Everyone knows that if you eat a plate of beans or a bowl of bran cereal, you're likely to get full pretty quickly. Now nutrition researchers now have a better idea why.

A study out of the University of California at Davis, published recently in the American Journal of Clinical Nutrition, indicates that increased fiber content in a meal boosts feelings of fullness in women and increases levels of a certain hormone associated with satiety.

Previous research has found that, when fat-containing food is eaten, a hormone is stimulated that tells the brain that the body is getting full.

Now it appears that fiber can trigger the same signaling mechanism as fat.

To test the theory, researchers fed a test group three different breakfast meals. The test meals were either low-fiber, low-fat; high-fiber, low-fat; or low-fiber, high-fat.

Blood samples were drawn before, during and after the meals were eaten, to measure hormone levels. They found that the release of the hormone correlated with the feelings of fullness reported by the participants.

The researchers found that in women, both the high-fat and high-fiber meals resulted in greater feelings of satiety and significantly higher levels of the hormone than did the low-fat, low-fiber meals.

In men, however, the two low-fat meals caused greater feelings of fullness, and there was not a significant difference in the hormonal increase between the various meals.

"These results indicate that the addition of fiber to a meal can increase a person's feeling of being full," said lead researcherBarbara Schneeman, a nutrition professor at the university.