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Soy, Sugar's Cohort in Causing Obesity

By Christopher Clark
July 31, 2015
Soy, Sugar's Cohort in Causing Obesity image

Since the 1930s, the US government has been heavily subsidizing corn, soy, wheat, and other so-called staple crops. Subsequently, these foods have remained artificially cheap for decades, leading to enormously increased consumption.

For a new study, just published in PLOS One, scientists at UC Riverside compared the effects of diets high in soybean oil with those high in fructose and/or coconut oil. They concluded that soybean oil, when consumed at typical American consumption levels, causes significant liver damage and promotes obesity and diabetes even more so than fructose.1

“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, the study’s lead scientist.2

This study is believed to be the first comparing the effects of unsaturated fat, saturated fat, and fructose on obesity, diabetes, insulin resistance and nonalcoholic fatty liver disease. While excessive sugar consumption has rightfully been criticized during the past several years, this study shows that industrial seed oils, particularly soybean oil, can be just as dangerous.

Soybean oil features prominently in many processed foods, especially margarine, salad dressings, and snack foods. It’s also the preferred cooking oil throughout the restaurant industry. In 2007, around 80 million tons of edible vegetable oils were produced globally, about half of which was soybean oil.3

Just how much money goes into keeping soy cheap and plentiful? Between 1995 and 2012, US soy subsidies totaled an astounding $27.8 billion, second only to corn, which amounted to $84.4 billion for the same period. In 2014, the US government replaced direct payments to farmers with Price Loss Coverage (PLC) and Agricultural Risk Coverage (ARC), but these new programs still cost taxpayers two-thirds as much as the direct payments did.4

Annual consumption of soybean oil increased from a miniscule 0.01 kg per person in 1909 to 11.2 kg in 1999.5 So what has been the impact on health? The UC Riverside scientists fed mice diets with 40% of calories coming from fat and supplemented those diets with fructose. Diet 1 consisted of 36 kcal% from coconut oil and 4 kcal% from soybean oil. Diet 2 consisted of 21 kcal% from coconut oil and 19 kcal% from soybean oil. These diets were formulated to mimic American consumption patterns with respect to saturated fat, soybean oil, and fructose.

Mice on Diet 2, the high soybean oil diet, exhibited increased weight gain, adiposity, fatty liver, insulin resistance, and diabetes, compared to mice on Diet 1. The scientists believe the mechanisms behind these outcomes involve changes in gene expression. Diet 2, for example, caused significant global dysregulation of several genes, particularly cytochrome P450, related to diabetes, obesity, lipid metabolism, and cancer.

Fructose had less severe metabolic effects than did soybean oil, which was a surprise to the scientists. More importantly, they determined that fructose combined with soybean oil works synergistically to undermine health.

Fructose induced neither diabetes nor insulin resistance in this study, although it did induce obesity. The scientists point out that fructose and its metabolic impact are very hotly debated within the nutrition science community. Further research will yield a more evolved perspective on fructose, but this study stresses the importance of dietary context. In other words, fructose seems to be much more damaging when paired with unhealthy oils compared to healthy sources of fat.

Many people within the Paleo community are concerned about fructose, even going so far as to completely eliminate fruit from their diets. While this might be appropriate for some people, it’s probably unnecessary for others. The fat in the Paleo diet comes mostly from high-quality sources of saturated and monounsaturated fat, with minimal amounts of high-quality polyunsaturated fat. The current study shows how foods interact and why a holistic approach to diet is essential. If America is serious about reversing degenerative diseases, soybean oil must share the spotlight with sugar during the many ongoing national discussions about nutrition.


[1] Deol, P., et al. (July 2015). Soybean Oil Is More Obesogenic and Diabetogenic than Coconut Oil and Fructose in Mouse: Potential Role for the Liver. PLOS One, 10(7).

[2] University of California - Riverside. (2015, July 22). Soybean oil causes more obesity than coconut oil, fructose: Scientists found mice on high soybean oil diet showed increased levels of weight gain, diabetes compared to mice on a high fructose diet or high coconut oil diet. ScienceDaily.

[3] Rosillo-Calle, F. (2009). A global overview of vegetable oils, with reference to biodiesel. CEP/Imperial College, Luc Pelkmans, VITO and Arnaldo Walter, UNICAMP for IEA Bioenergy Task 40.

[4] Haspel, T. (February 18, 2014). Farm bill: Why don’t taxpayers subsidize the foods that are better for us? The Washington Post.

[5] Blasbalg, TL, et al. (March 2011). Changes in consumption of omega-3 and omega-6 fatty acids in the United States during the 20th century. The American Journal of Clinical Nutrition, 93(5).

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