A daily dose of L-carnitine produced a reduction in levels of blood sugar of lean men 30 minutes after being fed 75 grams of glucose – called an oral glucose tolerance test – while the response was different in overweight and obese men, indicating that these individuals may not be as sensitive to insulin, according to findings published in journal Amino Acids.
“The pattern of response in glucose with L-carnitine supplementation in lean participants (earlier timing of peak glucose and lower 30 min glucose concentration) seems to support a mechanism of enhanced glucose disposal through a direct insulin-like action on skeletal muscle” report researchers led by Stuart Galloway from the University of Stirling in Scotland.
“The pattern of change in overweight/ obese with L-carnitine (delayed timing of peak glucose and higher 90 min glucose concentration) appears to support delayed gastric emptying, but these observations need further evaluation.
“This differential response to an oral glucose tolerance test (OGTT). in lean and overweight/obese participants following oral L-carnitine supplementation could explain some of the conflicting reports on metabolic responses to carnitine supplementation evident in the literature.”
L-Carnitine, a vitamin-like nutrient, occurs naturally in the human body and is essential for turning fat into energy. It is frequently used as a dietary supplement by physically active people to help with post-exercise recovery.
The potential health conditions of the ingredient include cardiovascular benefits, weight management potential, sports nutrition (energy and recover), and maintaining levels during pregnancy.
A recent report on L-carnitine from Global Industry Analysts Inc. predicted the global market to be worth $127 million by 2017, with sports drinks and nutritional powders continuing to drive end use.
While the market continues to be dominated by the likes of Lonza, the new report states that Chinese manufacturers have “seized the market reins” in a relatively short time, and China is now responsible for 48 percent of the global L-carnitine production (2008 values).
The L-carnitine used in the present study was administered in the form of L-carnitine L-tartrate and supplied by Lonza.
Dr Galloway and his co-workers recruited eight lean and eight overweight and obese men to participate in their 14 day study.
The men received either three grams of L-carnitine or three grams of glucose per day with their meals for 14 days. Subjects then underwent an oral glucose tolerance test (OGTT), which involved feeding them 75 grams of glucose, and then measuring the effects.
Blood sugar levels were found to be significantly lower in the L-carnitine group of lean men than in the glucose fed lean men 30 minutes after ingestion.
On the flip side, blood glucose levels were higher in overweight and obese men 90 minutes after ingesting L-carnitine, compared to placebo, indicating an effect of gastric emptying, said the researchers.
“It is concluded that L-carnitine supplementation induces changes in blood glucose handling/disposal during an OGTT, which is not influenced by [the gut hormone] GLP-1.
“The glucose handling/disposal response to oral L-carnitine is different between lean and overweight/obese suggesting that further investigation is required.
“L-carnitine effects on gastric emptying and/or direct ‘insulin-like’ actions on tissues should be examined in larger samples of overweight/obese and lean participants, respectively,” they added.
Source: Amino Acids
Volume 41, Number 2, 507-515, doi: 10.1007/s00726-010-0770-5
“Effects of oral l-carnitine supplementation on insulin sensitivity indices in response to glucose feeding in lean and overweight/obese males”
Authors: S.D.R. Galloway, T.P. Craig, S.J. Cleland