The High Fat Conundrum 

Healthy Aging

Bully fats can block C15:0

Last week, we shared exciting science that linked C15:0 to slower biological aging. This week, let’s talk about a strange conundrum – fats blocking fats. Specifically, studies showing that high fat diets can actually lower your C15:0 levels.

It’s a tough world for C15:0.

C15:0 is an essential odd-chain saturated fatty acid, and our primary dietary source of C15:0 is milkfat. So, it would seem to make sense that the more fat we have in our diet, the higher our C15:0 levels. Surprisingly, the opposite is true. At least for mice.

In a study by Jenkins et al., mice were given diets consisting of either 5%, 35%, or 70% fat. All diets had the same total volume. They showed that the higher the fat-calorie content in a mouse’s diet, the lower their C15:0 levels. In fact, a 30% increase in total dietary fat caused a 35% decrease in circulating C15:0 levels. Interestingly, this was not true for C15:0’s odd-chain sister, C17:0.

What type of fat lowered C15:0 levels?

Jenkins et al. increased the dietary fat content of mice using two sources: lard and fish oil. As an extra surprising finding, both lard and fish oil lowered circulating C15:0 levels. Worse yet, both C15:0 and C17:0 levels significantly decreased on the higher fish oil diet.

Yikes. What’s going on?

The researchers from Cambridge University suggest that this high fat conundrum could simply be due to competition. Think about C15:0 going into a subway station – if there are not many other fats around, C15:0 can easily hop onto our cellular gut subway and into our bodies. If the subway station is super packed with lots of other competing fats, however, little C15:0 may not make it onto the subway to be absorbed.

In contrast, C17:0 is more protected against this phenomenon because our bodies can make C17:0. Alas, our C15:0 levels are primarily driven by the C15:0 we eat.

This phenomenon included liver and gut health, too.

Another team from the UK dove further into this high fat conundrum. Ampong et al. showed that feeding mice high fat diets resulted in lower C15:0 not only in the blood, but in the liver, too. These decreases were big, with > 50% less C15:0 in the blood and liver of high fat diet mice compared to those given a baseline diet.

This team also showed that a high fat diet impaired liver metabolism and decreased good gut bacteria that produce odd-chain saturated fatty acids (specifically C3:0).