The research team has now published its findings in the journal Molecular Nutrition and Food Research (M. Kruse et al 2014; DOI 10.1002 / mnfr.201400446.). Researchers from the University of Hamburg and the University of Jena contributed to the study.
Numerous studies indicate that excess weight (obesity) is associated with chronic inflammation, which increases the risk of heart attack or stroke. Similarly, obese people often suffer from disorders of the lipid metabolism, hypertension and fatty liver, which are often precursors to type 2 diabetes or severe cardiovascular disease.
Various studies indicate that a high consumption of olive oil, as is customary in a Mediterranean diet, can help prevent these diseases.
“Since Northern Europeans do not use olive oil as extensively as Southern Europeans, we wanted to investigate whether native rapeseed oil might be an alternative because it is particularly rich in mono- as well as polyunsaturated fatty acids. So far there is a lack of nutritional studies that directly compare the effect of both oils,” said Michael Kruse, lead author of the study.
Eighteen obese men* between the ages of 39 and 63 took part in the study and were randomly divided by the physicians into two equal groups. In addition to a balanced diet over a period of four weeks, the study participants received a daily dietary supplement of 50 g refined rapeseed oil or cold-pressed olive oil (extra virgin), whereby both oils had about the same content of vitamin E and polyphenols**. The participants were supposed to consume the oils e.g. in the form of salad dressings or pesto.
As intended, after the four-week diet phase the participants had neither gained nor lost weight. Compared with the olive oil group, the LDL cholesterol levels of men who consumed rapeseed oil dropped to about 0.45 mmol / L. Likewise, their liver enzyme levels improved. For example, the value for the enzyme aspartate aminotransferase*** was reduced by 18 percent. In the fasting state, the subcutaneous adipose tissue of these men also produced significantly less proinflammatory interleukin-6, although the consumption of a test meal temporarily stimulated the synthesis of this cytokine.
“Permanently increased interleukin-6 levels, which are often observed in obesity, are suspected to promote insulin insensitivity of the body's cells and type 2 diabetes," said Kruse.
“So it is good if the adipose tissue synthesizes significantly less of this cytokine after the four-week diet phase than before.“
“From other studies we also know that muscle activity, for example through sports, can temporarily increase interleukin-6 levels in the blood by up to 100 times. At the same time, it is known that physical activity prevents metabolic diseases. That is why we suspect that that the acute but transient increase in interleukin-6 synthesis has more of a positive, hormetic**** effect,” said Pfeiffer, who heads the Department of Clinical Nutrition at the DIfE. “In summary, our results indicate that the daily intake of 50 g of rapeseed oil can help obese men improve their liver enzyme levels and cholesterol levels. However, further studies with a greater number of subjects are needed to investigate the effects we observed in more detail.”
* The Body Mass Index (BMI) is a measure for the assessment of body weight of an individual in relation to his/her body size. It is calculated by dividing body weight (measured in kilograms) by the square of the length (measured in meters) [kg / m2]. The participants in the pilot study had a BMI of 27-35. A person with a BMI over 25 is considered overweight, with a BMI over 30 as obese (obese).
** Polyphenols are aromatic compounds that are classified as secondary plant metabolites. Many polyphenols are considered to be health-promoting.
*** In laboratory diagnostics, the activity of the enzyme aspartate aminotransferase is determined from the plasma or serum to clarify whether a liver or biliary tract disease is present. Increased enzyme levels in the blood are usually a result of a liver or skeletal muscle disease and/or a heart attack. Large increases are found in all inflammatory liver diseases and in toxic liver injury (such as by fungal toxins). Under antibiotic therapy aspartate aminotransferase values are often elevated in otherwise healthy people. After treatment, the levels return to normal. (Source: Wikipedia).
**** Hormesis (from Greek „urge on, impel“, English: adaptive response) is the hypothesis already formulated by Paracelsus that small doses of harmful or toxic substances may have a positive effect on the organism. Today the term is used in a broader definition. In medically active substances, such a dose-dependent reverse effect (hormetic effect) is well-documented.