Protein and the Bones
by Annemarie Colbin, Ph.D.
Thanks to excellent marketing, most people know they should take care of their bones to prevent fractures. A lot of the attention has gone to “getting enough calcium,” through food and preferably supplements. Interestingly, I heard an exercise specialist talk about doing a dissection on an 85-year old woman. “There were calcium deposits everywhere,” she said, “in the muscles, in the joints, in the shoulders -- everywhere.” Perhaps, it would seem to me, too much calcium has its drawbacks too.
There is a fallacy in focusing on calcium alone to prevent fractures. Bones are composed of a latticed protein grounding or collagen matrix, which comprises about 35% of the bone and which gives it its flexibility. This matrix is laid down first, and then traps the mineral salt calcium phosphate, also known as hydroxyapatite, which occupies about 65% of the bone mass and which gives the bone its strength. In addition to the calcium salts, the bones are also the depositories of other minerals needed by the body, including magnesium, sodium, potassium, and others. The main component, then, to prevent fractures, is the bone’s flexibility, given by the collagen matrix, rather than the calcium.
Even though strong and hard, bones are not the equivalent of stones or rocks. Instead, like the rest of the tissues in the body, they are constantly moving and changing. They are continuously being built up, in a process called deposition or formation, and just as continuously being broken down, a process called resorption. During childhood and adolescence, this process is called modeling, which has old bone removed and new bone formed in another site of the same bone, sometimes simultaneously, to allow the bones to grow and shift in space. In adulthood, once the skeleton is set at its adult size, the same process is called remodeling, and is more sequential, in that specialized cells called osteoclasts break down old bone, and other cells called osteoclasts build new bone in that same site.
In adults, about 5 to 10 percent of bone is replaced yearly in this fashion, so that most of our adult skeleton is replaced about every ten years. After menopause, bone loss in women may accelerate to 2 to 5% per year, depending on a woman’s nutrition, exercise, pharmacological drug intake, and overall health.
Protein and Vitamin C
For quite some time, it was thought that protein weakened bone. However, the formation of collagen is dependent on sufficient protein in the diet, as well as Vitamin C, which stimulates the enzymes that form the collagen and connective tissue. A deficiency of either one could weaken the bone matrix, interfering with its ability to hold on to the calcium salts.
Both too much and too little protein can cause trouble with the bones. Some studies show that vegetarians have higher bone density than omnivores, or people who eat everything (and presumably much more animal protein, but perhaps also less plant foods). In one study published in the American Journal of Clinical Nutrition, the mean bone density of the 70 to 79-year old vegetarians was greater than that of the 50 to 59-year old omnivores. Therefore, it was thought that vegetarians have a lesser risk of osteoporosis. Another way to interpret these studies is to note the rest of the dietary context: it could mean that the “omnivores” eat too many sweets and not enough greens and other plant foods. The relationship between protein and calcium may be crucial: A 1997 Norwegian study found that there was an elevated risk of fracture in women with a high intake of protein and a concomitant low calcium intake.
More recent studies show a different picture. The Framingham Osteoporosis Study, published in December 2000, from the Harvard Medical School Division on Aging, established in a study of people aged 69 to 91 that those with the lowest protein intake had the most bone loss, and that lower animal protein intake was also significantly related to bone loss in both the hip and the spine1. Another study published in 2004, by B. Dawson-Hughes from the Bone Metabolism Laboratory at Tufts University, found that a doubling of protein intake from meats, together with a reduction of carbohydrates, not only didn’t increase calcium loss through the urine, but was associated with higher bone growth factors in the blood.2,3 Interestingly, soy was no better than meat in another study, where it was found that the substitution of 25 g high isoflavone soy protein for meat, in the presence of typical calcium intakes, did not improve or impair calcium retention or indicators of bone and cardiovascular health in postmenopausal women4. It is time to put to rest the outdated notion that meat makes the bones weaker!!
People who eat carelessly, focusing on packaged and processed foods and refined carbohydrates, and ignoring vegetables and protein, may be risking weak bones from collagen matrix insufficiency. Calcium supplements in these cases may be counterproductive: an excess of calcium and a lack of collagen matrix could make the bone hard but brittle, and so more easily breakable.
Here is a recipe rich in calcium, protein and Vitamin C, really good for your bones!
Salmon Omelette with dill and mesclun greens
1 7.5 oz can salmon, without oil or salt
¼ to ½ teaspoon sea salt
2 teaspoons lemon juice
1 tablespoon chopped fresh dill OR 1 teaspoon dry dill
freshly ground pepper
2 organic eggs
2 teaspoons unsalted or clarified butter or extra virgin olive oil
1. Drain the juice out of the can, and put the rest of the contents in a mixing bowl. With a fork, mash the salmon well to break up all the pieces, skin, and bones. Add the salt, lemon juice, herbs, and mix well with the fork. Grind in the pepper to taste.
2. Break the eggs into the salmon mixture, and mix in thoroughly.
3. Heat a 9" cast iron or other skillet, and add the butter until it foams. Pour in the salmon-egg mixture and smooth out with the fork or a spatula. Cook, covered, over very low heat for about 5-6 minutes, or until set. You should be able to shake the pan and have the whole omelet slide around. Turn over by sliding it onto a pot cover and turning it over into the pan, to cook another 3 minutes; alternately, finish under the broiler. Makes 2 servings. Serve with a mesclun salad with lemon and olive oil.
1. Hannan MT, Tucker KL, Dawson-Hughes B, Cupples LA, Felson DT, Kiel DP. Effect of dietary protein on bone loss in elderly men and women: the Framingham Osteoporosis Study. J Bone Miner Res. Dec 2000;15(12):2504-2512.
2. Dawson-Hughes B, Harris SS, Rasmussen H, Song L, Dallal GE. Effect of dietary protein supplements on calcium excretion in healthy older men and women. J Clin Endocrinol Metab. Mar 2004;89(3):1169-1173.
3. Roughead ZK, Johnson LK, Lykken GI, Hunt JR. Controlled high meat diets do not affect calcium retention or indices of bone status in healthy postmenopausal women. J Nutr. Apr 2003;133(4):1020-1026.
4. Roughead ZK, Hunt JR, Johnson LK, Badger TM, Lykken GI. Controlled substitution of soy protein for meat protein: effects on calcium retention, bone, and cardiovascular health indices in postmenopausal women. J Clin Endocrinol Metab. Jan 2005;90(1):181-189.
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Copyright ©1997 Annemarie Colbin, Ph.D.