Macrophages vs. Fat: Part I of the Sustenance Saga
Updated: Jun 22, 2020
This week's Microbial Monday topic was a request from my Mum. She wrote, "Hey, I have a question about lifestyle & immunity. How does your diet (sugar, refined carbs, meat, alcohol intake) and exercise or lack of exercise affect immunity?"
My first response was more or less, "It's really complicated, let me get back to you." I started to read into the topic, and it is indeed incredibly complex. This question crosses the fields of exercise science, metabolism, oncology, immunology, virology… A true abundance of "ologies". Because of the wealth of information on the topic, I'm splitting this answer into multiple parts on Microbial Mondays to give it the attention it deserves. This week, I'm focusing on some of the influences of the Western diet on immunity.
Much of the research on diet and immunity comes from the fact that what has become known as a "Western diet" doesn’t seem to be so great for our immune system - or our other bodily systems for that matter. Western diets are high in refined sugars, processed meats and grains (like salami and white flour), fats (and especially trans fats), and food additives. You would think with all the food we eat in richer societies today, we would get enough nutrients, but actually Western diets are typically lacking in fibre, and various vitamins, minerals, and antioxidants. To make things worse, Western lifestyles also often include relatively higher exposure to toxins via things like pollution, preservatives, and smoking, and excessive or prolonged stress because of the non-stop way we work and live these days.
But how does all this translate into an effect on our immune system?
You may not know this, but I am also a yoga teacher on the side. For years, I've been hearing people in the yoga community talk about how we need to reduce inflammation in our bodies to promote health. As I often do, I thought, 'yeah, yeah, just some more hippie talk. But it turns out, the hippies are kind of right on this one. Scientists have actually described molecular pathways connecting our fatty diets and our in-the-fast-lane lifestyles with inflammation, and the resultant inflammation with negative and prolonged effects on the immune system.
What a lot of it seems to come down to is one neat type of cell called macrophages. Macrophages are so-called 'innate immune cells', meaning that they aren't traditionally considered to have a long-term memory for the microbes and other microscopic problems that they hunt. Their name gives you a clue as to what their job is: "macro" and "phage": big eaters. Basically, when macrophages see a problem, they eat it. They're basically the emotional eaters of the immune system.
When people eat healthy, plant-rich, low-animal fat diets, macrophages aren't the only ones eating. When you eat, you are ultimately feeding each of the cells in your body. The food goes into your digestive system, is broken down into tiny pieces, and then enters your bloodstream. Your bloodstream is basically the 'ThuisBezorgd' or 'Uber Eats' bike bringing food to your cells, which will eat up the sugars and fats that you provide them.
In this ideal situation of eating a healthy diet, you and your cells both know when to stop eating, and stop taking in fat upon feeling full. However, eating too much fatty food messes up this system. Fat accumulates, and eventually cells don't know what do to with it. Eventually, cells will not be able to take up all of the fat in your system, and that Uber Eats bike, i.e. your bloodstream, gets bogged down with the fat it can not deliver. The result of this is so-called atherosclerotic plaques. Atherosclerotic plaque is just a fancy name for fat that's stuck to the walls of blood vessels, blocking the smooth flow of blood around your body.
When plaques start to form, macrophages see it for what it is: a big problem. If atherosclerotic plaques are not cleared up, they can cause heart attacks. So, macrophages get to work clearing up all of that excessive fat stuck to the blood vessels. However, the fat that accumulates in atherosclerotic plaques isn't smooth like butter on a molecular level. In our bodies, fat is normally stored within cells, in dedicated fatty organs. If it ends up being stored erroneously on the walls of our blood vessels, it can crystallize. And it's this sharp, crystallized fat that can lead to macrophages really sending out major danger signals. To make things worse, being exposed to environmental stressors such as toxins from air pollution, or stress from our busy lifestyles, can actually chemically change the fat in our bloodstreams to make it more likely to crystallize and freak out our macrophages, thereby putting the rest of our immune system on high alert.
You see, part of the role of macrophages is to be sentries of the immune system. They do indeed gobble up any potential problems they see, but they don't stop there. Macrophages then send out the alarm to the rest of the immune system if they come across something potentially dangerous. And this crystallized fat? That seems dangerous to these macrophages. They don't know that it's because you've stuffed yourself with butter or steak. They don't know it was a choice. They just know something is seriously wrong in your blood vessels, and so the macrophages send out the alarm - by instigating inflammation.
Of course, what I've just described would be on the small scale. But now imagine that you have been eating a fatty diet your whole life. This can put your body in a state of chronic inflammation. In other words, your immune system will constantly be on alert. This might sound like a good thing - your immune system is awake! But actually, constant, chronic inflammation is a risk factor for many of the chronic diseases that we see wrecking more and more havoc in Westernized countries, like type 2 diabetes, cardiovascular disease, neurodegenerative diseases, and cancers. Your immune system works best when it is focused on one foe that it can defeat. By eating a fatty Western diet, you might end up in a constant fight with your immune system. The fat becomes an unbeatable, unending, foe.
Of course, there is a lot more to this epic story of the Western diet and lifestyle, and its effects on the immune system - which is why I'll be elaborating in more upcoming Microbial Mondays posts! Stay tuned for more in this series that I'm calling, the "Sustenance Saga".
I hope you've enjoyed Part 1. Until next week - eat your greens!
This article was my main source of information in writing this blog post:
Christ A, Lauterbach M, Latz E. Western Diet and the Immune System: An Inflammatory Connection.Immunity. 2019;51(5):794-811. doi:10.1016/j.immuni.2019.09.020