Effects of hydrolysed casein, intact casein and intact whey protein on energy expenditure and appetite regulation: a randomised, controlled, cross-over study

Abstract

Casein and whey differ in amino acid composition and in the rate of absorption; however, the absorption rate of casein can be increased to mimic that of whey by exogenous hydrolysis. The objective of the present study was to compare the effects of hydrolysed casein (HC), intact casein (IC) and intact whey (IW) on energy expenditure (EE) and appetite regulation, and thereby to investigate the influence of amino acid composition and the rate of absorption. In the present randomised cross-over study, twenty-four overweight and moderately obese young men and women consumed three isoenergetic dietary treatments that varied in protein source. The study was conducted in a respiration chamber, where EE, substrate oxidation and subjective appetite were measured over 24 h at three independent visits. Moreover, blood and urine samples were collected from the participants. The results showed no differences in 24 h and postprandial EE or appetite regulation. However, lipid oxidation, estimated from the respiratory quotient (RQ), was found to be higher after consumption of IW than after consumption of HC during daytime (P¼ 0·014) as well as during the time after the breakfast meal (P¼0·008) when the food was provided. Likewise, NEFA concentrations were found to be higher after consumption of IW than after consumption of HC and IC (P,0·01). However, there was no overall difference in the concentration of insulin or glucagon-like peptide 1. In conclusion, dietary treatments when served as high-protein mixed meals induced similar effects on EE and appetite regulation, except for lipid oxidation, where RQ values suggest that it is higher after consumption of IW than after consumption of HC.

The effect of casein, hydrolyzed casein, and whey proteins on urinary and postprandial plasma metabolites in overweight and moderately obese human subjects

“…The postprandial plasma metabolome revealed a higher circulating level of isoleucine following whey protein ingestion compared with casein and HC, and a higher circulating level of tyrosine after consumption of casein and HC. Thus, the postprandial plasma AA profiles likely reflected the differences in the AA composition between casein and whey proteins and were in accordance with the reported AA differences between casein and whey proteins …”

“…Thus, based on the differences in absorption kinetics, it can be speculated that intake of casein and HC imposes different effects on appetite regulation. In a previous paper we showed that intake of casein, HC, and whey proteins induced similar effects on the 24 h and postprandial energy expenditure and appetite regulation . In this paper we did not observe any differences in the postprandial total plasma AA level between intake of casein, HC, and whey proteins.…”

“…The carbon skeleton from the glucogenic AAs can be metabolized to pyruvate, which can be converted readily into lactate by lactate dehydrogenase . The content of alanine in the IW solution was considerable higher (53.4 mg g −1 protein) than in the IC and HC solutions (32.9 mg g −1 protein and 33.0 mg g −1 protein respectively) . The present findings show that the postprandial plasma level and the urinary level of alanine are equal.…”

“…Urinary lactate may arise from various pathways, including increased glucose oxidation and metabolism of certain AAs . Previously, we reported data from the current intervention study showing that intake of whey proteins was associated with increased lipid oxidation and higher plasma levels of NEFAs . High levels of circulating NEFAs have been associated with an increased lipid and a reduced glucose oxidation .…”

“…However, to our knowledge, no studies have examined the effect of casein ingestion versus intake of HC in human subjects. Previously, we have reported data from this intervention trial in which we showed that intake of whey proteins was associated with higher lipid oxidation compared with intake of HC, as estimated from the respiratory quotient . Furthermore, the lower respiratory quotient values and greater lipid oxidation rates were supported by the higher plasma levels of nonesterified fatty acids (NEFAs) after consumption of whey proteins compared with casein and HC .…”