• In the video: Fructose as a secret fattening agent: This is how dangerous fruits are for your stomach

Foods and drinks with a lot of fructose not only promote obesity, they can also promote cancer growth a study in “Nature” revealed. Accordingly, cancer tumors benefit indirectly from fructose by using sugar metabolic products as building blocks for their cell membrane and growing faster. This finding could open up opportunities for new cancer therapies, but also explain why more and more young people are developing cancer.

Drinks and processed foods in our supermarkets increasingly contain fructose instead of glucose as a sweetener. Both types of sugar, also known as glucose and fructose, are chemically very similar, but fructose has a stronger sweetening power than glucose.

In addition, fructose was long considered healthier. As a result, the food industry has used fructose more and more over the past five decades, mostly in the form of corn syrup. As a result, we consume about 15 times more of this sugar today than we did in the 1960s.

Researchers examined how quickly tumors grew on foods high in fructose

At the same time, the number of cancer cases with various types of cancer increased among people under 50 years of age. There are numerous genetic and environmental influences that cause cancer. However, nutrition is considered an important factor. It is known that cancer cells, like all our body cells, can use glucose as an energy source. Fructose, on the other hand, can only be utilized by the cells in the small intestine and liver. But do cancer cells and tumors also feed on fructose?

A team led by Ronald Fowle-Grider from Washington University in St. Louis has now investigated this. To do this, the doctors fed zebrafish and mice with cancer either a normal diet or a high-fructose diet for several weeks and compared how quickly their tumors grew.

Fructose accelerated cancer growth by more than double

It was shown that the cancer tumors enlarged significantly faster when fructose was added to the animals’ food. All three tumor types examined – melanoma, breast cancer and cervical cancer – reacted strongly to the animals’ sugary diet.

“We looked at many different types of cancer in different tissues throughout the body and they all followed the same mechanism. In some cases, the growth rate of the tumors accelerated by twice or even more,” reports senior author Gary Patti from Washington University.

Cancer cells examined did not directly metabolize fructose

However, the animals’ body weight did not change as a result of the fructose administration, so the mice and zebrafish did not become fatter. The concentrations of glucose and insulin in the blood in the fasting state also did not change. This suggests that tumor growth is not due to altered sugar metabolism, but rather directly to fructose, as the researchers explain.

To test this interpretation, the doctors fed fructose to animal and human cancer cells cultured in the laboratory in a follow-up experiment. Surprisingly, however, the cells did not react like the tumors and grew slower rather than faster.

“In most cases, they grew almost as slowly as if we gave them no sugar at all,” says Patti. This suggests that, unlike glucose, the cancer cells cannot directly metabolize fructose themselves and use it as an energy source.

Colon cancer cells can process fructose into lipids using an enzyme

Fowle-Grider and his colleagues therefore suspected that the cancer cells benefit from fructose metabolic products, such as those produced when fructose is processed in the liver. To test this theory and find out what substances these are, the doctors again fed animals a diet rich in fructose and examined whether this changed the concentration of small metabolic products in the blood.

It was shown that an increasing number of lipid molecules appear in the blood of these animals; Among other things, there were more lysophosphatidylcholines (LPCs). Additional tests with liver cells cultured in the laboratory showed that they release such LPCs after being “fed” with fructose. This is made possible by two enzymes in liver cells, ketohexokinase (KHK) and aldolase B, as Fowle-Grider and his colleagues discovered. They conclude that the liver uses these enzymes to metabolize fructose into lipids and release them into the blood.

These enzymes are not present in the three tumor types examined – which explains why these cancer cells cannot process the fructose themselves. However, the enzymes could be present in other types of cancer that have not yet been studied. CHD has already been found in colon cancer.

Cancer tumors use lipids as building material

The cancer tumors apparently use the lipids produced in the liver as building material: they convert the LPCs into phosphatidylcholines (PCs) and incorporate them into their cell membrane, as the analyzes showed. In co-cell cultures of liver and tumor cells, the cancer cells grew and divided more when the researchers added fructose.

The cancer cells could produce the building blocks themselves in another way. However, getting them out of the environment or the blood is more convenient for them, as previous studies have already shown. This appears to be particularly easy with unsaturated LPCs because, unlike other lipids, they are highly soluble and easy to transport, as the team found.

Study author: Cancer patients should consider avoiding fructose

The discovery that the liver converts fructose into usable nutrients for cancer cells could now change the treatment of many different types of cancer: cancer patients could be given a low-fructose diet to “starve” the tumors. “If you’re unlucky enough to have cancer, you should probably think about avoiding fructose,” says Patti. A clinical study will now show whether this actually works.

The idea of ​​fighting cancer with targeted nutrition is not new. In this case, however, the effect would be indirect for the first time. “When we think about tumors, we’ve focused on what food they consume directly. But humans are complex. What we put into our bodies can be consumed by healthy tissue and then converted into something else that tumors use,” explains Patti.

Metabolism of healthy cells can be used to treat cancer

Follow-up studies should also clarify whether drugs can prevent tumors from receiving the lipids. Instead of targeting cancer cells, the preparations could also target liver cells, or more precisely their fructose-degrading enzyme KHK. The metabolism of healthy cells could potentially be used specifically to treat cancer.