Into the category of Learn Something Every Day goes the concept of gastric sieving:
Preventing Gastric Sieving by Blending a Solid/Water Meal Enhances Satiation in Healthy Humans, The Journal of Nutrition, July 2012
Separation of solids and liquids within the stomach allows faster gastric emptying of liquids compared with solids, a phenomenon known as sieving. We tested the hypothesis that blending a solid and water meal would abolish sieving, preventing the early rapid decrease in gastric volume and thereby enhancing satiety.
We carried out 2 separate studies. Study 1 was a 2-way, crossover, satiety study of 22 healthy volunteers who consumed roasted chicken and vegetables with a glass of water (1008 kJ) or the same blended to a soup. They completed satiety visual analogue scales at intervals for 3 h.
Study 2 was a 2-way, crossover, mechanistic study of 18 volunteers who consumed the same meals and underwent an MRI to assess gastric emptying, gallbladder contraction, and small bowel water content (SBWC) at intervals for 3 h.
In Study 1, the soup meal was associated with reduced hunger (P = 0.02).
In Study 2, the volume of the gastric contents after the soup meal decreased more slowly than after the solid/liquid meal (P = 0.0003). The soup meal caused greater gallbladder contraction (P < 0.04). SBWC showed a biphasic response with an initial “gastric” phase during which SBWC was greater when the solid/liquid meal was consumed (P < 0.001) and a later “small bowel” phase when SBWC was greater when the soup meal was consumed (P < 0.01).
Blending the solid/liquid meal to a soup delayed gastric emptying and increased the hormonal response to feeding, which may contribute to enhanced postprandial satiety.
So … What can make you feel full for longer?
1. Roasted chicken and vegetables with a glass of water.
2. The same meal, blended into a soup.
I saw this study on James Hamblin’s post, The Trick Smoothies Play on the Stomach. He interviewed Robin Spiller, a lead researcher in the study:
Spiller and his team compared the two options head to head in a study, and they found that when people drank the blended “soup,” it kept them from feeling hungry for about an hour longer than the whole-food meal.
“What we showed is that food separates in layers in the stomach,” said Spiller. Until pretty recently, that was only an assumption. “If, for example, you take a dense material like rice and a glass of water, the rice will sink into the dependent part of the stomach. Then the water will seep out. That means that when you stop ingesting your meal, the size of your stomach will go down much faster than had you mixed the rice and the water up into a homogenous gruel.”
This next part, I didn’t know. I kind of love how the body titrates food into itself:
The rate of stomach emptying is regulated by feedback from the duodenum, which has receptors that can tell the body about nutrient value of a meal. It uses this to adjust so that, more or less, you deliver one to two calories per minute into the small intestine. This ensures efficient digestion. If you overwhelm the intestine, it can’t cope. But at a regulated rate it can be very efficient at absorbing energy.
There are many variables that affect the speed at which the stomach empties, and so, how long you’ll feel full, including … how much fat is in the meal (fattier is slower), the meal’s temperature (hotter is slower), gastroparesis (a diabetes complication), the body’s position when eating (laying down is slower). To these I guess I’ll be adding viscosity.