The kind of consumed sugar – not only the taken quantity – can determine the risk of suffering from metabolic and vascular diseases, according to a study carried out on laboratory animals and led by Professor Marta Alegret, from the Faculty of Pharmacy and Food Sciences and the Institute of Biomedicine of the University of Barcelona (IBUB).
The new article, published in the journal American Journal of Physiology-Heart and Circulatory Physiology, reveals that consuming fructose has more damaging effects on the metabolism and vascular system in laboratory animals compared to glucose. The new study is also signed by the experts of the UB Gemma Sangüesa, Núria Roglans and Juan Carlos Laguna, and Sonali Shaligram, Farjana Akther and Roshanak Rahimian (University of the Pacific, United States).
Fructose is a simple sugar (monosaccharide) commonly found in fruit. This is one of the most common sweeteners in the food industry –it has a high sweetener power and low production cost- as a simple sugar, or as a compound from saccharose (a disaccharide made from glucose and fructose) or corn syrup (containing fructose).
In this new work, the scientific team divided a set of female rats – more sensitive to metabolic alterations than male rats – into groups that, during two months, took a glucose or fructose liquid complement, apart from their regular diet (solid food). Depending of the kind of sugar intake – glucose or fructose – the results show differences in body weight, level of triglycerides and vascular physiology, and in the studied animals.
According to Marta Alegret, member of CIBER of Physiopathology on Obesity and Nutrition (CIBERobn) of the Institute of Health Carlos III, "one of the outstanding metabolic effects is the high concentration of triglycerides in the plasma of the group of rats who were given fructose (instead of glucose). This effect cannot be only understood with a major synthesis of liver lipids, since both glucose and fructose induce hepatic lipogenesis."
"However, protein levels of a key enzyme in fatty acid oxidation – CPT1A – are only reduced in the rats that received fructose. This group underwent an increase of the expression of an essential protein – MTP – to move triglycerides from the liver to the plasma in the form of low-density lipoproteins. This suggests that, in a specific way, fructose is able to reduce fatty acid oxidation and increase the moving of triglycerides from the liver to the plasma, and this is probably caused by hypertriglyceridemia."
The new work also compares the differential response in indicators of vascular pathologies, through the study of the aorta arterial response after being exposed to substances that stimulate its relaxation or contraction.
"In rats that were given glucose, the aorta’s capacity to relax when exposed to an agent with nitric oxide (sodium nitroprusside) is higher, while it was lower in the rats that received fructose, compared to the control group. Therefore, from the vascular perspective, fructose produces a negative effect, since it complicates the aorta’s right relaxation. However, the effect of glucose turns out to be beneficial," says Alegret.
According to the results in laboratory animals and in vitro cultures, the beneficial effect of glucose results from the increase of plasma levels of adiponectin – an hormone which is created and secreted by the adipose tissue participating in the cell energy metabolism –, an increase that does not take place in rats treated with fructose.
The group of rats that took fructose showed signs linked to hepatic alterations. In previous studies, the team of the UB had already noted that, both in female and male rats, fructose produced fatty liver. Apart from vascular and hepatic alterations, there is a higher body weight gain in rats that took fructose, although they received fewer calories than the others.
"The fact that fructose reduces oxidation of fatty acids, and increases the synthesis of liver lipids, can lead to an increase of the lipid deposit of this organ, known as fatty liver. This accumulation of lipids in the liver, although it does not show any symptomatology at the first moment, can end up creating an inflammation in this organ and could provoke serious pathologies in the long run, which is why it is better to stop it."
"After lots of years studying the effects of fructose and its specific metabolism, it is not shocking to discover that it has effects that are not seen in other similar sugars, such as glucose. Although it seems that body weight gain is only associated with the increase of calorie intake, we know there are other factors involved. In particular, weight gain in the liver seen in the rats treated with fructose, not glucose, could be related to the accumulation of lipids in this organ and affect body weight."
The experts of the University of Barcelona are members of the Research Group Nuclear Receptors, Energy Metabolism and Therapy of Metabolic Diseases, led by Professor Juan Carlos Laguna and with an outstanding experience in researches on molecular bases of metabolic alterations and their relation with different pathologies (metabolic syndrome, diabetes, lipid disorders, cancer, etc.). The new study has received support of the European Regional Development Fund, in the Operational Program FEDER "Catalonia 2014-2020"