Gut study uncovers a surprising role for immune cells in nutrient absorption

The dawning of a new year is — for many of us — the supposed dawn of a new you. New year, new you, new New Year’s resolution to be healthy. You renew your gym membership and you start a diet. Just as well that the human small intestine can handle almost anything we throw at it. It’s one of many body parts evolved to process food. Though how it came to do so is not so well-known.

Inverse is counting down the ten most-surprising discoveries about your wondrous gut in 2021. This is #7. Read the original story here.

In a study was published earlier this year in the journal Science, scientists uncovered a direct role for immune cells in controlling nutrient absorption in the small intestine.

The discovery — Zuri Sullivan, a post-doctoral fellow in Harvard’s Department of Molecular and Cellular Biology and first author of the study, worked with her research team and found that a certain kind of T-cell, a kind of immune cell, is involved in absorbing nutrients as food makes its way through the intestines.

The researchers fed two groups of mice either a high-carbohydrate diet or a high-protein diet. They then used genetic sequencing tools to observe any changes in gene expression in the mice’s gut immune cells and how well they absorbed nutrients from their food.

They show how the expression of cytokine IL-22 in the intestines prevents nutrient absorption. In turn, intestinal lymphocytes, the T-cells, seemingly regulate IL-22 expression. Specifically, the T-cells suppress IL-22 cytokine production when nutrients pass through the small intestine.

Here’s the background — The small intestine wears many hats. Its primary role is to break down and absorb nutrients from food. The small intestine also protects the gut from foreign and potentially harmful microorganisms.

Several immune cells can influence gut health. For example, interleukin-22 (IL-22), another immune cell, promotes inflammation in response to infection. Recent research also suggests IL-22 can boost the proliferation of salmonella, a harmful gut microbe, and increase the risk of food poisoning.

Another is a white blood cell known as gamma delta T-cells. These cells, the T-cell in the study, help monitor the gut-body barrier and act as the first line of defense against viruses and foreign bacteria infiltrating the body’s cells via the gut.

Why it matters — This study could help explain how the small intestines efficiently take in the great variety of food we eat without causing us to fall sick.

We’ve come a long way from our species’ early days when the menu options were limited to mammoth, other dried meat, and perhaps some berries. However, be warned: If you abruptly switch up your diet, you may have to factor in some time to adjust your digestive system accordingly.

“If you’re a vegetarian, and you don’t eat meat for a year, let’s say, and then all of a sudden, you decide, ‘oh, you know, screw it, I’m gonna have a cheeseburger,’ you’ll have some serious digestive discomfort,” Sullivan previously told Inverse.

“And the reason we think that occurs is because the gut is adapting to what it’s being fed,” she adds.

While more research is needed, Sullivan says the results provide more insight into how malnutrition can occur. She says malnourished children tend to have frequent bacterial infections, and the results suggest this may have something to do with how immunity and nutrition function together in the intestines.