Obesity That Cannot Be Explained by Calories: The Latest Research on the Intersection of Soybean Oil, Genetics, and the Liver - The Precarious Relationship Between Soybean Oil and Modern Diets

1. "Which Oil You Fry With" Could Be the Deciding Factor for Obesity?

Vegetable oil, mayonnaise, snack foods, frozen foods, fast food——.
In the United States, the main oil used in such processed foods and dining out is "soybean oil." According to a summary by UC Riverside, the calories consumed from soybean oil have increased from about 2% to nearly 10% of the total over the past 100 years.news.ucr.edu

The study that reported "a hidden trigger causing obesity has been found" regarding soybean oil is gaining global attention, covered simultaneously by ScienceDaily, UC Riverside News, and various US media outlets.ScienceDaily

2. Overview of the Study: Mice That Gain Weight and Mice That Don't, Despite the Same Soybean Oil

The experiment was very simple, but the results were quite dramatic.ScienceDaily

• "Normal mice" fed a high-fat, soybean oil-rich diet
  → Significant weight gain, fat accumulation in the liver, and increased blood cholesterol.

• "Genetically modified mice" fed the exact same diet
  → Weight gain was significantly suppressed, less liver fat, and good mitochondrial function.

The difference was not in the mice's "appetite" or "activity level," but in theproteins and enzymes working in the liver.

The key is a protein called "HNF4α (Hepatocyte Nuclear Factor 4 Alpha)" that works in the liver. The research team created mice that express a "different version (P2-HNF4α)" of this protein in large amounts and fed them a high-fat, soybean oil diet. As a result, they became less prone to gaining weight from soybean oil.news.ucr.edu

What emerges from this is the possibility that

"The reason some people gain weight easily while others don't, even when eating the same food, might be due to different 'settings' in the liver."

3. The Key Is Not Calories but a Lipid Messenger Called "Oxylipin"

"So, in the end, isn't it just that soybean oil is fattening because it's high in calories?"
You might want to argue that, but what the researchers were looking at was **not calories, but 'what it gets converted into.'**

Soybean oil contains a large amount of linoleic acid, a type of omega-6 fatty acid. When linoleic acid is broken down in the body, it produces molecules called **oxylipins**.ScienceDaily

• Consuming a lot of linoleic acid
  → Increases oxylipins in the body
  → This is believed to be linked to inflammatory responses, fat accumulation, and metabolic changes in the liver

In this study, it was found that specific oxylipins (types produced from linoleic acid and α-linolenic acid) were strongly associated with weight gain in normal mice. On the other hand, genetically modified mice had fewer of these oxylipins and less liver fat.news.ucr.edu

However, the story is not that simple.
In genetically modified mice fed a low-fat diet, high levels of oxylipins did not lead to obesity. In other words,

rather than "oxylipins cause weight gain,"
it is more likely that "high-fat diet × oxylipins × individual differences" together make it easier to gain weight

, suggesting a "conditional trigger."news.ucr.edu

4. Differences in "Enzymes That Convert Fats" Determine Ease of Weight Gain?

A closer examination of the genetically modified mice revealed another significant difference.
It was the expression levels of **two enzyme families (CYP and lipoxygenase systems)** that convert linoleic acid into oxylipins.

• Normal mice
  → These enzymes are abundant, rapidly converting linoleic acid into oxylipins

• Genetically modified mice
  → Fewer enzymes, resulting in fewer oxylipins

The function of these enzymes is common not only to mice but to mammals, including humans,and is known to vary greatly with genetics, diet, medication, and age.news.ucr.edu

Even more interestingly,

it was "liver oxylipins" that were strongly correlated with ease of weight gain, not oxylipins in the blood
. This suggests that general blood tests might overlook such early metabolic changes.news.ucr.edu

5. Soybean Oil ≠ Bad, but "Quantity and Context" Are the Issue

Researchers are not condemning "soybean oil as an evil oil."
In fact, UC Riverside's press release cautiously states, "It's not that soybean oil itself is bad, but the 'quantity' we consume may not align with our body's evolution."news.ucr.edu

On the other hand, numerous recent reviews and epidemiological studies suggest that seed oils, centered around linoleic acid, may actually reduce cardiovascular risks and inflammation when consumed in moderation.Mayo Clinic MC Press

The current conclusion that can be drawn is that

• in mouse experiments, oxylipins derived from soybean oil are quite likely related to obesity

• However,it's too early to "apply this directly to humans."

• Especially in large-scale human studies, there is no data supporting a complete denial of seed oils

, indicating that we are at a "very interesting but still inconclusive" stage.PubMed

6. Reactions on Social Media: Joyful "Anti-Seed Oil Faction" and Calm Experts

As soon as this news broke, links to the paper were shared on X (formerly Twitter) and Facebook, sparking discussions about dietary habits.X (formerly Twitter)

Reactions from the Anti-Seed Oil Faction (Expected Comments):

• "See! I've been saying seed oils are 'poison' all along."

• "We should quit chips and fast food and go back to butter and lard."

• "I'm scared of myself for believing vegetable oil was healthy..."

Recently, extreme claims that "seed oils are the root of all diseases" have gained popularity on platforms like TikTok and podcasts, and this study is being used as "fuel" for those arguments.Medium

On the other hand, reactions from nutritionists and doctors (also typical comments):

• "You can't directly apply mouse experiment results to long-term human risks."

• "Reducing ultra-processed foods as a whole is far more important than eliminating seed oils entirely."

• "Weight is also significantly influenced by overall energy balance, exercise, sleep, and stress."

In fact, Mayo Clinic and major health media outlets have published explanatory articles stating that "seed oils are safe in moderation and can reduce cardiovascular and diabetes risks," attempting to soften the "seed oil villain narrative" on social media.Mayo Clinic MC Press

The confusion among general users is also real:

• "First, they said butter was bad, and now it's soybean oil? What should I believe?"

• "In the end, I guess I have to think for myself about 'what and how much to eat'..."

Thus, this study highlights the gap between "the world of science" and "the atmosphere on social media."

7. How Should We Change Our Dining Habits? Practical Application

So, how should we change our behavior after hearing this news? Let's organize feasible "compromises" based on the study's content and other evidence.

7-1. "Reduce Ultra-Processed Foods" Rather Than "Ban Soybean Oil"

• Soybean oil is commonly used in manyultra-processed foodssuch as snacks, fried foods, dressings, and mayonnaise.

• These foods generally have high sugar, salt, and