Increasing skeletal muscle carnitine content in older individuals increases whole-body fat oxidation during moderate-intensity exercise
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Abstract Intramyocellular lipid (IMCL) utilization is impaired in older individuals, and IMCL accumulation is associated with insulin resistance. We hypothesized that increasing muscle total carnitine content in older men would increase fat oxidation and IMCL utilization during exercise, and improve insulin sensitivity. Fourteen healthy older men (69 ± 1 year, BMI 26.5 ± 0.8 kg/m2) performed 1 h of cycling at 50% VO2max and, on a separate occasion, underwent a 60 mU/m2/min euglycaemic hyperinsulinaemic clamp before and after 25 weeks of daily ingestion of a 220 ml insulinogenic beverage (44.4 g carbohydrate, 13.8 g protein) containing 4.5 g placebo (n = 7) or L‐carnitine L‐tartrate (n = 7). During supplementation, participants performed twice‐weekly cycling for 1 h at 50% VO2max. Placebo ingestion had no effect on muscle carnitine content or total fat oxidation during exercise at 50% VO2max. L‐carnitine supplementation resulted in a 20% increase in muscle total carnitine content (20.1 ± 1.2 to 23.9 ± 1.7 mmol/kg/dm; p < 0.01) and a 20% increase in total fat oxidation (181.1 ± 15.0 to 220.4 ± 19.6 J/kg lbm/min; p < 0.01), predominantly due to increased IMCL utilization. These changes were associated with increased expression of genes involved in fat metabolism (ACAT1, DGKD & PLIN2; p < 0.05). There was no change in resting insulin‐stimulated whole‐body or skeletal muscle glucose disposal after supplementation. This is the first study to demonstrate that a carnitine‐mediated increase in fat oxidation is achievable in older individuals. This warrants further investigation given reduced lipid turnover is associated with poor metabolic health in older adults.
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Studies that have demonstrated a significant increase in muscle carnitine stores in omnivores have used doses >3 g/d.
“However, studies to have demonstrated a significant increase in muscle carnitine stores in omnivores have used doses >3 g/d [195,196,205].”
From Nutritional Considerations for the Vegan Athlete (2023) · cites this paper as [196]
Similar long-term carnitine coingestion supplementation studies reported ~20% increases in muscle carnitine content and beneficial shifts in muscle fuel selection in older adults.
“Supportive data can also be found in similar long-term carnitine coingestion supplementation studies (25 wk of 3 g of carnitine with an insulinogenic beverage containing 44 g carbohydrate and 14 g protein) where ∼20% increases in muscle carnitine content and beneficial shifts in muscle fuel selection were reported in older adults [196].”
From Nutritional Considerations for the Vegan Athlete (2023) · cites this paper as [196]
No adverse events have been reported with carnitine supplementation for up to 6 mo.
“To date, no adverse events have been reported with carnitine supplementation for up to 6 mo [196]”
From Nutritional Considerations for the Vegan Athlete (2023) · cites this paper as [196]
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- Authors
- Chee, C., Shannon, C. E., Burns, A., Selby, A. L., Wilkinson, D., Smith, K., Greenhaff, P. L., & Stephens, F. B.
- Affiliations
- University of Nottingham (GB)
- The University of Texas at San Antonio Health Science Center (US)
- University of Exeter (GB)
- Corresponding author
- Stephens, Francis B.
- ORCID
- Venue
- Aging Cell
- Publisher
- Wiley
- Published
- 2021-01-19
- Volume
- 20
- Issue
- 2
- Pages
- e13303-e13303
- ISSN
- 1474-9718 (ISSN-L)
- 1474-9726
- PMC
- PMC7884033
- OpenAlex
- W3122065648
- Cited by
- 29
- References
- 54
- Citations by year
- 2026: 4 · 2025: 4 · 2024: 8 · 2023: 7 · 2022: 4 · 2021: 2
- FWCI
- 2.74
- Type
- journal article
- Language
- en
- Open access
- gold
- doi.org
- Licence
- Locations
- Aging Cell (publishedVersion, cc-by)
- PubMed Central (publishedVersion, cc-by)
- PubMed (publishedVersion)
- Open Research Exeter (University of Exeter) (publishedVersion, cc-by)
- Repository@Nottingham (University of Nottingham) (acceptedVersion, other-oa)
- Repository@Nottingham (University of Nottingham) (submittedVersion, cc-by)
- Figshare (submittedVersion, cc-by)
- Funders
- Dunhill Medical Trust (R211/0711)
- Topics
- Life Sciences › Biochemistry, Genetics and Molecular Biology › Cell Biology › Muscle metabolism and nutrition
- Health Sciences › Medicine › Complementary and alternative medicine › Cardiovascular and exercise physiology
- Health Sciences › Medicine › Physiology › Adipose Tissue and Metabolism
- Keywords
- carnitine supplementation, fat oxidation, older adults, moderate-intensity exercise, insulin sensitivity, insulin resistance, lipid metabolism genes, ACAT1, PLIN2, glucose disposal
- MeSH terms
- Aged, Carnitine, Fats, Humans, Male, Oxidation-Reduction, Exercise, Muscle, Skeletal
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