“Everyone is consuming a lot of soy oil even if we don’t know it” ~Frances Sladek
Big food manufacturers love soy oil. They put it in millions of products, yet most Americans have no idea they’re eating it. In 2011, an article revealed that consumption of soy oil has increased 1000 fold over the past century, leading some to suggest that this change represents the largest, most rapid diet shift in all human history and to speculate it may play a special role in the obesity epidemic.
Soy Oil Calories More Fattening than Coconut Oil Calories
When a UC Riverside professor Frances Sladek read about the dramatic rise in soy oil consumption, she decided to investigate whether soy could possibly play a role in the dramatic rise in obesity we’ve seen over the time period since soy oil consumption has skyrocketted.
To better understand how soy impacts obesity, she formulated four special chows for her study mice to eat. The most interesting of the four was designed to effectively mimic the diet consumed by average Americans, composed of 40% fat (by caloric composition) and with a good portion of that fat coming from soy oil, while the carb came either from starch or fructose. She then fed each type of chow to different groups of mice for several months, and collected data on how each formulation affected the development of obesity.
The study results were published recently in the influential PLoS journal (Public Library of Science), and the title says it all: “Soybean Oil Is More Obesogenic and Diabetogenic than Coconut Oil and Fructose in Mouse.”
Above I’ve posted the most important figure 1 from the study. This figure graphs out the weight gain in mice eating three different formulas: 40% calories from fat mostly soy-oil based (orange line), 40% calories from fat mostly coconut-oil based (blue line), and standard high-carb rat chow with roughly 5% fat (grey line).
It’s important to know that all three mice were eating the same amount of total calories, yet the orange line shows that the mice eating the soy-oil formula (orange line) gained weight faster than those on the coconut formula (blue line), and the mice eating standard chow gained less than both of these high-fat groups.
Before we go running off and concluding that low-fat, high-carb diets are the answer again, let’s remember that these are mice in a cage eating pellets. For reasons I don’t have time to go into here, I still don’t believe low-fat, high-carb diets are the answer for humans eating real food. (Chapter 10 of Deep Nutrition explains why I recommend we limit our carb consumption).
What I think is important is the difference between the two different 40% fat diets because most Americans eat roughly 40% calories from fat. What we see is that compared to mice getting their fat mostly from coconut oil, mice that got their fat mostly from soy oil gained about 25% more fat by the end of the study even though both groups ate the same number of calories. In other words, soy oil is more fattening that coconut oil.
In an interview, the authors summarize: “The mice fed the soybean oil diet became much more obese, diabetic and insulin resistant than the mice fed the coconut oil diet even though they had similar food intake.”
Soy Oil Promotes Higher Blood Sugar than Fructose
Fructose has beeen vilified as a major contributor to the epidemic not just of obesity but also diabetes. And while high consumption of fructose is certainly an issue, a bigger issue may be the high consumption of soy.
The UC Riverside group also performed a test called a glucose tolerance test. This test can show how well or how poorly we can handle starches and sweets. The test is performed by providing subjects with a fixed amount of carbohydrate and simply measuring how high the subject’s blood sugar goes afterwards. The higher it goes, the more the subject is insulin resistant. Insulin resistance is associated with a high risk of heart attack, stroke, cancer and much more, and can ultimately lead to diabetes.
Their results showed that the mice that had been fattened by eating soy were far more glucose intolerant than the mice that had been fattened by eating fructose.
Soy Oil Found To Cause Liver Damage, Possibly Fatty Liver
The subtitle of the article is “Potential Role for the Liver,” because they authors were surprised at what they found when they examined the liver closely.
In an interview (link below), the authors explain “[The mice] also had large lipid droplets in their liver and ballooning, a sign of liver injury.” This would be expected to eventually lead to fatty liver, a condition that many overweight and diabetic patients experience.
Oddly, the mice eating soy oil had larger livers (shown below) with more of the cellular ballooning indicitive of injury than the mice eating soy oil plus fructose!
Biochemical Explanation: Oxidative Stress
Personally, I’ve been avoiding soy oil and other vegetable oils since 2002, when I’d learned my medical eduction had seriously misinformed me on the topic of fats. The fact that soy oil has finally been outed as obesogenic and liver toxic is gratifying, because it shows–once again–that predictions made based on biochemistry are highly accurate.
Along these lines, because of the way that soy would be processed by the liver, I’ve also been advising my patients with fatty liver to avoid soy and other vegetable oils. When they do, their labs improve.
The biochemistry that predicts soy oil would be unhealthy compared to coconut has to do with the reactions that can occur when the different kinds of fatty acids in these oils are exposed to oxygen and iron or copper (or other metals). Soy contains a lot of polyunsaturated fatty acids (PUFAs). Coconut oil contains a lot of saturated fatty acids, and almost no PUFAs. PUFAs react easily with oxygen. The names for these chemical reactions are lipid oxidation and lipid peroxidation. In the factory, these reactions lead to lowered content of antioxidants and vitamins as well as production of break down products of the PUFA fats that are very toxic. In the body, these reactions promote oxidative stress.
Oxidative stress is a biochemical process that leads to a cellular response called inflammation. Inflammation makes you pack on the pounds faster than what you’d predict from simply calorie counting because it tells your body to make more fat cells. The more fat cells you have, the more easily you store fat and gain weight. Essentially, oxidative stress brainwashes your body into growing more fat cells, and vegetable oil is oxidative stress in a bottle.
This process of cellular brainwashing that alters your body composition goes a long way towards explaining how certain foods can cause us to gain weight beyond their caloric content. I write about how this works at a cellular level in Deep Nutrition, Chapter 11 entitled “Beyond Calories.”
Bottom line? All fat has lots of calories. But this study suggests fats that promote oxidative stress make us store fat faster than those that don’t.
PLOS Article: Soybean Oil Is More Obesogenic and Diabetogenic than Coconut Oil and Fructose in Mouse: Potential Role for the Liver
Q & A With Soybean Oil Researchers: UC Riverside’s Frances Sladek and Poonamjot Deol explain research in which they compared a genetically modified soybean oil to conventional soybean oil
Bad sources: Walter Willet, from the Harvard School of Public Health prefers soy over coconut