WASHINGTON (AP) — Until recently, most Americans had never heard the term “seed oils,” even though they’ve likely cooked with and consumed them for decades.

It’s the catchy description coined by internet influencers, wellness gurus and some politicians to refer to common cooking oils — think canola, soybean and corn oil — that have long been staples in many home kitchens.

Those fiery critics refer to the top refined vegetable oils as “the hateful eight” and claim that they’re fueling inflammation and high rates of chronic diseases like obesity and diabetes.

Robert F. Kennedy Jr., the new health secretary, has said Americans are being “unknowingly poisoned” by seed oils and has called for fast-food restaurants to return to using beef tallow, or rendered animal fat, in their fryers instead.

In response to consumer concerns, some food-makers have stripped seed oils from their products. Restaurants like the salad chain Sweetgreen have removed them from their menus. Many Americans say they now avoid seed oils, according to a recent survey from the International Food Information Council, an industry trade group.

The seed oil discussion has exasperated nutrition scientists, who say decades of research confirms the health benefits of consuming such oils, especially in place of alternatives such as butter or lard.

“I don’t know where it came from that seed oils are bad,” said Martha Belury, an Ohio State University food science professor.

In a Senate hearing Thursday, Dr. Marty Makary, nominated to lead the U.S. Food and Drug Administration, called for a closer review of the products.

“I think seed oils are a good example of where we could benefit from a consolidation of the scientific evidence,” he said.

What are seed oils?

Simply put, they are oils extracted from plant seeds. They include eight commonly targeted by critics: canola, corn, cottonseed, grapeseed, soybean, sunflower, safflower and rice bran.

Seed oils are typically made by pressing or crushing the seeds and then processing them further with chemicals and heat to remove elements that can leave the oil cloudy or with an unpleasant taste or odor.

The result of such refining is a neutral-tasting oil that is inexpensive, shelf-stable and able to be heated at a high temperature without smoking, said Eric Decker, a food science professor at the University of Massachusetts Amherst.

By contrast, olive oil and avocado oil are considered fruit oils.

They’re often cold-pressed, which retains many of the plant-based compounds that benefit health — but also makes the oils more expensive and prone to smoking at high heat.

Seed oils are composed mostly of unsaturated fatty acids, including monounsaturated and polyunsaturated fat. Most seed oils are high in one type of fatty acid, omega-6, and low in another type, omega-3.

Those fatty acids are essential for human health, but our bodies don’t make them on their own, so we must get them from foods.

What are the claims about seed oils

and health?

Critics of seed oils make a range of claims that many scientists say are not borne out by research.

Some critics contend that the way the oils are produced leaves behind toxic byproducts of a chemical called hexane. Hexane is considered hazardous in a gas form, but Decker said the hexane used as a liquid solvent to extract the oil is evaporated off and that the residue that remains “is very low and would not present a risk.”

Another common claim is that the seed oils’ high omega-6 and low omega-3 composition causes an imbalance that may increase the risk of chronic conditions by boosting inflammation in the body.

Belury, who has studied fatty acids for three decades, says that claim is based on an oversimplification and misunderstanding of the science. Studies have shown that increased intake of linoleic acid, the most common omega-6, does not significantly affect concentrations of inflammatory markers in the blood, she said.

“Scientists who study omega-6 and omega-3 think we need both,” Belury said. “Seed oils do not increase acute or chronic inflammation markers.”

In addition, research from the American Heart Association and others has consistently shown that plant-based oils reduce so-called bad cholesterol, lowering the risk of heart disease and stroke, especially compared with sources high in saturated fat.