Date: 20 Aug 1994 07:49:17 -0700 From: taltar@vertigo.helix.net (Ted Altar) Subject: Zinc & Vegetarians (repost) Newsgroups: rec.food.veg Organization: Helix Internet Lines: 207 ZINC AND VEGETARIANS Ted Altar Topics Briefly Covered: A. Preamble B. Zinc And White Spots On The Fingernails. C. Official Rda Of Zinc D. Factors Associated With Increased Need [3] E. Problems With Zinc Excess: F. Foods High In Zinc G. Foods Low In Zinc And Bioavailability H. Factors Reducing Absorption: I. Zinc Deficiency And Vegans J. References: A. PREAMBLE Iron and zinc deficiencies are probably the leading world health dietary mineral problems. Since large amounts of zinc are found in seafood and meat, it is sometimes thought that vegetarians must therefore be at a greater risk of a zinc deficiency. Is this true? First, some background information. B. ZINC AND WHITE SPOTS ON THE FINGERNAILS. Physiological functions of zinc are diverse and include tissue growth, bone formation, skin integrity, cell-mediated immunity, and generalized host defense [3] Low levels do relate to dietary intake, but various diseases may cause these low levels. Symptoms of zinc deficiency include poor appetite, poor growth (hence, slow wound healing) and impaired taste (hypogeusia). With zinc treatment, appetite improves, taste becomes normal and catch-up growth occurs. Secondary symptoms include night blindness and mental lethargy [2]. People sometimes worry about zinc deficiencies since zinc deficiency (but also pyridoxine deficiency) *can* result in "spotted fingernails" [1]. That is, these are white spots *on* the fingernails. This, however, is not a reliable diagnostic. They may simpy be caused by banging the nails. Even plasma levels (normal range being 85 to 120 ug/dL) "may offer little information about total-body zinc nutriture" [3]. Zinc content of hair is even worst since many other factors affect the zinc concentration in hair (e.g., zinc from tap water or shampoo). The only routinely used test for zinc nutriture is plasma zinc but such a test should be used with corroborating evidence (e.g., functional tests like wound healing, or nitrogen retention) for normal persons. [3] C. OFFICIAL RDA OF ZINC Balance studies of healthy young men estimated that approximately 2.5 mg of *absorbed* zinc is needed. To allow for poor zinc absorption associated with high fiber/calcium diets, an absorption efficiency of only 20% was assumed, resulting the dietary zinc requirement being 12-12.5 mg/daily. Then is added a further margin of safety so that the U.S. 1989 RDA for zinc was set at 15 mg/daily for young men (adolescents whose need is greatest) and 12 for adult woman. D. FACTORS ASSOCIATED WITH INCREASED NEED [3] alcohol chronic illness stress trauma surgery malaborption oral contraceptive users elderly lactoovegetarians for males, too much sex :-( (prostatic fluids have the highest zinc level (approx. 600 - 800 ug/g) [3] heavy sweating renal disease, myocardial infarction E. PROBLEMS WITH ZINC EXCESS: Cases of ingestion of Zn in large amounts have been reported for cases where acid food or drink from a galvanized container was consumed resulting in vomiting and diarrhea. [2] "An acute toxicity can produce a metallic taste, nausea, vomiting, abdominal cramps, dizziness, and chills" [3] Prolonged ingestion of zinc supplements can result in a copper deficiency that in turn makes for anemia and abnormal cholesterol metabolism (elevated serum cholesterol). [3] F. FOODS HIGH IN ZINC Zinc is present in all natural foods. To give a rough idea, below are some foods quite high in zinc: [4] mg/100g wheat germ 17.0 wheat bran 16.2 nutritional yeast 8.0 pine nuts 6.5 thyme 6.2 cashew nuts 5.7 tahini paste 5.4 sesame 5.3 pecan nuts 5.3 sunflower seeds 5.1 lentils 3.9 oatmeal 3.3 black-eyed beans 3.2 chickpeas 3.0 peanuts 3.0 whole wheat flour 1.9 popcorn 1.7 raw peas 1.1 G. FOODS LOW IN ZINC AND BIOAVAILABILITY - Foods low in zinc mainly include processed foods [1] and fruits [1, 4] - Bioavailability varies widely (14% to 41%). Various dietary substances appear to form chelates with zinc that either can enhance or inhibit bioavailability, depending upon the digestibility and absorbability of the particular zinc chelates. - Heat treatment of certain foods, however, makes the foods resistant to hydrolysis which in turn complexes the zinc making it unavailable for absorption. Maillard reaction products consists of enzyme-resistant linkages between the amino acids of proteins and the carboxyl groups of reducing sugars formed during heat treatments and resulting in browning (as occurs in the baking and frying of foods). These amino acid-carbohydrate complexes trap the zinc [3] - Thrash & Thrash claim that better bioavailability occurs with leavened breads than with unleavened breads, this being due to the longer cooking that occurs when leavening is used. Grains usually need long, slow cooking (hence, cooking for time for grains used for porridge, mush or entire grain dishes should be over an hour at boiling temperatures. [1] H. FACTORS REDUCING ABSORPTION: Calcium and Phytate combination: High fiber and PHYTATE intake [2,] have been a subject of concern, but it turns out that it is ONLY in the presence of a high intraluminal CALCIUM that phytate exerts its inhibitory effect on zinc. Hence, "particularly at risk for a zinc deficiency are LACTOVEGETARIANS who may be consuming large quantities of calcium [3] Hence, calcium alone or phytate alone do not affect absorption. High intakes of zinc (via supplementation), however, can depress calcium absorption when calcium intake is low (does not seem to occur when dietary calcium is adequate. Excess copper consumption depresses zinc absorption, but this factor is usually of no practical concern since normally copper intake is low. Contrariwise, excessive intakes of zinc (via supplementation) can interfere with copper absorption (hence the recommendation that therapeutic doses be limited to 40 mg/daily). Excess cadmium [1, 3], has been reported as depressing absorption, but the evidence here is scant. I. ZINC DEFICIENCY AND VEGANS Gill Langley in her fine and well-documented book, reports of a Swedish study which measured the dietary intake of vegans and found the men to be averaging 13mg and the women 10mg, which actually turns out to be *higher* than the typical British omnivorous diet and satisfies the Canadian and WHO RDA's. The amount of zinc in 23 British pre-school vegan children, however, averaged 4mg/day (ranging from 1 to 8mg/day) which is below both Canadian and U.S. standards but still very similar to the intake of omnivorous children. As Gill Langley concludes, given this one study, the intakes of zinc by vegans is apparently about equal or greater to that of omnivores. Serum zinc levels, however, *may* be lower than those of omnivores but are still generally within the normal range. J. REFERENCES: [1] Thrash & Thrash (1982). NUTRITION FOR VEGETARIANS [2] Merck Manual (15th edition), 1987 [3] Hunt & Groff (1990). ADVANCED NUTRITION AND HUMAN MEATABOLISM. [4] McCance & Widdowson's (1991). THE COMPOSITION OF FOODS (5th Edition). [5] Gill Langley (1988). VEGAN NUTRITION: A SURVEY OF RESEARCH.