Biotin and egg whites....
Biotin's name comes from the Greek word for life, bios. Although biotin has been known to be essential for half a century, research has not yet fully revealed all of its roles. We know it is essential for the syntheses of protein and fatty acids, and to the metabolism of carbohydrates. In addition, biotin is an essential coenzyme in many enzyme reactions. We know that the thyroid and adrenal glands, the reproductive tract, the nervous system, and the skin depend on an adequate supply of the vitamin.
Some nutritionists maintain that a biotin deficiency can occur only when the biotin in the body is destroyed by an antagonist, such as raw egg white. On the other hand, there is also research which demonstrates that large numbers of people do indeed have low levels of biotin in their blood. These include the elderly, athletes, pregnant women, alcoholics, and people with achlorhydria (absence of hydrochloric acid in the stomach). In pregnant women, for example, the biotin level in the blood starts out lower than in other adults and decreases as pregnancy progresses. Biotin in mother's milk after birth, and for at least four days, is too low to be measured. After that, it varies from individual to individual. People with liver disease also have lower than normal levels of biotin. Blood plasma levels of biotin have been shown to drop below normal in children with burns and scalds, too.
The principal biotin antagonist is avidin, a component of raw egg white. Avidin combines with biotin (or binds it) and renders the vitamin unavailable for utilization.
A biotin deficiency may also be produced by antibiotics. Researchers believe that bacteria normally found in the intestines can synthesize biotin, which is absorbed into the bloodstream. Antibiotics can kill these bacteria and shut off a potentially important supply of biotin.
Biotin is available in supplement form in doses ranging from a few micrograms up to several hundred micrograms.
Where is it found?
Good dietary sources of biotin are liver and other organ meats, egg yolk, peanuts, filberts, mushrooms, bananas, soy, peanuts, and cauliflower. Whole grains are also good sources. Processed cereals and grains, such as white rice and flour, have had most of the biotin removed and none returned through fortification.
Who is likely to be deficient?
Certain rare inborn diseases can leave people with depletion of biotin due to the inability to metabolize the vitamin normally. A dietary deficiency of biotin, however, is quite uncommon, even in those consuming a diet low in this B vitamin. Nonetheless, if someone eats large quantities of raw egg whites, a biotin deficiency can develop, because a protein in the raw egg white inhibits the absorption of biotin. Cooked eggs do not present this problem. Long-term antibiotic use can interfere with biotin production in the intestine and increase the risk of deficiency symptoms, such as dermatitis, depression, hair loss, anemia, and nausea. Long-term use of anti-seizure medications may also lead to biotin deficiency. Alcoholics, people with inflammatory bowel disease, and those with diseases of the stomach have been reported to show evidence of poor biotin status; however, the usefulness of biotin supplementation for these individuals remains unclear. In animals, biotin deficiency can cause birth defects.
How much to take?
The ideal intake of biotin is unknown; however, the amount of biotin found in most diets, combined with intestinal production, appears to be adequate for preventing deficiency symptoms. Researchers have estimated that 30 mcg per day appears to be an adequate intake for adults. Typically, consumption from a Western diet has been estimated to be 30-70 mcg per day. Larger amounts of biotin (8-16 mg per day) may be supportive for diabetics by lowering blood glucose levels and preventing diabetic neuropathy. Biotin in the amount of 2.5 mg per day strengthened the fingernails of two-thirds of the individuals with brittle nails, according to one clinical trial.
Side effects
Excess intake of biotin is excreted in the urine; no toxicity symptoms have been reported.
Biotin works with some other B vitamins, such as folic acid, pantothenic acid (also known as vitamin B5) and vitamin B12; however, no solid evidence indicates that people supplementing with biotin need to also take these other vitamins. Symptoms of pantothenic acid or zinc deficiency have been reported to be lessened with biotin, though people with these deficiencies should supplement with the nutrients they are deficient in. Researchers have speculated that biotin and alpha lipoic acid may compete with each other for absorption or uptake into cells; but little is known about the importance of these interactions in humans.
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The Journal of Nutrition Vol. 128 No. 10 October 1998, pp. 1716-1722
Egg proteins contribute substantially to the daily nitrogen allowances in Western countries and are generally considered to be highly digestible. However, information is lacking on the true ileal digestibility of either raw or cooked egg protein. The recent availability of stable isotope-labeled egg protein allowed determination of the true ileal digestibility of egg protein by means of noninvasive tracer techniques. Five ileostomy patients were studied, once after ingestion of a test meal consisting of 25 g of cooked 13C- and 15N-labeled egg protein, and once after ingestion of the same test meal in raw form. Ileal effluents and breath samples were collected at regular intervals after consumption of the test meal and analyzed for 15N- and 13C-content, respectively. The true ileal digestibility of cooked and raw egg protein amounted to 90.9% (cooked) and 51.3% (raw) respectively. A significant negative correlation (r = 0.92, P < 0.001) was found between the 13C-recovery in breath and the recovery of exogenous N in the ileal effluents. In summary, using the 15N-dilution technique we demonstrated that the assimilation of cooked egg protein is efficient, albeit incomplete, and that the true ileal digestibility of egg protein is significantly enhanced by heat-pretreatment. A simple 13C-breath test technique furthermore proved to be a suitable alternative for the evaluation of the true ileal digestibility of egg protein........
Egg white protein is generally considered to be less digestible than heat-pretreated egg white protein. In this study, it was shown that after ingestion of 25 g of raw egg protein, almost 50% is malabsorbed over 24 h. The higher digestibility of cooked egg protein presumably results from structural changes in the protein molecule induced by heating, thereby enabling the digestive enzymes to gain broader access to the peptide bonds. It has been suggested that the reduced digestibility of raw egg white is at least partially related to the presence of trypsin inhibitors in raw egg white.
