Dietary Fats and Circadian Rhythms: Which Fats Disrupt Metabolic Timing?

This is my second article on food and the circadian system. The science of circadian rhythms is complicated. But, like diet and exercise, it’s worth investing some mental effort to understand the fundamental aspects of it because not only is it crucial to health and wellbeing, it is something you can take action on! In this article I’m going to focus on dietary fats and circadian rhythms, but let’s first briefly review what circadian rhythms are.

The circadian system helps our bodies coordinate physiology and behavior across the 24-hour period each day. The system is controlled by “clock genes” and the proteins they produce. A master clock in the brain is controlled mostly by light exposure through the eye. Each of our cells, however, has its own clocks. The master timekeeper synchronizes the clocks in the rest of our cells, and together they function as one coordinated system.

We can adjust our bodies’ clocks without causing health problems (as during slow changing of the seasons). Issues begin, however, when our timing systems become uncoordinated (misaligned). This can happen in several ways. The best understood way is due to high variability in when you are exposed to light from one day to the next. The resulting circadian system misalignment causes the equivalent of jet lag. But this is not the only way to misalign our rhythms – food choices and timing matters too.

In my previous article entitled When Is the Best Time to Eat, we discussed research on how enzymes that determine the rate of energy generation from glucose and fats wax and waned across the day. In normal mice, production of sugar burning enzymes – and rate of sugar metabolism – peaked when the animals sleep, whereas the production of fat burning enzymes – and rate of fat metabolism – peaked at a time when the mice are awake and physically active. In mice with deleted circadian genes, however, the amounts of these enzyme levels, and the rate of utilization of sugars and fats did not change over the day. This info suggests that a cells preference for different fuel types modifies over the day, which depends on the activity of clock proteins.

That study helps us better understand the mechanisms behind something that has already been recognized in previous research: erratic eating patterns – including eating very late in your day – appear to disturb the circadian system, which then disrupts metabolism. Here, we will look at a new study that shows how fat type and timing of intake can affect the timing system in our body.

To maintain a healthy metabolism, our body must precisely regulate levels of circulating energy substances – like fats and sugars. It must also regulate inflammatory signals from our immune system because they too affect metabolism. Eating certain types of saturated fat can cause low-grade inflammation, and being in this chronically inflamed state over time has associated with obesity, diabetes, and cardiovascular disease. So how do particular types of fats mess up our metabolism, and which types don’t?

Previously, work by this research group showed that a high-fat diet in mice slowed the clock timing for immune cells called macrophages, which mediate inflammation. That study also demonstrated that compromising the accuracy of our body clocks is key in how a high-fat diet (in mice) triggers and exaggerates inflammation in fat tissue, and promotes insulin resistance. Interesting, but do all fats cause this? This is a critical question, and as I stated in my article on what dietary fat is fattening, we can not judge all fats as one monolithic substance. Fats are a chemical class, and different fats do different things to the body. On top of that, there is variability to how individuals respond to different fat types. Some people, for example, will tolerate long-chain saturated fats better than others due to their genotype.

In their new study, different fats were administered to collagen-producing cells (fibroblasts) at various points across 24 hours. Then, the researchers observed the inflammatory effect that occurred in response to each fat and at each time point, and finally, how the different inflammatory responses coincided with clock functioning.

Here is what they found and what it could mean for you. First, the saturated fatty acid palmitate produces inflammatory signals, and that effect was maximal at what would be equivalent to you eating that fat around dinner. But again, this is in culture so it’s hard to know how this translate to humans until tested directly. Next, it is these inflammatory signals, stimulated by palmitate, that shift the timing of the clocks in the collagen-producing cells. The more clock timing shifted, the more exaggerated the inflammatory response was to palmitate. This suggests that the consumption of food sources containing palmitate – like beef, dairy, and eggs – is better handled by the body during breakfast and lunch and that avoiding this type of fat during dinner, or during snacks consumed close to bedtime, might be a wise choice.

Of key importance to this research is not only the idea that different fat types have different effects on our cell clocks but also that not all tissues respond in kind. In fact, Julie Pendergast at the University of Kentucky and colleagues showed that seven days of a high-fat diet advance cellular clock timing in the liver, but simultaneously delay clock timing in the spleen. So, eating the wrong type of fat at night is similar, physiologically, to effects from exposing yourself to wild fluctuations in the timing of light exposure day to day, which is another lifestyle pattern that causes clock misalignment, metabolic imbalance, and ultimately, disease. The findings from Kim discussed above lend further support to growing and consistent body of work.

The coordination of body rhythms is fundamental to long-term health. Obviously, more clinical work is needed on this specific subject, but so far, most of the research – from cell culture all the way to real-world human physiology – seems to align nicely. If you’re already managing your light exposure day, evening, and night, then managing the timing of different types of dietary fat ingestion may just be another way to optimize the system.