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5 days ago
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A common fatty acid in olive oil, as well as many other plant oils, has been found to stimulate the body's production of new fat cells, creating conditions that could – over time – lead to more fat storage and unintended weight gain. Until now, weight gain linked to this fatty acid was attributed to the high calorie content of foods that it's found in.
The University of Oklahoma researchers, along with Yale University and New York University medical scientists, have identified that oleic acid – a monounsaturated fatty acid broadly considered good for the heart and cholesterol, and a feature of the Mediterranean diet – can, in excess amounts, trigger the overproduction of a signaling protein known as AKT2 and subdue the activity of a regulating protein called LXR. The result of this saw an uptick in the growth of precursor cells that then differentiated into new fat cells.
"We know that the types of fat that people eat have changed during the obesity epidemic," said said Michael Rudolph, assistant professor of biochemistry and physiology at the University of Oklahoma College of Medicine. "We wanted to know whether simply overeating a diet rich in fat causes obesity, or whether the composition of these fatty acids that make up the oils in the diet is important. Do specific fat molecules trigger responses in the cells?"
Oleic acid, an omega-9 fatty acid, is the dominant fat in olive oil, but it's also found in canola, sunflower, avocado and peanut oil, as well as in many animal fats. And now, because oleic acid has been shown to extend oil shelf life, high-oleic versions of oils are widely used in commercial and fast foods.
In this study, mice were fed diets high in different types of fat – including lard, coconut oil and milk. Of the various fatty acids studied, only oleic acid triggered the body’s fat cell development pathway, which saw a boost in the production of adipocyte precursor cells (APC) and an acceleration in those cells maturing into fat cells. The same biological changes were also seen in isolated human APCs in the laboratory.
Under normal conditions, this process, known as adipogenesis, is natural, useful and regulated. Essentially, as our existing fat cells fill up, they signal for backup. Hearing the call, dormant APCs wake and convert into new fat cells to safely store more energy. This helps the body avoid overloading individual cells, which, if under too much pressure, can rupture and release fat into the bloodstream, liver and muscle, which can lead to serious health issues.
The researchers found that excessive oleic acid intake seemed to short-circuit this safety system, fueling the production of new APCs and activating existing dormant precursor cells, even when they're not needed.
"You can think of the fat cells as an army," Rudolph said. "When you give oleic acid, it initially increases the number of ‘fat cell soldiers’ in the army, which creates a larger capacity to store excess dietary nutrients. Over time, if the excess nutrients overtake the number of fat cells, obesity can occur, which can then lead to cardiovascular disease or diabetes if not controlled."
What's more, studies have shown how fat cells retain an epigenetic "muscle memory," so once they're formed, they don't disappear when we lose weight – they shrink, but can exist in this state for many years, making weight loss harder and weight gain much easier. By increasing both the number and readiness of fat cells, oleic acid may prime fat tissue to store more fat over time.
However, the study has a few key limitations. The obvious one is that it was conducted on mice and isolated human cells. The researchers were also unable to directly target APCs, so we don't know how other biological mechanisms contribute to this process. And finally, it's unclear if an uptick in APCs that differentiate into fat cells is a direct contributor to obesity. The study doesn't take into account long-term impacts on blood sugar, insulin levels or inflammation. So while we know how adipogenesis works, we don’t know if creating these new fat cells are actually good or bad news.
And crucially, context is important here. After all, in Mediterranean diets, where olive oil is consumed in moderation, oleic acid intake has been widely researched and identified as a key factor in lowering cholesterol and reducing the risk of cardiovascular disease, cancer and other diseases.
"I think the take-home message is moderation and to consume fats from a variety of different sources," Rudolph said. "Relatively balanced levels of oleic acid seem to be beneficial, but higher and prolonged levels may be detrimental. If someone is at risk for heart disease, high levels of oleic acid may not be a good idea."
The study was published in the journal Cell Reports.
Source: The University of Oklahoma
