Too much calls for trouble

There's no denying fruit's health benefits - it's packed with vitamins, fibre and antioxidants, which protect against disease. But if you are overweight or suffer from high cholesterol or diabetes, too much fruit could be trouble. It could also explain why, despite your healthy lifestyle, you're piling on the pounds.

People forget that fruit - like all food - contains calories. And the calories in fruit can make you just as overweight as those in chocolate, explains Dr Carel Le Roux, consultant in metabolic medicine at Imperial College London.

"Different people over-eat different things. But people who eat fruit to excess are often weight-conscious. I've seen patients who can't understand their obesity because they eat healthily, then it turns out they are eating way too much fruit or drinking fruit smoothies all day - glugging down 300 calories in a couple of minutes," Dr Le Roux is reported to have said.

Bypassing the 'stop button'

And it's not about lack of self-control. Fruit is packed with fructose (fruit sugar) and this doesn't make you feel full.

When we eat sugar, our body releases the hormone insulin, which tells the brain we've had enough to eat. High insulin levels dampen the appetite, but fructose doesn't trigger this insulin response, so the brain doesn't get the message that you are full.

Essentially, when we eat fruit we bypass this internal 'stop button', which could explain why some of us can absent-mindedly nibble away at slice after slice of melon or munch through a large bunch of grapes.

Fructose can also increase levels of triglycerides, a type of blood fat known to be linked to heart disease.

Sweet tooth, more decay

Then there's the damage fruit can cause to teeth. Chewing fruit releases sugar in the mouth, where it attacks the teeth. Fruit juice or smoothies are even more of a problem, as the juicing or blending breaks down the fruit further, so more sugar is released in the mouth.

Teeth are particularly vulnerable to acidic citrus fruits, which can soften tooth enamel. Although the enamel will harden again after about 30 minutes, if you brushed your teeth immediately after drinking orange juice, you would brush away some enamel, raising the risk of dental erosion.

How much is too much?

Unlike salt and saturated fats, there is no recommended daily allowance for fructose.

In a recent study at Colorado University, scientists looked at 4,500 people with no history of high blood pressure and discovered those who ate more than 74g of fructose a day increased their risk of the condition by up to 87%.

Though this is the equivalent of 10 apples or 30 oranges, you'd need only just over 3 large smoothies to top this figure (1 smoothie contains around 23g of fructose).

It is worth noting, too, that bananas and some other fruits, such as strawberries, become richer in fructose as they ripen and some of the starch is converted to sugar.

"People who are obese or have heart conditions should limit their fruit to 1 portion a day, along with 4 portions of vegetables," says Dr Le Roux. "You'd still have plenty of antioxidants, but you'd bring your fructose levels and calories down."

Pic: Ezran Kamal