Researchers from Wageningen University in the Netherlands asked 15 men to drink a series of four milkshakes. The only differences were their calorie contents—either 100 or 500 calories—and their viscosity—thin or thick.

After the men drank the shakes, they got MRI scans of their stomachs, which allowed researchers to determine the volume of the liquid there. For an hour and a half after ingestion, participants were asked every 10 minutes how full they felt.

Not surprisingly, the 100-calorie shakes were the fastest to leave the stomach. Adding fiber to the smoothie didn’t make it stay there longer, they found. But the shake’s viscosity—not the number of calories it had—was what made the men report feeling full. In fact, people who drank the thick 100-calorie shake felt even fuller than people who drank the thin 500-calorie shake.

The study authors dubbed this effect “phantom fullness”: being more satiated because of a food’s thickness, not its energy density.

It’s bad news for anyone who hopes the calories in a sugary soda or juice will tide over their hunger pangs; without that satisfying thickness, you’re likely to leave hungry.  These results are useful for those of us that prefer our drinks thick whether they’re milkshakes, smoothies or—we hope—an IQed Pineapple Whip, or an IQed Watermelon Smoothie!

Even though the study was small and there is nothing conclusive, use this information as a guide..  If looking to lose weight, perhaps try to incorporate thicker drinks in your diet and see if that helps.  On the other hand if you have a child that is a picky eater,  try to serve drinks that aren't too thick and see if that helps to keep their appetite up.

Study results found less calories in combination with a high dietary fibre content result in more satiation than high-calorie foods with less dietary fibres. However, the first combination results in an empty stomach. A study conducted by Wageningen University has shown that the effect of dietary fibres on satiation is not only caused by the length of time the high-fibre food remains in the stomach. The speed of eating, taste and mouthfeel can also effect the feeling of fullness. The results of the study have been published in the American Journal of Clinical Nutrition.

• AJCN Empty calories and phantom fullness: a randomized trial studying the relative effects of energy density and viscosity on gastric emptying determined by MRI and satiety http://ajcn.nutrition.org/content/early/2016/06/01/ajcn.115.129064.abstract
• Phantom Fullness:  Feeling Full On An Empty Stomach Press Release https://www.wageningenur.nl/en/newsarticle/Phantom-fullness-Feeling-full-on-an-empty-stomach-.htm