By Astrid Popovici
In the 1940s, American farmers were looking for ways to fatten up their pigs. They tried feeding them coconut oil, but it made them leaner. Thyroid-suppressing drugs were effective, but caused cancer in the pigs. But the farmers discovered that by feeding them corn and soybean oils, they could fatten the pigs for cheap, without any carcinogenic effects.
In part due to their low cost, seed oils are used in a wide variety of our foods—from junk food like chips, burgers, and cookies to bread, pasta sauce, and salad dressing. American consumption of these oils has increased dramatically over the past few decades.
Over the same time, obesity rates have risen sharply in the United States. It’s plausible that vegetable oils could have the same fattening effect on humans as they do on pigs. However, correlation is not causation, so we shouldn’t jump to the conclusion that vegetable oil makes you fat just yet. What if Americans are just eating more calories?
We are, and no doubt increased calorie consumption is one contributing factor to the rise in obesity. But this doesn’t take vegetable oils off the hook.
In 2012, scientists fed two groups of mice the same amount of calories, but one group got 8% of their energy from linoleic acid (a polyunsaturated fatty acid, and the main component of corn, soybean, sunflower and safflower oils), and the other group got only 1% from linoleic acid (they were fed 7% from saturated fats). Long story short, the high-linoleic-acid mice got significantly fatter:
According to the authors, “Consistent with this, we found a strong ecological relationship between apparent consumption of soybean oil, shortening, and poultry, the major dietary sources of LA, and the rise in obesity in the United States during the 20th century. Data on the apparent consumption is robustly associated with adipose concentrations of short chain (r = 0.92) and long chain (r = 0.88) PUFA across 11 countries ((39)). […] These ecological associations do not demonstrate that increasing LA caused increasing obesity in the United States during the 20th century. However, the results of the causal test of this inference in rodents are consistent with the interpretation that increasing dietary LA in human diets caused endocannabinoid hyperactivity and substantially contributed to increasing prevalence rates of obesity.” You can find the full study here.
So what can you do to avoid vegetable oils? First, check ingredient labels—you’ll be surprised how many items have them. Second, try to limit eating out: most restaurants cook with these oils. Third, do your cooking at home with butter, coconut oil or olive oil (all of which are low in linoleic acid). If you’re concerned about limiting your saturated fat intake, then olive oil, which is low in both linoleic acid and saturated fat, is a good choice.
The authors of the study also note that “The adipogenic effect of LA can be prevented by consuming sufficient EPA and DHA” (omega-3 fatty acids). Foods high in omega-3 fats include salmon, oysters, sardines, walnuts, and chia seeds.
Obesity is a complex problem, and it’ll take more than one simple fix to solve it. But removing these crude oils from our diet is a good place to start.