What we eat both builds and fuels every part of our bodies. Even though we have the notion that our bones just 'sit there' and do nothing, the foods we consume affect them both directly and indirectly. An important concept to help us under-stand the roles of calcium and other minerals is the acid-alkaline balance.
This is expressed by the pH (power of hydrogen) scale, ranging from 0 to 14. A pH of 7 is neutral, while below 7 is acid and above 7 is alkaline.
In the body, acids-which are corro-sive-generally result from metabolic processes such as moving or breath-ing, and are either excreted or buffered (neutralized) by minerals or mineral salts, which are alkaline. For proper metabolism, the blood has to be slightly alkaline with a pH of about 7.45, and going off this balance evena little has serious consequences. An alkaline pH of 7.9 can lead to tetany (lockjaw) and death, while an acidic pH of 6.9 can cause a possibly fatal diabetic coma. With a correct blood pH, the body is in homeostasis.
The body has a number of mech-anisms to keep the acid-alkaline balance just right:
- During breathing, cells exhale carbonic acid, which becomes car-bon dioxide that is expelled via the lungs, lowering the acid load;
- Muscle movements create lactic acid from glycogen (stored carbo-hydrate) breakdown, which pro-duces energy, increasing acidity;
- The kidneys regulate the blood acid-alkaline balance by excreting either a more acidic or a more alkaline urine as necessary;
- If the blood is too acidic, the bones release calcium and other buffer-ing minerals into the bloodstream via bone resorption (breakdown);
- Once metabolized, the food we eat adds to the acid-alkaline balance, depending on whether they leave acid (carbonic, phosphoric or sul-phuric) or buffering (mostly calci-um, iron, magnesium, potassium, and sodium) residues.
Most fresh produce is alkalizing, as are fruit, vegetables, seaweed, soy sauce, miso and salt. Protein and carbohydrate foods, such as sugar, flour, beans, grains, fish, poultry, meat and eggs, are acidic (WDDTY vol 9 no 10: 1-5).
The slightest tilt towards acidity in the bloodstream-called 'acidosis'-removes calcium from bones to alka-lize the blood (Am J Clin Nutr, 2004; 79: 4-5). Studies in mice have confirmed that metabolic acidosis does indeed stimulate bone resorption and inhibit bone formation (Curr Opin Nephrol Hypertens, 2004; 13: 423-36).
Dr T. Colin Campbell, of Cornell University, in collaboration with Oxford University and the Chinese Academy of Preventive Medicine in Beijing, conducted a landmark study of dietary patterns and nutritional status in the Chinese population in the early 1990s. They found that levels of acid and calcium in the urine of middle-aged and elderly women was considerably influenced by diet. Acid-forming foods increased calcium in the urine. Animal protein appeared to be a culprit, whereas plant protein was not (Campbell TC, Campbell TM. The China Study: The Most Comprehensive Study of Nutrition Ever Conducted and the Startling Implications for Diet, Weight Loss and Long-Term Health. Dallas, TX: Benbella Books, 2005). This may be why some studies show that vegetarians have lower rates of osteoporosis vs meat eaters.
So, excess intakes of acid-forming foods drain calcium and other minerals from the bones. Eating meat is one possible cause of acidosis but, more often, it's due to an excess consumption of flour and sugar, as the modern food supply includes lots of refined carbohydrates such as pasta, cookies, cakes, muffins, white bread and white rice.
Refined carbohydrates have received relatively little notice, mostly because of the unfortunate misconception that 'all carbohy-drates are equal'. Christiane Northrup, MD, author of The Wisdom of Menopause (Bantam, 2006), notes that osteoporosis is most frequently seen in countries where the diet habitually includes refined carbohy-drates. Milk products and tofu (if made with calcium carbonate) are buffering foods that will balance either side because they contain both calcium (alkalizing) and protein (acid-forming).
So, in a diet high in sugar, flour and/or meat, and low in vegetables and fruit, dairy products will alkalize the body because of the calcium content. Conversely, in a diet high in alkalizing fruit, green vegetables and potatoes, and low in protein or grains, dairy foods will provide acid-forming protein.
The trick, of course, is to eat from both acid-forming and alkalizing food groups. Too much acidic food draws minerals from the teeth and bones, while too much alkaline food creates cravings for sweets or carbs to provide some counterbalancing acid-forming foods.
The best alkalizing foods, especially in a diet with little or no dairy, as I recommend, are cooked or raw leafy green vegetables (kale, collard and mustard greens, watercress, arugula), roots (carrots, turnips, parsnips, radishes), broccoli and squash-and chopped fresh parsley, which contains calcium and vitamin C as well as ergosterol, a precursor of vitamin D, which helps the body to absorb and utilize calcium. Note, however, that although spinach and chard are rich in calcium, they are also high in oxalic acid, which interferes with calcium uptake.
Annemarie Colbin is an award-winning leader in the field of natural health. This article has been adapted from Dr Colbin's new book Whole-Food Guide to Strong Bones: A Holistic Approach (Oakland, CA: New Harbinger Publications, 2009).