Dr. Charles Zuker

But as far as the sweet receptor is concerned, they both activate the same receptor, trigger the same signal.

And if you give an animal an option of a bottle containing sugar or a sweetener versus water, this animal will drink 10 to one from the bottle containing sweet.

That's the taste system.

Animal Go samples each one, licks a couple of licks, and then says, uh-uh, that's the one I want because it's appetitive and because I love it.

Now we're gonna take the mice and we're gonna genetically engineer it.

to remove the sweet receptors.

So these mice no longer have in their oral cavity any sensors that can detect sweetness, be it a sugar molecule, be it an artificial sweetener, be it anything else that tastes sweet.

And if you give these mice an option between sweet versus water, it will drink equally well from both because it cannot tell them apart, because it doesn't have the receptors for sweet, so that sweet bottle tastes just like water.

But if I keep the mouse in that case,

For the next 48 hours, something extraordinary happens when I come 48 hours later, the mouse is drinking almost exclusively from the sugar bottle.

During those 48 hours, the mouse learn that there is something in that bottle that makes me feel good.

And that is the bottle I want to consume.

And that is the fundamental basis

of our unquenchable desire and our craving for sugar and is mediated by the gut-brain axis.

So we reason if this is true and it's the gut-brain axis that's driving sugar preference, then there should be a group of neurons in the brain that are responding to post-ingestive sugar.

And lo and behold, we identify a group of neurons in the brain that does this, and these neurons receive their input directly from the gut-brain axis.

And so what's happening is that sugar is recognized normally by the tongue, activates an appetitive response.

Now you ingest it, and now it activates a selective group of cells in your intestines.

that now sends a signal to the brain via the vagal ganglia that says, I got what I need.

The tongue doesn't know that you got what you need.