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Is vegetable oil really the best choice?
According to the diet-heart hypothesis introduced in the 1950s that associated animal fat with heart disease, the answer is yes, though many question the science behind it.
It’s understandable that we’re confused on this point. Both the FDA and American Heart Association insist that because vegetable oils are polyunsaturated fats (PUFAs), they’re absolutely safe and beneficial to health.
But there’s a dark side to a major component of vegetable oil…
Past research in mice has linked its main ingredient to ailments such as obesity, diabetes, insulin resistance, fatty liver disease, autism, Alzheimer’s disease, anxiety, depression and other neurological conditions.
And a recent study indicates it could wreak havoc in the gut as well…
The problem with vegetable oil
Did you know that vegetable oil is mostly made up of soybean oil? There may be some corn oils blended in, but soybean oil is the most consumed edible oil in the United States.
And it isn’t just used for cooking meals at home. Soybean oil is included in packaged foods such as margarine, shortening, mayonnaise, salad dressing, frozen foods, baked goods, imitation dairy and meat products.
When soybean oil is used for these purposes, it’s often refined, blended and hydrogenated. And when oils are hydrogenated, they morph into unhealthy trans fats that raise LDL (or “bad”) cholesterol and lower HDL (or “good”) cholesterol.
“Our work challenges the decades-old thinking that many chronic diseases stem from the consumption of excess saturated fats from animal products, and that, conversely, unsaturated fats from plants are necessarily more healthful,” says Poonamjot Deol, an assistant professional researcher at the University of California, Riverside (UC Riverside).
By work, Deol is referring to a recent study in mice that found a diet high in soybean oil can lead to ulcerative colitis, an inflammatory bowel disease (IBD) characterized by chronic inflammation of the large intestine.
The UC Riverside researchers consistently fed mice a soybean oil-rich diet for up to 24 weeks in the lab. When they examined their guts, they found a decrease in beneficial bacteria and an increase in harmful bacteria such as Escherichia coli. These conditions can lead to colitis.
Linoleic acid at the root
According to Deol, a co-corresponding author on the paper, the concern is the linoleic acid in soybean oil.
Linoleic acid is an omega-6 fatty acid. We’ve known for a while that the major problem with the modern Western diet is too many omega-6 fats.
“While our bodies need 1 to 2 percent of linoleic acid daily, based on the paleo diet, Americans today are getting 8 to 10 percent of their energy from linoleic acid daily, most of it from soybean oil,” she says, adding that excessive linoleic acid can harm the gut microbiome.
For instance, invasive E. coli uses linoleic acid as a source of nutrition. And several good gut bacteria are unable to withstand linoleic acid and die out.
“It’s the combination of good bacteria dying off and harmful bacteria growing out that makes the gut more susceptible to inflammation and its downstream effects,” Deol says. “Further, linoleic acid causes the intestinal epithelial barrier to become porous.”
That can lead straight to leaky gut, a condition where toxins leak out of the gut and enter the bloodstream. This greatly increases the risk of infections and chronic inflammatory conditions such as colitis.
To the research team’s surprise, the mice fed the high soybean oil diet also showed a reduction of endocannabinoids in the gut. These cannabis-like molecules made naturally by the body regulate a wide range of physiological functions.
At the same time, there was an increase in gut oxylipins, which are oxygenated PUFAs that control inflammation. The decrease in endocannabinoids and increase in oxylipins is consistent with IBD in humans, Deol says.
Toxicologist Frances M. Sladek, a professor at UC Riverside and a co-corresponding author on the paper, notes that for good heart health, the AHA recommends 5 to 10 percent of daily calories be from omega-6 PUFAs such as linoleic acid. The soybean oil used in the study had 19 percent linoleic acid.
“Every animal has to get linoleic acid from the diet,” Sladek said. “No animal can make it. A small amount of it is needed by the body. But just because something is needed does not mean a lot of it is good for you.”
Minimize the amount of soybean oil in your diet
Sladek notes that future studies are needed to determine the tipping point for how much daily linoleic acid consumption is safe.
Until then, Sladek and Deol recommend olive oil, given it has lower amounts of linoleic acid. Instead, olive oil consists of 70 to 80 percent oleic acid — the antithesis of linoleic acid.
“Olive oil, the basis of the Mediterranean diet, is considered to be very healthy; it produces less obesity and we have now found that, unlike soybean oil, it does not increase the susceptibility of mice to colitis,” Sladek says.
Because most processed foods in the U.S. contain soybean oil, Sladek advises staying away from those foods.
Also, since most restaurants cook with soybean oil, it’s a good idea to try to cook as much of your food as possible. Check that the oil you use to cook with doesn’t contain soybean oil, and check out this post by a colleague on 5 healthy cooking oils and how to use them.
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Widely consumed vegetable oil leads to an unhealthy gut — EurekAlert!
Polyunsaturated Fat — American Heart Association
US-Grown Soybean Oil Achieves FDA’s Qualified Heart Health Claim — Today’s Dietician
Trans fat is double trouble for heart health — Mayo Clinic