Leads with a photo of 'not-great industrial-scale bread', and even explicitly calls for 'slice of cheap bread' as an ingredient... it's not doing much to convince me that the described effect is due to starches converting that quickly. I'm fairly confident the packaging for the pictured slice would have listed sugar as an ingredient.
I’ve tested it on homemade bread without sugar and noticed it. It even works when you don’t tell people ahead of time why they’re doing the experiment.
The link was chosen arbitrarily, you can find plenty of other examples if you’re concerned about its authenticity. But, it’s not a very strong flavor so you do want a bland bread.
https://www.thenakedscientists.com/get-naked/experiments/whi...
Cut out enough sugar from your diet as you can start to notice the sweetness without exaggerated mastication.