Recent evidence indicates up to 20% of the energy from walnuts is not absorbed. This low bio accessibility is comparable to almonds with markedly different physical properties and much higher than for pistachios with similar physical characteristics. These counter-intuitive findings require mechanistic explanations so they may be accepted and used to formulate policy and clinical recommendations. It is proposed that the differences in the structure of nuts accounts for the energy yield results. In addition, the whole nut yields superior effects on fullness and this leads to focus on oral processing. It may be that the mechanical act of chewing generates satiety sensations or it may be that the mechanical disruption of the parenchymal call walls releases lipid and protein and their higher concentrations activate the release of gut peptides associated with satiety.