• Increased consumption of foods processed with added fructose is associated with a greater incidence of metabolic diseases, according to our partner The Conversation.

  • A question then arises: are these pathologies also favored by the simple consumption of fruit, also rich in fructose?

  • The analysis of this phenomenon was carried out by Juan Carlos Laguna Egea, professor of pharmacology and Marta Alegret Jorda, researcher in pharmacology and therapeutic chemistry (both at the University of Barcelona/Spain).

Fruits, along with vegetables, are an essential part of any healthy and somewhat balanced diet.

They are often characterized, among other things, by their sweetness – especially when fully ripe.

This sweet taste so appreciated comes from their high content of a type of sugar which, we will not be very surprised… is called fructose!

They also contain glucose, but in much lower quantities.

We will focus on the first of these two sugars.

Because, paradoxically, fructose could well be the most harmful to our health.

Fructose is, along with glucose, a component of white (or table) sugar and corn syrup.

Both of these sweeteners are used as common ingredients in the preparation of processed foods, sauces and condiments, sweets and sugary soft drinks.

This is where the problem begins.

Numerous studies associate increased consumption of these products with a greater incidence of metabolic diseases such as obesity, diabetes, hepatic steatosis (excess fat in the liver) and blood lipids.

​Quantity and quality, the two key parameters

Regarding the question of quantity.

The increase in consumption of food products rich in sweeteners leads, in parallel, to the absorption of calories.

Calories which, if not burned, accumulate in the form of fat in the body and will promote the development of the metabolic diseases indicated above.

Fructose and glucose are used in the preparation of the aptly named “sweets” © PxHere

Unfortunately, this type of high-calorie diet, low in fruit and vegetables and high in fat and fructose, has become global – hence the epidemic growth of these pathologies.

However, if you consult a dietician or a nutritionist, you will always find the same advice: to be healthy, eat about five servings of fruits and vegetables, spread over the different meals of the day.

The moderate daily consumption of a natural and unprocessed food, such as a fruit, is however healthy.

And let's use common sense: it's not about eating two kilos of pears and a melon a day!

As for quality, now.

Fructose turns into fat very easily in the liver.

For the same amount of fructose and glucose, the former will produce more fat in the liver.

This means that excess fructose is more likely to alter our metabolism and facilitate the onset of metabolic diseases than other sugars.

Beware of the slogan "Eat five servings of fruit and vegetables a day" © Peggy Greb / ​​Pixnio CC0

But then… Are these pathologies also favored by the simple consumption of fruits, also rich in fructose?

It's all in the packaging

A little reminder, already, on the evolution of our species.

We are, whatever some may think, monkeys, and chimpanzees are our distant cousins.

For millions of years, our ancestors have adapted to a varied diet rich in vegetables, seeds and foraged fruits.

When we take fructose in the traditional way, so to speak, we do not ingest it alone but associated with its natural "packaging": the fruit as a whole, with all its other components - fibers, minerals, vitamins, etc

This is why we must conscientiously chew every morsel we eat.

In doing so, we mix these different components, including the abundant fibers, with our saliva and digestive juices.

This means that the fructose contained in the fruit is slowly incorporated and associated with many other elements in our organism.

This allows our intestinal cells to absorb and consume the vast majority of the fructose that arrives.

So that in the end, only a very small part of it reaches the liver via the blood to be transformed into fat.

The problem with fructose taken in processed form, and especially liquid (juice and soda), is that it is absorbed too quickly and in too large quantities © New Africa / Shutterstock (via The Conversation)

This is how processed sugar works in our body

Conversely, when we absorb a large quantity of fructose "taken out of its natural environment", whether in a candy, a sauce, an ice cream or, worse, in liquid form, in a sugary drink for example, the situation is very different.

We literally flood our digestive tract with fructose dissolved in water.

The latter is quickly absorbed by the intestinal cells, but they are quickly overwhelmed and a large part therefore continues its way to the liver.

Where it will be turned into fat…

The liver is responsible for distributing this excess fat throughout the body.

If it happens in isolation, it hardly matters.

But heavy and frequent consumption will exceed our ability to regulate and, in the long term, lead to health problems.

This excess fat deposited in our body can lead to obesity, diabetes, hypercholesterolemia etc.

Over time, metabolic disorders also increase the risk of suffering a heart attack or even cancer.

For example, a study was recently published showing that the higher the sugar consumption, the greater the incidence of cancer.

Evolution of obesity in France by sex © Yoqtan / Wikimedia CC BY-SA 4.0

But beware !

This dangerous fructose-pathology connection applies mainly to the consumption of sugar in liquid form.

Moreover, when the association between the appearance of cancers and consumption of fruit juice is specifically studied, it is positive: the higher the consumption of fruit juice, the greater the incidence of cancer.

​Fruit sugar: good or bad?

If you have read the above, you guess the answer… Consuming fruits is obviously good because we crunch them, chew them, mix them with other foods to make them easier to digest.

In this way, their various components, including fructose, are slowly incorporated into our body.

But when we drink fruit juice, the situation is different.

We absorb a lot more fruits than if we had to peel them, chew them, etc.

Also, since we don't take fructose in its “natural package”, it is absorbed all at once, quickly, hits the liver and once there, we figured out what was going on.

Our "SUGAR" file

The fruits are therefore preferably to be consumed as such, and the juices a pleasure to which one can indulge from time to time.

And if you decide to drink a juice, do not remove the pulp!

The pulp helps the sugar contained in the fruit to enter our organism more slowly, just as it happens when we eat the fruit directly…


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This analysis was written by Gaëlle Chagny, CNRS researcher in mathematics (statistics) and Thierry de la Rue, CNRS researcher in mathematics, both at the University of Rouen Normandy.

The original article was published on The Conversation website.

Declaration of interests

Juan Carlos Laguna Egea received funding from the Ministry of Science and Innovation and the Generalitat de Catalunya to carry out his research activities.

Marta Alegret Jorda has received funding from the Ministry of Science and Innovation and the Generalitat de Catalunya for her research activities.

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