Unless you prepare all of your food at home and eat nothing out of a package, it’s hard to avoid soybean oil. When you dine out at an inexpensive restaurant, your food was very likely prepared in soybean oil and when you grab a packaged food or convenience food at the supermarket, check the ingredient list and you’ll probably see soybean oil in tiny print. According to the United States Department of Agriculture, soybean oil makes up about 30% of all fats and oils produced.
Where does soybean oil come from? To make this ubiquitous cooking oil, manufacturers crack open soybeans and heat them to a temperature as high as 190 degrees Fahrenheit. After pressing them into flakes, the chemical hexane is used to extract the oil. The oil is then further processed and refined. Restaurants like soybean oil because it has a high smoke point and is inexpensive – but is it healthy?
If you look at the way soybean oil is processed by exposure to high heat and chemical extraction, it’s clear that soybean oil, like other oils you find in clear plastic bottles at the grocery store, is highly refined. You may have heard about soybean oil in the context of trans-fats. In the past, some manufacturers took an additional step and partially “hydrogenated” soybean oil, creating the much- maligned trans-fat. Although partially hydrogenated oils, including partially hydrogenated soybean oil, is slowly being phased out, this type of soybean oil is still alive and well on store shelves and in packaged foods.
Does Soybean Oil Contribute to Weight Gain?
Many people in the general population believe soybean oil is healthy, but there’s evidence that soybean oil might contribute to weight gain. In one study, researchers divided mice into groups. All groups ate a diet containing 40% dietary fat. One group got their fat primarily from coconut oil, high in plant-based saturated fat while the other got their fat mostly from soybean oil. Some mice also ate a high-fat diet with fructose.
With so much talk about fructose being unhealthy, you might think the mice that ate the diet with fructose would gain the most weight. Instead, it was the mice who ate the soybean oil diet without fructose that packed on more weight – about 9% more. When comparing mice that ate coconut oil versus the soybean oil eating mice, the latter gained 25% more weight. It wasn’t just weight gain the soybean oil eating mice experienced, they also developed signs of fatty liver and insulin resistance, indicating worsening metabolic health.
Keep in mind, this study was carried out in mice, not humans, so it’s too soon to say this necessarily applies to humans. Still, there are other reasons to limit the amount of soybean oil in your diet.
Soybean Oil and Omega-6s
What makes soybean oil so questionable? One problem with soybean oil is its fatty acid composition. Soybean oil is high in a type of fat called omega-6 and low in omega-3. Ideally, for health, you should aim for a ratio of omega-6 to omega-3 of 1:1 or no more than 2:1. The Western diet has a ratio of around 15:1. In other words, we’re getting too much omega-6 fats and not enough omega-3s. What are the consequences of this?
Some research suggests such an unbalanced ratio creates a low-grade inflammatory state in our bodies that may contribute to health problems like heart disease, type 2 diabetes, autoimmune disease, and cancer. Safflower oil, sunflower oil, sesame oil, corn oil, and peanut oil also have a high ratio of omega-6 to omega3s.
The problem is omega-6 fatty acids compete with omega-3s for certain enzymes involved in pathways that promote inflammation. The more omega-6s in your diet, from sources like soybean oil, the more omega-3s you need to compensate. Unfortunately, most people don’t eat a lot of foods high in omega-3s like fatty fish, flaxseed, walnuts etc.
Most Soy is Genetically Modified
While there’s no proof that genetically modified foods pose a health risk, it might be wise to avoid GMO foods until more research comes available. The majority of soybeans are genetically modified. Although organic soybeans aren’t genetically modified, soybean oil is so heavily refined that even soybean oil made from organic soybeans isn’t healthy.
Sources of Soybean Oil
Where are you likely to find soybean oil? Everywhere. You’ll find it packaged salad dressings, potato chips, mayonnaise, crackers, snack foods – it’s really in most conventional processed foods. You may not think about the oil your favorite restaurant uses, but you’re probably getting hit with soybean oil there too unless you eat at an Italian restaurant that uses olive oil. The fact that soybean oil is so inexpensive makes it appealing to food manufacturers and restaurants alike.
So what are your options? Use olive oil when you prepare foods, unless you’re heating them to a temperature that exceeds olive oil’s smoke point. Olive oil is ideal for sautéing and for making salad dressings etc. Plus, it’s a source of heart-healthy monounsaturated fats, one of the healthiest types of fat.
Just as importantly, remove most processed foods from your diet since they’re a prime source of exposure to soybean oil. Fortunately, there are healthier oils available, particularly olive oil, and you have control over which oil you use when you prepare meals.
The Bottom Line
Soybean oil isn’t the healthiest choice of cooking oil for a variety of reasons, mostly because it’s highly refined and has an unfavorable ratio of omega-6 to omega-3 fats. While there’s no proof it contributes to weight gain in humans, at least one animal study suggests that it could. So, choose your cooking oils wisely, and leave soybean oil on the shelf.
United States Department of Agriculture, Agricultural Statistics 2004. Table 3-51.
REI. The Super Common Oil That Science Now Shows is Worse Than Sugar”
Am J Clin Nutr June 2006. vol. 83 no. 6 S1483-1493S.
Biochem Pharmacol. 2009 Mar 15;77(6):937-46. doi: 10.1016/j.bcp.2008.10.020. Epub 2008 Oct 28.
Medical Daily. “Soybeans Make The Unhealthiest Vegetable Oil, Could Lead To Obesity And Type 2 Diabetes: Study” June 22, 2015.
Biomed Pharmacother. 2002 Oct;56(8):365-79.
PLOS One. “Soybean Oil Is More Obesogenic and Diabetogenic than Coconut Oil and Fructose in Mouse: Potential Role for the Liver” July 22, 2015.