The crunchy shells of insects are a nutritional sprinkling that many of us would rather avoid in our meals.
But a new study suggests the nutrients can trigger an innate immune response that improves a mammal's metabolism.
When researchers from Washington University in St. Louis (WUSL) fed mice a diet that included chitin – an abundant polysaccharide present in insect exoskeletons, crustacean shells, and fungi – the animals' stomachs became distended, triggering a specialized immune response.
The ultimate effect was the production of a unique gut enzyme called AMCase, needed for chitin digestion, as well as activation of cells that regulate fat tissues.
Mammals don't usually produce enzymes strong enough to break down bulky polysaccharides that they eat, but chitin seems to be an exception – one with deep evolutionary roots.
Before the demise of the dinosaurs, some evidence suggests that ancient mammals once feasted on insects at much higher rates than they do today. Studies also indicate that some mammals adapted to digesting chitin long ago.
To this day, many mammals still eat insects, even some humans. Not only are insects safe for our species to consume, they can also provide vital nutrients, like protein, and can be harvested sustainably.
As such, some scientists think they should be a bigger part of our diet, although it might take some convincing.
Figuring out which parts of the insect are most nutritious and why could help scientists devise tastier ways to reap the nutritional benefits.
In the current study from WUSL, mice that were fed chitin alongside a high-fat diet ultimately showed improved metabolic readings compared to mice that were fed a high-fat diet without chitin.
Similar to previous studies on mice, the researchers found that eating chitin seems to promote a healthy microbiome in the lower gastrointestinal tract.
To dig further into the mechanisms, researchers impaired the ability of some mice to produce the AMCase enzyme and thereby digest chitin.
The team then fed these mice a high-fat diet alongside chitin. Compared to the other groups, mice without the ability to digest chitin showed resistance to weight gain, even when fed a high-fat diet simultaneously.
The researchers noted an increased level of type 2 innate lymphoid cells (ILC2) in these mice – a byproduct of the gut's immune response triggered by the chitin. These cells were recently found to be involved in the regulation of fat tissues.
"We think chitin digestion mainly relies on the host's own chitinases. The stomach cells change their enzymatic output through a process we refer to as adaptation," explains immunologist Steven Van Dyken.
"But it is surprising that this process is happening without microbial input, because bacteria in the gastrointestinal tract are also sources of chitinases that degrade chitin."
But it's not bacteria that are producing the enzymes to break down chitin in the mouse models. By disrupting a mammal's digestion of dietary chitin, researchers seem to have figured out a possible way to prolong the immune and metabolic benefits of this nutrient in the gut.
"We have several ways to inhibit stomach chitinases," says Van Dyken. "Pairing those approaches with a chitin-containing food might have a very real metabolic benefit."
Van Dyken and colleagues hope to now extend their findings to human participants.
The study was published in Science.