Can the modulation of protein digestion kinetics impact satiety?
Résumé
Many strategies have been implemented to increase satiety of foods and snacks. Because proteins were shown to play a major role on food intake control, many works addressed the effect of the level and the type of proteins on appetite. Milk proteins were especially studied due to the presence of two fractions which digestion kinetics are very different, but results remain controversial. We addressed this question in two studies.
In 83 overweight volunteers, we aimed to determine whether casein (slowly digested), whey (rapidly digested) or a combination of both (intermediary kinetic) influenced satiety. Volunteers were divided in 3 parallel groups. Each subject followed two sessions. The first one was a control in which satiety was assessed after the ingestion of a snack containing 60 g of CHO. For the second session, the snack contained 30 g of protein and 30 g of CHO. We thus evaluated the additional effect of proteins compared to CHO only. We also followed the digestion kinetics in a subgroup using intestinal tubes and 15N labeling of proteins. The digestion time was only 2 h with whey, 6 h with caseins and 4h with the mix. In all subjects, proteins increased satiety duration compared to CHO by 18 min, without any effect of the type of proteins despite their important difference in digestion speed. However, a stratified analysis revealed that in subjects with a short satiety duration at control (i.e. after CHO), snacks containing whey were more efficient than casein, increasing satiety time to more than 40 min.
We also assessed the satiating effect of eggs cooked as an omelette and cottage cheese in 30 healthy volunteers in a crossover design. Both snacks were comparable regarding energy and nutrient composition. Hormonal profiles (insulin, GIP, and GLP1) as well as plasma urea and amino acids indicated that the omelette was digested slower than cottage cheese. However, satiety duration, energy intake at lunch and appetite ratings were similar after both snacks. We also challenged the association between nutrients and appetite and found unexpected relationships, showing that postprandial waves and appetite may be independent.
These two studies show that using protein dose (20-30 g) compatible with supplement strategies, the modulation of kinetics is not a sufficient lever to increase satiety. This conclusion is discussed regarding the existing literature.