There are good and bad fats, nutritionists say. But not all polyunsaturated fats, the so-called good fats, are created equal. CA&ES food chemist Ameer Taha is exploring whether eating too much linoleic acid—a type of polyunsaturated fat found mainly in vegetable oils and processed foods—can cause chronic inflammation, migraine headaches and other health problems.
“Researchers have shown that too much linoleic acid could be bad for the heart,” said Taha, an assistant professor with the Department of Food Science and Technology. “My research shows that it might also be bad for the adult brain.”
Humans need some linoleic acid to stay healthy, but people in the United States are getting three to six times the amount they need, which can be linked to the nation’s appetite for processed foods.
“You can trace the rise in linoleic consumption in North America to the rise in use of soybean and other vegetables oils in processed food,” Taha said.
In collaboration with colleagues at the National Institutes of Health (NIH), Taha conducted dietary tests with people who suffer from drug-resistant, chronic migraine headaches. When migraine sufferers reduced linoleic acid and increased consumption of long-chain omega-3 fatty acids—polyunsaturated fats found in foods like fish—their migraines decreased 40 percent.
Taha has also shown that in rats, too much dietary linoleic acid reduces the brain’s capacity to cope with inflammation, which can cause migraines. Taha is now exploring whether excess linoleic acid can affect the developing brain.
Good fat/bad fat
The dietary fat debate goes something like this: If we replace the saturated fats found in foods like beef and cheese with polyunsaturated fats—like those in vegetable oil—we will reduce our total cholesterol and improve our health.
That’s not necessarily so. Christopher Ramsden, a clinical investigator at NIH, has shown that replacing saturated fat with linoleic acid does not decrease the risk of heart attacks or death, despite lowering blood cholesterol. Taha was a postdoctoral fellow at NIH where he researched linoleic acid alongside Ramsden before joining the UC Davis faculty in 2014.
“Chris and his colleagues went back through data from the 1960s and found that study participants who ate a diet low in saturated fat and enriched with high-linoleic acid oils reduced their cholesterol by an average of 14 percent, but the low-saturated-fat diet did not reduce mortality,” Taha said. “In fact, they found that the greater the drop in cholesterol, the higher the risk of death during the trial.”
For healthy fats, Taha says it’s better to choose ones that are relatively low in linoleic acid, like butter, olive oil, coconut oil and canola oil, and to consume foods that are high in omega-3 fatty acids, like salmon.
“Replacing saturated fats with vegetable oils, such as soybean and corn oil, may not be the best strategy because it may increase oxidized levels of LDL cholesterol, the so-called bad cholesterol, which can cause inflammation and many health concerns.”
How much is too much?
Researchers haven’t yet established how dietary needs for linoleic acid change with age and disease. Taha and his team are developing innovative methods to measure linoleic-acid requirements, looking at how much linoleic acid is secreted by the liver, for example, and how much the heart and brain consume.
“When we measure how much the liver puts into the blood in relation to how much is consumed by organs, we can start to understand how much linoleic acid we should consume when we’re 2 and 20 and 70,” Taha said.
Taha is investigating a wide range of lipids like linoleic acid and lipid-like environmental toxins such as pesticides, flame retardants and antibiotics. He’s especially interested in the impact these compounds have on neurodevelopment.
In addition to the link between linoleic acid and brain function, Taha is exploring whether a mother’s exposure to pesticides can impact neurodevelopmental disorders like autism and whether certain levels of antibiotics in farmed seafood can affect human health.
“When we understand the mechanisms and risks associated with exposure to certain compounds, we can help devise strategies to establish dietary safety limits and improve health and well-being,” Taha said.