Body is not just mouthfeel
Viscosity is one reason two products with similar calories can feel different. A thin sweet drink may leave the stomach quickly and give very little sensory resistance. A thicker fibre-containing shake may create more body, slower movement, and a stronger sense of substance.
That does not make thickness automatically better. Too much viscosity can be unpleasant, hard to drink, or unsuitable for the format. The goal is controlled body, not accidental sludge. For satiety-oriented nutrition, fibre selection has to consider hydration rate, final viscosity, mouthfeel, grit, flavour release, and how the product changes over time after mixing. The useful range is narrow.