Studies have shown that timing of
protein intake,
leucine content, and speed of digestion significantly affect postprandial
protein utilization. Our aim was to determine if one can spare lean body mass during energy restriction by varying the quality and the timing of
protein intake. Obese volunteers followed a 6-wk restricted energy diet. Four groups were compared:
casein pulse,
casein spread, milk-soluble
protein (MSP, = whey) pulse, and MSP spread (n = 10-11 per group). In
casein groups,
caseins were the only
protein source; it was MSP in MSP groups.
Proteins were distributed in four meals per day in the proportion 8:80:4:8% in the pulse groups; it was 25:25:25:25% in the spread groups. We measured
weight, body composition,
nitrogen balance,
3-methylhistidine excretion, perception of hunger, plasma parameters, adipose tissue metabolism, and whole body
protein metabolism. Volunteers lost 7.5 ± 0.4 kg of weight, 5.1 ± 0.2 kg of fat, and 2.2 ± 0.2 kg of lean mass, with no difference between groups. In adipose tissue, cell size and
mRNA expression of various genes were reduced with no difference between groups. Hunger perception was also never different between groups. In the last week, due to a higher inhibition of protein degradation and despite a lower stimulation of
protein synthesis, postprandial balance between whole body
protein synthesis and degradation was better with
caseins than with MSP. It seems likely that the positive effect of
caseins on
protein balance occurred only at the end of the experiment.