Yep! Lustig has a book, Metabolical, that goes into kind of a simple explanation of the underlying mechanism here, and it's roughly like this: fiber-rich foods contain a combination of soluble and insoluble fiber, the insoluble fiber basically forms a sort of "net" of chunks and strings and such that you can't digest, and the soluble fiber forms a "gel" which gets stuck in the net and traps other foods. This gel is infused with various enzymes to break down foods in the duodenum, and then passes to the first and second half of the "zig-zag" parts of the small intestine -- the jejunum and the ileum.
The combination of fibers then leads to a given packet of calories traveling further down the jejunum as it gets absorbed, which makes more of the bacteria living along the length of the intestine happy with you, as well as protecting from blood glucose spikes that come with concomitant "crashes".
I am not saying that is wrong, but there are many mysterious claims in that book. I especially found the claim that "the most expensive burden to society is sugar" by a large margin was pretty astonishing. It lacks wide support in literature. As do many other claims in the book. Like refined carbohydrates being the main cause of weight gain through a rise in insulin. That is - at best - generally disputed, but is touted as fact.
I mean, what he prescribed is fine. Eat "real food". But how he comes to that stance is rather opaque to me. He is obviously literate, but checking some sources in the book very few of them strongly supported the claims he made with that reference.
I also found that first one surprising, even if he gives his back-of-the-envelope calculation (He guesstimates, 75% of healthcare spending is for metabolic-syndrome type chronic diseases, and then he guesstimates that 75% of that is preventable, $3.5T times .75 times .75 gives his figure of $1.9T/year.)
But even if the margin is not quite as wide as the back-of-the-envelope calculates, it's still bigger by a decent margin, right? For instance [1] estimates with more detailed methodology that it's $2.9T over 3 years or ~$1T/year, with at least 44% of that attributable to obesity, so like ~$400B/year, whereas [2] talks about $240B/year cigarettes, $250B/year alcohol.
Of course Lustig would say "TOFI people exist, obesity isn't the problem, obesity is just another symptom of metabolic syndrome, so 44% is an underestimate for the costs of bad nutrition." Not sure I agree there but he'd defend higher numbers even if we agreed to use these sources as kicking off points.
And yeah I agree that the question of "what do we do about it" is something that he appears to have a very opinionated take on, but I'd like to see more hard data. Like I'm happy for him that he had a big study that showed reversal of metabolic syndrome symptoms just by switching sugary food out for starchy food while holding weight and calorie consumption constant, but how we get from there to "eat real food -- the problem is not what's on the nutrition label but all of the antibiotics and adulteration that they don't have to tell you about on that label" stuff seems a bit opaque.
The combination of fibers then leads to a given packet of calories traveling further down the jejunum as it gets absorbed, which makes more of the bacteria living along the length of the intestine happy with you, as well as protecting from blood glucose spikes that come with concomitant "crashes".