Fullness has several influences
Food amount, energy content, protein, texture, eating rate and individual circumstances can all influence appetite. Fibre is one part of that picture. Two foods with the same fibre amount can have different structures and eating characteristics.
A thick drink can feel different from a thin one, but that observation alone does not establish how long someone will feel full or how much they will eat later.
Why viscosity is studied
Some fibres swell or form gels in water, changing the texture of the food that contains them. Researchers have studied whether these properties affect subjective appetite, later food intake or body weight.
A systematic review of randomised trials found that effects varied between fibre types and outcomes. Appetite ratings, energy intake and body-weight change are different measures. A finding for one should not be presented as proof of all three.
Set a useful formulation target
For a shake or soup, define the intended texture at mixing, serving and the end of the expected consumption period. Measure viscosity under those conditions and include sensory checks for grit, gumminess and mouth coating.
Protein, minerals, acids and temperature can affect the result. Evaluate the complete formula instead of treating a water-only fibre test as a finished-product result.
Match the claim to the evidence
A product described as thick or creamy makes a different statement from one said to reduce hunger or cause weight loss. Any appetite claim needs relevant evidence, an appropriate serving and a review of the final wording.
For everyday meals, choose foods and portions that suit your nutritional needs. Fibre-containing foods can contribute useful variety, but discomfort or excessive thickness should not be treated as evidence that a product is working.