I recently attended a conference where I heard a researcher talk about a fascinating study he had conducted. In a nutshell over 50 adults were fed a liquid beverage (imagine Kool-Aid) or a solid snack (like a gelatin cube), but before it was consumed they were given one of four expectations:

One group given the liquid was told it would remain a liquid once it was swallowed.

Another group, given the liquid, was told it would turn into a solid after it was swallowed.

One group given a solid was told it would remain solid after swallowing.

Another group given a solid was told it would turn into a liquid after it was swallowed.

In reality both the liquid and solids remained or turned in liquids in the stomach, so all of the subjects ended up with a tummy full of liquid. As you might expect, those who were told that the liquid or solid would remain solid after it was swallowed reported feeling more full. But here’s what’s really interesting: it wasn’t just in their heads. The perception of having a liquid in their stomachs rather than a solid actually triggered physiological changes. The ‘perceived liquid’ subjects’ stomachs emptied more quickly than those who thought they had a solid, and they experienced a different hormonal response. The hormone responsible for upping appetite, for example, was not suppressed as effectively compared to those who thought they had a solid in their stomachs. And the ‘perceived liquid’ group ate more later in the day—about 400 calories more than the ‘perceived’ solid group.

The researchers conclude that the sensory and cognitive qualities of a food or meal are powerful and impact how the body physically responds. In other words, if you don’t think something is going to fill you up, you may physically feel hungrier and, if you do think something is going to fill you up, you may physically feel more full.

So how do you use this information to your advantage? If you’re watching your weight choose foods and meals that you perceive to be more filing. Volume may be a factor. For example, three cups of popped popcorn and one slice of whole grain bread both count as a serving of whole grain, but your perception may be that you’ll feel fuller after eating the popcorn. Finely chopping or shredding veggies may also help, or choosing foods that take longer to eat, like soup. Or foods that you perceive to be particularly filling and satisfying, like nut butter. Bottom line: perception is persuasive. If before, during, or after a meal your brain senses that the meal will or won’t fill you up, your body actually may respond in kind.

What are your thoughts on this intriguing study? Please share your thoughts or tweet them to @cynthiasass and @Shape_Magazine.

Cynthia Sass is a registered dietitian with master's degrees in both nutrition science and public health. Frequently seen on national TV, she's a SHAPE contributing editor and nutrition consultant to the New York Rangers and Tampa Bay Rays. Her latest New York Times best seller is S.A.S.S. Yourself Slim: Conquer Cravings, Drop Pounds and Lose Inches.

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