrients, while small amounts of cooked brown rice can be scattered around enclosures to encourage foraging.

Animals do still get bananas if they are unwell and the keepers need to make sure they take medication.

Dr Plowman said: "Putting it in a piece of banana works really well, as it's such a treat now."

Paignton Zoo's fruit-free diet is bringing improvements in physical health and changes in some behaviours.

Senior head keeper of mammals Matthew Webb said: "We have noticed an improvement in the condition of primate coats - in particular the colour and thickness of the fur of the Sulawesi crested black macaques.

"Smaller monkeys such as tamarins and marmosets are highly-strung animals and live in tight-knit social groups which can be quite aggressive at times. Reducing the sugar in their diets has calmed them down and made their groups more settled."