When I cut back on processed food and my numbers get better, what is it that's actually working?

The two sides are not measuring the same thing, and that is the most important thing to know here. Lustig's outcome is metabolic biomarkers in children who already have metabolic syndrome, eating a provided diet, with calories held constant by design. Hall's outcome is how much healthy adults spontaneously choose to eat when food is put in front of them.

Cutting sugar could improve a liver measurement without changing how much anyone eats, and ultra-processed food could drive overeating without sugar being the reason. Both can be true at once, and a user reading only the headlines would think they cannot.

Total, on the action, and it should be shown before anything else. Lustig reviewed Hall's trial in print and concluded 'this study shows that real food works, and processed food doesn't, take it to the bank.' Hall's own conclusion says the recommendation 'could potentially be embraced across a wide variety of healthy dietary approaches'.

Both also agree the mechanism is unresolved: Lustig lists six live candidates in the same review (fiber, energy density, carbohydrate, insulin and leptin, the microbiome, satiety) and says the trial cannot separate them. Neither has any commercial interest in this particular question.