Are there any concerns or considerations?
Lack of clarity over benefits of short-term supplementation.
Short term supplementation studies which have been undertaken on athletes and active individuals have shown no consistent responses to exercise performance or metabolism. This is due to a wide variance in supplementation duration (single dose pre-exercise through to 4 weeks daily supplementation), training status of participants, the implementation of dietary or exercise controls before testing, and the actual exercise test used/ outcome measured.
Long term supplementation requires each dose to be co-ingested with a significant amount of carbohydrate.
Very few studies have shown an uptake of supplemental carnitine into muscle, but the limited evidence suggests a large dose of carbohydrate (80g with each dose) is required over at least 12 weeks in order to achieve this. There has been no research on whether this dose of carbohydrate could be altered according to body weight or if this could be adjusted according to co-ingestion with other macronutrients, possibly enabling guidance to be adjusted to merely encourage ingestion at main meals. The additional carbohydrate, and the requirement to specifically be timed with the carnitine supplement twice daily, is unlikely to align with the caloric needs and nutrient timing that is optimal for each athlete, during each phase of training, over the period of supplementation.
Very few studies have been undertaken on elite athletes.
As such, the applicability of the research to elite athletes is uncertain.
L-carnitine may increase fasting plasma trimethylamine-N-oxide (TMAO) levels.
Increased TMAO has been linked to atherogenesis and a higher risk of cardiovascular events.5
L-carnitine consumption may cause mild gastrointestinal symptoms.
- Some reports of nausea, vomiting, stomach cramps and diarrhoea have been reported during supplementation. Akin to guidance for other supplements that can result in intestinal symptoms, co-ingestion with meals may be advisable.
- Consuming more than 3g/day may result in a ‘fishy’ body odour.