Gut Microbes and Metabolism: Glucose, Hunger, and the Microbiome
By: Gunnar De Winter
Tags: Biology, Health, Neuroscience, Science, Food

Gut Microbes and Metabolism: Glucose, Hunger, and the Microbiome

In mice, gut microbes influence the number of specific neurons that affect glucose control and feeding behavior

(Pixabay, geralt)

The reach of the microbiome

We are all ecosystems. We house numerous creatures on and in our bodies. Among them, veritable communities of micro-organisms. Microbiome is the term that refers to these microbial ecosystems.

The most well-known of these microbial communities we host is the gut microbiome. Our gut microbes have made the news often in the past few years. As we learn more about them, we begin to see how they are implicated in many aspects of our daily lives.

How we metabolize food, our propensity for certain diseases, our risk for Alzheimer’s, even our personality traits, our gut residents seem to have their say in many of the processes underlying these factors. They also affect our risk for cancer, and they might even improve chemotherapy. Their reach can even span generations since the maternal microbiome can affect brain development in their kids. (Gee, thanks, mom…)

Both the number and diversity of gut microbe species seems to be important, with functional diversity apparently being a major factor. That is because many of the effects of gut microbes are mediated through the chemicals they produce (which can be affected by what we eat and how we treat our gut, aka it’s a complex relationship of give and take).

The second brain

Most of us think of the brain when we hear the word ‘neurons’. No surprise there. Our brains are, after all, the most complicated collection of neurons we know.

However, there is another network of neurons in our body that is surprisingly complicated: the enteric nervous system, the mesh of neurons coating our gastrointestinal tract. It is actually called our second brain due to its complexity.

Wait a minute… Gut and neurons. Gut and microbes. What about gut microbes and gut neurons?

Time for science.

(Wikimedia commons, BruceBlausen)

In a new study, the researchers first looked at our second brain in more detail. They found that a group of neurons (CART+ neurons) are disproportionally more present in the ileum and colon, the further parts of our intestines. This is also where most of our gut microbiome houses.

Coincidence?

Nope.

The scientist found that the gut microbiome (in mice) controlled the number of these CART+ neurons through the molecules caspase 11 and NLRP6. They checked this by removing the microbiome.

Antibiotics → less microbes → less caspase 11 and NLRP6 → less CART+ neurons.

Now, what do these CART+ neurons do?

Some tests later:

Gut CART+ neurons are therefore both sufficient and necessary to modulate blood glucose through glucoregulatory organs…changes in feeding behavior are dependent on iEAN-specific neuronal [refers to the CART+ neurons] stimulation.

No CART+ neurons → crappy blood glucose control + more hunger.

The researchers conclude:

Targeting peripheral-restricted circuits, such as the one uncovered here, could bypass undesirable CNS [central nervous system] effects for the treatment of metabolic disorders, such as type 2 diabetes.

So, gut microbes tune the number of neurons in your ‘gut brain’, which affects blood glucose control and feelings of hunger.

But, two important caveats!

Mice are not human. A mouse metabolism is not a human metabolism. Yes, we too have CART+ neurons, and they are involved in appetite control, but that doesn’t mean the above findings map one to one.

This does not alter the laws of thermodynamics. Or, calories in calories out always applies for weight loss. Yes, gut microbes might change the calories in (by making you hungry and eat more, for example), or the calories out (by affecting how much of your food you actually absorb), but to lose weight, calories in has to be less than calories out. Nothing changes that.

Listen to both your brains.