Fructose (fruit sugar) is a double-edged sword. On the one hand, natural fructose is also found in fruits, as part of the fruit’s own sugar, on the other hand, highly concentrated and industrially produced fructose is used as a sweetener in the food industry, for example in many sweets, ready meals or soft drinks.
A diet high in fructose is generally considered to be harmful to the liver. Because high amounts of fructose – as discovered by researchers at the Joslin Diabetes Center – prevent the liver from properly metabolizing fats. This liver-inhibiting effect is a specific property of fructose. It can cause fatty liver and increase the risk of Type 2 diabetes.
With glucose (grape sugar), however, such an effect on the liver cannot be observed. On the contrary, glucose apparently improves fat burning in the liver – in the amounts in which fructose is harmful to the liver.
This also explains why a high-fructose diet is more harmful to health than a high-glucose diet, even though both types of sugar have the same calorie content, according to the Joslin scientists.
Unfortunately, in the food industry in particular, pure grape sugar is hardly ever used, but more and more pure fructose. However, fructose is not only harmful to the liver, but also a booster of obesity and fat metabolism disorders.
“With our studies, we wanted to find out what role a high-fructose diet plays with regard to insulin resistance and metabolic syndrome,” explains C. Ronald Kahn, professor of medicine at Harvard Medical School and author of the study, which appeared in the journal Cell Metabolism (1, 3).
According to Kahn, “Fructose causes fat to accumulate in the liver, almost as if you were eating fat and not sugar. This is not the case with glucose. It even promotes the fat-burning properties of the liver and is, therefore, more beneficial for metabolism. ”
These findings were based on a series of studies in which animals were given six different diets:
Different markers were investigated that can be used to identify fatty liver, e. B. Acylcarnitine in liver cells. High acylcarnitine levels indicate high-fat accumulation, so it’s a bad sign.
The acylcarnitine values were particularly high in those animals that had been given a diet high in fat and fructose. It was interesting that the values in the high-fat and high-glucose diet group were lower than in the high-fat (i.e. sugar-free) diet group. The latter indicates that glucose stimulates fat burning, i.e. it helps to inhibit fat storage in a high-fat diet.
The values for CPT1a were also checked. This is an important enzyme, the values of which are higher the more fat is burned. So high values on CPT1a are a good sign. They indicate that the mitochondria are doing full work, i.e. that the fat is burned so that it is stored in the liver to a lesser extent.
In the high-fat and high-fructose diet group, the CPT1a values were low, so that apparently hardly any corresponding fat-burning processes took place in the mitochondria. In addition, the mitochondria were even deformed, i.e. damaged, so that they were not able to burn fat at all. In the high-fat and high-glucose diet group, on the other hand, the mitochondria were normally shaped and able to perform well.
Overall, it was found (also on markers other than the two described) that both the fat-fructose diet and the high-fat diet (without fructose) damage the mitochondria in equal measure and cause the liver to store fat (instead of burning it).
And even if it seems that glucose seems to be significantly less harmful to the body than fructose, an excess of glucose is of course also problematic, damages the teeth (although not as much as table sugar (2)), irritates the blood sugar level and can contribute to cancer.
Dr. Kahn and colleagues are now of the opinion that the development of a drug to inhibit the fructose metabolism could prevent the negative effects of a high-fructose diet and thus fatty liver and diabetes. Instead of advising those affected to change their diet, they would rather prescribe a drug. But that will not work, because an unhealthy diet has significantly more negative effects, so it certainly does not “only” lead to fatty liver and all its consequences. Not alone thinking of the side effects of the drug itself.
So if you want to break out of the typical spiral of illnesses and drugs, take matters into your own hands and take care of a healthy – that is, a low-fat and low-industrial sugar – diet!
If you want to eat a high-fat diet, you can also do that, but then you have to adhere to the guidelines of the ketogenic diet (which was certainly not the case in the above animal study). Then the high-fat diet can also help protect against fatty liver.
In the above article, fructose means the industrially produced, highly concentrated and isolated fructose in soft drinks and finished products. But agave syrup and honey are also very rich in fructose. The more liquid honey it is, the more fructose it contains. Solid honey usually contains a little more glucose than fructose. In contrast, fructose, which is consumed in the form of fresh fruits, does not pose a threat to health in general.
Eating a healthy diet is not the same for everybody and in the end you have to find what works best for you. Clearly staying away from industrial sugar has proven to be a good thing.