Many of us believe that fruit can only be healthy and so make an effort to boost our intake – carrying apples in our bags, eating grapes or bananas at our desk and trying to stick to fruit salad for dessert.
But it seems some people are actually eating too much fruit, leading to health problems such as obesity, and to tooth decay.
There’s no denying fruit’s health benefits – it’s packed with vitamins, fibre and antioxidants, which protect against disease.
Marilyn Monroe would probably have had a shock if she had eaten that fruit expecting it to be a low-calorie snack
It’s considered so beneficial that the government’s five-a-day guideline is a minimum recommendation for the amount of fruit and vegetables we should eat.
But while it is fine to exceed this amount if you are a healthy weight, 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.
One of the problems is 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,’ he says. ‘But the 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.’
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, explains dietician Ursula Arens of the British Dietetic Association.
‘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,’ she says.
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.
Weight gain isn’t the only health problem associated with too much fructose. It can increase levels of triglycerides, a type of blood fat known to be linked to heart disease.
Dr Le Roux says: ‘We tell patients with high cholesterol to be careful with fruit. Too much drives up triglycerides. Diabetics should also take care, as the high fructose content can raise blood glucose levels.
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.
Dried fruit is another problem, because it’s not only high in sugar but is also very sticky.
Dr Anjali Shahi, a Cheshire-based dentist, says: ‘Little bits can stick to the teeth for a long time and dental cavities can result.’
She adds that raisins are as bad for the teeth as sweets. ‘This is a problem for children, who are often given raisins by health-conscious mums. I’ve noticed a rise in dental cavities now the healthy fruit message is so strong.’
Even those who don’t actually eat much fruit could be getting far more fructose than they realise – regular sugar that you add to your tea consists of 50 per cent glucose and 50 per cent fructose.
Fructose is often added to manufactured products, such as fizzy drinks, yoghurts and cereal bars in the form of glucose-fructose syrup. You can get as much as 30g of fructose from one fizzy drink.
So how much fruit is too much? Unlike salt and saturated fats, there is no recommended daily allowance for fructose. And this is unlikely to change soon.
As Ursula Arens, of the British.
Dietetic Association, points out: ‘Too many nutritionists would jump up and down if the public picked up the message that eating an apple wasn’t good for them.’
Yet one possible guideline emerged after 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 per cent.
Though this is the equivalent of ten apples or 30 oranges, you’d need only just over three large smoothies to top this figure (one 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.
The secret is to get your five a day with a mix of fruit and vegetables.
‘People who are obese or have heart conditions should limit their fruit to one portion a day, along with four portions of vegetables,’ says Dr Le Roux. ‘You’d still have plenty of antioxidants, but you’d bring your fructose levels and calories down.’
However,most people find fruit easier to eat and it should remain a key part of a healthy diet.
As Glenys Jones, a nutritionist at the Medical Research Council of Human Nutrition, says: ‘Everything in moderation. Just as you make a decision not to eat a packet of biscuits, you should think about portion control when it comes to fruit.’
She sticks to a banana and a glass of apple juice with her cereal, an orange mid-morning and an apple mid-afternoon. ‘And if I get the urge to eat chocolate at night, I’ll sometimes have raisins. Even so, I still limit how many raisins I eat.