Obesity has become a serious health problem over the past century. While many factors are involved, including lifestyle, physical activity, and the growing availability of highly processed foods, researchers are paying increasing attention to the types of fats people eat every day.
A new study from the University of California, Riverside has added another piece to this puzzle by looking closely at soybean oil, the most widely used cooking oil in the United States.
Soybean oil is found in countless foods sold in supermarkets. It is commonly used in salad dressings, baked goods, chips, snack bars, fast food products, and many packaged meals.
Because it is inexpensive and versatile, its use has grown enormously over the last 100 years. Researchers estimate that soybean oil now makes up nearly 10% of the average American diet, compared with only about 2% a century ago.
The new research suggests that this dramatic increase may have important effects on health. Scientists found that soybean oil could contribute to weight gain, but the process is more complicated than previously thought.
To investigate, researchers carried out experiments using mice. Most of the mice were fed a high-fat diet rich in soybean oil. As expected, many of them gained significant amounts of weight. However, one special group of mice responded very differently.
These mice had been genetically modified to produce a slightly altered version of a protein found in the liver. This protein helps control how the body handles fats. Even though these mice ate the same high-fat diet, they gained much less weight than the other mice.
The researchers discovered that the altered protein changed how the animals processed linoleic acid, a fatty acid that is abundant in soybean oil.
Linoleic acid itself is not necessarily harmful. In fact, it is considered an essential fatty acid because the body needs small amounts of it for normal health. The concern may arise when people consume very large amounts over long periods of time.
The study suggests that the real problem may be what happens after linoleic acid is broken down inside the body. During this process, it is converted into compounds called oxylipins. These compounds are involved in many biological processes, including inflammation and the storage of body fat.
The genetically modified mice produced lower amounts of these oxylipins. They also showed healthier liver function and better-performing mitochondria, which are often described as the power plants of cells because they generate energy. These healthier mitochondria may have helped the animals burn energy more efficiently and avoid excessive weight gain.
The research team also found that the modified mice had lower levels of certain enzymes that convert linoleic acid into oxylipins. Interestingly, similar enzymes exist in humans. Their activity can vary depending on a person’s genes, age, sex, medications, and overall diet. This means some people may react differently to soybean oil than others.
One surprising finding was that high levels of oxylipins did not always lead to weight gain. Some of the genetically modified mice had elevated oxylipin levels but still remained relatively lean. This suggests that obesity is influenced by multiple biological pathways rather than a single factor.
Another important discovery involved where the oxylipins were located. Researchers found that oxylipin levels inside the liver were closely linked to weight gain, while levels circulating in the blood were not. This finding suggests that standard blood tests may not detect some of the early changes taking place inside the body.
The study also raises questions about cholesterol. Soybean oil contains no cholesterol because it comes from plants. However, mice that consumed large amounts of soybean oil developed higher cholesterol levels. Scientists are now trying to understand exactly why this happens.
The researchers are also expanding their work to investigate other commonly used vegetable oils that contain high amounts of linoleic acid. These include corn oil, sunflower oil, and safflower oil. Future studies will explore whether these oils produce similar effects.
Professor Frances Sladek, one of the study’s lead researchers, emphasizes that soybean oil is not necessarily dangerous when consumed in moderation. The concern is that modern diets contain far more soybean oil than people consumed in the past. When it appears in many processed foods eaten every day, total intake can become quite high.
According to the researchers, excessive consumption over many years may contribute to obesity, liver disease, and other metabolic health problems. However, they stress that more research is needed before firm conclusions can be made about human health.
The team has not yet conducted human clinical trials, but they hope their findings will encourage further research and help people become more aware of the oils present in their diets. Understanding how different fats affect the body could eventually help improve nutrition guidelines and public health recommendations.
If you care about weight loss, please read studies that hop extract could reduce belly fat in overweight people, and early time-restricted eating could help lose weight .
For more health information, please see recent studies about a simple path to weight loss, and results showing a non-invasive treatment for obesity and diabetes.
The study was published in the Journal of Lipid Research.
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