Protein ingestion acutely inhibits insulin-stimulated muscle carnitine uptake in healthy young men

Shannon, Chris E.; Nixon, Aline Victoria; Greenhaff, Paul L.; Stephens, Francis B.

Abstract

BACKGROUND:
Increasing skeletal muscle carnitine content represents an appealing intervention in conditions of perturbed lipid metabolism such as obesity and type 2 diabetes but requires chronic L-carnitine feeding on a daily basis in a high-carbohydrate beverage.
OBJECTIVE:
We investigated whether whey protein ingestion could reduce the carbohydrate load required to stimulate insulin-mediated muscle carnitine accretion.
DESIGN:
Seven healthy men [mean ± SD age: 24 ± 5 y; body mass index (in kg/m(2)): 23 ± 3] ingested 80 g carbohydrate, 40 g carbohydrate + 40 g protein, or control (flavored water) beverages 60 min after the ingestion of 4.5 g L-carnitine tartrate (3 g L-carnitine; 0.1% (2)[H]3-L-carnitine). Serum insulin concentration, net forearm carnitine balance (NCB; arterialized-venous and venous plasma carnitine difference × brachial artery flow), and carnitine disappearance (Rd) and appearance (Ra) rates were determined at 20-min intervals for 180 min.
RESULTS:
Serum insulin and plasma flow areas under the curve (AUCs) were similarly elevated by carbohydrate [4.5 ± 0.8 U/L · min (P < 0.01) and 0.5 ± 0.6 L (P < 0.05), respectively] and carbohydrate+protein [3.8 ± 0.6 U/L · min (P < 0.01) and 0.4 ± 0.6 L (P = 0.05), respectively] consumption, respectively, compared with the control visit (0.04 ± 0.1 U/L · min and -0.5 ± 0.2 L). Plasma carnitine AUC was greater after carbohydrate+protein consumption (3.5 ± 0.5 mmol/L · min) than after control and carbohydrate visits [2.1 ± 0.2 mmol/L · min (P < 0.05) and 1.9 ± 0.3 mmol/L · min (P < 0.01), respectively]. NCB AUC with carbohydrate (4.1 ± 3.1 μmol) was greater than during control and carbohydrate-protein visits (-8.6 ± 3.0 and -14.6 ± 6.4 μmol, respectively; P < 0.05), as was Rd AUC after carbohydrate (35.7 ± 25.2 μmol) compared with control and carbohydrate consumption [19.7 ± 15.5 μmol (P = 0.07) and 14.8 ± 9.6 μmol (P < 0.05), respectively].
CONCLUSIONS:
The insulin-mediated increase in forearm carnitine balance with carbohydrate consumption was acutely blunted by a carbohydrate+protein beverage, which suggests that carbohydrate+protein could inhibit chronic muscle carnitine accumulation.

Citation

Shannon, C. E., Nixon, A. V., Greenhaff, P. L., & Stephens, F. B. (2016). Protein ingestion acutely inhibits insulin-stimulated muscle carnitine uptake in healthy young men. American Journal of Clinical Nutrition, 103(1), https://doi.org/10.3945/ajcn.115.119826

• Journal Article Type: Article
• Acceptance Date: Oct 26, 2015
• Online Publication Date: Dec 16, 2015
• Publication Date: Jan 1, 2016
• Deposit Date: Jul 18, 2016
• Journal: American Journal of Clinical Nutrition
• Print ISSN: 0002-9165
• Electronic ISSN: 1938-3207
• Publisher: Oxford University Press
• Peer Reviewed: Peer Reviewed
• Volume: 103
• Issue: 1
• DOI: https://doi.org/10.3945/ajcn.115.119826
• Keywords: doubly labeled water, energy requirement, resting energy expenditure, short bowel syndrome, total energy expenditure
• Public URL: https://nottingham-repository.worktribe.com/output/979161
• Publisher URL: http://ajcn.nutrition.org/content/103/1/276.long