Filling the stomach with liquid food does not cause us to eat less, while chewing can have an inhibitive effect. Wageningen researchers are the first to study how these two influences can together affect the feeling of being 'full'.
Curiously enough, the test persons who had a lot of cake solution in their stomachs ate as much lunch as those who had a little of the solution. This result differs from those of earlier studies in which filling the stomach did result in a clear difference. 'We suspect that the liquid food in this study passed through the stomach too quickly and did not have any noticeable effect,' says Anne Wijlens, PhD student at Human Nutrition. 'A supply of concentrated solid food would be more realistic. After all, we normally eat a mix of foodstuffs, such as vegetables, potatoes and meat.'
On the other hand, chewing can have a big effect on the appetite, according to Wijlens' data. Just one minute of chewing reduced the appetite by 10 percent. This went down even more to almost 20 percent after eight minutes. Signals from the mouth therefore have a big influence on the feeling of hunger. 'This fits in more with the notion that our taste system is in fact a nutrient sensor,' says Wijlens.
Wijlens finds it difficult to judge how general these results are, especially since the stomach had hardly any influence in this set-up. She therefore has many ideas on further research. 'For example, we want to examine the speed at which the stomach is emptied.' This can be done by 'marking' food with so-called stable isotopes. These are heavier variants of normal elements such as carbon and hydrogen. Upon leaving the stomach, these spread out throughout the body and can be detected in the breath.
The research was carried out jointly with food giant Nestlé, which also provided the funds. Their researchers helped to formulate the key question and also supervised the research work and publication. There was no contact with the commercial departments, says Wijlens. The research is therefore purely fundamental in nature, according to her. The results are published in the journal Obesity.