Scientists behind the research called the conclusions a "major surprise."
In the competition for unhealthiest food, both sugar and fat have wrestled for the title over the years, with favor wavering from one to the other as new research emerges. Nowadays, with renewed fervor for fats and the tremendous popularity of the fat-loving ketogenic diet – fat is in better standing and sugar is a big no-no.
But not all fats are created equally.Sure, most of us know that trans-fats are bad, and that healthy fats are good. But even beyond that, there are differences. However research from the University of California, Riverside found that one oil in particular, soybean oil, appears to be particularly devilish.
Here's what the study found: Given a diet exactly equal in calories, mice whose diets included soybean oil fared terribly. Soybean oil is primarily polyunsaturated fats and is a main ingredient in vegetable oil.
(Note: I abhor the use of animals in research so much that I tend to not even write about studies that include them, but this report was so surprising to me that I am making an exception ... my sympathy to the mice.)
The research team devised four types of diets, each containing 40 percent fat, a similar percentage to what Americans currently consume.
Diet 1: Included coconut oil, which consists primarily of saturated fat.
Diet 2: Included half coconut oil and half soybean oil.
Diets 3 and 4: Included added fructose, comparable to the amount consumed by many Americans.
All four diets contained an equal amount of calories and around the same amount of food. So one would think that their weight must have stayed about the same. But nope. The mice on the soybean oil-enriched diet gained almost 25 percent more weight than the mice on the coconut oil diet and 9 percent more weight than those on the fructose-enriched diet. And the mice on the fructose-enriched diet gained 12 percent more weight than those on a coconut oil rich diet.
According to the University, the conclusions are pretty remarkable:
"Compared to mice on the high coconut oil diet, mice on the high soybean oil diet showed increased weight gain, larger fat deposits, a fatty liver with signs of injury, diabetes and insulin resistance, all of which are part of the Metabolic Syndrome. Fructose in the diet had less severe metabolic effects than soybean oil although it did cause more negative effects in the kidney and a marked increase in prolapsed rectums, a symptom of inflammatory bowel disease (IBD), which like obesity is on the rise."
"This was a major surprise for us - that soybean oil is causing more obesity and diabetes than fructose - especially when you see headlines everyday about the potential role of sugar consumption in the current obesity epidemic," said Poonamjot Deol, a professor of cell biology and neuroscience who directed the project.
In a Q & A with the researchers, I found these two answers to be especially revelatory:
Q. So, the soybean oils with unsaturated fats were less healthy than the coconut oil with the saturated fat?
A. Yes, that is correct, in terms of obesity, diabetes and liver effects.
Q. But saturated fats are supposed to be unhealthy and unsaturated fats healthy?
A. That is the dogma based on large epidemiological studies from the 1950s and 1960s that showed the risk for heart disease correlated with the consumption of animal fat, which is largely saturated fat. Since saturated fat was found to be unhealthy, it was automatically assumed that unsaturated fat was healthy although it was never really properly tested in long-term studies until recently. The type of saturated fat in coconut oil is not exactly the same as the saturated fat in animal lard. There are many different types of saturated (and unsaturated) fat.
In the past 40 years or so, Americans have been eating a lot more soybean oil, much in part thanks to the advice to replace saturated fats from animal products with plant oils. (Which is still a good idea, just not soybean oil.) Meanwhile, the agricultural sector began growing more and more soybeans, leading to a remarkable increase in the consumption of the crop's oil, which gets sneaked into processed foods, margarines, salad dressings, snack foods, and more. Hey, if you have it, better find places to put it – much like the way high-fructose corn syrup has found its way into everything as well.
"Soybean oil now accounts for 60 percent of edible oil consumed in the United States," notes the University. "That increase in soybean oil consumption mirrors the rise in obesity rates in the United States in recent decades."
So in the end, this round goes to soybean oil as the dietary foe, with sugar close behind and coconut oil snatching a gold star for better health. Who knows what we'll be hearing next year, but I know that I'm sticking with coconut oil, olive oil, and a distinct absence of both soybean oil and sugar for now.
You can read more about the research at the website for the University of California, Riverside.