Texture, energy density & learning : implications for food intake

Introduction
Food texture has been shown to be an important factor in the regulation of food (energy) intake. Liquid foods e.g. elicit weaker satiety responses than solid foods with a similar energy content, and texture affects satiation, i.e. ad libitum food intake. Whether theeffect of food texture on food intake stays the same over repeated exposure requires further investigation.           
Aim
The aim of this thesis is to investigate the role of food texture in learned satiation. We assessed the effect of texture on changes in ad libitum intake and expected satiation after repeated consumption of foods with different energy density.          
Methods
We conducted a series of learning experiments with healthy young adults. Participants repeatedly consumed a low-energy-dense (LED) and a high-energy-dense (HED) yogurt, which were either low (n=24) or high (n=22) in viscosity in one study; and consumed with a straw (liquid yogurt, n=34) or with a spoon (liquid yogurt, n=36; semi-solid yogurt, n=35) in a second study.              
Next, we investigated changes in expected satiation and intake after repeated consumption of a LED soup (n=32) or a HED soup (n=32) with similar appearance; and of a liquid and a semi-solid custard with a similar energy density (n=53). Additionally, we assessed the effect of texture, flavour and means of consumption on expected satiation of iso-caloric dairy products in 3 single-meal experiments.             
Finally, we served a fixed amount of a LED or HED food - either liquid or semi-solid - at each meal on 3 consecutive days, and measured ad libitum buffet intake directly after consumption of these foods (n=27).

Results
Texture clearly affected satiation:ad libitum intake was up to 30% higher of liquid foods when compared with semi-solids foods in all experiments (p<0.0001). Participants expected semi-solid foods to be more satiating than iso-caloric liquid foods (p<0.01), irrespective of the product’s flavour or its means of consumption. The texture of a fixed amount of food did not affect subsequent intake of other foods.

Participants were able to learn about the foods’ satiating capacity after repeated consumption. Ad libitum intake of a HED high-viscous yogurt decreased and was 10% lower compared with a LED high-viscous yogurt after repeated consumption, while intake of a LED and HED low-viscous yogurt did not differ (interaction effect: p=0.04). We also observed thatappetite sensations changed when participants repeatedly consumed a liquid and semi-solid custard with a similar energy density (p<0.05). In addition, participants increased their intake from the ad libitum buffet after repeated consumption of a LED food (from 1745 ± 577 to 1979 ± 567 kcal), while their intake did not change after a HED food (interaction effect: p=0.02). This increase was observed irrespective of the texture of the test foods.         
Ad libitum intake was higher of liquid foods when compared with semi-solid foods, also after learning about the energy content of a food over repeated exposure.
Participants did not adjust their intake and expected satiation consistently. Intake did not change when participants consumed a LED and a HED yogurt with a straw or with a spoon. We also did not observe profound changes in the expected satiation of a LED and HED soup or a liquid and semi-solid custard.  
Conclusions
Healthy young adults learned about the foods’ satiating capacity after repeated consumption. Changes in intake and expectations in response to learning did not depend on food texture.          
Food intake and expected satiation were not easily changed. The effect of food texture on satiation is important in the regulation of food intake, also after repeated exposure.