Saw this on r/science, their deffinition of western diet - western breakfast - "On Days 1 and 8, these participants received a laboratory breakfast of a toasted sandwich and a milk shake, high in saturated fat and added sugar"

While the control group: "Control group On Days 1 and 8, these participants received a laboratory breakfast consisting of a toasted sandwich and a milk shake, low in saturated fat and added sugar"

Their definition of "western diet" is flimsy to say the least. I'd throw this in to the bucket of junk science.

It's been know for years, as in the thnks giving myth about turkey, as mentioned in this video for instance: https://www.youtube.com/watch?v=dzvsk_N3FBM and there are others, that digestion is the main culprit of grogginess at thnks giving. In their experiment they:

They were then presented with each food again, but this time they were asked to consume it, and rate how much they liked it (scale as above) and how much more of it they would like now (anchors: None, A lot).

Participants then undertook a modified form of matrix reasoning

From the original study: https://royalsocietypublishing.org/doi/10.1098/rsos.191338

So as they were digesting, they took the test. Seems like the group with the highest digestive effort scored lower, not ground breaking science, and does misrepresent the whole "western diet" thing. In sum, junk science.