Their study involving 20 healthy women of normal weight was the first to compare the satiation effects for humans of intact whey protein and a mixture of free amino acids, which simulates the amino acid composition of whey protein.
The study saw the women given a breakfast preload meal of toast and an orange-flavoured spread with tea or coffee.
The spread was either enriched with intact whey protein isolate (WPI) or a free amino acid mixture (AAM), with each equating to about 1,800 kJ and 52 g of amino acid.
The women were then asked to record their subjective feelings of hunger when given a regular second meal of hot fried-rice with chicken, eggs and vegetables two hours later.
They found no difference between the amount the women ate of the second meal or their feelings of fullness and appetite after eating the first whey or the amino acid meal.
This suggested each had a similar effect on satiety.
Plate full of theories
This in turn suggested the satiating effect of whey protein may be related to its specific amino acid composition, rather than the whole protein or bioactive peptides released during digestion.
“The similar effect of preload meals enriched with whey protein or its equivalent free amino acids in inducing satiety, as observed in the present study, provides novel information that total amino acids (TAA), rather than constituent proteins and derived peptides, may be involved in the satiating response to whey protein,” wrote the researchers from the Riddet Institute at the Massey University and the AgResearch Grasslands Research Centre in New Zealand.
“Several studies have reported more rapid increases in plasma TAA and BCAA [Branch Chain Amino Acids] following consumption of whey protein in comparison with other protein sources.”
However the researchers called for further investigation into these mechanisms as well as a comparison of whey with other protein sources.
“It is known that proteins differ in their amino acid composition, but it is not clear whether such differences are the underlying causes for reported differences between proteins in the promotion of satiety.”
Bitter sweet
Amino acids in such high levels can have an unpleasant bitter taste.
In this study this was masked by the orange-flavoured marmalade spread.
The researchers said this was effective and the women did not report any adverse effects or differences in ratings of nausea of the amino acid-enriched meal, despite preferring the whey meal.
“Although the preload meal containing the free amino acids was perceived as being the least liked (overall likeability), least pleasant in taste and least sweet in relation to the WPI preload meal, no correlation between the perceived sensory characteristics of the preload meal and subsequent food energy intake was observed, thus indicating that these dietary characteristics did not influence the outcomes of the study.”
The study was financially independent but used whey protein donated by New Zealand supplier Fonterra and amino acids from German firm Evonik.
Source: British Journal of Nutrition
Published online ahead of print, doi.org/10.1017/S0007114516003767
“Effect of whey protein and a free amino acid mixture simulating whey protein on measures of satiety in normal-weight women”
Authors: S. M. S. Chungchunlam, S. J. Henare, S. Ganesh and P. J. Moughan