That’s a great question, and the straight forward answer is I’ve really been blown away by the enormity of their impact, both in terms of the diverse number of processes that are influenced as well as the magnitude of the effects. I love chronobiology, I love time of day, and I love nutrition too, but I’m gonna focus here a little bit on the chronobiology. My lab is really interested in circadian clocks, which coordinate biological processes in a temporal manner. I like to think of these clocks a little bit like the conductor of an orchestra. Each musician in the orchestra are professionals, they know how to play their instrument and they’re going to do a great job. However, in order to make beautiful music, the conductor needs to ensure that each musician within the orchestra plays at the right time. If not, and subsequently if you didn’t have this type of temporal control, this orchestration would simply lead to chaotic noise and you wouldn’t make beautiful music. Well, the same is true at a biological level. What these circadian clocks do is they orchestrate cellular processes in a temporal fashion. They make sure that these processes are only active at specific times of the day which really has several noteworthy implications.
“For example, if circadian clocks become dysfunctional, you lose temporal control and that invariably leads to disease. Shift workers are a great example. They disrupt their circadian clocks through behaviors and they have increased risk of obesity, diabetes, cardiovascular disease, and even cancer.”
Secondly, because these clocks exist and you have this temporal control of pathways, it means your body responds to the environment depending on the time of the day at which it’s stimulated. A great example is that second thing that you were talking about – nutrition. So because metabolic pathways change throughout the day, the time at which you consume nutrients impacts whether your body is going to take those nutrients and burn them as a fuel, or is instead going to store them as some kind of fuel, which could lead to weight gain. It could even take the carbon from nutrients and convert it into some kind of signaling molecules leading to accumulation and cellular dysfunction, all of which is going to be time of day dependent.
Here’s a great example that we recently reported on and, to this day, it still shocks me. There are a family of amino acids known as the branched-chain amino acids that are abundant in protein rich foods such as red meat. It’s well known that an elevation of branched-chain amino acids in our blood circulation is associated with many of the diseases we study, like obesity and diabetes and cardiovascular disease. Several years ago we asked a very simple question: if we were to eat branched-chain amino acids at specific times of the day, would the heart respond differently to that nutrient? So we did this in mice; we fed them either branched-chain amino acids for breakfast or for dinner. We found that when we fed branched-chain amino acids to the mice at breakfast, we weren’t able to see a big impact on the heart. However, when we fed branched-chain amino acids to mice at dinner time, within four hours, the heart cells increased in size by 70%, a huge number. It really to this day just blows my mind and it really shows the impact the time of day can have on our response to nutrients.