The Centers for Disease Control and Prevention reports that two-thirds of Americans are overweight or obese. As a result of the "obesity epidemic," the National Institutes of Health reports that the United States could be facing its first sustained drop in life expectancy in modern history. Overweight individuals are seeking ways to regain their health and prevent the onset of obesity-related diseases, and they are increasingly interested in the roles of nutrients such as L-carnitine and biotin in fat metabolism.
Positive Fat Balance
According to the National Center for Health Statistics, Americans are eating more calories than they did 30 years ago, primarily as the result of higher carbohydrate consumption. After they enter your intestine, dietary carbohydrates are broken down into simple sugars, which are then absorbed and used for energy in your cells. Sugars that are not immediately needed for energy are converted to fatty acids and stored in your adipose tissue. Continued consumption of too many carbohydrates forces your body into a "positive fat balance." Biotin and L-carnitine are intimately involved in the metabolism of fatty acids.
L-Carnitine
L-Carnitine is a compound produced in your liver and kidneys from the amino acids lysine and methionine. It can also be found in red meats, fish, poultry, milk products, tempeh and avocados. L-carnitine is an essential transport molecule which transfers fatty acids from the cytoplasm of your cells, where they are synthesized, to the interior of your mitochondria, where they are "burned" for energy. Without L-carnitine, fatty acids cannot be metabolized efficiently.
Biotin
The Linus Pauling Institute at Oregon State University reports that biotin, a B vitamin, serves as a co-factor for two carboxylase enzymes that are involved in fatty acid metabolism. The first of these biotin-dependent enzymes is required for the synthesis of fatty acids in the cytoplasm of your cells. The second acts as a control valve for the oxidation of fatty acids inside the mitochondria of your cells. When your cells have enough energy, the entry of fatty acids into your mitochondria is inhibited, thus decreasing fatty acid oxidation. A biotin-containing enzyme plays a role in this "slow-down" of fatty acid metabolism, but it is the energy demands of your cells -- not biotin levels, per se -- that determine whether your mitochondria burn more fatty acids.
Considerations
Biotin is required for the proper function of enzymes that synthesize and regulate the oxidation of fatty acids. Biotin is an essential nutrient, with daily needs ranging from 5 mcg for infants to 35 mcg for lactating females. L-carnitine, an amino acid produced in your liver and kidneys, is a transporter molecule that carries fatty acids into mitochondria for oxidation. L-carnitine, at a dose of 1,000 mg to 2,000 mg daily, is often used for weight loss, but a November 2004 "American Family Physician" review states there is no evidence that supplemental L-carnitine is useful for this purpose.
References
- Centers for Disease Control and Prevention: Obesity and Overweight
- "NIH News"; Obesity Threatens to Cut U.S. Life Expectancy, New Analysis Suggests; March 2005
- Centers for Disease Control and Prevention: Calorie Consumption on the Rise in United States, Particularly among Women
- Linus Pauling Institute at Oregon State University: Biotin
- "American Family Physician"; Common Dietary Supplements for Weight Loss; R.B. Saper, et al.; November 2004
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