Soybean Oil Causes Obesity

If you don't believe in rodent studies, you may want to skip this blog. I don't either, but felt that this study needs to be reproduced in humans – highly unlikely. It does raise some interesting ideas and even Tom Naughton covers this in his blog here.

Scientists at the University of California, Riverside have found that mice on a high soybean oil diet showed increased levels of weight gain and diabetes compared to mice on a high fructose or high coconut oil diet. The scientists fed male mice a series of four diets that contained 40 percent fat, similar to what Americans currently consume.

1. In one diet, the researchers used coconut oil, which consists primarily of saturated fat.
2. In the second diet about half of the coconut oil was replaced with soybean oil, which contains primarily polyunsaturated fats and is a main ingredient in vegetable oil.
3. The other two diets had added fructose, comparable to the amount consumed by many Americans.
4. All four diets contained the same number of calories and there was no significant difference in the amount of food eaten by the mice on the diets.

Yes, the study is on rodents. Will it give the same results in homo sapiens? While the statistics are interesting, something says it will not be the same in humans.

In the U.S. the consumption of soybean oil has increased greatly in the last four decades due to a number of factors, including results from studies in the 1960s that found a positive correlation between saturated fatty acids and the risk of cardiovascular disease. As a result of these studies, nutritional guidelines were created that encouraged people to reduce their intake of saturated fats, commonly found in meat and dairy products, and increase their intake of polyunsaturated fatty acids found in plant oils, such as soybean oil.

Implementation of those new guidelines, as well as an increase in the cultivation of soybeans in the United States, has led to a remarkable increase in the consumption of soybean oil, which is found in processed foods, margarines, salad dressings and snack foods. Soybean oil now accounts for 60 percent of edible oil consumed in the United States. That increase in soybean oil consumption mirrors the rise in obesity rates in the United States in recent decades.

During the same time, fructose consumption in the United States significantly increased, from about 37 grams per day in 1977 to about 49 grams per day in 2004.

The study also includes extensive analysis of changes in gene expression and metabolite levels in the livers of mice fed these diets. The most interesting results were those showing that soybean oil significantly affects the expression of many genes that metabolize drugs and other foreign compounds that enter the body. This suggests that a soybean oil-enriched diet could affect one's response to drugs and environmental toxicants, if humans show the same response as mice.

The UC Riverside researchers also did a study with corn oil, which induced more obesity than coconut oil but not quite as much as soybean oil. They are currently doing tests with lard and olive oil. They have not tested canola oil or palm oil.