Diet and Your Immune System

Last week, we began our two-month exploration of the immune system. We looked at the damaging effects of stress and how to protect yourself from them. This week, we will look at how an unhealthy diet can undermine your immune system.

A comprehensive 2019 review in the journal Nutrients described diet’s relationship to immunity. Food shortages and famines in developing countries have taught us that malnutrition impairs immunity. Bad nutrition can undermine immune cells, which undermines the immune system. Even more important, it reduces immunity by changing the composition of gut bacteria.

Diet and Your Immune System

You won’t find any scientists who would state it this simply, but if bad nutrition weakens immunity, then good nutrition strengthens it.

You probably already know what good nutrition looks like. And it doesn’t include a lot of doughnuts, potato chips, pizza, soft drinks, or ice cream. It looks a lot like the illustration that accompanies this post. The image shows fresh fruits and vegetables, nuts and seeds, beans, whole grains, and sources of healthy fat. You see, when you eat, you’re not just feeding yourself. You’re feeding the community of bacteria and other microorganisms that live in your digestive tract. It is a complex and sizable community, and researchers have begun to study it through the lens of biodiversity. You are an ecosystem, in other words. The health of that ecosystem, just like the health of any ecosystem, depends on the balance of species in it. Endanger a species, and you can endanger the system itself.

Research on gut bacteria is still in its infancy. But one of the first things researchers have discovered is that they play an important role in controlling your body’s immune responses. They help your immune cells stay active, but they also help to discourage them from becoming hyperactive, which leads to autoimmune disorders. Researchers are now cataloging species in the human digestive tract and trying to understand their role in immunity. It’s a moving target. The makeup of your gut bacteria depends a lot on what you feed them, so your bacteria are likely to be as individual your diet.

Dietary Variety Promotes Biodiversity

But one thing is emerging as very clear: the healthiest diet has a great deal of variety. Broad selections of fruits, vegetables, nuts, seeds, and legumes, together with healthy fats such as olive oil and artisan cheeses, tend to promote the greatest diversity in your gut’s community. And that diversity helps to protect you from all kinds of infections and diseases by activating and regulating your immune system.

There’s a lot of nutritional advice on the web, including a great deal of pseudoscience, flim flam, and hocus pocus. Your best bet is to go with genuine scientific research, and fortunately, there is some of that, too. A paper published in 2020 detailed a one-year experiment among 612 elderly patients. The researchers wanted to know if they could change the gut bacteria of the patients by putting them on the well-known Mediterranean Diet.

Changing the Gut Bacteria

Not only did they manage to change the composition of the patients’ gut bacteria, but the change affected the health of the patients. They found bacteria enriched by the diet “were positively associated with several markers of lower frailty and improved cognitive function, and negatively associated with inflammatory markers including C-reactive protein and interleukin-17.”

The researchers focused on elderly patients, because they knew that gut biodiversity tends to decline as you age. This can even explain why immune response weakens in the elderly, which is why people over 65 are at higher risk for Covid-19.

A Mediterranean Diet, then, is a recognized path to diverse gut bacteria, which are an essential component of a healthy immune system. For details on this diet, check out Healthline, which offers an article titled “Mediterranean Diet 101: A Meal Plan and Beginner’s Guide.”