Germ-free mice show how eating common oils affects our microbiomes

New research adds to our knowledge about how the oils we eat affect our bodies

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Fat, oil, and lard. The purported nutritional value of each has changed over the past decade, and while health experts now assert that not all fat is bad for you, it can be challenging for the everyday person to figure out which one to eat. 

Oil from soybeans is the most widely consumed oil in America. However, its effects on the gut microbiome are poorly understood. Studying this oil and how it interacts with gut bacteria can help us to understand the its impacts on our health. 

A study published recently in the Journal of Nutritional Biochemistry looked at how soybean oil interacts with mouse microbiomes, as a model for how it affects human microbiomes. Soybean oil is rich in health-promoting omega-6 fatty acids, which are broken down into smaller molecules called sphingolipids and ceramides. In healthy mice, increased levels of ceramides found in the liver have been shown to result in insulin resistance while those found in the blood are associated with cardiovascular disease. 

To model human diets, standard lab mice and mice devoid of all microorganisms (germ-free mice) were fed either low fat diets or diets supplemented with soybean oil for 10 weeks. The researchers measured fatty acid and sphingolipid levels in their blood and livers, and analyzed microbial DNA from their feces to determine the amount of gut bacteria present. 

One group of germ-free mice was found to be contaminated with bacteria at low levels due to difficulties in sterilizing the diet. This group led the researchers to find that large amounts of gut bacteria present may increase the amount of ceramides in the liver regardless of how little or excess fat is consumed. High soybean oil levels made the mice gain fat, but those with colonized microbiomes were able to accumulate more fat than the germ-free mice. Therefore, they concluded that sphingolipids in the liver are more affected by our gut microbiomes than the amount of fat in our diets.

This study suggests that soybean oil consumption in Western diets should be moderated with future interest in finding alternative sources of omega-6 fatty acids.