Carnitine

Carnitine is essential for fatty acid translocation and muscle function and some studies have shown that carnitine supplementation improves exercise performance. Choline is a lipotropic agent that prevents deposition of fat in the liver.

Recently, the authors reported interactive effects of choline and carnitine in normal healthy humans and guinea pigs. Choline supplementation resulted in significant conservation of carnitine. However, there have been some contradictory results found in other animal studies. Therefore, two researchers from the University of Tennessee set out to test their hypothesis that choline and carnitine supplementation with or without exercise would alter carnitine status, body fat and biochemical markers of fat oxidation in free-living humans.

At baseline, habitual dietary intake was assessed and anthropometric measurements were taken. After the baseline period, 19 women were randomly assigned to the placebo (n=7) or supplement groups. Supplement groups were randomly divided into two subgroups, supplement 1(S1) and supplement 2(S2). The S1 group received only choline during week one followed by the addition of carnitine in weeks two and three. The S2 group received only carnitine during week one followed by the addition of choline in weeks 2 and 3. All subjects were asked to undertake >20 minutes of aerobic activity, 3 to 5 days a week over and above their normal physical activity. In addition, all of the women were asked to wear a pedometer during week 3. Body composition was measured three times through bioelectrical impedance (BIA), skinfold measurements, and BMI calculation.

Although there were no changes in the placebo group, serum and urinary carnitine decreased in the choline-supplemented group during week one. Introduction of carnitine to the choline group restored serum and urinary carnitine. Serum and urinary carnitine increased during week one in the carnitine-supplemented group and, although the introduction of choline to this group depressed serum and urinary carnitine, they remained significantly greater than the control. Serum -hydroxybutyrate and serum as well as urinary acetylcarnitine were elevated by the supplements. A mild exercise regimen increased the concentration of serum betahydroxybutyrate and serum and urinary acylcarnitines; it also decreased serum leptin levels in all groups. The effects of supplements were sustained until week two after cessation of choline plus carnitine supplementation and exercise.

The mild exercise routine enhanced fat utilization as energy substrate in both supplemented groups, but not in the placebo group, as indicated by the increase in the concentrations of serum beta-hydroxybutyrate beyond that raised by the supplements alone. The effect of exercise on acetylcarnitine was very small, but consistent with the idea of enhanced fatty acid oxidation. The rest of the data presented here is also in agreement with the observations in animal models and allows the conclusion that choline promotes carnitine conservation and accretion by tissues that favor incomplete oxidation of fatty acids.

Nobuko Hongu and Dileep S. Sachan, Carnitine and choline supplementation with exercise alter carnitine profiles, biochemical markers of fat metabolism and serum leptin concentration in healthy women, J. Nutr 133:84-89 (January 2003) [Address correspondence to: Dileep S. Sachan, Department of Nutrition and Agricultural Experiment Station The University of Tennessee. Knoxville, TN 37996-1900. E-mail: dsachan@utk.edu]

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