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from The Aquarian,
Spring 2004
Condensed and adapted from Becoming Vegetarian: The Complete Guide to Adopting a Healthy Vegetarian Diet, by Vesanto Melina, M.Sc., R.D., and Brenda Davis, R.D. (Wiley Canada, 2003). By VESANTO MELINA and BRENDA DAVIS Go into a Grade 3 classroom and ask the children why we need calcium. What will they say? "To build strong bones, of course." Everyone knows that. Some may even tell you that if you don't eat enough calcium, you'll get osteoporosis when you are old. Ask the children where we get our calcium. They will not hesitate to tell you that it comes from milk. Some will even mention cheese, yogurt, or other dairy products. There is no doubt about it; few nutrition messages are more strongly promoted than this one. Yet while we know that milk is a rich source of calcium, could there be something missing in this nutrition education message? Despite calcium intakes that are among the highest in the world, North American rates of osteoporosis are also among the highest in the world. One in four Canadian women and one in eight men over the age of fifty has osteoporosis. The good news is that studies have shown that even in our later years, we can increase bone density and even repair some osteoporotic damage. But exactly how do we do this? Is the solution calcium, calcium, and more calcium? Myth: Getting enough calcium ensures strong bones. Relying on just one mineral to prevent osteoporosis is like trying to play baseball with only a pitcher on your team. In truth, we need other team members on bases, behind the plate, and in key spots out in the field. Bone health involves a similar team of players, including calcium, vitamin D, protein, magnesium, boron, copper, zinc, manganese, fluoride, and vitamins K, C, B12, B6, and folic acid. Physical activity, which is so vital, would no doubt take the position of "team coach." Here are a few examples of roles played by the members of the bone team. Vitamin C, found in fruits and vegetables, helps build cross-links between molecules of collagen, a protein in bone. Vitamin K, from leafy greens, binds calcium to three types of protein that make up bone structure. Boron, a mineral in apples and other fruits, flaxseeds, nuts, vegetables, and legumes, plays a role in preventing calcium loss and seems to support the action of vitamin D. Still, calcium is the pitcher. Let's look at its crucial role in building bones that last. Calcium in the body: a fine balance Our bodies carefully maintain calcium levels in blood and other fluids. If levels drop, we simply make a withdrawal from the bone calcium bank account. Eventually, of course, repeated withdrawals result in fragile bones which is why attaining good bone mass during our first few decades of life is extremely important for long-term bone health. Generally, when we most need calcium, we absorb the highest percentage from our diet. Absorption is greatest during pregnancy, lactation and the growing years. Thus, children may absorb up to 75 percent of dietary calcium, as compared with rates of 20–40 percent in young adults and 15–20 percent in most adults. When intake and output (from fecal loss and urinary excretion) are roughly equal, we are said to be "in calcium balance." This is a good goal during our adult years. Beyond about forty-five years, bone mass typically declines as much as 0.5 percent each year. In the decade before and after menopause, women's calcium losses accelerate to as much as 2–5 percent of total bone mass in a single year, and then it slows. Though adequate calcium intake is important, it is just one part of the rather complex equation of calcium balance. A study of hundreds of women showed that only 11 percent of calcium balance is determined by calcium intake, 15 percent by absorption, and fully 51 percent by urinary excretion. Calcium absorption and excretion are extremely important for long-term bone health. Ignoring excretion is like trying to fill your bathtub without putting in the plug! There can be a great deal of variation in how we absorb and retain calcium.
Protein. Research has shown that for every gram of dietary protein above 47 grams per day, we lose about 0.5 milligrams of calcium through the urine. This happens because a byproduct of protein breakdown combines with calcium and carries it out of the body. The byproduct is sulphate from the sulphur-containing amino acids. Sulphates make our blood more acidic than is optimal, and we restore pH balance by drawing on calcium reserves — our bones — or with calcium from our diet. All dietary protein contributes to urinary calcium losses; however, meat, fish, poultry, and eggs are particularly high in protein and in the sulphur-containing amino acids. Dairy products, legumes, and grains contain moderate amounts, while fruits and vegetables contain even less. Protein is essential for building body tissues (including bone), and meeting recommended allowances is important. But too much protein can have a negative effect on calcium balance, especially when calcium intakes are low. This excess is an important factor in the epidemic of osteoporosis among affluent North Americans. Sodium. The amount of sodium we require each day is very low, about 500 milligrams. Intakes of North Americans tend to be about five to ten times that amount. Seventy-five percent of that intake comes via processed foods such as salad dressings, soups, pickles, fast foods and snacks. High sodium intakes decrease our kidneys' ability to reabsorb calcium. For every 1,000 milligrams (1 gram) of sodium in our diets, we lose about 20–40 milligrams of calcium that has been absorbed. If we absorb only 15–20 percent of our dietary calcium, this means that each extra gram of sodium in our diets should be counterbalanced by about 100–267 milligrams of dietary calcium. Scientists have calculated that in adult women, each extra gram of sodium could produce an additional rate of bone loss of I percent per year if all of the calcium loss comes from the skeleton. Research on postmenopausal women supports these estimates. To protect our bones as we age, we should check amounts of sodium on labels of our favourite foods and replace some of the salt in our cooking with other seasonings. Aim for about 2,400 milligrams of sodium or less per day. Sodium in Foods
Coffee. If we have two or three cups of coffee per day or less, the effect on calcium balance appears to be negligible, as long as our diet meets recommended calcium intakes. However studies have shown that even two cups of coffee can encourage bone loss in women whose calcium intake is less than 800 milligrams per day. Phosphoric acid. Some of the most popular sodas (cola beverages) contain phosphoric acid which can increase calcium excretion, although the effects are considered relatively minor. However, if these beverages become a primary fluid, it can be more of a problem. Hormonal balance. Estrogen appears to aid in calcium absorption and help our bones retain calcium. Vegetarians tend to have lower lifelong serum estrogen. This is thought to be due to the later age of menarche, lower fat intakes, and increased fecal output of estrogen (due to higher fibre diets). The reduced estrogen levels, while an advantage when it comes to cancer, may increase risk of osteoporosis. For about five years around menopause, women may lose as much as three percent of their total bone mass each year. Hormone–replacement therapy has been used by post–menopausal women to prevent calcium loss; however, there can be unwanted side effects. New research is exploring the gentler effects of similar plant estrogens derived from soyfoods (isoflavones) and flaxseeds (lignans). Regular consumption of tofu and other soyfoods may have helped the bone health of Chinese and Japanese women in past centuries, and this practice is being adopted by increasing numbers of North Americans today. Exercise. Apart from diet, there is nothing we can do that is more valuable for our bones than to exercise. Exercise communicates a powerful message to the bones to preserve calcium and keep bones strong. Taking part in forty–five minutes to an hour of weight–bearing exercise (such as walking, running, cycling, or dancing) three to five times a week, plus a session with free weights, exercise machines, or life activities that provide similar resistance exercise two to three times a week are our best ways to help our bones retain calcium. Bones appreciate being used! Meeting your need for calcium Because there are so many variables that interact in the equation of
calcium balance, it's difficult to determine exactly how much we need.
However, combining the wisdom of scientists in Canada, the United States
and other countries, the following amounts have been set as Acceptable
Intakes (a sort of "best guess") for various ages.
It is well-known that many people in less developed countries, whose diets are mainly plant-based, have strong bones despite calcium intakes that are far below the adult intakes recommended above. We also know that excessive intakes of animal protein increase urinary calcium losses and that requirements could theoretically be lower when these excesses are avoided. But it's a myth that vegetarians need much less calcium than meat-eaters. People in other cultures who manage on these low calcium intakes often lead lives that are far different from ours in North America. Their main mode of transportation may be walking outdoors in the sunshine. Carrying heavy loads such as children, water, and food is a part of their everyday life. In contrast, we may be indoors much of the time, sitting at a desk during the day and watching TV at night. Even when we exercise, we drive to the gym or use a golf cart. When we are outside, we often smear on the sunscreen. Some of us also live at northern latitudes. These factors affect our calcium retention. Vegetarians, including vegans, should meet the calcium intakes recommended for their age group. Many people find it easier to meet recommended calcium levels if fortified foods or supplements are included as part of the day's intake. One good predictor of our bone health may be the ratio between our calcium and protein intakes. The ideal ratio appears to be 16 milligrams of calcium for every gram of protein in our diet. Lacto-ovo vegetarians fit this pattern very closely. The ratios for nonvegetarians and vegans are fairly similar and lower — between 9 and 12 milligrams calcium for each gram of protein in the diet. Vegans have the advantage of less excessive protein intakes, but this is countered by lower calcium intakes. However, most studies of vegan dietary patterns were done before excellent calcium-fortified products appeared in the marketplace. The availability of calcium-fortified beverages (such as soymilk and orange juice) and foods (such as calcium-set tofu) has improved immensely in recent years. Though kale, calcium-set tofu, and other non-dairy sources of calcium are not yet listed on national food guides, our range of choices is becoming more widely known. Vegans, and people whose intakes fall short of recommendations, would be well advised to take advantage of the many calcium sources available to them. As the following tables show, there are a great many ways for the calcium that originates in the earth's crust to become part of our bones! Calcium in Foods*
Calcium from Foods, Estimated Absorption
Ten Tips for Strong Bones 1. Get calcium savvy. Get familiar with the variety of dietary sources of calcium and plan your menu accordingly. 2. Eat dark green vegetables daily. Include broccoli, kale, collards, bok choy and Chinese cabbage on your regular shopping list. Learn delicious ways to prepare greens. Some minerals (and vitamins) are lost in the cooking water, so steam vegetables or use the mineral-rich cooking water in soups or in grain preparation. 3. Use calcium-set tofu. For those people who haven't tried tofu, realize that, like flour, it is an ingredient. Tofu can be made into everything from soup to dessert, so it can be used often without your menus becoming repetitious. 4. Take advantage of the calcium-fortified beverages. Fortified non-dairy milks and juices can help raise your total calcium intake to recommended levels. 5. Make almonds, almond butter, sesame tahini, and blackstrap molasses a part of your meals and snacks. Every time you replace 30 millilitres (2 tablespoons) of peanut butter with an equal amount of almond butter, you increase your calcium intake by 73 milligrams. By replacing 15 millilitres (I tablespoon) of jam with the equivalent of molasses, you gain a surprising 168 milligrams of calcium. 6. Don't keep company with the calcium thieves. Avoid high intakes of salt, alcohol, and caffeine, excessive amounts of animal protein, and a sedentary lifestyle. 7. When you go out for dinner, frequent Japanese, Chinese, Middle Eastern and vegetarian restaurants. These cuisines do a masterful job of teaching us about the many wonderful sources of calcium that are seldom recognized in the Western world. You may learn delicious ways to use sea vegetables, such as hijiki, in stir-fries and soups. You'll discover flavourful dishes made with tofu, greens, beans and tahini. 8. Build strong bones during the growing years. Emphasize a broad spectrum of calcium-rich foods, along with a balanced, varied diet for children. Infants need breast milk or commercial infant formula; as children get older, they can switch to fortified soymilk or cow's milk. (Other plant milks lack sufficient protein.) 9. Add some sunshine to your day. You'll not only feel good, but ten minutes (for Caucasians) to thirty minutes (for dark-skinned people) of sunlight helps achieve your vitamin D quota for the day. 10. Exercise! Walking, jogging, dancing, ballgames, hiking, step
exercises or other weight-bearing exercise is essential for lifelong bone
health. Even in the elderly, these activities strengthen bones. With bones,
it's a case of use 'em or lose 'em.
Canadian dietitians Vesanto Melina (www.nutrispeak.com) and Brenda Davis (www.hope-care.org) are two of the world's most respected authorities on vegetarian nutrition. The Journal of the American Dietetic Association praised the first edition of their book, Becoming Vegetarian, noting that "few books on vegetarian nutrition are as comprehensive and accurate." Melina and Davis also co-authored Becoming Vegan. Their other recent books include Raising Vegetarian Children (Melina and Joanne Stepaniak) and Defeating Diabetes (Davis and Tom Barnard). |
Becoming Vegetarian By Vesanto Melina, M.Sc., R.D., and Brenda Davis, R.D Amazon.com | Amazon.ca.
Vitamin D for Dull Days When we expose our hands or face to warm sunlight, even for just a few minutes, our skin cells form vitamin D. Vitamin D is also added to two types of foods: milks (dairy and fortified plant milks) and margarine. The only significant natural dietary source is oily fish (about 300 international units [IU] per 100 gram serving) and fish liver oil. Eggs (25 IU each) and liver (30 IU per serving) also contribute a small amount. If our bodies have too little vitamin D, the skeleton will be inadequately mineralized, leading to a condition called rickets in children and osteomalacia in adults. To get enough vitamin D from sun exposure, a general guideline for North Americans is an average of ten to fifteen minutes daily, mid-morning to late afternoon, on the face and hands, for light-skinned people. Darker-skinned people need more (thirty minutes to three hours daily, depending on skin colour). Because overexposure can increase risk of skin cancer; moderate sun exposure seems the wisest course. In Canada, infants and children cannot depend on adequate skin exposure to sunlight for vitamin D synthesis due to our northern latitudes, especially between November and March. All breast-fed babies and toddlers should receive vitamin D drops (available at pharmacies), especially if, while pregnant, you did not get adequate vitamin D from dietary sources or from a prenatal supplement, or if you wore sunscreen whenever you were outside. Guidelines set in 1998 advise that if we do not have adequate exposure to sunlight, our intake should be 5 micrograms (200 IU) of vitamin D per day up to the age of fifty-one, and then double that amount until the age of seventy-one when it increases again by 50 percent. Requirements increase as we get older because our skin production drops. Vitamin D supplementation has proven to be effective in preventing bone loss and is deemed especially necessary after seventy years of age. Labels on supplements may list vitamin D in micrograms (also listed as mcg or ?) or as international units or IU (I mcg is equivalent to 40 IU). There are two forms of vitamin D, vitamin D2 (ergocalciferol, generally made from yeast) and vitamin D3 (cholecalciferol, from the skins of sheep, cows, and pigs, and from sheep's wool). Our bodies can use either form. Researchers have found vitamin D2 to be about 60 percent as effective as vitamin D3 in raising serum vitamin D levels. It makes sense for vegetarians who prefer to use the form that is not of animal origin (vitamin D2) to increase their intakes accordingly (multiply by 1.7). V.M. and B.D.
Myth: Due to its high protein content, milk actually drains our bodies of calcium. Rumours circulate among vegetarians that cow's milk is not a good source of calcium and even that it depletes us of calcium. Is this true? No. Cow's milk has an excellent calcium-to-protein ratio, which is reflected in both the diet and bone density of lacto-ovo vegetarians. The proportion of calcium that is absorbed is respectable, about 32 percent. While it's not as high as the calcium from low-oxalate greens, it is comparable to that in tofu. V.M. and B.D.
Vitamin A and Fractures A growing body of research suggests men and women who consume more than the recommended daily allowance of retinol — the form of vitamin A found in animal foods and many supplements — are at an increasingly higher risk of suffering osteoporotic bone fractures. No such risk has been found for a higher intake of the plant-based precursor to vitamin A, beta-carotene. Medical experts are therefore beginning to recommend that people choose multivitamins containing much less retinol and more beta-carotene. The Aquarian
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