Linoleic acid, the main omega-6 fat in vegetable oils such as soybean oil, drives abdominal obesity more than total fat does. In mice, an 8% linoleic acid diet caused severe abdominal obesity on medium- and high-fat diets alike. Adding omega-3 (EPA and DHA) prevented it.
Summary: Eating less total fat did not considerably cut the rate of abdominal fat buildup, and obesity has gone up. Studies suggest this rise is due more to eating more linoleic acid (LA), an omega-6 fatty acid. It happened as people switched from animal fats to eating more vegetable oils. That switch also meant less omega-3 in the diet. Experimental studies confirm that eating less LA may considerably help lower the risk of obesity. Adding omega-3 to the diet may bring an extra benefit by countering the harmful effects of LA. That would help lower obesity rates.
Keywords: linoleic acid (LA), omega-6 fatty acids, omega-3 fatty acids, eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), endocannabinoid system
Do vegetable oils cause obesity?
New experimental data indicate that a high intake of omega-6 and a fairly low intake of omega-3 have more to do with obesity than total fat intake does. The same goes for buildup of visceral fat (fat packed around the organs) and insulin resistance (when cells stop answering insulin). Correcting the omega-6: omega-3 ratio in the diet may be the key to countering obesity.
Abdominal obesity has grown at an alarming rate in the last 40-50 years in the US. Historical data shows that in men, it rose from 12.7% to 38.3%. In women, it grew from 19.4% to almost 60% between 1960 and 2000. This tripling of abdominal obesity is hard to explain by the total fat in the diet alone1.
Researchers think the rise in abdominal obesity has more to do with the quality of the fats people eat. Some researchers suggest that humans evolved to eat omega-6 and omega-3 fatty acids in almost equal amounts. But in the modern diet, the ratio runs from ~10:1 to 25:1. That’s a severe imbalance2.
If that is the case, correcting the omega-6 to omega-3 ratio may solve much of the obesity problem. That means eating more omega-3 and less omega-6. But before making any firm recommendation, there has to be strong evidence for the theory.
Researchers think some evidence comes from tracking how diets changed over history. For example, data shows that omega-6 intake rose sharply from 1900 onwards. That is when people in the western world switched from butter or lard to more vegetable oils, like soybean oil. This brought a two-fold increase in linoleic acid (LA), the main omega-6 fatty acid in vegetable oils. It now makes up 8 to 10% of total calorie intake3.
A systematic review of studies further supports this. It indicates that LA content in subcutaneous tissues (the fat under the skin) in the US has gone up 2.5 times.
Can cutting omega-6 or adding omega-3 prevent obesity?
Researchers ran lab experiments in mice to understand the effect of LA on obesity. They also wanted to learn more about the role of a high-fat diet4.
Firstly, they split mice into two groups. One was fed a medium-fat diet (35% of total calorie intake). The other got a high-fat diet (65% of the total calorie intake). They split the mice into two groups again. One was fed a diet with 1% LA and the other an 8% LA diet. That means 1% and 8% of energy came from LA.
Interestingly, they found that eating more fat was not much related to obesity. There was not much difference between the 1% LA groups on the medium-fat and high-fat diets.
But there was a clear and high association between obesity and high LA intake, no matter the total fat intake. Thus, the 8% LA mice on both the medium-fat and high-fat diets developed severe abdominal obesity.
Next, they wanted to understand the role of omega-3 fatty acids in the diet. So they added omega-3 (eicosapentaenoic acid (EPA) + docosahexaenoic acid (DHA)) to the diet of the mice in the 8% LA group.
They found that a diet rich in omega-3 may help prevent obesity and so metabolic disorders. To their surprise, omega-3 could help control obesity in mice on an 8% LA diet. Total fat in the diet did not have much impact on it. So omega-3 fatty acids prevented fat buildup in the 8% LA and medium-fat diet group. They did the same in the 8% LA and high-fat diet group.
It confirmed the following things:
• LA is the primary cause of abdominal obesity, on a low fat or a high-fat diet. So LA intake needs to be limited.
• Eating a diet rich in omega-3 fatty acids (EPA+DHA) may help counter the obesity-causing effects of LA.
How does linoleic acid cause weight gain?
Researchers think this power of LA to cause obesity can be explained by changes inside cells from eating a lot of LA. It mainly stimulates the endocannabinoid system (a body signaling system). That leads to impaired fat storage and changes in behavior and appetite. So it raises the risk of obesity.
Total calorie intake counts. But perhaps how many calories the body gets from fat matters less. Even a high-fat diet will not cause obesity if it is low in LA-containing fats. And adding omega-3 fatty acids rich in EPA and DHA may help counter these obesity-causing effects of LA.
Frequently asked questions
Are seed oils bad for you?
Yes, at the levels Americans now eat them. Linoleic acid, the main omega-6 fat in vegetable oils such as soybean oil, drives abdominal obesity more than total fat does. In mice, an 8% linoleic acid diet caused severe abdominal obesity on both medium- and high-fat diets, whatever the total fat. Linoleic acid now supplies 8 to 10% of total calories.
Why is everyone suddenly against seed oils?
Because the timing fits. From 1900 on, people in the western world swapped butter and lard for vegetable oils like soybean oil. That doubled linoleic acid intake and lowered omega-3. Between 1960 and 2000, abdominal obesity rose from 12.7% to 38.3% in men and from 19.4% to almost 60% in women. Total fat alone does not explain that jump.
Should I stop using seed oils?
Yes. Cut them out. Cutting linoleic acid is the main lever this research points to. That is because even a high-fat diet did not cause obesity when it was low in linoleic acid. Adding omega-3 fats, EPA and DHA, helps counter what omega-6 does. Our ancestors ate omega-6 and omega-3 in roughly equal amounts. The modern diet runs from about 10:1 to 25:1.
References
1. Okosun IS, Chandra KMD, Boev A, et al. Abdominal adiposity in US adults: prevalence and trends, 1960–2000. Preventive Medicine. 2004;39(1):197-206. doi:10.1016/j.ypmed.2004.01.023
2. Simopoulos AP. Evolutionary Aspects of the Dietary Omega-6/Omega-3 Fatty Acid Ratio: Medical Implications. In: Alvergne A, Jenkinson C, Faurie C, eds. Evolutionary Thinking in Medicine: From Research to Policy and Practice. Advances in the Evolutionary Analysis of Human Behaviour. Springer International Publishing; 2016:119-134. doi:10.1007/978-3-319-29716-3_9
3. DiNicolantonio JJ, O’Keefe JH. Omega-6 vegetable oils as a driver of coronary heart disease: the oxidized linoleic acid hypothesis. Open Heart. 2018;5(2):e000898. doi:10.1136/openhrt-2018-000898
4. Alvheim AR, Malde MK, Osei-Hyiaman D, et al. Dietary Linoleic Acid Elevates Endogenous 2-AG and Anandamide and Induces Obesity. Obesity (Silver Spring). 2012;20(10):1984-1994. doi:10.1038/oby.2012.38
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Medically reviewed by Dr. Gurpreet Singh Padda, MD, MBA, MHP
Interventional pain physician, addiction medicine specialist and obesity medicine diplomate.
Licensed in Missouri and Illinois.
Last reviewed June 18, 2026
