Carnitine serves as an important transporter of fatty acids from the cytosol into the mitochondria of the cell. Theoretically, increasing cellular levels of carnitine would thereby enhance transport of fats into the mitochondria and fat metabolism. For this reason, L-carnitine has been one of the most common nutrients found in various weight-loss supplements. Over the years, a number of studies have been conducted on the effects of L-carnitine supplementation on fat metabolism, exercise capacity and body composition. Although some data shows that L-carnitine supplementation may be beneficial for some patient populations, most well controlled studies indicate that L-carnitine supplementation does not affect muscle carnitine content, fat metabolism, or weight loss in overweight or trained subjects. For example, Villani et al. reported that L-carnitine supplementation (2 g/d for 8 weeks) did not affect weight loss, body composition, or markers of fat metabolism in overweight women. In our view, although there may be some therapeutic and ergogenic value to L-carnitine supplementation (e.g., to enhance tolerance to training), it appears to have little value as a fat-loss supplement. This may be due, in part, to the manner in which carnitine is ingested. New fat-melt tablets have been reported to have better bioavailability and absorption characteristics, which may enhance the impact on fat oxidation.
Chromium
Interest in chromium as a potential body composition modifier emanated from studies suggesting that chromium may enhance insulin sensitivity and glucose disposal in diabetics. Initial studies reported that chromium supplementation during resistance training improved fat loss and gains in lean body mass as determined by skinfold measurements. However, recent studies using more accurate methods of assessing body composition have mostly reported no effects on body composition in healthy nondiabetic individuals. For example, Walker and colleagues reported that chromium supplementation (200 μg/d for 14 weeks) did not affect body composition alterations in healthy wrestlers during training. Likewise, Lukaski and associates reported that 8 weeks of chromium supplementation during resistance training did not affect strength or dual energy x-ray absorptiometry (DEXA) determined body composition changes. However, Crawford and coworkers107 reported that niacin bound chromium supplementation (600 μg/d for 8-wks) promoted a significant loss in body fat and maintenance in muscle mass in 20 overweight African-American women following a modest diet and exercise program. It is our view that, although most studies indicate that short-term (4–12 weeks) chromium supplementation (200–400 μg/d) does not appear to significantly affect body composition in athletes undergoing training, there may be some benefit in diabetics or overweight populations that deserves additional study.
