Zoekresultaten

Reduced oxidation rates of ingested glucose during prolonged exercise with low endogenous CHO availability

This paper descibes a study that shows that glycogen-lowering exercise, performed the evening before an exercise bout in combination with glycogen restriction leads to a reduction of the oxidation rate of ingested glucose during moderate-intensity exercise

Whole body protein oxidation unaffected after a protein restricted diet in healthy young males

Sensitivity of a 13C-protein oxidation breath test investigated with a protein restricted diet in healthy subjects

RATIONALE: Disturbed protein metabolism may result in malnutrition. A non-invasive low cost clinical tool to measure protein metabolism is lacking. Explorative research (n=1) with a newly developed non-invasive 13C-protein breath test suggested a decrease in protein oxidation after a protein restricted diet. Now, we aimed to test the effect of protein restriction in more subjects, to assess sensitivity of the test.METHODS: In this exploratory study, 14 healthy male subjects (23±3 y) participated. Habitual intake was assessed by a 4-day food diary. Next, subjects were instructed to use a 4-day isocaloric protein restricted diet (0.25 g protein/kg bw/day). After an overnight fast, a 30 g naturally enriched 13C-milk protein test drink was consumed, followed by collection of breath samples up to 330 min. Protein oxidation was analyzed by Isotope Ratio Mass Spectrometry. 24-h urine was collected on day 4 of the habitual diet, and on every day of the 4-day protein restricted diet, to assess actual change in protein intake.RESULTS: After the protein restricted diet, 30.2%±7.7 of the 30 g 13C-milk protein was oxidized over 330 min, compared to 30.6%±6.2 (NS) after the subject’s habitual diet (1.4±0.3 g protein/kg bw/day). Within subjects, both increase and decrease in oxidation was found. During the 4-day protein restricted diet, urinary urea:creatinine ratio decreased by 56%±10, consistent with a reduction in protein intake of 44%±15 (g/day) and 53%±12 (g/kg bw/day), based on urea and food diary, respectively.CONCLUSIONS: The breath test shows variation within subjects and between diets, which could be related to the sensitivity of the test. We cannot explain the variation by the measured variables. Alternatively, our results may implicate that in some of our subjects, protein intake did not sufficiently decrease to levels that could alter protein metabolism.

Sensitivity of a 13C-protein oxidation breath test investigated with a protein restricted diet in healthy subjects

RATIONALE: Disturbed protein metabolism may result in malnutrition. A non-invasive low cost clinical tool to measure protein metabolism is lacking. Explorative research (n=1) with a newly developed non-invasive 13C-protein breath test suggested a decrease in protein oxidation after a protein restricted diet. Now, we aimed to test the effect of protein restriction in more subjects, to assess sensitivity of the test.METHODS: In this exploratory study, 14 healthy male subjects (23±3 y) participated. Habitual intake was assessed by a 4-day food diary. Next, subjects were instructed to use a 4-day isocaloric protein restricted diet (0.25 g protein/kg bw/day). After an overnight fast, a 30 g naturally enriched 13C-milk protein test drink was consumed, followed by collection of breath samples up to 330 min. Protein oxidation was analyzed by Isotope Ratio Mass Spectrometry. 24-h urine was collected on day 4 of the habitual diet, and on every day of the 4-day protein restricted diet, to assess actual change in protein intake.RESULTS: After the protein restricted diet, 30.2%±7.7 of the 30 g 13C-milk protein was oxidized over 330 min, compared to 30.6%±6.2 (NS) after the subject’s habitual diet (1.4±0.3 g protein/kg bw/day). Within subjects, both increase and decrease in oxidation was found. During the 4-day protein restricted diet, urinary urea:creatinine ratio decreased by 56%±10, consistent with a reduction in protein intake of 44%±15 (g/day) and 53%±12 (g/kg bw/day), based on urea and food diary, respectively.CONCLUSIONS: The breath test shows variation within subjects and between diets, which could be related to the sensitivity of the test. We cannot explain the variation by the measured variables. Alternatively, our results may implicate that in some of our subjects, protein intake did not sufficiently decrease to levels that could alter protein metabolism.

Dietary protein, exercise, and frailty domains

Increasing awareness of the impact of frailty on elderly people resulted in research focusing on factors that contribute to the development and persistence of frailty including nutrition and physical activity. Most effort so far has been spent on understanding the association between protein intake and the physical domain of frailty. Far less is known for other domains of frailty: Cognition, mood, social health and comorbidity. Therefore, in the present narrative review, we elaborate on the evidence currently known on the association between protein and exercise as well as the broader concept of frailty. Most, but not all, identified studies concluded that low protein intake is associated with a higher prevalence and incidence of physical frailty. Far less is known on the broader concept of frailty. The few studies that do look into this association find a clear beneficial effect of physical activity but no conclusions regarding protein intake can be made yet. Similar, for other important aspects of frailty including mood, cognition, and comorbidity, the number of studies are limited and results are inconclusive. Future studies need to focus on the relation between dietary protein and the broader concept of frailty and should also consider the protein source, amount and timing.