Measure protein metabolism via a breath test.

Researching protein oxidation in a non-invasive way could be an interesting approach to perform more research on protein metabolism. Our 30 gram 13C-protein breath test enables us to measure protein oxidation over 5,5 hours. With the knowledge that protein metabolism consists mainly of primarily incorporation of amino acids and secondarily oxidation of surplus amino acids we can make statements about total protein metabolism. In this trial, we will measure the effects of subjects' habitual diets (rich in protein, average 1.15 g protein/kg bw/ day) versus a 4-day low protein diet (0.25 g protein/kg bw/day) on the protein oxidation measured bythe breath test performed on the fifth day. We expect to measure less of the 30 g protein being oxidized after a 4-day low protein diet compared to their habitual diet, similar to results aquired during our pilot experiment.

Protein metabolism consists of amino acid incorporation and amino acid oxidation. We have developed a breath test which is able to measure the oxidation of ingested 13C-protein. We hypothesize that a diet low in protein before the breath test will result in a shortage of protein the body. During the test we expect to measure less 13C-protein to be oxidized compared to a normal protein diet.

Baseline breath sample at t = -5 minutes
30 g 13C-protein in 500 ml water consumption at t = 0 (09:15)
Breath samples every ten minutes starting at 09:25 untill 14:45

4 days of high protein diet (1,35 g protein / kg bodyweight /day) at habitual energy intake followed on day 5 by the protein oxidation breath test.

4 days of medium protein diet (0,8 g protein / kg bodyweight /day) at habitual energy intake followed on day 5 by the protein oxidation breath test.

4 days of low protein diet (0,25 g protein / kg bodyweight /day) at habitual energy intake followed on day 5 by the protein oxidation breath test.