In restaurants or shops selling ready and fast
A new study done in experimental animals is that we must not use the same oil again and again to cook, as we do many times when we want to fry potatoes for example.
According to an article published in Cancer Prevention Research, a team of experts from the University of Illinois observed that mice that had consumed chemicals contained in heat-treated cooking oil had genetic changes that promoted the progression of end-stage breast cancer.
Thermally battered cooking oil is what has been heated at high temperatures repeatedly.
Researchers argue that it can be a toxicological stimulant that promotes proliferation of tumors, metastases and changes in lipid metabolism.
Mice after a week of low fat diet were divided into two groups: one consuming fresh raw soybean oil and the other heat-treated oil for the next 16 weeks. Soybean oil was preferred in the study because it is what is typically used in the food industry for frying.
The scientific team simulated end-stage breast cancer by injection of mammary tumor cells 4T1 into the tibia of each mouse. 4T1 are aggressive cells that can give spontaneous metastases to multiple distal points of the body, including the lungs, liver and lymph nodes.
Twenty days after inoculation with the cancer cells, the primary tumors tumors of the heat-consuming mice consumed more than four times the metastatic growth from the experimental animals consuming the fresh soybean oil. And when the researchers examined the rodents’ lungs, they found more metastases among those who consumed heat-treated oil.
“We found duplicate tumors in the lungs and were even more aggressive and more invasive,” says William G. Helferich, professor of Food Science and Human Nutrition, head of the scientific team.
By examining both groups of mice, the researchers observed that metastatic lung tumors in rodents consuming the refined oil more expressed the Ki-67 protein that is strictly related to cell proliferation.
Also in these animals gene expression in their liver was modified, and when the experts did RNA sequencing, they found 455 genes in which the expression was at least twice or, on the contrary, twice reduced, compared to mice that ate fresh soybean oil.
Modified gene expression was associated with oxidative stress and metabolism of foreign substances.
When oil is heated repeatedly, triglycerides are broken down, free fatty acids are oxidized and acrolein is released, a toxic substance having carcinogenic properties.
Scientists have known for years that heat-treated oil contains acrolein and studies have linked lipid peroxides to it with various health problems such as atherosclerosis and heart disease.
“Also, as the oil is degraded, polymers accumulate, raising nutritional and toxicological concerns,” the US experts say.
It is worth noting that in Europe regulators have set limits to the amount of polar materials in frying oil, which are chemically modified triglycerides and fatty acids used as chemical indicators of oil decomposition. Typically, these standards allow restaurants to use frying oil containing up to 24-27% polar material.
In contrast, heat-treated oils in this study contained about 15% polar material, while fresh soybean oil 2-4% or less.