Fructose - Are fruit sugars really as harmful as they're made out to be?
The title says it all: sugar in general has a terrible reputation and fruit sugar, also known as fructose, doesn’t escape the criticism. But wait – fruit is supposed to be healthy and now the sugar in fruits (fructose) is supposedly more harmful than regular table sugar? Or can even reverse weight loss? In this article, we will get to the bottom of this statement and look at what exactly fructose is, what distinguishes it from other sugars, and how these assumptions have come about.
What is fructose?
Fructose belongs to the carbohydrates group and is a simple sugar, just like glucose. Glucose is also known as dextrose. The combination of glucose and fructose creates common table sugar, which is often obtained from sugar beets and is a disaccharide.
Note: the longer the chain of carbohydrates, the longer it takes to digest them.
Fructose, as the name suggests, is found mainly in fruits and honey and is what makes them so sweet. In addition, fructose is also found in many vegetables, but in smaller amounts.
One gram of fructose contains 4 kcal / g just like any other carbohydrate, including glucose and household sugar. In contrast to table sugar, however, its sweetening power is higher. This means that fewer grams of fructose are needed to achieve the same sweetness as with industrial sugar. This naturally saves resources and thus money in food production. This is the reason why high fructose corn syrup (better known as glucose-fructose or fructose-glucose syrup) is produced, especially in the USA. The order of the name is determined according to the ratio of the two sugars.
The difference between fructose and glucose
Another difference between glucose and fructose is that fructose is initially metabolised in the liver. There, the process of fructose conversion into glucose is independent of insulin. The glucose produced is then released into the bloodstream. However, the subsequent metabolism of glucose is then insulin-dependent.
Due to the delay caused by the conversion of fructose into glucose, the blood sugar level rises more slowly and over a longer period of time than when glucose is consumed directly. The release of insulin is therefore lower. As a result, it used to be recommended more often to diabetics for sweetening. In contrast, glucose is transported to all body cells during metabolism and converted into energy or energy reserves.
Excess glucose from food that is not needed for energy production is stored as glycogen mainly in the liver and muscles. The glycogen can be used as an energy source during periods of fasting. Our blood sugar level is regulated by the neurotransmitters insulin and glucagon. If the blood sugar level rises, insulin is released to transport the glucose into the storage cells. If our blood sugar level is too low, glucagon is released, which causes a conversion of the stored glycogen, mainly from the liver, into glucose. This creates a constant exchange between stored glycogen and freely available glucose. Muscle glycogen serves as an energy source during exercise, regardless of blood glucose levels.
Why do we need fructose in our bodies?
We can use fructose to produce energy. However, it is only a middling source of energy without specific benefits. Of primary importance are the micronutrients associated with fruit consumption.Fruits contain many vitamins, trace elements and lots of fibre which are all essential for a healthy diet.
We all know that an excessive amount of sugar consumption is not healthy and can lead to what some might call an addiction, obesity, tooth decay and diabetes. Fructose would therefore be a slightly better alternative, because it does not allow the blood sugar level to rise quite so quickly. But unfortunately, fructose also has its downsides. Especially the industrially produced variant of sugar as high fructose corn syrup has been shown in studies to have negative health effects.
The syrup is mainly found in processed foods such as baked goods or soft drinks. Studies have shown a link between the incidence of obesity and the consumption of fructose. Unlike glucose, excess fructose cannot be stored, so it is converted into fatty acids. If the blood sugar level is low, on the other hand, fructose is converted into glucose in the liver and used as an energy source. This also happens when the stores in the liver and muscles become empty and the body wants to replenish them.
Risks of excessive fructose consumption
What happens, however, when the stores are already full and the blood sugar level is already high? Unlike glucose, fructose automatically ends up in the liver, as it must be converted anyway, and so the path to becoming fat deposits is very short for fructose. Studies suggest that with an additional factor – e.g. high sugar consumption, little exercise – fructose leads to “obesity” faster than glucose. This also applies to people who are not necessarily overweight, but have abnormally high proportions of visceral fat (fat stored around the internal organs). After some time, this can lead to a row of diseases like:
- Non-alcoholic fatty liver disease
- High blood pressure
- A lipid metabolism disorder
- Obesity
- Increased uric acid production and thus increased risk of gout disease
It should be noted, however, that overconsumption of fructose does not result from the consumption of moderate amounts of fruit, but rather from the frequent consumption of ultra processed foods, which contain added sugar in the form of high fructose corn syrup. Ultra processed foods should also be avoided in a healthy diet.
Remember: eating fruit is healthy. Drink juices in moderation and preferably diluted with water.
High fructose diet
The following table shows how many grams of fructose per 100g are in the following ingredients:
| Foods | Fructose content in grams per 100g |
|---|---|
| Apple | 5.7 g |
| Banana | 3.0 g |
| Strawberry | 2.3 g |
| Orange | 3.0 g |
| Kiwi | 4.6 g |
| Tomato | 1.36 g |
| Pepper (red) | 3.7 g |
| Potato | 0.2 g |
| Energy drink | 2.39 g |
| Lemonade with fruit juice | 5.8 g |
Dried fruit contains proportionally the most fructose and fewer micronutrients, as some water-soluble vitamins are lost through drying. Dried fruit is on the healthier side of sweet foods, but should be treated like a “dessert” and eaten in very small amounts, not like fresh fruit in a balanced diet.Some fresh fruit, especially grapes, pears and apples, contain a lot of fructose. Peaches, papaya, honeydew melons and tangerines, on the other hand, have little fructose. Fruit not only contains fructose, but also glucose in smaller quantities.
It should also be noted that a “portion” of soft drink, at 300 – 400 ml, is consumed relatively quickly and a portion of fruit, usually measuring only 50 to 100 g, is consumed relatively slowly. This means that, on average, higher amounts of fructose are absorbed more quickly through drinks than through a portion of fruit.
Dried fruits in particular have a high amount of fruit sugar.
How does fructose affect weight loss?
At the recommended consumption, fruit can help with weight loss. It’s a healthy snack or side dish with essential vitamins and fibre. Fibre improves digestion and keeps you full for longer. Fructose also has a lower glycaemic index than glucose. As a result blood sugar does not rise as much, which leads to fewer food cravings and longer satiety.
If too much fructose is consumed, release of the hormone leptin may be inhibited. Leptin is responsible for our feeling of satiety. A lower release of leptin is counterproductive for weight loss. Without satiety, we don’t notice that we are eating more energy than we require.
When attempting to lose weight, the most important factor is a calorie deficit. This means consuming fewer calories than you burn. You can find out which types of fruit are particularly suitable for weight loss here.
Fructose does not really help with weight loss, as it’s only slightly different to conventional sugar. The alternative of not artificially sweetening your food at all is much better.
How much fructose should you consume in a day?
The NHS published a new recommendation for maximum daily sugar intake in 2020. The daily energy intake from free sugar should not be more than 5 % of the energy (calories) you get from food and drink. For an energy intake of 2,000 kcal / day, that is up to 30 grams of free sugar per day. This specification serves as an upper limit and not as a recommended intake. Even though there is no chemical difference between the fructose from fruit and that from glucose-fructose syrup, it still matters whether you consume it in the form of a soft drink or fruit. Unlike fruit, soft drinks do not contain essential nutrients, just a lot more energy which is why they are often called ’empty calories’. The RDI (recommended daily intake) for fruit is 2 servings per day. This equals, for example, an apple and a handful of berries.
Conclusion - Does fructose reverse or prevent weight loss?
Fructose is neither an enemy nor a hero when it comes to weight loss. Consumption in the form of fruit is fine, as it involves an intake of micronutrients. In general, however, you should make sure to minimise your sugar consumption when losing weight. This means that fructose in natural foods is harmless, in contrast to its role as a sweetener in processed products.
Frequently Asked Questions
In what form does fruit contain the most fructose?
It is best to always eat fruit in its fresh form. Dried fruit contains much more sugar per 100 g, since the fruit no longer contains water. When buying canned fruit, you should make sure that no additional sugar has been added, but even then the preservation process often means that hardly any vitamins are left.
Can too much fruit be unhealthy?
Yes, too much fruit can be unhealthy, but only in certain types of very “fruit-heavy” diets where several kilos of fruit are consumed per day. As a result, there may be digestive disorders and a lack of nutrients.
What is fructose intolerance?
Fructose intolerance is an intolerance to fruit sugar. There are two forms: fructose malabsorption (failure to absorb nutrients) and hereditary fructose intolerance. In the process of malabsorption, fructose can not be absorbed into the blood in an optimal way and enters the large intestine undigested. As a result, gases are formed there, which can lead to abdominal pain and bloating.
In the case of hereditary fructose intolerance, fructose enters the blood but cannot be converted by the liver because it lacks a necessary enzyme. With this disease, fructose must be strictly avoided.
What is the difference between high-fructose corn syrup and glucose fructose syrup?
The difference between high-fructose corn syrup and glucose fructose syrup is the proportion of its components. Glucose fructose syrup contains less than 50 % of fructose and is more common in Europe. High fructose corn syrup contains more fructose (typically 55 %) than glucose and is more commonly found in the US.
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