Too much sugar is unhealthy, but it's not just the high calorie content that is problematic. Even moderate amounts of added fructose and table sugar double the body's own fat production in the liver, as researchers from the University Hospital Zurich and the University of Zurich have shown. Over a longer period of time, this favors the development of diabetes or a fatty liver.
Sugar is added to many foods. The Swiss consume more than 100 grams of it every day. The high calorie content of sugar in particular promotes overweight and obesity – and the associated secondary diseases. Does too much sugar have other harmful effects if it is consumed regularly? And if so, which sugar?
Even moderate amounts of sugar increase fat synthesis
Researchers at the University Hospital Zurich (USZ) and the University of Zurich (UZH) have been investigating these questions. In comparison to previous studies, which mainly investigated the consumption of very high amounts of sugar, their results show that even moderate amounts lead to an actual “switch” in the metabolism of the test participants. “80 grams of sugar a day, which corresponds to around 8 dl of a commercially available soft drink, stimulates fat production in the liver. And the overactivity persists for a long time, even if no more sugar is consumed,” says study leader Philipp Gerber from the Department of Endocrinology, Diabetology and Clinical Nutrition.
94 young healthy men took part in the study. They consumed a drink sweetened with different types of sugar every day for seven weeks, while the control group did not. The sweet drink contained either fruit sugar (fructose), dextrose (glucose) or household sugar (sucrose), which consists of fruit and dextrose. Using so-called “tracers” – labeled substances whose path in the body can be tracked – the researchers analyzed the effect of the sweet drinks on fat metabolism.
Fructose and table sugar sustainably double fat production
Overall, the test subjects did not consume more calories than before the study. They have reduced their other calorie intake due to a certain satiety from the sweet drink. Nevertheless, the researchers observed that fructose has a negative effect: “The body’s own fat production in the liver was twice as high in the ‘fructose group’ as in the ‘glucose group’ or the control group – and this more than twelve hours after the last meal or the last sugar consumption,” says Gerber. What was particularly surprising was that the most frequently consumed household sugar boosted fat synthesis even more than the same amount of fructose. Until now, it was mainly fructose that was suspected of causing such changes.
Development of fatty liver or diabetes is favored
Increased fat production in the liver is a crucial first step in the development of widespread diseases such as fatty liver or type 2 diabetes. From a health perspective, the World Health Organization recommends limiting daily sugar consumption to around 50 grams or, even better, 25 grams. “But we are still a long way from that in Switzerland,” emphasizes Philipp Gerber. “Our results are a decisive step in researching the harmful effects of added sugar and will be very important for future dietary recommendations.”
About the study