The effect of meal composition on the degree of satiation following a test meal and possible mechanisms involved.

1. Possible links between metabolism and satiation were investigated using volunteer subjects given test meals based on milk solids. Satisfaction was rated by the subjects on a six-point scale and the course of metabolism was followed by measurement of the respiratory quotient (RQ). 2. The time-course of satiation was the same for a high-carbohydrate, a high-fat and a high-protein meal, in spite of the very different time-course of metabolism. The degree of satiation was reduced by added sodium chloride, without affecting the RQ rise. On the other hand, calcium chloride produced a suppression of the RQ rise without altering the satiation. 3. It is proposed that the results indicate that the primary receptors responsible for post-prandial satiation lie within the gut wall and that there is probably a number of receptor types. Likely candidates for these receptors are the gut hormone-secreting cells. 4. Although very-low-protein meals produce less satiation than meals containing 220 g protein/kg dry weight, there is no additional satiation obtained by increasing the protein level further. This is not inconsistent with the possibility of a protein hunger separate from an energy hunger.