High Protein Diets Require Calcium

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Nutr 2003 Mar;133(3):852S-4S Related Articles, Links


Interaction of dietary calcium and protein in bone health in humans.

Dawson-Hughes B.

Calcium and Bone Metabolism Laboratory at the Jean Mayer U.S. Department of Agriculture Human Nutrition Research Center on Aging at Tufts University, Boston, MA.

Protein has both positive and negative effects on calcium balance, and the net effect of dietary protein on bone mass and fracture risk may be dependent on the dietary calcium intake. In addition to providing substrate for bone matrix, dietary protein stimulates the production of insulin-like growth factor-1 (IGF-1), a factor that promotes osteoblast-mediated bone formation. Protein also increases urinary calcium losses, by several proposed mechanisms. Increasing calcium intake may offset the negative impact of dietary protein on urinary calcium losses, allowing the favorable effect of protein on the IGF-1 axis to dominate. Several, although not all, studies are either compatible with or support this hypothesis. Protein supplements significantly reduced bone loss in elderly hip-fracture patients in a study in which both the protein and control groups received supplemental calcium. In an observational study, total protein intake was positively associated with favorable 3-y changes in femoral neck and total body bone mineral density in volunteers who received supplemental calcium citrate malate and vitamin D, but not in volunteers taking placebos. In conclusion, an adequate calcium intake may help promote a favorable effect of dietary protein on the skeleton in older individuals.
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Advertisers would have us believe that we need to consume dairy products to meet our daily calcium requirements. Actually, a large portion of our global population doesn't use dairy products as a source of calcium. They rely instead on plants. Many people are not aware that calcium is available throughout our food supply. Practically every food has a minute amount, while certain foods have significant amounts of calcium. Studies have revealed the amount of calcium absorbed from plant sources is greater than that absorbed from milk.

Many of the foods you currently eat are rich sources of calcium. The most noteworthy fruits and vegetables are oranges, apricots, pears, raisins, dates, prunes, dried figs, broccoli, okra, sweet potatoes and most dark green leafy vegetables such as kale, collard greens, dandelion greens and bok choy. Calcium is significant in Brazil nuts, hazelnuts, chestnuts, filberts, sesame seeds, tahini (sesame seed paste), sunflower seeds and pumpkin seeds. Among fish and seafood, salmon (with bones), sardines, mackerel, flounder and shrimp are the best choices, followed by clams and oysters. Amaranth, quinoa, oats and barley are good calcium sources along with beans, peas, soy products, seaweeds, sprouts and blackstrap molasses. Alfalfa, cayenne, chamomile, kelp, lemongrass, paprika, parsley and peppermint are among the numerous herbs containing calcium.

Some foods that are high in calcium are also high in oxalic acid, which interferes with calcium absorption. When these two substances bind in the intestines, the insoluble salts that are formed can't be assimilated. Foods high in calcium and oxalic acid include spinach, rhubarb, almonds, cashews, beet and turnip greens. Some of the calcium in high oxalate vegetables can be released by adding a teaspoon of lemon juice or vinegar to the cooking liquid. It is still preferable to avoid inhibiting calcium absorption by not overindulging in foods with a high oxalic content.

Antacids are not an appropriate source of calcium. The stomach acid required in the breakdown of calcium for ultimate absorption can be neutralized by the antacids.